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Title: Artificial Light - Its Influence upon Civilization
Author: Luckiesh, Matthew, 1883-1967
Language: English
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[Illustration: LIGHT AND LIBERTY]

              The Century Books of Useful Science

                      ARTIFICIAL LIGHT


                         M. LUCKIESH


   Author of "Color and Its Applications," "Light and Shade
          and Their Applications," "The Lighting Art,"
                  "The Language of Color," etc.

                    _ILLUSTRATED WITH

                          NEW YORK
                      THE CENTURY CO.

                    Copyright, 1920, by
                      THE CENTURY CO.




In the following pages I have endeavored to discuss artificial light for
the general reader, in a manner as devoid as possible of intricate
details. The early chapters deal particularly with primitive artificial
light and their contents are generally historical. The science of
light-production may be considered to have been born in the latter part
of the eighteenth century and beginning with that period a few chapters
treat of the development of artificial light up to the present time.
Until the middle of the nineteenth century _mere_ light was available,
but as the century progressed, the light-sources through the application
of science became more powerful and efficient. Gradually _mere_ light
grew to _more_ light and in the dawn of the twentieth century _adequate_
light became available. In a single century, after the development of
artificial light began in earnest, the efficiency of light-production
increased fifty-fold and the cost diminished correspondingly. The next
group of chapters deals with various economic influences of artificial
light and with some of the byways in which artificial light is serving
mankind. On passing through the spectacular aspects of lighting we
finally emerge into the esthetics of light and lighting.

The aim has been to show that artificial light has become intricately
interwoven with human activities and that it has been a powerful
influence upon the progress of civilization. The subject is too
extensive to be treated in detail in a single volume, but an effort has
been made to present a discussion fairly complete in scope. It is hoped
that the reader will gain a greater appreciation of artificial light as
an economic factor, as an artistic medium, and as a mighty influence
upon the safety, efficiency, health, happiness, and general progress of



It is a pleasant duty to acknowledge the coöperation of various
companies in obtaining the photographs which illustrate this book. With
the exception of Plates 2 and 7, which are reproduced from the excellent
works of Benesch and Allegemane respectively, the illustrations of early
lighting devices are taken from an historical collection in the
possession of the National Lamp Works of the General Electric Co. To
this company the author is indebted for Plates 1, 3, 4, 5, 6, 9, 11, 15,
18b, 20, 21, 29; to Dr. McFarlan Moore for Plate 10; to Macbeth Evans
Glass Co. for Plate 12; to the Corps of Engineers, U. S. Army, for Plate
13; to Lynn Works of G. E. Co. for Plates 14, 16; to Edison Lamp Works of
G. E. Co. for Plates 17, 24; to Cooper Hewitt Co. for Plate 18a; to
R. U. V. Co. for Plate 19; to New York Edison Co. for Plates 22, 26, 30;
to W. D'A. Ryan and the Schenectady Works of G. E. Co. for Plates 23, 25,
31; to National X-Ray Reflector Co. for Plate 28. Besides the companies
and the individuals particularly involved in the foregoing, the author
is glad to acknowledge his appreciation of the assistance of others
during the preparation of this volume.


CHAPTER                                               PAGE

     I LIGHT AND PROGRESS                                3

    II THE ART OF MAKING FIRE                           15

   III PRIMITIVE LIGHT-SOURCES                          24

   IV THE CEREMONIAL USE OF LIGHT                       38


   VI EARLY GAS-LIGHTING                                63


 VIII MODERN GAS-LIGHTING                               97

   IX THE ELECTRIC ARCS                                111


   XI THE LIGHT OF THE FUTURE                          143

  XII LIGHTING THE STREETS                             152

 XIII LIGHTHOUSES                                      163

  XIV ARTIFICIAL LIGHT IN WARFARE                      178

   XV SIGNALING                                        194

  XVI THE COST OF LIGHT                                208

 XVII LIGHT AND SAFETY                                 225

XVIII THE COST OF LIVING                               238


   XX LIGHT AND HEALTH                                 269

  XXI MODIFYING ARTIFICIAL LIGHT                       284

XXII SPECTACULAR LIGHTING                              298

XXIII THE EXPRESSIVENESS OF LIGHT                      310

 XXIV LIGHTING THE HOME                                325

  XXV LIGHTING--A FINE ART?                            341

      READING REFERENCES                               357

      INDEX                                            359


Light and Liberty                           _Frontispiece_
Primitive fire-baskets                                  16

Crude splinter-holders                                  16

Early open-flame oil and grease lamps                   17

A typical metal multiple-wick open-flame oil-lamp       32

A group of oil-lamps of two centuries ago               33

Lamps of a century or two ago                           56

Elaborate fixtures of the age of candles                57

Flame arc                                              128

Direct current arc                                     128

On the testing-racks of the manufacturer of
incandescent filament lamps                            129

Carbon-dioxide tube for accurate color-matching        160

The Moore nitrogen tube                                160

Modern street lighting                                 161

A completed lighthouse lens                            176

Torro Point Lighthouse, Panama Canal                   176

American search-light position on Western Front in
1919                                                   177

American standard field search-light and power unit    177

Signal-light for airplane                              232

Trench light-signaling outfit                          232

Aviation field light-signal projector                  232

Signal search-light for airplane                       232

Unsafe, unproductive lighting worthy of the dark ages  233

The same factory made safe, cheerful, and more
productive by modern lighting                          233

Locomotive electric headlight                          240

Search-light on a fire-boat                            240

Building ships under artificial light at Hog Island
Shipyard                                               241

Artificial light in photography                        256

Sterilizing water with radiant energy from quartz
mercury-arcs                                           257

Judging color under artificial daylight                272

Artificial daylight                                    273

Fireworks and illuminated battle-fleet at
Hudson-Fulton Celebration                              288

Fireworks exhibition on May Day at Panama-Pacific
Exposition                                             289

The new flood lighting contrasted with the old
outline lighting                                       304

Niagara Falls flooded with light                       305

Artificial light honoring those who fell and those
who returned                                           320

The expressiveness of light in churches                321

Obtaining two different moods in a room by a portable
lamp which supplies direct and indirect components
of light                                               336

The lights of New York City                            337

Artificial light in community affairs                  352

Panama-Pacific Exposition                              353




The human race was born in slavery, totally subservient to nature. The
earliest primitive beings feasted or starved according to nature's
bounty and sweltered or shivered according to the weather. When night
fell they sought shelter with animal instinct, for not only were
activities almost completely curtailed by darkness but beyond its screen
lurked many dangers. It is interesting to philosophize upon a
distinction between a human being and the animal just below him in the
scale, but it may serve the present purpose to distinguish the human
being as that animal in whom there is an unquenchable and insatiable
desire for independence. The effort to escape from the bondage of nature
is not solely a human instinct; animals burrow or build retreats through
the instinct of self-preservation. But this instinct in animals is soon
satisfied, whereas in human beings it has been leading ever onward
toward complete emancipation.

The progress of civilization is a long chain of countless achievements
each one of which has increased man's independence. Early man perhaps
did not conceive the idea of fire and then set out to produce it. His
infant mind did not operate in this manner. But when he accidentally
struck a spark, produced fire by friction, or discovered it in some
other manner, he saw its possibility. It is thrilling to picture
primitive man at his first bonfire, enjoying the warmth, or at least
interested in it. But how wonderful it must have become as twilight's
curtain was drawn across the heavens! This controllable fire emitted
_light_. It is easy to imagine primitive man pondering over this
phenomenon with his sluggish mind. Doubtless he cautiously picked up a
flaming stick and timidly explored the crowding darkness. Perhaps he
carried it into his cave and behold! night had retreated from his abode!
No longer was it necessary for him to retire to his bed of leaves when
daylight failed. The fire not only banished the chill of night but was a
power over darkness. Viewed from the standpoint of civilization, its
discovery was one of the greatest strides along the highway of human
progress. The activities of man were no longer bounded by sunrise and
sunset. The march of civilization had begun.

In the present age of abundant artificial light, with its manifold
light-sources and accessories which have made possible countless
applications of light, mankind does not realize the importance of this
comfort. Its wonderful convenience and omnipresence have resulted in
indifference toward it by mankind in general, notwithstanding the fact
that it is essential to man's most important and educative sense. By
extinguishing the light and pondering upon his helplessness in the
resulting darkness, man may gain an idea of its overwhelming importance.
Those unfortunate persons who suffer the terrible calamity of blindness
after years of dependence upon sight will testify in heartrending terms
to the importance of light. Milton, whose eyesight had failed, laments,

    O first created beam and thou great Word
    "Let there be light," and light was over all,
    Why am I thus bereaved thy prime decree?

Perhaps only through a similar loss would one fully appreciate the
tremendous importance of light to him, but imagination should be capable
of convincing him that it is one of the most essential and
pleasure-giving phenomena known to mankind.

A retrospective view down the vista of centuries reveals by contrast the
complexity with which artificial light is woven into human activities of
the present time. Written history fails long before the primitive races
are reached, but it is safe to trust the imagination to penetrate the
fog of unwritten history and find early man huddled in his cave as
daylight wanes. Impelled by the restless spirit of progress, this
primitive being grasped the opportunity which fire afforded to extend
his activities beyond the boundaries of daylight. The crude art upon the
walls of his cave was executed by the flame of a smoking fagot. The fire
on the ledge at the entrance to his abode became a symbol of home, as
the fire on the hearth has symbolized home and hospitality throughout
succeeding ages. The accompanying light and the protection from cold
combined to establish the home circle. The ties of mated animals
expanded through these influences to the bonds of family. Thus light was
woven early into family life and has been throughout the ages a
moralizing and civilizing influence. To-day the residence functions as a
home mainly under artificial light, for owing to the conditions of
living and working, the family group gathers chiefly after daylight has

From the pine knot of primitive man to the wonderfully convenient
light-sources of to-day there is a great interval, consisting, as
appears retrospectively, of small and simple steps long periods apart.
Measured by present standards and achievements, development was slow at
first and modern man may be inclined to impatience as he views the
history of light and human progress. But the achievements of early
centuries, which appear so simple at the present time, were really great
accomplishments when considered in the light of the knowledge of those
remote periods. Science as it exists to-day is founded upon proved
facts. The scientist, equipped with a knowledge of physical and chemical
laws, is led by his imagination into the darkness of the unexplored
unknown. This knowledge illuminates the pathway so that hypotheses are
intelligently formed. These evolve into theories which are gradually
altered to fit the accumulating facts, for along the battle area of
progress there are innumerable scouting-parties gaining secrets from
nature. These are supported by individuals and by groups, who verify,
amplify, and organize the facts, and they in turn are followed by
inventors who apply them. Liaison is maintained at all points, but the
attack varies from time to time. It may be intense at certain places and
other sectors may be quiet for a time. There are occasional reverses,
but the whole line in general progresses. Each year witnesses the
acquirement of new territory. It is seen that through the centuries
there is an ever-growing momentum as knowledge, efficiency, and
organization increase the strength of this invading army of scientists
and inventors.

The burning fagot rescued mankind from the shackles of darkness, and the
grease-lamp and tallow-candle have done their part. Progress was slow in
those early centuries because the great minds of those ages
philosophized without a basis of established facts: scientific progress
resulted more from an accumulation of accidental discoveries than by a
directed attack of philosophy supported by the facts established by
experiment. It was not until comparatively recent times, at most three
centuries ago, that the great intellects turned to systematically
organized scientific research. Such men as Newton laid the foundation
for the tremendous strides of to-day. The store of facts increased and
as the attitude changed from philosophizing to investigating, the
organized knowledge grew apace. All of this paved the way for the
momentous successes of the present time.

The end is not in sight and perhaps never will be. The unexplored region
extends to infinity and, judged by the past, the momentum of discovery
will continue to increase for ages to come, unless the human race decays
through the comfort and ease gained from utilizing the magic secrets
which are constantly being wrested from nature. Among the achievements
of science and invention, the production and application of artificial
light ranks high. As an influence upon civilization, no single
achievement surpasses it.

Without artificial light, mankind would be comparatively inactive about
one half its lifetime. To-day it has been fairly well established that
the human organism can flourish on eight hours' sleep in a period of
twenty-four hours. Another eight hours spent in work should settle man's
obligation to the world. The remaining hours should be his own.
Artificial light has made such a distribution of time possible. The
working-periods in many cases may be arranged in the interests of
economy, which often means continuous operations. The sun need not be
considered when these operations are confined to interiors or localized

Thus, artificial light has been an important factor in the great
industrial development of the present time. Man now burrows into the
earth, navigates under water, travels upon the surface of land and sea,
and soars among the clouds piloted by light of his own making. Progress
does not halt at sunset but continues twenty-four hours each day.
Building, printing, manufacturing, commerce, and other activities are
prosecuted continuously, the working-shifts changing at certain periods
regardless of the rising or setting sun. Adequate artificial lighting
decreases spoilage, increases production, and is a powerful factor in
the prevention of industrial accidents.

It has ever been true since the advent of artificial light that the
intellect has been largely nourished after the completion of the day's
work. The highly developed artificial lighting of the present time may
account for much of the vast industry of publication. Books, magazines,
and newspapers owe much to convenient and inexpensive artificial light,
for without it fewer hours would be available for recreation and
advancement through reading. Schools, libraries, and art museums may be
attended at night for the betterment of the human race. The immortal
Lincoln, it is said, gained his early education largely by the light of
the fireplace. But all were not endowed with the persistence of Lincoln,
so that illiteracy was more common in his day than in the present age of
adequate illumination.

The theatrical stage not only depends for its effectiveness upon
artificial light but owes its existence and development largely to this
agency. In the moving-picture theater, pictures are projected upon the
screen by means of it and even the production of the pictures is
independent of daylight. These and a vast number of recreational
activities owe much, and in some cases their existence, to artificial

Not many centuries ago the streets at night were overrun by thieves and
to venture outdoors after dark was to court robbery and even bodily
harm. In these days of comparative safety it is difficult to realize the
influence that abundant illumination has had in increasing the safety of
life and property. Maeterlinck in his poetical drama, "The Bluebird,"
appropriately has made _Light_ the faithful companion of mankind. The
Palace of Night, into which _Light_ is not permitted to enter, is the
abode of many evils. Thus the poet has played upon the primitive
instincts of the impressiveness of light and darkness.

By combining the symbolism of light, color, and darkness with the
instincts which have been inherited by mankind from its superstitious
ancestry of the age of mythology, another field of application of
artificial light is opened. Light has gradually assumed such attributes
as truth, knowledge, progress, enlightenment. Throughout the early ages
light was more or less worshiped and thus artificial lights became woven
in many religious ceremonies. Some of these have persisted to the
present time. The great pageants of peace celebrations and world's
expositions appropriately feature artificial light. In drawing upon the
potentiality of the expressiveness and impressiveness of light and
color, artificial light is playing a major part. Doubtless the future
generations will be entertained by gorgeous symphonies of light.
Experiments are performed in this direction now and then, and it is
reasonable to expect that after many centuries of cultivation of the
appreciation of light-symphonies, these will take a place among the
arts. The elaborate and complicated music of the present time is
appreciated by civilized nations only after many centuries of slow
cultivation of taste and understanding.

Light-therapy is to-day a distinct science and art. The germicidal
action of light-rays and of some of the invisible rays which ordinarily
accompany the luminous rays is well proved. Wounds are treated
effectively and water is sterilized by the ultraviolet radiant energy in
modern artificial illuminants.

Thousands of lighthouses, light-ships, and light-buoys are scattered
along sea-coasts, rivers, and channels. They guide the wheelman and warn
the lookout of shoals and reefs. Some of these send forth flashes of
light whose intensities are measured in millions of candle-power. Many
are unattended for days and even months. These powerful lights dominated
by automatic mechanisms have replaced the wood-fires which were
maintained a few centuries ago upon certain prominent points.

Signal-lights now guide the railroad train through the night. A burning
flare dropped from the rear of a train keeps the following train at a
safe distance. Huge search-lights penetrate the night air for many
miles. When these are equipped with shutters, a code may be flashed from
one ship to another or between the vessel and land. A code from a
powerful search-light has been read a hundred miles away because the
flashes were projected upon a layer of high clouds and were thus visible
far beyond the horizon.

Artificial light played its part in the recent war. Huge search-light
equipments were devised for portability. This mobile apparatus was
utilized against enemy aircraft and in various other ways. Small
hand-lamps are used to send out a pencil of light as directed by a pair
of sights and the code is flashed by means of a trigger. Raiding-parties
are no longer concealed by the curtain of darkness, for rockets and
star-shells are used to illuminate large areas. Flares sent upward to
drift slowly downward supported by parachutes saved and cost many lives
during the recent war. Rockets are used by ships in distress and also by
beleaguered troops.

Experiments are being prosecuted to ascertain the possibilities of
artificial light in the forcing of plant-growth, and even chickens are
made to work longer hours by its use.

Artificial light is now modified in color or spectral character to meet
many requirements. Daylight has been reproduced in spectral quality so
that certain processes requiring accurate discrimination of color are
now prosecuted twenty-four hours a day under artificial daylight.
Colored light is made of the correct quality which does not affect
photographic plates of various sensibilities. Monochromatic light is
utilized in photo-micrography for the best rendition of detail.
Light-waves have been utilized as standards of length because they are
invariable and fundamental. Numerous other interesting adaptations of
artificial light are in daily use.

This is in reality the age of artificial light, for mankind has not only
become independent of daylight in certain respects, but has improved
upon natural light. The controllability of artificial light makes it
superior to natural light in many ways. In fact, uses have been made of
artificial light which are impossible with natural light. Light-sources
may be made of a vast variety of shapes, and those may be transported
wherever desired. They may be equipped with reflectors and other optical
devices to direct or to diffuse the light as required.

Thus, artificial light to-day has numerous advantages over light which
has been furnished by the Creator. It is sometimes stated that it can
never compete with daylight in cheapness, inasmuch as the latter costs
nothing. But this is not true. Even in the residence, daylight costs
something, because windows are more expensive than plain walls. The
expense of washing windows is an appreciable percentage of the cost of
gas or electricity. And there is window-breakage to be considered.

In the more elaborate buildings of the congested portions of cities,
daylight is satisfactory a lesser number of hours than in the outlying
districts. In some stores, offices, and factories artificial light is
used throughout the day. Still, the daylighting-equipment is installed
and maintained. Furthermore, when it is considered that much expensive
area is given to light-courts and much valuable wall space to windows,
it is seen that the cost of daylight in congested cities is in reality
considerable. Of course, the daylighting-equipment has value in
ventilating, but ventilation may be taken care of in a very satisfactory
manner as a separate problem.

The cost of skylights in museums and other large buildings is far
greater than that of ordinary ceilings and walls, and the extra
allowance for heating is appreciable. The expense of maintenance of some
skylights is considerable. Thus it is seen that the cost and maintenance
of daylighting-equipment, the loss of valuable rental space and of wall
area, and the increased expense of heating are factors which challenge
the statement that daylight costs nothing. In fact, it is not surprising
to find that occasionally the elimination of daylighting--the reliance
upon artificial light alone--has been seriously contemplated. When the
possibilities of the latter are considered, it is reasonable to expect
that it will make greater and greater inroads and that many buildings of
the future will be equipped solely with artificial-lighting systems.

Naturally, with the tremendous development of artificial light during
the present age, a new profession has arisen. The lighting expert is
evolving to fill the needs. He is studying the problems of producing and
utilizing artificial illumination. He deals with the physics of
light-production. His studies of utilization carry him into the vast
fields of physiology and psychology. His is a profession which
eventually will lead into numerous highways and byways of enterprise,
because the possibilities of lighting extend into all those activities
which make their appeal to consciousness through the doorway of vision.
These possibilities are limited only by the boundaries of human endeavor
and in the broadest sense extend even beyond them, for light is one of
the most prominent agencies in the scheme of creation. It contributes
largely to the safety, the efficiency, and the happiness of civilized
beings and beyond all it is a powerful civilizing agency.



Scattered over the earth at the present time various stages of
civilization are to be found, from the primitive savages to the most
highly cultivated peoples. Although it is possible that there are tribes
of lowly beings on earth to-day unfamiliar with fire or ignorant of its
uses, savages are generally able to make fire. Thus the use of fire may
serve the purpose of distinguishing human beings from the lower animals.
Surely the savage of to-day who is unable to kindle fire or who
possesses a mind as yet insufficiently developed to realize its
possibilities, is quite at the mercy of nature's whims. He lives merely
by animal prowess and differs little in deeds and needs from the beasts
of the jungle. In this imaginary journey to the remote regions beyond
the outskirts of civilization it soon becomes evident that the
development of artificial light may be a fair measure of civilization.

In viewing the development of artificial light it is seen that preceding
the modern electrical age, man depended universally upon burning
material. Obviously, the course of civilization has been highly complex
and cannot be symbolized adequately by the branching tree. From its
obscure beginning far in the impenetrable fog of prehistoric times, it
has branched here and there. These various branches have been subjected
to many different influences, with the result that some flourished and
endured, some retrogressed, some died, some went to seed and fell to
take root and to begin again the upward climb. The ultimate result is
the varied civilization of the present time, a study of which aids in
penetrating the veil that obscures the ages of unrecorded writing.
Likewise, material relics of bygone ages supply some threads of the
story of human progress and mythology aids in spanning the misty gap
between the earliest ages of man and the period when historic writings
were begun. Throughout these various stages it becomes manifest that the
development of artificial light is associated with the progress of

According to a certain myth, Prometheus stole fire from heaven and
brought this blessing to earth. Throughout the mythologies of various
races, fire and, as a consequence, light have been associated with
divinity. They have been subjects of worship perhaps more generally than
anything else, and these early impressions have survived in the
ceremonial uses of light and fire even to the present time. The origin
of fire as represented in any of the myths of the superstitious beings
of early ages is as suitable as any other, inasmuch as definite
knowledge is unavailable. Active volcanoes, spontaneous combustion,
friction, accidental focusing of the sun's image, and other means may
have introduced primitive beings to fire. A study of savage tribes of
the present age combined with a survey of past history of mythology, of
material relics, and of the absence of lamps or other lighting utensils
leads to the conclusion that the earliest source of light was the wood




Even to-day the savages of remote lands have not advanced further than
the wood-fire stage, and they may be found kneeling upon the ground
energetically but skilfully rubbing sticks together until the friction
kindles a fire. In using these fire-sticks they convert mechanical
energy into heat energy. This is a fundamental principle of physics,
employed by them as necessity demands, but they are totally ignorant of
it as a scientific law. The things which these savages learn are the
result of accidental discovery. Until man pondered over such simple
facts and coördinated them so that he could extend his knowledge by
general reasoning, his progress could not be rapid. But the sluggish
mind of primitive man is capable of devising improvements, however
slowly, and the art of making fire by means of rubbing fire-sticks
gradually became more refined. Mechanical improvements resulted from
experience, with the consequence that finally one stick was rubbed to
and fro in a groove, or was rapidly twirled between the palms of the
hands while one end was pressed firmly into a hole in a piece of wood.
In the course of a few seconds or a minute, depending upon skill and
other conditions, a fire was obtained. It is interesting to note how
civilized man is often compelled by necessity to adopt the methods of
primitive beings. The rubbing of sticks is an emergency measure of the
master of woodcraft at the present time, and the production of fire in
this manner is the proud accomplishment or ambition of every Boy Scout.

Where only such crude means of kindling fire were available it became
the custom in some cases to maintain a fire burning continuously in a
public place. Around this pyrtaneum the various civil, political, and
religious affairs were carried on by the light and warmth of the public
fire. Many quaint customs evolved, apparently, from this ancient

The tinder-box of modern centuries doubtless originated in very early
times, for it is inconceivable that the earliest beings did not become
aware of the production of sparks when certain stones were struck
together. In the stone age, when human beings spent much of their time
chiseling implements and utensils from stone by means of tools of the
same substance, it appears certain that this means of producing fire was
ever apparent. Many of their sharp implements, such as knives and
arrow-heads, were made of quartz and similar material and it is likely
that the use of two pieces of quartz for producing a spark originated in
those remote periods. Alaskan and Aleutian tribes are known to have
employed two pieces of quartz covered with native sulphur. When these
were struck together with skill, excellent sparks were obtained.

Later, when iron and steel became available, the more modern tinder-box
was developed. An early application of the flint-and-steel principle was
made by certain Esquimo tribes who obtained fire by striking a piece of
quartz against a piece of iron pyrites. The latter is a yellow sulphide
of iron, of crystalline form, best known as "fool's gold." Doubtless,
the more primitive beings used dried grass, leaves, and moss as
inflammable material upon which the sparks were showered. In later
centuries the tinder-box was filled with charred grass, linen, and
paper. There was a long interval between the development of fire-sticks
and that of the tinder-box as measured by the progress of civilization.
During recent centuries ordinary brown paper soaked in saltpeter and
dried was utilized satisfactorily as an inflammable material. Such
devices have been employed in past ages in widely separated regions of
the earth. Elaborate specimens of tinder-boxes from Jamaica, Japan,
China, Europe, and various other countries are now reposing in the
collections in the possession of museums and of individuals.

If the radiant energy from the sun is sufficiently concentrated upon
inflammable material, the latter will ignite. Such concentration may be
achieved by means of a convex lens or a concave mirror. This method of
producing fire does not antedate the more primitive methods such as
striking quartz or rubbing wooden sticks, because the materials required
are not readily found or prepared, but it is of very remote origin.
Aristophanes in his comedy "The Clouds," which is a satire aimed at the
science and philosophy of his period (488-385 B. C.), mentions
the "burning lens." Nearly every one is familiar with an achievement
attributed to Archimedes in which he destroyed the ships at Syracuse by
focusing the image of the sun upon them by means of a concave mirror.
The ancient Egyptians were proficient in the art of glass-making, so it
is likely that the "burning-glass" was employed by them. Even a crude
lens of glass will focus an image of the sun sufficiently well to cause
inflammable material to ignite.

The energy in sunlight varies enormously, even on clear days, because
the water-vapor in the atmosphere absorbs some of the radiant energy
emitted by the sun. This absorbed radiation is chiefly known as
infra-red energy, which does not arouse the sensation of light. When the
water-vapor content of the atmosphere is high, the sun, though it may
appear as bright to the eye, in reality is not as hot as it would be if
the water-vapor were not present. However, a fire may be kindled by
concentrating only the visible rays in sunlight because of the enormous
intensity of sunlight. A convex lens fashioned from ice by means of a
sharp-edged stone and finally shaped by melting the surfaces as they are
rubbed in the palms of the hands, will kindle a fire in highly
inflammable material if the sun is high and the atmosphere is fairly
clear. Burning-glasses are used to a considerable extent at the present
time in certain countries and it is reported that British soldiers were
supplied with them during the Boer War. Indicative of the predominant
use to which the glass lens was applied in the past is the employment of
the term "burning-glass" instead of lens in the scientific writings as
late as a century or two ago.

As civilization advanced, leading intellects began to inquire into the
mysteries of nature and the periods of pure philosophy gave way to an
era of methodical research. Alchemy and superstition began to retire
before the attacks of those pioneers who had the temerity to believe
that the scheme of creation involved a vast network of invariable laws.
In this manner the powerful sciences of physics and chemistry were born
a few centuries ago. Among other things the production of fire and light
received attention and the "dark ages" were doomed to end. The crude,
uncertain, and inconvenient methods of making fire were replaced by
steadily improving scientific devices.

Matches were at first cumbersome, dangerous, and expensive, but these
gradually evolved into the safety matches of the present time. Although
they were primarily intended for lighting fires and various kinds of
lamps, billions of them are now used yearly as convenient light-sources.
Smoldering hemp or other material treated with niter and other
substances was an early form of match used especially for discharging
firearms. The modern wax-taper is an evolutionary form of this type of

Phosphorus has long played a dominant rôle in the preparation of
matches. The first attempt at making them in their modern form appears
to have occurred about 1680. Small pieces of phosphorus were used in
connection with small splints of wood dipped in sulphur. This type of
match did not come into general use until after the beginning of the
nineteenth century, owing to its danger and expense. White or yellow
phosphorus is a deadly poison; therefore the progress of the phosphorus
match was inhibited until the discovery of the relatively harmless form
known as red phosphorus. The first commercial application of this form
was made in about 1850.

An early ingenious device consisted of a piece of phosphorus contained
in a tube. A piston fitted snugly into the tube, by means of which the
air could be compressed and the phosphorus ignited. Sulphur matches were
ignited from the burning tinder, the latter being fired by flint and
steel. In 1828 another form of match consisted of a glass tube
containing sulphuric acid and surrounded by a mixture of chlorate of
potash and sugar. A pair of nippers was supplied with each box of these
"matches," by means of which the tip of the glass tube could be broken
off. This liberated the acid, which upon mixing with the other
ingredients set fire to them. To this contrivance a roll of paper was
attached which was ignited by the burning chemicals.

The lucifer or friction matches appeared in about 1827, but successful
phosphorus matches were first made in about 1833. The so-called safety
match of the present time was invented in the year 1855. To-day, the
total daily output of matches reaches millions and perhaps billions.
Automatic machinery is employed in preparing the splints of wood and in
dipping them into molten paraffin wax and finally into the igniting

During recent years the principle of the tinder-box has been revived in
a device in which sparks are produced by rubbing the mineral cerite (a
hydrous silicate of cerium and allied metals) against steel. These
sparks ignite a gas-jet or a wick soaked in a highly inflammable liquid
such as gasolene or alcohol. This device is a tinder-box of the modern
scientific age.

Naturally with the advent of electricity, electrical sparks came into
use for lighting gas-jets and mantles and in isolated instances they
have served as light-sources. Doubtless, every one is familiar with the
parlor stunt of igniting a gas-jet from the discharge from the
finger-tips of static electricity accumulated by shuffling the feet
across the floor-rug.

Although many of these methods and devices have been used primarily for
making fire, they have served as emergency or momentary light-sources.
In the outskirts of civilization some of them are employed at the
present time and various modern light-sources require a method of



Many are familiar with the light of the firefly or of its larvæ, the
glow-worm, but few persons realize that a vast number of insects and
lower organisms are endowed with the superhuman ability of producing
light by physiological processes. Apparently the chief function of these
lighting-plants within the living bodies is not to provide light in the
sense that the human being uses it predominantly. That is, these
wonderful light-sources seem to be utilized more for signaling, for
luring prey, and for protection than for strictly illuminating-purposes.
Much study has been given to the production of light by animals, because
the secrets will be extremely valuable to mankind. As one floats over
tide-water on a balmy evening after dark and watches the pulsating spots
of phosphorescent light emitted by the lowly jellyfishes, his
imaginative mood formulates the question, "Why are these lowly organisms
endowed with such a wonderful ability?"

Despite his highly developed mind and body and his boasted superiority,
man must go forth and learn the secrets of light-production before he
may emancipate himself from darkness. If man could emit light in
relative proportion to his size as compared with the firefly, he would
need no other torch in the coal-mine. How independent he would be in
extreme darkness where his adapted eyes need only a feeble
light-source! Primitive man, desiring a light-source and having no means
of making fire, imprisoned the glowing insects in a perforated gourd or
receptacle of clay, and thus invented the first lantern perhaps before
he knew how to make fire. The fireflies of the West Indies emit a
continuous glow of considerable luminous intensity and the natives have
used these imprisoned insects as light-sources. Thus mankind has
exhibited his superiority by adapting the facilities at hand to the
growing requirements which his independent nature continuously
nourished. His insistent demand for independence in turn has nourished
his desire to learn nature's secrets and this desire has increased in
intensity throughout the ages.

The act of imprisoning a glowing insect was in itself no greater stride
along the highway of progress than the act of picking a tasty fruit from
its tree. However, the crude lantern perhaps directed his primitive mind
to the possibilities of artificial light. The flaming fagot from the
fire was the ancestor of the oil-lamp, the candle, the lantern, and the
electric flash-light. It is a matter of conjecture how much time elapsed
before his feeble intellect became aware that resinous wood afforded a
better light-source than woods which were less inflammable.
Nevertheless, pine knots and similar resinous pieces of wood eventually
were favored as torches and their use has persisted until the present
time. In some instances in ancient times resin was extracted from wood
and burned in vessels. This was the forerunner of the grease-and the
oil-lamp. In the woods to-day the craftsman of the wilds keeps on the
lookout for live trees saturated with highly inflammable ingredients.

Viewed from the present age, these smoking, flickering light-sources
appear very crude; nevertheless they represent a wide gulf between their
users and those primitive beings who were unacquainted with the art of
making fire. Although the wood fire prevailed as a light-source
throughout uncounted centuries, it was subjected to more or less
improvement as civilization advanced. When the wood fire was brought
indoors the day was extended and early man began to develop his crude
arts. He thought and planned in the comfort and security of his cave or
hut. By the firelight he devised implements and even decorated his stone
surroundings with pictures which to-day reveal something of the thoughts
and activities of mankind during a civilization which existed many
thousand years ago.

When it was too warm to have a roaring fire upon the hearth, man devised
other means for obtaining light without undue warmth. He placed glowing
embers upon ledges in the walls, upon stone slabs, or even upon
suspended devices of non-inflammable material. Later he split long
splinters of wood from pieces selected for their straightness of grain.
These burning splinters emitting a smoking, feeble light were crude but
they were refinements of considerable merit. A testimonial of their
satisfactoriness is their use throughout many centuries. Until very
recent times the burning splinter has been in use in Scotland and in
other countries, and it is probable that at present in remote districts
of highly civilized countries this crude device serves the meager needs
of those whose requirements have been undisturbed by the progress of
civilization. Scott, in "The Legend of Montrose," describes a table
scene during a feast. Behind each seat a giant Highlander stood, holding
a blazing torch of bog-pine. This was also the method of lighting in the
Homeric age.

Crude clay relics representing a human head, from the mouth of which the
wood-splinters projected, appear to corroborate the report that the
flaming splinter was sometimes held in the mouth in order that both
hands of a workman would be free. Splinter-holders of many types have
survived, but most of them are of the form of a crude pedestal with a
notch or spring clip at its upper end. The splinter was held in this
clip and burned for a time depending upon its length and the character
of the wood. It was the business of certain individuals to prepare
bundles of splinters, which in the later stages of civilization were
sold at the market-place or from house to house. Those who have observed
the frontiersman even among civilized races will be quite certain that
the wood for splinters was selected and split with skill, and that the
splinters were burned under conditions which would yield the most
satisfactory light. It is a characteristic of those who live close to
nature, and are thus limited in facilities, to acquire a surprising
efficiency in their primitive activities.

An obvious step in the use of burning wood as a light-source was to
place such a fire on a shelf or in a cavity in the wall. Later when
metal was available, gratings or baskets were suspended from the ceiling
or from brackets and glowing embers or flaming chips were placed upon
them. Some of these were equipped with crude chimneys to carry away the
smoke, and perhaps to increase the draft. In more recent centuries the
first attempt at lighting outdoor public places was by means of metal
baskets in which flaming wood emitted light. It was the duty of the
watchman to keep these baskets supplied with pine knots. In early
centuries street-lighting was not attempted, and no serious efforts
worthy of consideration as adequate lighting were made earlier than
about a century ago. As a consequence the "link-boy" came into
existence. With flaming torch he would escort pedestrians to their homes
on dark nights. This practice was in vogue so recently that the
"link-boy" is remembered by persons still living. In England the
profession appears to have existed until about 1840.

Somewhat akin to the wood-splinter, and a forerunner of the candle, was
the rushlight. In burning wood man noticed that a resinous or fatty
material increased the inflammability and added greatly to the amount of
light emitted. It was a logical step to try to reproduce this condition
by artificial means. As a consequence rushes were cut and soaked in
water. They were then peeled, leaving lengths of pith partially
supported by threads of the skin which were not stripped off. These
sticks of pith were placed in the sun to bleach and to dry, and after
they were thoroughly dry they were dipped in scalding grease, which was
saved from cooking operations or was otherwise acquired for the purpose.
A reed two or three feet long held in the splinter-holder would burn for
about an hour. Thus it is seen that man was beginning to progress in the
development of artificial light. In developing the rushlight he was
laying the foundation for the invention of the candle. Pliny has
mentioned the burning of reeds soaked in oil as a feature of funeral
rites. Many crude forerunners of the candle were developed in various
parts of the world by different races. For example, the Malays made a
torch by wrapping resinous gum in palm leaves, thus devising a crude
candle with the wick on the outside.

Many primitive uses of vegetable and animal fats were forerunners of the
oil-lamp. In the East Indies the candleberry, which contains oily seeds,
has been burned for light by the natives. In many cases burning fish and
birds have served as lamps. In the Orkney Islands the carcass of a
stormy petrel with a wick in its mouth has been utilized as a
light-source, and in Alaska a fish in a split stick has provided a crude
torch for the natives. These primitive methods of obtaining artificial
light have been employed for centuries and many are in use at the
present time among uncivilized tribes and even by civilized beings in
the remote outskirts of civilization. Surely progress is limited where a
burning fish serves as a torch, or where, at best, the light-sources are
feeble, smoking, flickering, and ill-smelling!

Progress insisted upon a light-source which was free from the defects of
the crude devices already described and the next developments were
improvements to the extent at least that combustion was more thorough.
The early oil-lamps and candles did not emit much smoke, but they were
still feeble light-sources and not always without noticeable odors.
Nevertheless, they marked a tremendous advance in the production of
artificial light. Although they were not scientific developments in the
modern sense, the early oil-lamp and the candle represented the great
possibilities of utilizing knowledge rather than depending upon the raw
products of nature in unmodified forms. The advent of these two
light-sources in reality marked the beginning of the civilization which
was destined to progress and survive.

Although such primitive light-sources as the flaming splinter and the
glowing ember have survived until the present age, lamps consisting of a
wick dipped into a receptacle containing animal and vegetable oils have
been in use among the more advanced peoples since prehistoric times.
Oil-lamps are to be seen in the earliest Roman illustrations. During the
height of ancient civilization along the eastern shores of the
Mediterranean Sea, elaborate lighting was effected by means of the
shallow grease-or oil-lamp. It is difficult to estimate the age in which
this form of light-source originated, but some lamps in existence in
collections at the present time appear to have been made as early as
four or five thousand years before the Christian era. It is noteworthy
that such lamps did not differ materially in essential details from
those in use as late as a few centuries ago.

At first the grease used was the crude fat from animals. Vegetable oils
also were burned in the early lamps. The Japanese, for example,
extracted oil from nuts. When the demands of civilization increased,
extensive efforts were made to obtain the required fats and oils.
Amphibious animals of the North and the huge mammals of the sea were
slaughtered for their fat, and vegetable sources were cultivated.
Later, sperm and colza were the most common oils used by the advanced
races. The former is an animal oil obtained from the head cavities of
the sperm-whale; the latter is a vegetable oil obtained from rape-seed.
Mineral oil was introduced as an illuminant in 1853, and the modern lamp
came into use.

The grease-and oil-lamps in general were of such a form that they could
be carried with ease and they had flat bottoms so that they would rest
securely. The simplest forms had a single wick, but in others many wicks
dipped into the same receptacle. The early ones were of stone, but
later, lamps were modeled from clay or terra cotta and finally from
metals. They were usually covered and the wick projected through a hole
in the top near the edge. Large stone vases filled with a hundred pounds
of liquid fat are known to have been used in early times. As a part of
the setting in the celebration of festivals the ancient nations of Asia
and Africa placed along the streets bronze vases filled with liquid fat.
The Esquimaux to-day use this form of lamp, in which whale-oil and seal
blubber is the fuel. Incidentally, these lamps also supply the only
artificial heat for their huts and igloos. The heat from these feeble
light-sources and from their bodies keeps these natives of the arctics
warm within the icy walls of their abodes.

Very beautiful oil-lamps of brass, bronze, and pewter evolved in such
countries as Egypt. Many of these were designed for and used in
religious ceremonies. The oil-lamps of China, Scotland, and other
countries in later centuries were improved by the addition of a pan
beneath the oil-receptacle, to catch drippings from the wick or oil
which might run over during the filling. The Chinese lamps were
sometimes made of bamboo, but the Scottish lamps were made of metal. A
flat metal lamp, called a crusie, was one of the chief products of
blacksmiths and was common in Scotland until the middle of the
nineteenth century. This type of lamp was used by many nations and has
been found in the catacombs of Rome. The crusie was usually suspended by
an iron hook and the flow of oil to the wick could be regulated by
tilting. The wick in the Scottish lamps consisted of the pith of rushes,
cloth, or twisted threads. These early oil-lamps were almost always
shallow vessels into which a short wick was dipped, and it was not until
the latter part of the eighteenth century that other forms came into
general use. The change in form was due chiefly to the introduction of
scientific knowledge when mineral oil was introduced. As early as 1781
the burning of naptha obtained by distilling coal at low temperatures
was first discussed, but no general applications were made until a later
period. This was the beginning of many marked improvements in oil-lamps,
and was in reality the birth of the modern science of light-production.



As the activities of man became more complex he met from his growing
store of knowledge the increasing requirements of lighting. In
consequence, many ingenious devices for lighting were evolved. For
example, in England in the seventeenth century man was already burrowing
into the earth for coal and of course encountered coal-gases. These
inflammable gases were first known for the direful effects which they so
often produced rather than for their useful qualities. Although they
were known to miners long before they received scientific attention, the
earliest account of them in the Transactions of the Royal Society was
presented in the year 1667. A description of early gas-lighting has been
reserved for a later chapter, but the foregoing is noted at this point
to introduce a novel early method of lighting in coal-mines where
inflammable gases were encountered. In discussing this coal-gas another
early writer stated that "it will not take fire except by flame" and
that "sparks do not affect it." One of the early solutions of the
problem of artificial lighting under such conditions is summarized as

     Before the invention of Sir Humphrey Davy's Safety Lamp, this
     property of the gas gave rise to a variety of contrivances for
     affording the miners sufficient light to pursue their
     operations; and one of the most useful of these inventions was
     a mill for producing light by sparks elicited by the collision
     of flint and steel.

Such a stream of sparks may appear a very crude and unsatisfactory
solution as judged by present standards, but it was at least an
ingenious application of the facilities available at that time. Various
other devices were resorted to in the coal-mines before the introduction
of a safety lamp.

In discussing the candle it is necessary again to go back to an early
period, for it slowly evolved in the course of many centuries. It is the
natural descendant of the rushlight, the grease-lamp, and various
primitive devices. Until the advent of the more scientific age of
artificial lighting, the candle stood preëminent among early
light-sources. It did not emit appreciable smoke or odor and it was
conveniently portable and less fragile than the oil-lamp. Candles have
been used throughout the Christian era and some authorities are inclined
to attribute their origin to the Phoenicians. It is known that the
Romans used them, especially the wax-candles, in religious ceremonies.
The Phoenicians introduced them into Byzantium, but they disappeared
under the Turkish rule and did not come into use again until the twelfth

The wax-candle was very much more expensive than the tallow-candle until
the fifteenth century, when its relative cost was somewhat reduced,
bringing it within the means of a greater proportion of the people.
Nevertheless it has long been used, chiefly by the wealthy; the
departing guest of the early Victorian inn would be likely to find an
item on his bill such as this: "For a gentleman who called himself a
gentleman, wax-lights, 5/." Poor men used tallow dips or went to bed in
the dark. It is interesting to note the importance of the candle in the
household budget of early times in various sayings. For example, "The
game is not worth the candle," implies that the cost of candle-light was
not ignored. In these days little attention is given to the cost of
artificial light under similar conditions. If a person "burns a candle
at both ends" he is wasteful and oblivious to the consequences of
extravagance whether in material goods or in human energy.

With the rise of the Christian church, candles came to be used in
religious ceremonies and many of the symbolisms, meanings, and customs
survive to the present time. Some of the finest art of past centuries is
found in the old candlesticks. Many of these antiques, which ofttimes
were gifts to the church, have been preserved to posterity by the
church. The influence of these lighting accessories is often noted in
modern lighting-fixtures, but unfortunately early art often suffers from
adaptation to the requirements of modern light-sources, or the eyesight
suffers from a senseless devotion to art which results in the use of
modern light-sources, unshaded and glaring, in places where it was
unnecessary to shade the feeble candle.

The oldest materials employed for making candles are beeswax and tallow.
The beeswax was bleached before use. The tallow was melted and strained
and then cotton or flax fibers were dipped into it repeatedly, until the
desired thickness was obtained. In early centuries the pith of rushes
was used for wicks. Tallow is now used only as a source of stearine.
Spermaceti, a fatty substance obtained from the sperm-whale, was
introduced into candle-making in about 1750 and great numbers of men
searched the sea to fill the growing demands. Paraffin wax, a mixture of
solid hydrocarbons obtained from petroleum, came into use in 1854 and
stearine is now used with it. The latter increases the rigidity and
decreases the brittleness of the candle. Some of the modern candles are
made of a mixture of stearine and the hard fat extracted from
cocoanut-oil. Modern candles vary in composition, but all are the
product of much experience and of the application of scientific
knowledge. The wicks are now made chiefly of cotton yarn, braided or
plaited by machinery and chemically treated to aid in complete
combustion when the candle is burned. Their structure is the result of
long experience and they are now made so that they bend and dip into the
molten fuel and are wholly consumed. This eliminates the necessity of

Candles have been made in various ways, including dipping, pouring,
drawing, and molding. Wax-candles are made by pouring, because wax
cannot be molded satisfactorily. Drawing is somewhat similar to dipping,
except that the process is more or less continuous and is carried out by
machinery. Molding, as the term implies, involves the use of molds, of
the size and shape desired.

The candlestick evolved from the most primitive wooden objects to
elaborately designed and decorated works of art. The primitive
candlestick was crude and was no more than a holder of some kind for
keeping the candle upright. Later a form of cup was attached to the stem
of the holder, to catch the dripping wax or fat. The latter improvement
has persisted throughout the centuries. The modern candle is by no means
an unsatisfactory light-source. Those who have had experience with it in
the outskirts of civilization will testify that it possesses several
desirable characteristics. Supplies of candles are transported without
difficulty; the lighted candle is easily carried about; and the light in
a quiescent atmosphere is quite satisfactory, if common sense is used in
shading and placing the candle. Although in a sense a primitive
light-source, it is a blessing in many cases and, incidentally, it is
extensively used to-day in industries, in religious ceremonies, as a
decorative element at banquets, and in the outposts of civilization.

This account of the evolution of light-sources has crossed the threshold
of what may be termed modern scientific light-production in the case of
the candle and the oil-lamp. There is a period of a century or more
during which scientific progress was slow, but those years paved the way
for the extraordinary developments of the last few decades.



Inasmuch as the symbolisms and ceremonial uses of light originated in
the childhood of the human race and were nourished throughout the age of
mythology, the early light-sources are associated more with this phase
of artificial light than modern ones. For this reason it appears
appropriate to present this discussion before entering into the later
stages of the development and utilization of artificial light.
Furthermore, many of the traditions of lighting at the present time are
survivors of the early ages. Lighting-fixtures show the influence of
this byway of lighting, and in those cases where the ceremonial use of
light has survived to the present time, modern light-sources cannot be
employed wisely in replacing more primitive ones without consideration
of the origin and existence of the customs. In fact, candles are likely
to be used for hundreds of years to come, owing to the sentiment
connected with them and to the established customs founded upon
centuries of traditional use.

Doubtless, the sun as a source of heat and light and of the blessings
which these bring to earth, is responsible largely for the divine
significance bestowed upon light. Darkness very deservingly acquired
many uncomplimentary attributes, for danger lurked behind its veil and
it was the suitable abode of evil spirits. It harbored all that was the
antithesis of goodness, happiness, and security. Light naturally became
sacred, life-giving, and symbolic of divine presence. Fire was to
primitive beings the most impressive phenomenon over which they had any
control, and it was sufficiently mysterious in its operation to warrant
a connection with the supernatural. Thus it was very natural that these
earlier beings worshiped it as representing divine presence. The sun, as
Ra, was one of the chief gods of the ancient Egyptians; and the
Assyrians, the Babylonians, the ancient Greeks, and many other early
peoples gave a high place to this deity. Among simpler races the sun was
often the sole object of worship, and those peoples who worship Light as
the god of all, in a sense are not far afield. Fire-worshipers generally
considered fire as the purest representation of heavenly fire, the
origin of everything that lives.

Light was considered such a blessing that lamps were buried with the
dead in order that spirits should be able to have it in the next world.
This custom has prevailed widely but the fact that the lamps were
unlighted indicates that only the material aspect was considered. It is
interesting to note that the lamps and other light-sources in pagan
temples and religious processions were not symbolical but were offerings
to the gods. In later centuries a deeper symbolical meaning became
attached to light and burning lamps were placed upon the tombs of
important personages. The burying of lamps with the dead appears to have
originated in Asia. The Phoenicians and Romans apparently continued
the custom, but no traces of it have been found in Greece and Egypt.

Fire and light have been closely associated in various religious creeds
and their ceremonies. The Hindu festival in honor of the goddess of
prosperity is attended by the burning of many lamps in the temples and
homes. The Jewish synagogues have their eternal lamps and in their
rituals fire and light have played prominent rôles. The devout Brahman
maintains a fire on the hearth and worships it as omniscient and divine.
He expects a brand from this to be used to light his funeral pyre, whose
fire and light will make his spirit fit to enter his heavenly abode. He
keeps a fire burning on the altar, worships Agni, the god of fire, and
makes fire sacrifices on various occasions such as betrothals and
marriages. To the Mohammedans lighted lamps symbolize holy places, and
the Kaaba at Mecca, which contains a black stone supposed to have been
brought from heaven, is illuminated by thousands of lamps. Many of the
uses to which light was put in ancient times indicate its rarity and
sacred nature. Doubtless, the increasing use of artificial light at
festivals and celebrations of the present time is partly the result of
lingering customs of bygone centuries and partly due to a recognition of
an innate appeal or attribute of light. Certainly nothing is more
generally appropriate in representing joy and prosperity.

Throughout all countries ancient races had woven natural light and fire
into their rites and customs, so it became a natural step to utilize
artificial light and fire in the same manner. It would be tedious and
monotonous to survey the vast field of ancient worship of light, for the
underlying ideas are generally similar. The mythology of the Greeks is
illustrative of the importance attached to fire and light by the
cultivated peoples of ancient times. The myth of Prometheus emphasizes
the fact that in those remote periods fire and light were regarded as of
prime importance. According to this myth, fire and light were contained
in heaven and great cunning and daring were necessary in order to obtain
it. Prometheus stole this heavenly fire, for which act he was chained to
the mountain and made to suffer. The Greeks mark this event as the
beginning of human civilization. All arts are traced to Prometheus, and
all earthly woe likewise. As past history is surveyed it appears natural
to think of scientific men who have become martyrs to the quest of
hidden secrets. They have made great sacrifices for the future benefit
of civilization and not a few of them have endured persecution even in
recent times. The Greeks recognized that a new era began with the
acquisition of artificial light. Its divine nature was recognized and it
became a phenomenon for worship and a means for representing divine
presence. The origin of fire and light made them holy. The fire on the
altar took its place in religious rites and there evolved many
ceremonial uses of lamps, candles, and fire.

The Greeks and Romans burned sacred lamps in the temples and utilized
light and fire in many ceremonies. The torch-race, in which young men
ran with lighted torches, the winner being the one who reached the goal
first with his torch still alight, originated in a Grecian ceremony of
lighting the sacred fire. There are many references in ancient Roman and
Grecian literature to sacred lamps burning day and night in sanctuaries
and before statues of gods and heroes. On birthdays and festivals the
houses of the Romans were specially ornamented with burning lamps. The
Vestal Virgins in Rome maintained the sacred fire which had been brought
by fugitives from Troy. In ancient Rome when the fire in the Temple of
Vesta became extinguished, it was rekindled by the rubbing of a piece of
wood upon another until fire was obtained. This was carried into the
temple by the Vestal Virgin and the sacred fire was rekindled. The fire
produced in this manner, for some reason, was considered holy.

The early peoples displayed many lamps on feast-days and an example of
extravagance in this respect is an occasion when King Constantine
commanded that the entire city of Constantinople be illuminated by
wax-candles on Christmas Eve. Candelabra, of the form of the branching
tree, were commonly in use in the Roman temples.

The ceremonial use of light in the Christian church evolved both from
adaptations of pagan customs and of the natural symbolisms of fire and
light. However, these acquired a deeper meaning in Christianity than in
early times because they were primarily visible representations or
manifestations of the divine presence. The Bible contains many
references to the importance and symbolisms of light and fire. According
to the First Book of Moses, the achievement of the Creator immediately
following the creation of "the heavens and the earth" was the creation
of light. The word "light" is the forty-sixth word in Genesis. Christ is
"the true light" and Christians are "children of light" in war against
the evil "powers of darkness." When St. Paul was converted "there
shined about him a great light from heaven." The impressiveness and
symbolism of fire and light are testified to in many biblical
expressions. Christ stands "in the midst of seven candle-sticks" with
"his eyes as a flame of fire." When the Holy Ghost appeared before the
apostles "there appeared unto them cloven tongues of fire." When St.
Paul was preaching the gospel of Christ at Alexandria "there were many
lights" suggesting a festive illumination.

According to the Bible, the perpetual fire which came originally from
heaven was to be kept burning on the altar. It was holy and those whose
duty it was to keep it burning were guilty of a grave offense if they
allowed it to be extinguished. If human hands were permitted to kindle
it, punishment was meted out. The two sons of Aaron who "offered strange
fire before the Lord" were devoured by "fire from the Lord." The
seven-branched candlestick was lighted eternally and these burning
light-sources were necessary accompaniments of worship.

The countless ceremonial uses of fire and light which had evolved in the
past centuries were bound to influence the rites and customs of the
Christian church. The festive illumination of pagan temples in honor of
gods was carried over into the Christian era. The Christmas tree of
to-day is incomplete without its many lights. Its illumination is a
homage of light to the source of light. The celebration of Easter in the
Church of the Holy Sepulchre in Jerusalem is a typical example of
fire-worship retained from ancient times. At the climax of the services
comes the descent of the Holy Fire. The central candelabra suddenly
becomes ablaze and the worshipers, each of whom carries a wax taper,
light their candles therefrom and rush through the streets. The fire is
considered to be of divine origin and is a symbol of resurrection. The
custom is similar in meaning to the light which in older times was
maintained before gods.

During the first two or three centuries of the Christian era the
ceremonial use of light does not appear to have been very extensive.
Writings of the period contain statements which appear to ridicule this
use to some extent. For example, one writer of the second century states
that "On days of rejoicing ... we do not encroach upon daylight with
lamps." Another, in the fourth century, refers with sarcasm to the
"heathen practice" in this manner: "They kindle lights as though to one
who is in darkness. Can he be thought sane who offers the light of lamps
and candles to the Author and Giver of all light?"

That candles were lighted in cemeteries is evidenced by an edict which
forbade their use during the day. Lamps of the early centuries of the
Christian era have been found in the catacombs of Rome which are thought
to have been ceremonial lamps, for they were not buried with the dead.
They were found only in niches in the walls. During these same centuries
elaborate candelabra containing hundreds of candles were kept burning
before the tombs of saints. Notwithstanding the doubt that exists as to
the extent of ceremonial lighting in the early centuries of the
Christian era, it is certain that by the beginning of the fifth century
the ceremonial use of light in the Christian church had become very
extensive and firmly established. That this is true and that there were
still some objections is indicated by many controversies. Some thought
that lamps before tombs were ensigns of idolatry and others felt that no
harm was done if religious people thus tried to honor martyrs and
saints. Some early writings convey the idea that the ritualistic use of
lights in the church arose from the retention of lights necessary at
nocturnal services after the hours of worship had been changed to

Passing beyond the early controversial period, the ceremonial use of
light is everywhere in evidence at ordinary church services. On special
occasions such as funerals, baptisms, and marriages, elaborate
altar-lighting was customary. The gorgeous candelabra and the eternal
lamp are noted in many writings. Early in the fifth century the pope
ordered that candles be blessed and provided rituals for this ceremony.
Shortly after this the Feast of Purification of the Virgin was
inaugurated and it became known as Candlemas because on this day the
candles for the entire year were blessed. However, it appears that the
blessing of candles was not carried out in all churches. Altar lights
were not generally used until the thirteenth century. They were
originally the seven candles carried by church officials and placed near
the altar.

The custom of placing lighted lamps before the tombs of martyrs was
gradually extended to the placing of such lamps before various objects
of a sacred or divine relation. Finally certain light-sources themselves
became objects of worship and were surrounded by other lamps, and the
symbolisms of light grew apace. A bishop in the sixth century heralded
the triple offering to God represented by the burning wax-candle. He
pointed out that the rush-wick developed from pure water; that the wax
was the product of virgin bees; and that the flame was sent from heaven.
Each of these, he was certain, was an offering acceptable to God.
Wax-candles became associated chiefly with religious ceremonies. The wax
later became symbolic of the Blessed Virgin and of the body of Christ.
The wick was symbolical of Christ's soul, the flame represented his
divine character, and the burning candle thus became symbolical of his
death. The lamp, lantern, and taper are frequently symbols of piety,
heavenly wisdom, or spiritual light. Fire and flames are emblems of zeal
and fervor or of the sufferings of martyrdom and the flaming heart
symbolizes fervent piety and spiritual or divine love.

By the time the Middle Ages were reached the ceremonial uses of light
became very complex, but for the Roman Catholic Church they may be
divided into three general groups: (1) They were symbolical of God's
presence or of the effect of his presence; of Christ or of "the children
of light"; or of joy and content at festivals. (2) They may be offered
in fulfillment of a religious vow; that is, as an act of worship. (3)
They may possess certain divine power because of their being blessed by
the church, and therefore may be helpful to soul and body. The three
conceptions are indicated in the prayers offered at the blessing of the
candles on Candlemas as follows: (1) "O holy Lord ... who ... by thy
command didst cause this liquid to come by the labor of bees to the
perfection of wax, ... we beseech thee ... to bless and sanctify these
candles for the use of men, and the health of bodies and souls...." (2)
"...these candles, which we thy servants desire to carry lighted to
magnify thy name; that by offering them to thee, being worthily inflamed
with the holy fire of thy most sweet charity, we may deserve...." (3) "O
Lord Jesus Christ, the true light, ... mercifully grant, that as these
lights enkindled with visible fire dispel nocturnal darkness, so our
hearts illuminated by visible fire," etc.

In general, the ceremonial uses of lights in this church were originated
as a forceful representation of Christ and of salvation. On the eve of
Easter a new fire, emblematic of the arisen Christ, is kindled, and all
candles throughout the year are lighted from this. During the service of
Holy Week thirteen lighted candles are placed before the altar and as
the penitential songs are sung they are extinguished one by one. When
but one remains burning it is carried behind the altar, thus symbolizing
the last days of Christ on earth. It is said that this ceremony has been
traced to the eighth century. On Easter Eve, after the new fire is
lighted and blessed, certain ceremonies of light symbolize the
resurrection of Christ. From this new fire three candles are lighted and
from these the Paschal Candle. The origin of the latter is uncertain,
but it symbolizes a victorious Christ. From it all the ceremonial lights
of the church are lighted and they thereby are emblematic of the
presence of the light of Christ.

Many interesting ceremonial uses may be traced out, but space permits a
glimpse of only a few. At baptismal services the paschal candle is
dipped into the water so that the latter will be effective as a
regenerative element. The baptized child is reborn as a child of light.
Lighted candles are placed in the hands of the baptized persons or of
their god-parents. Those about to take vows carry lights before the
church official and the same idea is attached to the custom of carrying
or of holding lights on other occasions such as weddings and first
communion. Lights are placed around the bodies of the dead and are
carried at the funeral. They not only protect the dead from the powers
of darkness but they symbolize the dead as still living in the light of
Christ. The use of lighted candles around bodies of the dead still
survives to some extent among Protestants, but their significance has
been lost sight of. Even in the eighteenth century funerals in England
were accompanied by lighted tapers, but the carrying of lights in other
processions appears to have ceased with the Reformation. In some parts
of Scotland it is still the custom to place two lighted candles on a
table beside a corpse on the day of the funeral.

With the importance of light in the ritual of the church it is not
surprising that the extinction of lights is a part of the ceremony of
excommunication. Such a ceremony is described in an early writing thus:
"Twelve priests should stand about the bishop, holding in their hands
lighted torches, which at the conclusion of the anathema or
excommunication they should cast down and trample under foot." When the
excommunicant is reinstated, a lighted candle is placed in his hands as
a symbol of reconciliation. These and many other ceremonial uses of
light have been and are practised, but they are not always mandatory.
Furthermore, the customs have varied from time to time, but the few
which have been touched upon illustrate the impressive part that light
has played in religious services.

During the Reformation the ceremonial use of lights was greatly altered
and was abolished in the Protestant churches as a relic of superstition
and papal authority. In the Lutheran churches ceremonial lights were
largely retained, in the Church of England they have been subjected to
many changes largely through the edicts of the rulers. In the latter
church many controversies were waged over ceremonial lights and their
use has been among the indictments of a number of officials of the
church in impeachment cases before the House of Commons. Many uses of
light in religious ceremonies were revived in cathedrals after the
Restoration and they became wide-spread in England in the nineteenth
century. As late as 1889 the Archbishop of Canterbury ruled that certain
ceremonial candles were lawful according to the Prayer-Book of Edward
VI, but the whole question was left open and unsettled.

These byways of artificial light are complex and fascinating because
their study leads into many channels and far into the obscurity of the
childhood of the human race. A glimpse of them is important in a survey
of the influence of artificial light upon the progress of civilization
because in these usages the innate and acquired impressiveness of light
is encountered. Although many ceremonial uses of light remain, it is
doubtful if their significance and especially their origin are
appreciated by most persons. Nevertheless, no more interesting phase of
artificial light is encountered than this, which reaches to the
foundation of civilization.



It will be noted that the light-sources throughout the early ages were
flames, the result of burning material. This principle of
light-production has persisted until the present time, but in the latter
part of the nineteenth century certain departures revolutionized
artificial lighting. However, it is not the intention to enter the
modern period in this chapter except in following the progress of the
oil-lamp through its period of scientific development. The oil-lamp and
the candle were the mainstays of artificial lighting throughout many
centuries. The fats and waxes which these light-sources burned were many
but in the later centuries they were chiefly tallow, sperm-oil,
spermaceti, lard-oil, olive-oil, colza-oil, bees-wax and vegetable
waxes. Those fuels which are not liquid are melted to liquid form by the
heat of the flame before they are actually consumed. The candle is of
the latter type and despite its present lowly place and its primitive
character, it is really an ingenious device. Its fuel remains
conveniently solid so that it is readily shipped and stored; there is
nothing to spill or to break beyond easy repair; but when it is lighted
the heat of its flame melts the solid fuel and thus it becomes an
"oil-lamp." Animal and vegetable oils were mainly used until the middle
of the nineteenth century, when petroleum was produced in sufficient
quantities to introduce mineral oils. This marked the beginning of an
era of developments in oil-lamps, but these were generally the natural
offspring of early developments by Ami Argand.

Before man discovered that nature had stored a tremendous supply of
mineral oil in the earth he was obliged to hunt broadcast for fats and
waxes to supply him with artificial light. He also was obliged to endure
unpleasant odors from the crude fuels and in early experiments with fats
and waxes the odor was carefully noted as an important factor. Tallow
was a by-product of the kitchen or of the butcher. Stearine, a
constituent of tallow, is a compound of glyceryl and stearic acid. It is
obtained by breaking up chemically the glycerides of animal fats and
separating the fatty acids from glycerin. Fats are glycerides; that is,
combinations of oleic, palmetic, and stearic acids. Inasmuch as the
former is liquid at ordinary temperatures and the others are solid, it
follows that the consistency or solidity of fats depend upon the
relative proportions of the three constituents. The sperm-whale, which
lives in the warmer parts of all the oceans, has been hunted
relentlessly for fuels for artificial lighting. In its head cavities
sperm-oil in liquid form is found with the white waxy substance known as
spermaceti. Colza-oil is yielded by rape-seed and olive-oil is extracted
from ripe olives. The waxes are combinations of allied acids with bases
somewhat related to glycerin but of complex composition. Fats and waxes
are more or less related, but to distinguish them carefully would lead
far afield into the complexities of organic chemistry. All these animal
and vegetable products which were used as fuels for light-sources are
rich in carbon, which accounts for the light-value of their flames. The
brightness of such a flame is due to incandescent carbon particles, but
this phase of light-production is discussed in another chapter. These
oils, fats, and waxes are composed by weight of about 75 to 80 per cent.
carbon; 10 to 15 per cent. hydrogen; and 5 to 10 per cent. oxygen.

Until the middle of the eighteenth century the oil-lamps were shallow
vessels filled with animal or vegetable oil and from these reservoirs
short wicks projected. The flame was feeble and smoky and the odors were
sometimes very repugnant. Viewing such light-sources from the present
age in which light is plentiful, convenient, and free from the great
disadvantages of these early oil-lamps, it is difficult to imagine the
possibility of the present civilization emerging from that period
without being accompanied by progress in light-production. The
improvements made in the eighteenth century paved the way for greater
progress in the following century. This is the case throughout the ages,
but there are special reasons for the tremendous impetus which
light-production has experienced in the past half-century. These are the
acquirement of scientific knowledge from systematic research and the
application of this knowledge by organized development.

The first and most notable improvement in the oil-lamp was made by
Argand in 1784. Our nation was just organizing after its successful
struggle for independence at the time when the production of light as a
science was born. Argand produced the tubular wick and contributed the
greatest improvement by being the first to perform the apparently simple
act of placing a glass chimney upon the lamp. His burner consisted of
two concentric metal tubes between which the wick was located. The inner
tube was open, so that air could reach the inner surface of the wick as
well as the outer surface. The lamp chimney not only protected the flame
from drafts but also improved combustion by increasing the supply of
air. It rested upon a perforated flange below the burner. If the glass
chimney of a modern kerosene lamp be lifted, it will be noted that the
flame flickers and smokes and that it becomes steady and smokeless when
the chimney is replaced. The advantages of such a chimney are obvious
now, but Argand for his achievements is entitled to a place among the
great men who have borne the torch of civilization. He took the first
step toward adequate artificial light and opened a new era in lighting.

The various improvements of the oil-lamp achieved by Argand combined to
effect complete combustion, with the result that a steady, smokeless
lamp of considerable luminous intensity was for the first time
available. Many developments followed, among which was a combination of
reservoir and gravity feed which maintained the oil at a constant level.
In later lamps, upon the adoption of mineral oil, this was found
unnecessary, perhaps owing to the construction of the wick and to the
physical characteristics of the oil which favored capillary action in
the wick. However, the height of the oil in the reservoir of modern
oil-lamps makes some difference in the amount of light emitted.

The Carcel lamp, which appeared in 1800, consisted of a double piston
operated by clockwork. This forced the oil through a tube to the burner.
Franchot invented the moderator lamp in 1836, which, because of its
simplicity and efficiency soon superseded many other lamps designed for
burning animal and vegetable oils. The chief feature of the moderator
lamp is a spiral spring which forces the oil upward through a vertical
tube to the burner. These are still used to some extent in France, but
owing to the fact that "mechanical" lamps eventually were very generally
replaced by more simple ones, it does not appear necessary to describe
these complex mechanisms in detail.

When coal is distilled at moderate temperatures, volatile liquids are
obtained. These hydrocarbons, being inflammable, naturally attracted
attention when first known, and in 1781 their use as fuel for lamps was
suggested. However, it was not until 1820 that the light oils obtained
by distilling coal-tar, a by-product of the coal-gas industry which was
then in its early stage of development, were burned to some extent in
the Holliday lamp. In this lamp the oil is contained in a reservoir from
the bottom of which a fine metal tube carries the oil down to a
rose-burner. The oil is heated by the flame and the vaporized mineral
oil which escapes through small orifices is burned. This type of lamp
has undergone many physical changes, but its principle survives to the
present time in the gasolene and kerosene burners hanging on a pole by
the side of the street-peddler's stand.

Although petroleum products were not used to any appreciable extent for
illuminating-purposes until after the middle of the nineteenth century,
mineral oil is mentioned by Herodotus and other early writers. In 1847
petroleum was discovered in a coal-mine in England, but the supply
failed in a short time. However, the discoverer, James Young, had found
that this oil was valuable as a lubricant and upon the failure of this
source he began experiments in distilling oil from shale found in coal
deposits. These were destined to form the corner-stone of the oil
industry in Scotland. In 1850 he began producing petroleum in this
manner, but it was not seriously considered for illuminating-purposes.
However, in Germany about this time lamps were developed for burning the
lighter distillates and these were introduced into several countries.
But the price of these lighter oils was so great that little progress
was made until, in 1859, Col. E. L. Drake discovered oil in Pennsylvania.
By studying the geological formations and concluding that oil should be
obtained by boring, Drake gave to the world a means of obtaining
petroleum, and in quantities which were destined to reduce the price of
mineral oil to a level undreamed of theretofore. To his imagination,
which saw vast reservoirs of oil in the depths of the earth, the world
owes a great debt. Lamps were imported from Germany to all parts of the
civilized world and the kerosene lamp became the prevailing
light-source. Hundreds of American patents were allowed for oil-lamps
and their improvements in the next decade.



The crude petroleum, of course, is not fit for illuminating purposes,
but it contains components which are satisfactory. The various
components are sorted out by fractional distillation and the oil for
burning in lamps is selected according to its volatility, viscosity,
stability, etc. It must not be so volatile as to have a dangerously
low flashing-point, nor so stable as to hinder its burning well. In this
fractional distillation a vast variety of products are now obtained.
Gasolene is among the lighter products, with a density of about 0.65;
kerosene has a density of about 0.80; the lubricating-oils from 0.85 to
0.95; and there are many solids such as vaseline and paraffin which are
widely used for many purposes. This process of refining oils is now the
source of paraffin for making candles, in which it is usually mixed with
substances like stearin in order to raise its melting-point.

Crude petroleum possesses a very repugnant odor; it varies in color from
yellow to black; and its specific gravity ranges from about 0.80 to
1.00, but commonly is between 0.80 and 0.90. Its chemical constitution
is chiefly of carbon and hydrogen, in the approximate ratio of about six
to one respectively. It is a mixture of paraffin hydrocarbons having the
general formula of C_{n}H_{2n+2} and the individual members of this
series vary from CH_{4} (methane) to C_{15}H_{32} (pentadecane),
although the solid hydrocarbons are still more complex. Petroleum is
found in many countries and the United States is particularly blessed
with great stores of it.

The ordinary lamp consisting of a wick which draws up the mineral oil
and feeds it to a flame is efficient and fairly free from danger. It
requires care and may cause disaster if it is upset, but it has been
blamed unjustly in many accidents. A disadvantage of the kerosene lamp
over electric lighting, for example, is the relatively greater
possibility of accidents through the carelessness of the user. This
point is brought out in statistics of fire-insurance companies, which
show that the fires caused by kerosene lamps are much more numerous than
those from other methods of lighting. If in a modern lamp of proper
construction a close-fitting wick is used and the lamp is extinguished
by turning down and blowing across the chimney, there is little danger
in its use excepting accidental breakage or overturning.

In oil-lamps at the present time mineral oils are used which possess
flashing-points above 75°F. The highly volatile components of petroleum
are dangerous because they form very explosive mixtures with air at
ordinary temperatures. A mineral oil like kerosene, to be used with
safety in lamps, should not be too volatile. It is preferable that an
inflammable vapor should not be given off at temperatures under 120°F.
The oil must be of such physical characteristics as to be drawn up to
the burner by capillarity from the reservoir which is situated below. It
is volatilized by the heat of the flame into a mixture of hydrogen and
hydrocarbon gases and these are consumed under the heat of the process
of consumption by the oxygen in the air. The resulting products of this
combustion, if it is complete, are carbon dioxide and water-vapor. For
each candle-power of light per hour about 0.24 cubic foot of carbon
dioxide and 0.18 cubic foot of water-vapor are formed by a modern
oil-lamp. That an open flame devours something from the air is easily
demonstrated by enclosing it in an air-tight space. The flame gradually
becomes feeble and smoky and finally goes out. It will be noted that a
burning lamp will vitiate the atmosphere of a closed room by consuming
the oxygen and returning in its place carbon dioxide. This is similar to
the vitiation of the atmosphere by breathing persons and tests indicate
that for each two candle-power emitted by a kerosene flame the vitiation
is equal to that produced by one adult person. Inasmuch as oil-lamps are
ordinarily of 10 to 20 candle-power, it is seen that one lamp will
consume as much oxygen as several persons.

In order that oil-lamps may produce a brilliant light free from smoke,
combustion must be complete. The correct quantity of oil must be fed to
the burner and it must be properly vaporized by heat. If insufficient
oil is fed, the intensity of the light is diminished and if too much is
available at the burner, smoke and other products of incomplete
combustion will be emitted. The wick is an important factor, for,
through capillarity, it feeds oil forcefully to the burner against the
action of gravity. This action of a wick is commonly looked upon with
indifference but in reality it is caused by an interesting and really
wonderful phenomenon. Wicks are usually made of high-grade cotton fiber
loosely spun into coarse threads and these are woven into a loose plait.
The wick must be dry before being inserted into the burner; and it is
desirable that it be considerably longer than is necessary merely to
reach the bottom of the reservoir. A flame burning in the open will
smoke because insufficient oxygen is brought in contact with it. The
injurious products of this incomplete combustion are carbon monoxide and
oil vapors, which are a menace to health.

To supply the necessary amount of oxygen (air) to the flame, a forced
draft is produced. Chimneys are simple means of accomplishing this, and
this is their function whether on oil-lamps or factories. Other means of
forced draft have been used, such as small fans or compressed air. In
the railway locomotive the short smoke-stack is insufficient for
supplying large quantities of air to the fire-box so the exhausted steam
is allowed to escape into the stack. With each noisy puff of smoke a
quantity of air is forcibly drawn into the fire-box through the burning
fuel. In the modern oil-lamp the rush of air due to the "pull" of the
chimney is broken and the air is diffused by the wire gauze or holes at
the base of the burner. These metal parts, being hot, also serve to warm
the oil before it reaches the burning end of the wick, thus serving to
aid vaporization and combustion.

The consumption of oil per candle-power per hour varies considerably
with the kind of lamp and with the character of the oil. The average
consumption of oil-lamps burning a mineral oil of about 0.80 specific
gravity and a rather high flashing-point is about 50 to 60 grams of oil
per candle-power per hour for well-designed flame-lamps. Kerosene weighs
about 6.6 pounds per gallon; therefore, about 800 candle-power hours per
gallon are obtained from modern lamps employing wicks. Kerosene lamps
are usually of 10 to 20 candle-power, although they are made up to 100
candle-power. These luminous intensities refer to the maximum horizontal
candle-power. The best practice now deals with the total light output,
which is expressed in lumens, and on this basis a consumption of one
gallon of kerosene per hour would yield about 8000 lumens.

Oil-lamps have been devised in which the oil is burned as a spray
ejected by air-pressure. These burn with a large flame; however, a
serious feature is the escape of considerable oil which is not burned.
These lamps are used in industrial lighting, especially outdoors, and
possess the advantage of consuming low-grade oils. They produce about
700 to 800 candle-power hours per gallon of oil. Lamps of this type of
the larger sizes burn with vertical flames two or three feet high. The
oil is heated as it approaches the nozzle and is fairly well vaporized
on emerging into the air. The names of Lucigen, Wells, Doty, and others
are associated with this type of lamp or torch, which is a step in the
direction of air-gas lighting.

During the latter part of the nineteenth century numerous developments
were made which paralleled the progress in gas-lighting. Experiments
were conducted which bordered closely upon the next epochal event in
light-production--the appearance of the gas mantle. One of these was the
use of platinum gauze by Kitson. He produced an apparatus similar to the
oil-spray lamp, on a small and more delicate scale. The hot blue flame
was not very luminous and he attempted to obtain light by heating a
mantle of fine platinum gauze. Although these mantles emitted a
brilliant light for a few hours, their light-emissivity was destroyed by
carbonization. After the appearance of the Welsbach mantle, Kitson's
lamp and others met with success by utilizing it. From this point,
attention was centered upon the new wonder, which is discussed in a
later chapter after certain scientific principles in light-production
have been discussed.

The kerosene or mineral-oil lamp was a boon to lighting in the
nineteenth century and even to-day it is a blessing in many homes,
especially in villages, in the country, and in the remote districts of
civilization. Its extensive use at the present time is shown by the fact
that about eight million lamp-chimneys are now being manufactured yearly
in this country. It is convenient and safe when carelessness is avoided,
and is fairly free from odor. Its vitiation of the atmosphere may be
counteracted by proper ventilation and there remains only the
disadvantage of keeping it in order and of accidental breakage and
overturning. The kerosene lantern is widely used to-day, but the danger
due to accident is ever-present. The consequences of such accidents are
often serious and are exemplified in the terrible conflagration in
Chicago in 1871, when Mrs. O'Leary's cow kicked over a lantern and
started a fire which burned the city. Modern developments in lighting
are gradually encroaching upon the territory in which the oil-lamp has
reigned supreme for many years. Acetylene plants were introduced to a
considerable extent some time ago and to-day the self-contained
home-lighting electric plant is being installed in large numbers in the
country homes of the land.



Owing to the fact that the smoky, flickering oil-lamp persisted
throughout the centuries and until the magic touch of Argand in the
latter part of the eighteenth century transformed it into a commendable
light-source, the reader is prepared to suppose that gas-lighting is of
recent origin. Apparently William Murdock in England was the first to
install pipes for the conveyance of gas for lighting purposes. In an
article in the "Philosophical Transactions of the Royal Society of
London" dated February 25, 1808, in which he gives an account of the
first industrial gas-lighting, he states:

     It is now nearly sixteen years, since, in a course of
     experiments I was making at Redruth in Cornwall, upon the
     quantities and qualities of the gases produced by distillation
     from different mineral and vegetable substances, I was induced
     by some observation I had previously made upon the burning of
     coal, to try the combustible property of the gases produced
     from it....

Inasmuch as he is credited with having lighted his home by means of
piped gas, this experimental installation may be considered to have been
made in 1792. In his first trial he burned the gas at the open ends of
the pipes; but finding this wasteful, he closed the ends and in each
bored three small holes from which the gas-flames diverged. It is said
that he once used his wife's thimble in an emergency to close the end of
the pipe; and, the thimble being much worn and consequently containing a
number of small holes, tiny gas-jets emerged from the holes. This
incident is said to have led to the use of small holes in his burners.
He also lighted a street lamp and had bladders filled with gas "to carry
at night, with which, and his little steam carriage running on the road,
he used to astonish the people." Apparently unknown to Murdock, previous
observations had been made as to the inflammability of gas from coal.
Long before this Dr. Clayton described some observations on coal-gas,
which he called "the spirit of coals." He filled bladders with this gas
and kept them for some time. Upon his pricking one of them with a pin
and applying a candle, the gas burned at the hole. Thus Clayton had a
portable gas-light. He was led to experiment with distillation of coal
from some experiences with gas from a natural coal bed, and he thus
describes his initial laboratory experiment:

     I got some coal, and distilled it in a retort in an open fire.
     At first there came over only phlegm, afterwards a black _oil_,
     and then likewise, a _spirit_ arose which I could no ways
     condense; but it forced my lute and broke my glasses. Once when
     it had forced my lute, coming close thereto, in order to try to
     repair it, I observed that the spirit which issued out _caught
     fire_ at the _flame_ of the _candle_, and continued burning
     with violence as it _issued out_ in a _stream_, which I blew
     out, and lighted again alternately several times.

He then turned his attention to saving some of the gas and hit upon the
use of bladders. He was surprised at the amount of gas which was
obtained from a small amount of coal; for, as he stated, "the spirit
continued to rise for several hours, and filled the bladders almost as
fast as a man could have blown them with his mouth; and yet the quantity
of coals distilled was inconsiderable."

Although this account appeared in the Transactions of the Royal Society
in 1739, there is strong evidence that Dr. Clayton had written it many
years before, at least prior to 1691.

But before entering further into the early history of gas-lighting, it
is interesting to inquire into the knowledge possessed in the
seventeenth century pertaining to natural and artificial gas. Doubtless
there are isolated instances throughout history of encounters with
natural gas. Surely observant persons of bygone ages have noted a small
flame emanating from the end of a stick whose other end was burning in a
bonfire or in the fireplace. This is a gas-plant on a small scale; for
the gas is formed at the burning end of the wooden stick and is
conducted through its hollow center to the cold end, where it will burn
if lighted. If a piece of paper be rolled into the form of a tube and
inclined somewhat from a horizontal position, inflammable gas will
emanate from the upper end if the lower end is burning. By applying a
match near the upper end, we can ignite this jet of gas. However, it is
certain that little was known of gas for illuminating purposes before
the eighteenth century.

The literature of an ancient nation is often referred to as revealing
the civilization of the period. Surely the scientific literature which
deals with concrete facts is an exact indicator of the technical
knowledge of a period! That little was known of natural gas and
doubtless of artificial gas in the seventeenth century is shown by a
brief report entitled "A Well and Earth in Lancashire taking Fire at a
Candle," by Tho. Shirley in the Transactions of the Royal Society in
1667. Much of the quaint charm of the original is lost by inability to
present the text in its original form, but it is reproduced as closely
as practicable. The report was as follows:

     About the latter End of _Feb._ 1659, returning from a Journey
     to my House in Wigan, I was entertained with the Relation of an
     odd Spring situated in one Mr. _Hawkley's_ Ground (if I mistake
     not) about a Mile from the Town, in that Road which leads to
     _Warrington_ and _Chester_: The People of this Town did
     confidently affirm, That the Water of this Spring did burn like

     When we came to the said Spring (being 5 or 6 in Company
     together) and applied a lighted Candle to the Surface of the
     Water; there was 'tis true, a large Flame suddenly produced,
     which burnt the Foot of a Tree, growing on the Top of a
     neighbouring Bank, the Water of which Spring filled a Ditch
     that was there, and covered the Burning-place; I applied the
     lighted Candle to divers Parts of the Water contained in the
     said Ditch, and found, as I expected, that upon the Touch of
     the Candle and the Water the Flame was extinct.

     Again, having taken up a Dish full of water at the flaming
     Place, and held the lighted Candle to it, it went out. Yet I
     observed that the Water, at the Burning-place, did boil, and
     heave, like Water in a Pot upon the Fire, tho' by putting my
     Hand into it, I could not perceive it so much as warm.

     This Boiling I conceived to proceed from the Eruption of some
     bituminous or sulphureous Fumes; considering this Place was not
     above 30 or 40 Yards distant from the Mouth of a Coal-Pit
     there: And indeed _Wigan_, _Ashton_, and the whole Country, for
     many Miles compass, is underlaid with Coal. Then, applying my
     Hand to the Surface of the Burning-place of the Water, I found
     a strong Breath, as it were a Wind, to bear against my Hand.

     When the Water was drained away, I applied the Candle to the
     Surface of the dry Earth, at the same Point where the Water
     burned before; the Fumes took fire, and burned very bright and
     vigorous. The Cone of the Flame ascended a Foot and a half from
     the Superficies of the Earth; and the Basis of it was of the
     Compass of a Man's Hat about the Brims. I then caused a Bucket
     full of Water to be pour'd on the Fire, by which it was
     presently quenched. I did not perceive the Flame to be
     discoloured like that of sulphurous Bodies, nor to have any
     manifest Scent with it. The Fumes, when they broke out of the
     Earth, and press'd against my Hand, were not, to my best
     Remembrance, at all hot.

Turning again to Dr. Clayton's experiments, we see that he pointed out
striking and valuable properties of coal-gas but apparently gave no
attention to its useful purposes. Furthermore, his account appears to
have attracted no particular notice at the time of its publication in
1739. Dr. Richard Watson in 1767 described the results of experiments
which he had been making with the products arising from the distillation
of coal. In his process he permitted the gas to ascend through curved
tubes, and he particularly noted "its great inflammability as well as
elasticity." He also observed that "it retained the former property
after it had passed through a great quantity of water." His published
account dealt with a variety of facts and computations pertaining to the
quantities of coke, tar, etc., produced from different kinds of coal and
was a scientific work of value, but apparently the usefulness of the
property of inflammability of coal-gas did not occur to him.

It is usually the habit of the scientific explorer of nature to return
from excursions into her unfrequented recesses with new knowledge, to
place it upon exhibition, and to return for more. The inventor passes by
and sees applications for some of these scientific trophies which are
productive of momentous consequences to mankind. Sir Humphrey Davy
described his primitive arc-lamp three quarters of a century before
Brush developed an arc-lamp for practical purposes. Maxwell and Hertz
respectively predicted and produced electromagnetic waves long before
Marconi applied this knowledge and developed "wireless" telegraphy. In a
similar manner scientific accounts of the production and properties of
coal-gas antedated by many years the initial applications made by
Murdock to illuminating purposes.

Up to the beginning of the nineteenth century the civilized world had
only a faint glimpse of the illuminating property of gas, but
practicable gas-lighting was destined soon to be an epochal event in the
progress of lighting. The dawn of modern science was coincident with the
dawn of a luminous era.

At Soho foundry in 1798 Murdock constructed an apparatus which enabled
him to exhibit his lighting-plan on a larger scale and to experiment on
purifying and burning the gas so as to eliminate odor and smoke. Soho
was an unique institution described as a place

     to which men of genius were invited and resorted from every
     civilized country, to exercise and to display their talents.
     The perfection of the manufacturing arts was the great and
     constant aim of its liberal and enlightened proprietors,
     Messrs. Boulton and Watt; and whoever resided there was
     surrounded by a circle of scientific, ingenious, and skilful
     men, at all times ready to carry into effect the inventions of
     each other.

The Treaty of Amiens, which gave to England the peace she was sorely in
need of, afforded Murdock an opportunity in 1802 favorable for making a
public display of gas-lighting. The illumination of the Soho works on
this occasion is described as "one of extraordinary splendour." The
fronts of the extensive range of buildings were ornamented with a large
number of devices which displayed the variety of forms of gas-lights. At
that time this was a luminous spectacle of great novelty and the
populace came from far and wide "to gaze at, and to admire, this
wonderful display of the combined effects of science and art."

Naturally, Murdock had many difficulties to overcome in these early
days, but he possessed skill and perseverance. His first retorts for
distilling coal were similar to the common glass retort of the chemist.
Next he tried cast-iron cylinders placed perpendicularly in a common
furnace, and in each were put about fifteen pounds of coal. In 1804 he
constructed them with doors at each end, for feeding coal and
extracting coke respectively, but these were found inconvenient. In his
first lighting installation in the factory of Phillips and Lee in 1805
he used a large retort of the form of a bucket with a cover on it.
Inside he installed a loose cage of grating to hold the coal. When
carbonization was complete the coke could be removed as a whole by
extracting this cage. This retort had a capacity of fifteen hundred
pounds of coal. He labored with mechanical details, varied the size and
shape of the retorts, and experimented with different temperatures, with
the result that he laid a solid foundation for coal-gas lighting. For
his achievements he is entitled to an honorable place among the
torch-bearers of civilization.

The epochal feature of the development of gas-lighting is that here was
a possibility for the first time of providing lighting as a public
utility. In the early years of the nineteenth century the foundation was
laid for the great public-utility organizations of the present time.
Furthermore, gas-lighting was an improvement over candles and oil-lamps
from the standpoints of convenience, safety, and cost. The latter points
are emphasized by Murdock in his paper presented before the Royal
Society in 1808, in which he describes the first industrial installation
of gas-lighting. He used two types of burners, the Argand and the
cockspur. The former resembled the Argand lamp in some respects and the
latter was a three-flame burner suggesting a fleur-de-lis. In this
installation there were 271 Argand burners and 636 cockspurs. Each of
the former "gave a light equal to that of four candles; and each of the
latter, a light equal to two and a quarter of the same candles; making
therefore the total of the gas light a little more than 2500 candles."
The candle to which he refers was a mold candle "of six in the pound"
and its light was considered a standard of luminous intensity when it
was consuming tallow at the rate of 0.4 oz. (175 grains) per hour. Thus
the candle became very early a standard light-source and has persisted
as such (with certain variations in the specifications) until the
present time. However, during recent years other standard light-sources
have been devised.

According to Murdock, the yearly cost of gas-lighting in this initial
case was 600 pounds sterling after allowing generously for interest on
capital invested and depreciation of the apparatus. The cost of
furnishing the same amount of light by means of candles he computed to
be 2000 pounds sterling. This comparison was on the basis of an average
of two hours of artificial lighting per day. On the basis of three hours
of artificial lighting per day, the relative cost of gas-and
candle-lighting was about one to five. Murdock was characteristically
modest in discussing his achievements and his following statement should
be read with the conditions of the year 1808 in mind:

     The peculiar softness and clearness of this light with its
     almost unvarying intensity, have brought it into great favour
     with the work people. And its being free from the inconvenience
     and danger, resulting from sparks and frequent snuffing of
     candles, is a circumstance of material importance, as tending
     to diminish the hazard of fire, to which cotton mills are known
     to be exposed.

Although this installation in the mill of Phillips and Lee is the first
one described by Murdock, in reality it is not the first industrial
gas-lighting installation. During the development of gas apparatus at
the Soho works and after his luminous display in 1802, he gradually
extended gas-lighting to all the principal shops. However, this in a
sense was experimental work. Others were applying their knowledge and
ingenuity to the problem of making gas-lighting practicable, but Murdock
has been aptly termed "the father of gas-lighting." Among the pioneers
was Le Bon in France, Becher in Munich, and Winzler or Winsor, a German
who was attracted to the possibilities of gas-lighting by an exhibition
which Le Bon gave in Paris in 1802. Winsor learned that Le Bon had been
granted a patent in Paris in 1799 for making an illuminating gas from
wood and tried to obtain the rights for Germany. Being unsuccessful in
this, he set about to learn the secrets of Le Bon's process, which he
did, perhaps largely owing to an accumulation of information directly
from the inventor during the negotiations. Winsor then turned to England
as a fertile field for the exploitation of gas-lighting and after
conducting experiments in London for some time he made plans to organize
the National Heat and Light Co.

Winsor was primarily a promoter, with little or no technical knowledge;
for in his claims and advertisements he disregarded facts with a
facility possessed only by the ignorant. He boasted of his inventions
and discoveries in the most hyperbolical language, which was bound to
provoke a controversy. Nevertheless, he was clever and in 1803 he
publicly exhibited his plan of lighting by means of coal-gas at the
Lyceum Theatre in London. He gave lectures accompanied by interesting
and instructive experiments and in this manner attracted the public to
his exhibition. All this time he was promoting his company, but his
promoting instinct caused his representations to be extravagant and
deceptive, which exposed him to the ridicule and suspicion of learned
men. His attempt to obtain certain exclusive rights by Act of Parliament
failed because of opposition of scientific men toward his claims and of
the stand which Murdock justly made in self-protection. These years of
controversy yield entertaining literature for those who choose to read
it, but unfortunately space does not permit dwelling upon it. The
investigations by committees of Parliament also afford amusing
side-lights. Throughout all this Murdock appeared modest and
conservative and had the support of reputable scientific men, but Winsor
maintained extravagant claims.

During one of these investigations Sir Humphrey Davy was examined by a
committee from the House of Commons in 1809. He refuted Winsor's claims
for a superior coke as a by-product and stated that the production of
gas by the distillation of coal had been well known for thirty or forty
years and the production of tar as long. He stated that it was the
opinion of the Council of the Royal Society that Murdock was the first
person to apply coal-gas to lighting in actual practice. As secretary of
the Society, Sir Humphrey Davy stated that at the last session it had
bestowed the Count Rumford medal upon Murdock for "his economical
application of the gas light."

Winsor proceeded to float his company without awaiting the Act of
Parliament and in 1807 lighted a street in Pall Mall. Through the
opposition which he aroused, and owing to the just claims of priority on
the part of Murdock, the bill to incorporate the National Heat and Light
Co. with a capital of 200,000 pounds sterling was thrown out. However,
he succeeded in 1812 in receiving a charter very much modified in form,
for the Chartered Gas Light and Coke Co. which was the forerunner of the
present London Gas Light and Coke Co.

The conditions imposed upon this company as presented in an early
treatise on gas-lighting (by Accum in 1818) were as follows:

     The power and authorities granted to this corporate body are
     very restricted and moderate. The individuals composing it have
     no exclusive privilege; their charter does not prevent other
     persons from entering into competition with them. Their
     operations are confined to the metropolis, where they are bound
     to furnish not only a stronger and better light to such streets
     and parishes as chuse to be lighted with gas, but also at a
     cheaper price than shall be paid for lighting the said streets
     with oil in the usual manner. The corporation is not permitted
     to traffic in machinery for manufacturing or conveying the gas
     into private houses, their capital or joint stock is limited to
     £200,000, and his Majesty has the power of declaring the
     gas-light charter void if the company fail to fulfil the terms
     of it.

The progress of this early company was slow at first, but with the
appointment of Samuel Clegg as engineer in 1813 an era of technical
developments began. New stations were built and many improvements were
introduced. By improving the methods of purifying the gas a great
advance was made. The utility of gas-lighting grew apace as the
prejudices disappeared, but for a long time the stock of the company
sold at a price far below par. About this time the first gas explosion
took place and the members of the Royal Society set a precedent which
has lived and thrived: they appointed a committee to make an inquiry.
But apparently the inquiry was of some value, for it led "to some useful
alterations and new modifications in its apparatus and machinery."

Many improvements were being introduced during these years and one of
them in 1816 increased the gaseous product from coal by distilling the
tar which was obtained during the first distillation. In 1816 Clegg
obtained a patent for a horizontal rotating retort; for an apparatus for
purifying coal-gas with "cream of lime"; and for a rotative gas-meter.

Before progressing too far, we must mention the early work of William
Henry. In 1804 he described publicly a method of producing coal-gas.
Besides making experiments on production and utilization of coal-gas for
lighting, he devoted his knowledge of chemistry to the analysis of the
gas. He also made analytical studies of the relative value of wood,
peat, oil, wax, and different kinds of coal for the distillation of gas.
His chemical analyses showed to a considerable extent the properties of
carbureted hydrogen upon which illuminating value depended. The results
of his work were published in various English journals between 1805 and
1825 and they contributed much to the advancement of gas-lighting.

Although Clegg's original gas-meter was complicated and cumbersome, it
proved to be a useful device. In fact, it appears to have been the most
original and beneficial invention occasioned by early gas-lighting.
Later Samuel Crosley greatly improved it, with the result that it was
introduced to a considerable extent; but by no means was it universally
adopted. Another improvement made by Clegg at this time was a device
which maintained the pressure of gas approximately constant regardless
of the pressure in the gasometer or tank. Clegg retired from the service
of the gas company in 1817 after a record of accomplishments which
glorifies his name in the annals of gas-lighting. Murdock is undoubtedly
entitled to the distinction of having been the first person who applied
gas-lighting to large private establishments, but Clegg overcame many
difficulties and was the first to illuminate a whole town by this means.

In London in 1817 over 300,000 cubic feet of coal-gas was being
manufactured daily, an amount sufficient to operate 76,500 Argand
burners yielding 6 candle-power each. Gas-lighting was now exciting
great interest and was firmly established. Westminster Bridge was
lighted by gas in 1813, and the streets of Westminster during the
following year. Gas-lighting became popular in London by 1816 and in the
course of the next few years it was adopted by the chief cities and
towns in the United Kingdom and on the Continent. It found its way into
the houses rather slowly at first, owing to apprehension of the
attendant dangers, to the lack of purification of the gas, and to the
indifferent service. It was not until the latter half of the nineteenth
century that it was generally used in residences.

The gas-burner first employed by Murdock received the name "cockspur"
from the shape of the flame. This had an illuminating value equivalent
to about one candle for each cubic foot of gas burned per hour. The next
step was to flatten the welded end of the gas-pipe and to bore a series
of holes in a line. From the shape of the flames this form of burner
received the name "cockscomb." It was somewhat more efficient than the
cockspur burner. The next obvious step was to slit the end of the pipe
by means of a fine saw. From this slit the gas was burned as a sheet of
flame called the "bats-wing." In 1820 Nielson made a burner which
allowed two small jets to collide and thus form a flat flame. The
efficiency of this "fish-tail" burner was somewhat higher than that of
the earlier ones. Its flame was steadier because it was less influenced
by drafts of air. In 1853 Frankland showed an Argand burner consisting
of a metal ring containing a series of holes from which jets of gas
issued. The glass chimney surrounded these, another chimney, extending
somewhat lower, surrounded the whole, and a glass plate closed the
bottom. The air to be fed to the gas-jets came downward between the two
chimneys and was heated before it reached the burner. This increased the
efficiency by reducing the amount of cooling at the burner by the air
required for combustion. This improvement was in reality the forerunner
of the regenerative lamps which were developed later.

In 1854 Bowditch brought out a regenerative lamp and, owing to the
excessive publicity which this lamp obtained, he is generally credited
with the inception of the regenerative burner. This principle was
adopted in several lamps which came into use later. They were all based
upon the principle of heating both the gas and the air required for
combustion prior to their reaching the burner. The burner is something
like an inverted Argand arranged to produce a circular flame projecting
downward with a central cusp. The air- and gas-passages are directly
above the flame and are heated by it. In 1879 Friedrich Siemens brought
out a lamp of this type which was adapted from a device originally
designed for heating purposes, owing to the superior light which was
produced. This was the best gas-lamp up to that time. Later, Wenham,
Cromartie, and others patented lamps operating on this same principle.

Murdock early modified the Argand burner to meet the requirements of
burning gas and by using the chimney obtained better combustion and a
steadier flame than from the open burners. He and others recognized that
the temperature of the flame had a considerable effect upon the amount
of light emitted and non-conducting material such as steatite was
substituted for the metal, which cooled the flame by conducting heat
from it. These were the early steps which led finally to the
regenerative burner.

The increasing efficiency of the various gas-burners is indicated by the
following, which are approximately the candle-power based upon equal
rates of consumption, namely, one cubic foot of gas per hour:

                                              per cubic foot of
                                              gas per hour

     Fish-tail flames, depending upon size      0.6 to 2.5
     Argand, depending upon improvements        2.9 to 3.5
     Regenerative                                 7 to 10

It is seen that the possibilities of gas lighting were recognized in
several countries, all of which contributed to its development. Some of
the earlier accounts have been drawn chiefly from England, but these are
intended merely to serve as examples of the difficulties encountered.
Doubtless, similar controversies arose in other countries in which
pioneers were also nursing gas-lighting to maturity. However, it is
certain that much of the early progress of lighting of this character
was fathered in England. Gas-lighting was destined to become a thriving
industry, and is of such importance in lighting that another chapter is
given its modern developments.



In previous chapters much of the historical development of artificial
lighting has been presented and several subjects have been traced to the
modern period which marks the beginning of an intensive attack by
scientists upon the problems pertaining to the production of efficient
and adequate light-sources. Many historical events remain to be touched
upon in later chapters, but it is necessary at this point for the reader
to become acquainted with certain general physical principles in order
that he may read with greater interest some of the chapters which
follow. It is seen that from a standpoint of artificial lighting, the
"dark age" extended well into the nineteenth century. Oil-lamps and
gas-lighting began to be seriously developed at the beginning of the
last century, but the pioneers gave attention chiefly to mechanical
details and somewhat to the chemistry of the fuels. It was not until the
science of physics was applied to light-sources that rapid progress was

All the light-sources used throughout the ages, and nearly all modern
ones, radiate light by virtue of the incandescence of solids or of solid
particles and it is an interesting fact that carbon is generally the
solid which emits light. This is due to various physical characteristics
of carbon, the chief one being its extremely high melting-point.
However, most practicable light-sources of the past and present may be
divided into two general classes: (1) Those in which solids or solid
particles are heated by their own combustion, and (2) those in which the
solids are heated by some other means. Some light-sources include both
principles and some perhaps cannot be included under either principle
without qualification. The luminous flames of burning material such as
those of wood-splinters, candles, oil-lamps, and gas-jets, and the
glowing embers of burning material appear in the first class; and
incandescent gas-mantles, electric filaments, and arc-lamps to some
extent are representative of the second class. Certain "flaming" arcs
involve both principles, but the light of the firefly, phosphorescence,
and incandescent gas in "vacuum" tubes cannot be included in this
simplified classification. The status of these will become clear later.

It has been seen that flames have been prominent sources of artificial
light; and although of low luminous efficiency, they still have much to
commend them from the standpoints of portability, convenience, and
subdivision. The materials which have been burned for light, whether
solid or liquid, are rich in carbon, and the solid particles of carbon
by virtue of their incandescence are responsible for the brightness of a
flame. A jet of pure hydrogen gas will burn very hot but with so low a
brightness as to be barely visible. If solid particles are injected into
the flame, much more light usually will be emitted. A gas-burner of the
Bunsen type, in which complete combustion is obtained by mixing air in
proper proportions with the gas, gives a hot flame which is of a pale
blue color. Upon the closing of the orifice through which air is
admitted, the flame becomes bright and smoky. The flame is now less hot,
as indicated by the presence of smoke or carbon particles, and
combustion is not complete. However, it is brighter because the solid
particles of carbon in passing upward through the flame become heated to
temperatures at which they glow and each becomes a miniature source of

A close observer will notice that the flame from a match, a candle, or a
gas-jet, is not uniformly bright. The reader may verify this by lighting
a match and observing the flame. There is always a bluish or darker
portion near the bottom. In this less luminous part the air is combining
with the hydrogen of the hydrocarbon which is being vaporized and
disintegrated. Even the flame of a candle or of a burning splinter is a
miniature gas-plant, for the solid or liquid hydrocarbons are vaporized
before being burned. Owing to the incoming colder air at this point, the
flame is not hot enough for complete combustion. The unburned carbon
particles rise in its draft and become heated to incandescence, thus
accounting for the brighter portion. In cases of complete combustion
they are eventually oxidized into carbon dioxide before they are able to
escape. If a piece of metal be held in the flame, it immediately becomes
covered with soot or carbon, because it has reduced the temperature
below the point at which the chemical reaction--the uniting of carbon
with oxygen--will continue. An ordinary flat gas-flame of the
"bats-wing" type may vary in temperature in its central portion from
300°F. at the bottom to about 3000°F. at the top. The central portion
lies between two hotter layers in which the vertical variation is not so
great. The brightness of the upper portion is due to incandescent carbon
formed in the lower part.

When scientists learned by exploring flames that brightness was due to
the radiation of light by incandescent solid matter, the way was open
for many experiments. In the early days of gas-lighting investigations
were made to determine the relation of illuminating value to the
chemical constitution of the gas. The results combined with a knowledge
of the necessity for solid carbon in the flame led to improvements in
the gas for lighting purposes. Gas rich in hydrocarbons which in turn
are rich in carbon is high in illuminating value. Heating-effect depends
upon heat-units, so the rating of gas in calories or other heat-units
per cubic foot is wholly satisfactory only for gas used for heating. The
chemical constitution is a better indicator of illuminating value.

As scientific knowledge increased, efforts were made to get solid matter
into the flames of light-sources. Instead of confining efforts to the
carbon content of the gas, solid materials were actually placed in the
flame, and in this manner various incandescent burners were developed. A
piece of lime placed in a hydrogen flame or that of a Bunsen burner is
seen to become hot and to glow brilliantly. By producing a hotter flame
by means of the blowpipe, in which hydrogen and oxygen are consumed, the
piece of lime was raised to a higher temperature and a more intense
light was obtained. In Paris there was a serious attempt at
street-lighting by the use of buttons of zirconia heated in an
oxygen-coal-gas flame, but it proved unsuccessful owing to the rapid
deterioration of the buttons. This was the line of experimentation which
led to the development of the lime-light. The incandescent burner was
widely employed, and until the use of electricity became common the
lime-light was the mainstay for the stage and for the projection of
lantern slides. It is in use even to-day for some purposes. The origin
of the phrase "in the lime-light" is obvious. The luminous intensity of
the oxyhydrogen lime-light as used in practice was generally from 200 to
400 candle-power. The light decreases rapidly as the burner is used, if
a new surface of lime is not presented to the flame from time to time.
At the high temperatures the lime is somewhat volatile and the surface
seems to change in radiating power. Zirconium oxide has been found to
serve better than lime.

Improvements were made in gas-burners in order to obtain hotter flames
into which solid matter could be introduced to obtain bright light. Many
materials were used, but obviously they were limited to those of a
fairly high melting-point. Lime, magnesia, zirconia, and similar oxides
were used successfully. If the reader would care to try an experiment in
verification of this simple principle, let him take a piece of magnesium
ribbon such as is used in lighting for photography and ignite it in a
Bunsen flame. If it is held carefully while burning, a ribbon of ash
(magnesia) will be obtained intact. Placing this in the faintly luminous
flame, he will be surprised at the brilliance of its incandescence when
it has become heated. The simple experiment indicates the possibilities
of light-production in this direction. Naturally, metals of high
melting-point such as platinum were tried and a network of platinum
wire, in reality a platinum mantle, came into practical use in about
1880. The town of Nantes was lighted by gas-burners using these
platinum-gauze mantles, but the mantles were unsuccessful owing to their
rapid deterioration. This line of experimentation finally bore fruit of
immense value for from it the gas-mantle evolved.

A group of so-called "rare-earths," among which are zirconia, thoria,
ceria, erbia, and yttria (these are oxides of zirconium, etc.) possess a
number of interesting chemical properties some of which have been
utilized to advantage in the development of modern artificial light.
They are white or yellowish-white oxides of a highly refractory
character found in certain rare minerals. Most of them are very
brilliant when heated to a high temperature. This latter feature is
easily explained if the nature of light and the radiating properties of
substances are considered. Suppose pieces of different substances, for
example, glass and lime, are heated in a Bunsen flame to the same
temperature which is sufficiently great to cause both of them to glow.
Notwithstanding the identical conditions of heating, the glass will be
only faintly luminous, while the piece of lime will glow brilliantly.
The former is a poor radiator; furthermore, the lime radiates a
relatively greater percentage of its total energy in the form of
luminous energy.

The latter point will become clearer if the reader will refresh his
memory regarding the nature of light. Any luminous source such as the
sun, a candle flame, or an incandescent lamp is sending forth
electromagnetic waves not unlike those used in wireless telegraphy
excepting that they are of much shorter wave-length. The eye is capable
of recording some of these waves as light just as a receiving station is
tuned to record a range of wave-lengths of electromagnetic energy. The
electromagnetic waves sent forth by a light-source like the sun are not
all visible, that is, all of them do not arouse a sensation of light.
Those that do comprise the visible spectrum and the different
wave-lengths of visible radiant energy manifest themselves by arousing
the sensations of the various spectral colors. The radiant energy of
shortest wave-length perceptible by the visual apparatus excites the
sensation of violet and the longest ones the sensation of deep red.
Between these two extremes of the visible spectrum, the chief spectral
colors are blue, green, yellow, orange, and red in the order of
increasing wave-lengths. Electromagnetic energy radiated by a
light-source in waves of too great wave-length to be perceived by the
eye as light is termed as a class "infra-red radiant energy." Those too
short to be perceived as light are termed as a class "ultraviolet
radiant energy." A solid body at a high temperature emits
electro-magnetic energy of all wave-lengths, from the shortest
ultra-violet to the longest infra-red.

Another complication arises in the variation in visibility or luminosity
of energy of wave-lengths within the range of the visible spectrum.
Obviously, no amount of energy incapable of exciting the sensation of
light will be visible. The energy of those wave-lengths near the ends
of the visible spectrum will be inefficient in producing light. That
energy which excites the sensation of yellow-green produces the greatest
luminosity per unit of energy and is the most efficient light. The
visibility or luminous efficiency of radiant energy may be ranged
approximately in this manner according to the colors aroused:
yellow-green, yellow, green, orange, blue-green, red, blue, deep red,

Newton, an English scientist, first described the discovery of the
visible spectrum and this is of such fundamental importance in the
science of light that the first paragraph of his original paper in the
"Transactions of the Royal Society of London" is quoted as follows:

     In the Year 1666 (at which time I applied my self to the
     Grinding of Optick Glasses of other Figures than Spherical) I
     procured me a Triangular Glass-Prism, to try therewith the
     celebrated Phaenomena of Colours. And in order thereto, having
     darkened my Chamber, and made a small Hole in my Window-Shuts,
     to let in a convenient Quantity of the Sun's Light, I placed my
     Prism at its Entrance, that it might be thereby refracted to
     the opposite Wall. It was at first a very pleasing
     Divertisement, to view the vivid and intense Colours produced
     thereby; but after a while applying my self to consider them
     more circumspectly, I became surprised to see them in an oblong
     Form; which, according to the receiv'd Law of Refractions, I
     expected should have been circular. They were terminated at the
     Sides with streight Lines, but at the Ends the Decay of Light
     was so gradual, that it was difficult to determine justly what
     was the Figure, yet they seemed Semicircular.

Even Newton could not have had the faintest idea of the great
developments which were to be based upon the spectrum.

Now to return to the peculiar property of rare-earth oxides--namely,
their unusual brilliance when heated in a flame--it is easy to
understand the reason for this. For example, when a number of substances
are heated to the same temperature they may radiate the same amount of
energy and still differ considerably in brightness. Many substances are
"selective" in their absorbing and radiating properties. One may radiate
more luminous energy and less infra-red energy, and for another the
reverse may be true. The former would appear brighter than the latter.
The scientific worker in light-production has been searching for such
"selective" radiators whose other properties are satisfactory. The
rare-earths possess the property of selectivity and are fortunately
highly refractory. Welsbach used these in his mantle, whose efficiency
is due partly to this selective property. Recent work indicates that
much higher efficiencies of light-production are still attainable by the
principles involved in the gas-mantle.

Turning again to flames, another interesting physical phenomenon is seen
on placing solutions of different chemical salts in the flame. For
example, if a piece of asbestos is soaked in sodium chloride (common
salt) and is placed in a Bunsen flame, the pale-blue flame suddenly
becomes luminous and of a yellow color. If this is repeated with other
salts, a characteristic color will be noted in each case. The yellow
flame is characteristic of sodium and if it is examined by means of a
spectroscope, a brilliant yellow line (in fact, a double line) will be
seen. This forms the basis of spectrum analysis as applied in chemistry.

Every element has its characteristic spectrum consisting usually of
lines, but the complexity varies with the elements. The spectra of
elements also exhibit lines in the ultra-violet region which may be
studied with a photographic plate, with a photo-electric cell, and by
other means. Their spectral lines or bands also extend into the
infra-red region and here they are studied by means of the bolometer or
other apparatus for detecting radiant energy by the heat which it
produces upon being absorbed. Spectrum analysis is far more sensitive
than the finest weighing balance, for if a grain of salt be dissolved in
a barrel of water and an asbestos strip be soaked in the water and held
in a Bunsen flame, the yellow color characteristic of sodium will be
detectable. A wonderful example of the possibilities of this method is
the discovery of helium in the sun before it was found on earth! Its
spectral lines were detected in the sun's spectrum and could not be
accounted for by any known element. However, it should be stated that
the spectrum of an element differs generally with the manner obtained.
The electric spark, the arc, the electric discharge in a vacuum tube,
and the flame are the means usually employed.

The spectrum has been dwelt upon at some length because it is of great
importance in light-production and probably will figure strongly in
future developments. Although in lighting little use has been made of
the injection of chemical salts into ordinary flames, it appears certain
that such developments would have risen if electric illuminants had not
entered the field. However, the principle has been applied with great
success in arc-lamps. In the first arc-lamps plain carbon electrodes
were used, but in some of the latest carbon-arcs, electrodes of carbon
impregnated with various salts are employed. For example, calcium
fluoride gives a brilliant yellow light when used in the carbons of the
"flame" arc. These are described in detail later.

Following this principle of light-production the vacuum tubes were
developed. Crookes studied the light from various gases by enclosing
them in a tube which was pumped out until a low vacuum was produced. On
connecting a high voltage to electrodes in each end, an electrical
discharge passed through the residual gas making it luminous. The
different gases show their characteristic spectra and their desirability
as light-producers is at once evident.

However, the most general principle of light-production at the present
time is the radiation of bodies by virtue of their temperature. If a
piece of wire be heated by electricity, it will become very hot before
it becomes luminous. At this temperature it is emitting only invisible
infra-red energy and has an efficiency of zero as a producer of light.
As it becomes hotter it begins to appear red, but as its temperature is
raised it appears orange, until if it could be heated to the temperature
of the sun, about 10,000°F., it would appear white. All this time its
luminous efficiency is increasing, because it is radiating not only an
increasing percentage of visible radiant energy but an increasing amount
of the most effective luminous energy. But even when it appears white, a
large amount of the energy which it radiates is invisible infra-red and
ultra-violet, which are ineffective in producing light, so at best the
substance at this high temperature is inefficient as a light-producer.

In this branch of the science of light-production substances are sought
not only for their high melting-point, but for their ability to radiate
selectively as much visible energy as possible and of the most luminous
character. However, at best the present method of utilizing the
temperature radiation of hot bodies has limitations.

The luminous efficiencies of light-sources to-day are still very low,
but great advances have been made in the past half-century. There must
be some radical departures if the efficiency of light-production is to
reach a much higher figure. A good deal has been said of the firefly and
of phosphorescence. These light-sources appear to emit only visible
energy and, therefore, are efficient as radiators of luminous radiant
energy. But much remains to be unearthed concerning them before they
will be generally applicable to lighting. If ultra-violet radiation is
allowed to impinge upon a phosphorescent material, it will glow with a
considerable brightness but will be cool to the touch. A substance of
the same brightness by virtue of its temperature would be hot; hence
phosphorescence is said to be "cold" light.

An acquaintance with certain terms is necessary if the reader is to
understand certain parts of the text. The early candle gradually became
a standard, and uniform candles are still satisfactory standards where
high accuracy is not required. Their luminous intensity and
illuminating value became units just as the foot was arbitrarily adopted
as a unit of length. The intensity of other light-sources was
represented in terms of the number of candles or fraction of a candle
which gave the same amount of light. But the luminous intensity of the
candle was taken only in the horizontal direction. In the same manner
the luminous intensities of light-sources until a short time ago were
expressed in candles as measured in a certain direction. Incandescent
lamps were rated in terms of mean horizontal candles, which would be
satisfactory if the luminous intensity were the same in all directions,
but it is not. Therefore, the candle-power in one direction does not
give a measure of the total light-output.

If a source of light has a luminous intensity of one candle in all
directions, the illumination at a distance of one foot in any direction
is said to be a foot-candle. This is the unit of illumination intensity.
A lumen is the quantity of light which falls on one square foot if the
intensity of illumination is one foot-candle. It is seen that the area
of a sphere with a radius of one foot is 4 pi or 12.57 square feet;
therefore, a light-source having a luminous intensity of one candle in
all directions emits 12.57 lumens. This is the satisfactory unit, for it
measures total quantity of light, and luminous efficiencies may be
expressed in terms of lumens per watt, lumens per cubic foot of gas per
hour, etc.

Of course, the efficiencies of light-sources are usually of interest to
the consumer if they are expressed in terms of cost. But from a
practical point of view there are many elements which combine to make
another important factor, namely, satisfactoriness. Therefore, the
efficiency of artificial lighting from the standpoint of the consumer
should be the ratio of satisfactoriness to cost. However, the scientist
is interested chiefly in the efficiency of the light-source which may be
expressed in lumens per watt, or the amount of light obtained from a
given rate of consumption or of emission of energy. This method of
rating light-sources penalizes those radiating considerable energy which
does not produce the sensation of light or which at best is of
wave-lengths that are inefficient in this respect. That radiant energy
which is wholly of a wave-length of maximum visibility, or, in other
words, excites the sensation of yellow-green, is the most efficient in
producing luminous sensation. Of course, no illuminants are available
which approach this theoretical ideal and it is not likely that this
would be a practical ideal. Under monochromatic yellow-green light the
magical drapery of color would disappear and the surroundings would be a
monochrome of shades of this hue. Having no colors with which to
contrast this color, the world would be colorless. This should be
obvious when it is considered that an object which is red under an
illuminant containing all colors such as sunlight would be black or dark
gray under monochromatic yellow-green light. The red under present
conditions is kept alive by contrast with other colors, because the
latter live by virtue of the fact that most of our present illuminants
contain their hues. It is assumed that the reader knows that a red
object, for example, appears red because it reflects (or transmits) red
rays and absorbs the other rays in the illuminant. In other words, color
is due to selective absorption reflection, or transmission.

Perhaps the ideal illuminant, which is most generally satisfactory for
general activities, is a white light corresponding to noon sunlight. If
this is chosen as the scientific ideal, the illuminants of the present
time are much more "efficient" than if the most efficient light is the

The luminous efficiency of the radiant energy most efficient in
producing the sensation of light (yellow-green) is about 625 lumens per
watt. That is, if energy of this wave-length alone were radiated by a
hypothetical light-source, each watt would produce 625 lumens. The
luminous efficiency of the most efficient white light is about 265
lumens per watt; in other words, if a hypothetical light-source radiated
energy of only the visible wave-lengths and in proportions to produce
the sensation of white, each watt would produce 265 lumens. If such a
white light were obtained by pure temperature radiation--that is, by a
normal radiator at a temperature of 10,000°F., which is impracticable at
present--the luminous efficiency would be about 100 lumens per watt. The
normal radiator which emits energy by virtue of its temperature without
selectively radiating more or less energy in any part of the spectrum
than indicated by the theoretical radiation laws is called a
"black-body" or normal radiator. Modern illuminants have luminous
efficiencies ranging from 5 to 30 lumens per watt, so it is seen that
much is to be done before the limiting efficiencies are reached.

The amount of light obtained from various gas-burners for each cubic
foot of gas consumed per hour varies for open gas-flames from 5 to 30
lumens; for Argand burners from 35 to 40 lumens; for regenerative lamps
from 50 to 75 lumens; and for gas-mantles from 200 to 250 lumens.

In the development of light-sources, of course, any harmful effects of
gases formed by burning or chemical action must be avoided. Some of the
fumes from arcs are harmful, but no commercial arc appears to be
dangerous when used as it is intended to be used. Gas-burners rob the
atmosphere of oxygen and vitiate it with gases, which, however, are
harmless if combustion is complete. That adequate ventilation is
necessary where oxygen is being consumed is evident from the data
presented by authorities on hygiene. A standard candle when burning
vitiates the air in a room almost as much as an adult person. An
ordinary kerosene lamp vitiates the atmosphere as much as a half-dozen
persons. An ordinary single mantle burner causes as much vitiation as
two or three persons.

In order to obtain a bird's-eye view of progress in light-production,
the following table of relative luminous efficiencies of several
light-sources is given in round numbers. These efficiencies are in terms
of the most efficient (yellow-green) light.

                                                 in per cent.
     Sperm-candle                                    0.02
     Open gas-flame                                   .04
     Incandescent gas-mantle                          .19
     Carbon filament lamp                             .05
     Vacuum Mazda lamp                               1.3
     Gas-filled Mazda lamp                           2 to 3
     Arc-lamps                                       2 to 7
     White light radiated by "black-body"           16
     Most efficient white light                     40
     Firefly                                        95
     Most efficient light (yellow-green)           100

The luminous efficiency of a light-source is distinguished from that of
a lamp. The former is the ratio of the light produced to the amount of
energy radiated by the light-source. The latter is the ratio of the
light produced to the total amount of energy consumed by the device. In
other words, the luminous efficiency of a lamp is less than that of the
light-source because the consumption of energy in other parts of the
lamp besides the light-source are taken into account. These additional
losses are appreciable in the mechanisms of arc-lamps but are almost
negligible in vacuum incandescent filament lamps. They are unknown for
the firefly, so that its luminous efficiency only as a light-source can
be determined. Its efficiency as a lighting-plant may be and perhaps is
rather low.



As has been seen, the lighting industry, as a public service, was born
in London about a century ago and companies to serve the public were
organized on the Continent shortly after. From this early beginning
gas-light remained for a long time the only illuminant supplied by a
public-service company. It has been seen that throughout the ages little
advance was made in lighting until oil-lamps were improved by Argand in
the eighteenth century. Candles and open-flame oil-lamps were in use
when the Pyramids were built and these were common until the approach of
the nineteenth century. In fact, several decades passed after the first
gas-lighting was installed before this form of lighting began to
displace the improved oil-lamps and candles. It was not until about 1850
that it began to invade the homes of the middle and poorer classes.
During the first half of the nineteenth century the total light in an
average home was less than is now obtained from a single light-source
used in residences; still, the total cost of lighting a residence has
decreased considerably. If the social and industrial activities of
mankind are visualized for these various periods in parallel with the
development of artificial lighting, a close relation is evident. Did
artificial light advance merely hand in hand with science, invention,
commerce, and industry, or did it illuminate the pathway?

Although gas-lighting was born in England it soon began to receive
attention elsewhere. In 1815 the first attempt to provide a gas-works in
America was made in Philadelphia; but progress was slow, with the result
that Baltimore and New York led in the erection of gas-works. There are
on record many protests against proposals which meant progress in
lighting. These are amusing now, but they indicate the inertia of the
people in such matters. When Bollman was projecting a plan for lighting
Philadelphia by means of piped gas, a group of prominent citizens
submitted a protest in 1833 which aimed to show that the consequences of
the use of gas were appalling. But this protest failed and in 1835 a
gas-plant was founded in Philadelphia. Thus gas-lighting, which to Sir
Walter Scott was a "pestilential innovation" projected by a madman,
weathered its early difficulties and grew to be a mighty industry.
Continued improvements and increasing output not only altered the course
of civilization by increased and adequate lighting but they reduced the
cost of lighting over the span of the nineteenth century to a small
fraction of its initial cost.

Think of the city of Philadelphia in 1800, with a population of about
fifty thousand, dependent for its lighting wholly upon candles and
oil-lamps! Washington's birthday anniversary was celebrated in 1817 with
a grand ball attended by five hundred of the élite. An old report of the
occasion states that the room was lighted by two thousand wax-candles.
The cost of this lighting was a hundred times the cost of as much light
for a similar occasion at the present time. Can one imagine the present
complex activities of a city like Philadelphia with nearly two million
inhabitants to exist under the lighting conditions of a century ago?
To-day there are more than fifty thousand street lamps in the city--one
for each inhabitant of a century ago. Of these street lamps about
twenty-five thousand burn gas. This single instance is representative of
gas-lighting which initiated the "light age" and nursed it through the
vicissitudes of youth. The consumption of gas has grown in the United
States during this time to three billion cubic feet per day. For
strictly illuminating purposes in 1910 nearly one hundred billion cubic
feet were used. This country has been blessed with large supplies of
natural gas; but as this fails new oil-fields are constantly being
discovered, so that as far as raw materials are concerned the future of
gas-lighting is assured for a long time to come.

The advent of the gas-mantle is responsible for the survival of
gas-lighting, because when it appeared electric lamps had already been
invented. These were destined to become the formidable light-sources of
the approaching century and without the gas-mantle gas-lighting would
not have prospered. Auer von Welsbach was conducting a spectroscopic
study of the rare-earths when he was confronted with the problem of
heating these substances. He immersed cotton in solutions of these salts
as a variation of the regular means for studying elements by injecting
them into flames. After burning the cotton he found that he had a
replica of the original fabric composed of the oxide of the metal, and
this glowed brilliantly when left in the flame.

This gave him the idea of producing a mantle for illuminating purposes
and in 1885 he placed such a mantle in commercial use. His first mantles
were unsatisfactory, but they were improved in 1886 by the use of
thoria, an oxide of thorium, in conjunction with other rare-earth
oxides. His mantle was now not only stronger but it gave more light.
Later he greatly improved the mantles by purifying the oxides and
finally achieved his great triumph by adding a slight amount of ceria,
an oxide of cerium. Welsbach is deserving of a great deal of credit for
his extensive work, which overcame many difficulties and finally gave to
the world a durable mantle that greatly increased the amount of light
previously obtainable from gas.

The physical characteristics of a mantle depend upon the fabric and upon
the rare-earths used. It must not shrink unduly when burned, and the ash
should remain porous. It has been found that a mantle in which thoria is
used alone is a poor light-source, but that when a small amount of ceria
is added the mantle glows brilliantly. By experiment it was determined
that the best proportions for the rare-earth content are one part of
ceria and ninety-nine parts of thoria. Greater or less proportions of
ceria decreased the light-output. The actual percentage of these oxides
in the ash of the mantle is about 10 per cent., making the content of
ceria about one part in one thousand.

Mantles are made by knitting cylinders of cotton or of other fiber and
soaking these in a solution of the nitrates of cerium and thorium. One
end of the cylinder is then sewed together with asbestos thread, which
also provides the loop for supporting the mantle over the burner. After
the mantle has dried in proper form, it is burned; the organic matter
disappears and the nitrates are converted into oxides. After this
"burning off" has been accomplished and any residual blackening is
removed, the mantle is dipped into collodion, which strengthens it for
shipping and handling. The collodion is a solution of gun-cotton in
alcohol and ether to which an oil such as castor-oil has been added to
prevent excessive shrinkage on drying.

The materials and structure of the fabric of mantles have been subjected
to much study. Cotton was first used; then ramie fibers were introduced.
The ramie mantle was found to possess a greater life than the cotton
mantle. Later the mantles were mercerized by immersion in ammonia-water
and this process yielded a stronger material. The latest development is
the use of an artificial silk as the base fabric, which results in a
mantle superior to previous mantles in strength, flexibility, permanence
of form, and permanence of luminous property. This artificial silk
mantle will permit of handling even after it has been in use for several
hundred hours. This great advance appears to be due to the fact that
after the artificial-silk fibers have been burned off, the fibers are
solid and continuous instead of porous as in previous mantles.

The color-value of the light from mantles may be varied considerably by
altering the proportions of the rare-earths. The yellowness of the light
has been traced to ceria, so by varying the proportions of ceria, the
color of the light may be influenced.

The inverted mantle introduced greater possibilities into gas-lighting.
The light could be directed downward with ease and many units such as
inverted bowls were developed. In fact, the lighting-fixtures and the
lighting-effects obtainable kept pace with those of electric lighting,
notwithstanding the greater difficulties encountered by the designer of
gas-lighting fixtures. Many problems were encountered in designing an
inverted burner operating on the Bunsen principle, but they were finally
satisfactorily solved. In recent years a great deal of study has been
given to the efficiency of gas-burners, with the result that a high
level of development has been reached.

Several methods of electrical ignition have been evolved which in
general employ the electric spark. Electrical ignition and developments
of remote control have added great improvements especially to
street-lighting by means of gas. Gas-valves for remote control are
actuated by gas pressure and by electromagnets. In general, the
gas-lighting engineers have kept pace marvelously with electric
lighting, when their handicaps are considered.

Various types of burners have appeared which aimed to burn more gas in a
given time under a mantle and thereby to increase the output of light.
These led to the development of the pressure system in which the
pressure of gas was at first several times greater than usual. The gas
is fed into the mixing tube under this higher pressure in a manner which
also draws in an adequate amount of air. In this way the combustion at
the burner is forced beyond the point reached with the usual pressure.
Ordinary gas pressure is equal to that of a few inches of water, but
high-pressure systems employ pressures as great as sixty inches of
water. Under this high-pressure system, mantle-burners yield as high as
500 lumens per cubic foot of gas per hour.

The fuels for gas-lighting are natural gas, carbureted water-gas, and
coal-gas obtained by distilling coal, but there are different methods of
producing the artificial gases. Coal-gas is produced analytically by
distilling certain kinds of coal, but water-gas and producer-gas are
made synthetically by the action of several constituents upon one
another. Carbureted water-gas is made from fixed carbon, steam, and oil
and also from steam and oil. Producer-gas is made by the action of steam
or air or both upon fixed carbon. Water-gas made from steam and oil is
usually limited to those places where the raw materials are readily
available. The composition of a gas determines its heating and
illuminating values, and constituents favorable to one are not
necessarily favorable to the other. Coal-gas usually is of lower
illuminating value than carbureted water-gas. It contains more hydrogen,
for example, than water-gas and it is well known that hydrogen gives
little light on burning.

It has been seen in a previous chapter that the distillation of gas from
coal for illuminating purposes began in the latter part of the
eighteenth century. From this beginning the manufacture of coal-gas has
been developed to a great and complex industry. The method is
essentially destructive distillation. The coal is placed in a retort and
when it reaches a temperature of about 700°F. through heating by an
outside fire, the coal begins to fuse and hydrocarbon vapors begin to
emanate. These are generally paraffins and olefins. As the temperature
increases, these hydrocarbons begin to be affected. The chemical
combinations which have long existed are broken up and there are
rearrangements of the atoms of carbon and hydrogen. The actual chemical
reactions become very complex and are somewhat shrouded in uncertainty.
In this last stage the illuminating and heating values of the gas are
determined. Usually about four hours are allowed for the complete
distillation of the gaseous and liquid products from a charge of coal.
Many interesting chemical problems arise in this process and the
influences of temperature and time cannot be discussed within the scope
of this book. Besides the coal-gas, various by-products are obtained
depending upon the raw materials, upon the procedure, and upon the

After the coal-gas is produced it must be purified and the sulphureted
hydrogen at least must be removed. One method of accomplishing this is
by washing the gas with water and ammonia, which also removes some of
the carbon dioxide and hydrocyanic acid. Various other undesirable
constituents are removed by chemical means, depending upon the
conditions. The purified gas is now delivered to the gas-holder; but, of
course, all this time the pressure is governed, in order that the
pressure in the mains will be maintained constant.

Much attention has been given to the enrichment of gas for illuminating
purposes; that is, to produce a gas of high illuminating value from
cheap fuel or by inexpensive processes. This has been done by
decomposing the tar obtained during the distillation of coal and adding
these gases to the coal-gas; by mixing carbureted water-gas with
coal-gas; by carbureting inferior coal-gases; and by mixing oil-gas with
inferior coal-gas.

Water-gas is of low illuminating value, but after it is carbureted it
burns with a brilliant flame. The water-gas is made by raising the
temperature of the fuel bed of hard coal or coke by forced air, which is
then cut off, while steam is passed through the incandescent fuel. This
yields hydrogen and carbon monoxide. To make carbureted water-gas,
oil-gas is mixed with it, the latter being made by heating oil in

A great many kinds of gas are made which are determined by the
requirements and the raw materials available. The amount of illuminating
gas yielded by a ton of fuel, of course, varies with the method of
manufacture, with the raw material, and with the use to which the fuel
is to be put. The production of coal-gas per ton of coal is of the order
of magnitude of 10,000 cubic feet. A typical yield by weight of a
coal-gas retort is,

     10,000 cubic feet of gas     17 per cent.
     coke                         70  "    "
     tar                           5  "    "
     ammoniacal liquid             8  "    "

The coke is not pure carbon but contains the non-volatile minerals which
will remain as ash when the coke is burned, just as if the original coal
had been burned. On the crown of the retort used in coal-gas production,
pure carbon is deposited. This is used for electric-arc carbons and for
other purposes. From the tar many products are derived such as aniline
dyes, benzene, carbolic acid, picric acid, napthalene, pitch,
anthracene, and saccharin.

A typical analysis of the gas distilled from coal is very approximately
as follows,

     Hydrocarbons         40 per cent.
     Hydrogen             50  "   "
     Carbon monoxide       4  "   "
     Nitrogen              4  "   "
     Carbon dioxide        1  "   "
     Various other gases   1  "   "

It is seen that illuminating gas is not a definite compound but a
mixture of a number of gases. The proportion of these is controlled in
so far as possible in order to obtain illuminating value and some of
them are reduced to very small percentages because they are valueless as
illuminants or even harmful. The constituents are seen to consist of
light-giving hydrocarbons, of gases which yield chiefly heat, and of
impurities. The chief hydrocarbons found in illuminating gas are,

     ethylene    C_{2}H_{4}    crotonylene  C_{4}H_{6}
     propylene   C_{3}H_{6}    benzene      C_{6}H_{6}
     butylene    C_{4}H_{8}    toluene      C_{7}H_{8}
     amylene     C_{5}H_{10}   xylene       C_{8}H_{10}
     acetylene   C_{2}H_{2}    methane      C H_{4}
     allylene    C_{3}H_{4}    ethane       C_{2}H_{6}

A gas which has played a prominent part in lighting is acetylene,
produced by the interaction of water and calcium carbide. No other gas
easily produced upon a commercial scale yields as much light, volume for
volume, as acetylene. It has the great advantage of being easily
prepared from raw material whose yield of gas is considerably greater
for a given amount than the raw materials which are used in making other
illuminating gases. The simplicity of the manufacture of acetylene from
calcium carbide and water gives to this gas a great advantage in some
cases. It has served for individual lighting in houses and in other
places where gas or electric service was unavailable. Where space is
limited it also had an advantage and was adopted to some extent on
automobiles, motor-boats, ships, lighthouses, and railway cars before
electric lighting was developed for these purposes.

The color of the acetylene flame is satisfactory and it is extremely
brilliant compared with most flames. An interesting experiment is found
in placing a spark-gap in the flame and sending a series of sparks
across it. If the conditions are proper the flame will became very much
brighter. When the gas issues from a proper jet under sufficient
pressure, the flame is quite steady. Its luminous efficiency gives it an
advantage over other open gas-flames in lighting rooms, because for the
same amount of light it vitiates the air and exhausts the oxygen to a
less degree than the others. Of course, in these respects the gas-mantle
is superior.

The reaction which takes place when water and calcium carbide are
brought together is a double decomposition and is represented by,

     CaC_{2} + H_{2}O = C_{2}H_{2} + CaO

It will be seen that the products are acetylene gas and calcium oxide or
lime. The lime, being hydroscopic and being in the presence of water or
water-vapor in the acetylene generator, really becomes calcium hydroxide
Ca(OH)_{2}, commonly called slaked lime. If there are impurities in the
calcium carbide, it is sometimes necessary to purify the gas before it
may be safely used for interior lighting.

The burners and mantles used in acetylene lighting are essentially the
same as those for other gas-lighting, excepting, of course, that they
are especially adapted for it in minor details.

The chief source of calcium carbide in this country is the electric
furnace. Cheap electrical energy from hydro-electric developments, such
as the Niagara plants, have done much to make the earth yield its
elements. Aluminum is very prevalent in the soil of the earth's surface,
because its oxide, alumina, is a chief constituent of ordinary clay. But
the elements, aluminum and oxygen, cling tenaciously to each other and
only the electric furnace with its excessively high temperatures has
been able to separate them on a large commercial scale. Similarly,
calcium is found in various compounds over the earth's surface.
Limestone abounds widely, hence the oxide and carbonate of lime are
wide-spread. But calcium clings tightly to the other elements of its
compounds and it has taken the electric furnace to bring it to
submission. The cheapness of calcium carbide is due to the development
of cheap electric power. It is said that calcium carbide was discovered
as a by-product of the electric furnace by accidentally throwing water
upon the waste materials of a furnace process. The discovery of a
commercial scale of manufacture of calcium carbide has been a boon to
isolated lighting. Electric lighting has usurped its place on the
automobile and is making inroads in country-home lighting. Doubtless,
acetylene will continue to serve for many years, but its future does not
appear as bright as it did many years ago.

The Pintsch gas, used to some extent in railroad passenger-cars in this
country, is an oil-gas produced by the destructive distillation of
petroleum or other mineral oil in retorts heated externally. The product
consists chiefly of methane and heavy hydrocarbons with a small amount
of hydrogen. In the early days of railways, some trains were not run
after dark and those which were operated were not always lighted. At
first attempts were made at lighting railway cars with compressed
coal-gas, but the disadvantage of this was the large tank required.
Obviously, a gas of higher illuminating-value per volume was desired
where limited storage space was available, and Pintsch turned his
attention to oil-gas. Gas suffers in illuminating-value upon being
compressed, but oil-gas suffers only about half the loss that coal-gas
does. In about 1880 Pintsch developed a method of welding cylinders and
buoys which satisfied lighthouse authorities and he was enabled to
furnish these filled with compressed gas. Thus the buoy was its own
gas-tank. He devised lanterns which would remain lighted regardless of
wind and waves and thus gained a start with his compressed-gas systems.
He compressed the gas to a pressure of about one hundred and fifty
pounds per square inch and was obliged to devise a reducer which would
deliver the gas to the burner at about one pound per square inch. This
regulator served well throughout many years of exacting service. The
system began to be adopted on ships and railroads in 1880 and for many
years it has served well.

Although gas-lighting has affected the activities of mankind
considerably by intensifying commerce and industry and by advancing
social progress, the illuminants which eventually took the lead have
extended the possibilities and influences of artificial light. In the
brief span of a century civilized man is almost totally independent of
natural light in those fields over which he has control. What another
century will bring can be predicted only from the accomplishments of the
past. These indicate possibilities beyond the powers of imagination.



Early in 1800 Volta wrote a letter to the President of the Royal Society
of London announcing the epochal discovery of a device now known as the
voltaic pile. This letter was published in the Transactions and it
created great excitement among scientific men, who immediately began
active investigations of certain electrical phenomena. Volta showed that
all metals could be arranged in a series so that each one would indicate
a positive electric potential when in contact with any metal following
it in the series. He constructed a pile of metal disks consisting of
zinc and copper alternated and separated by wet cloths. At first he
believed that mere contact was sufficient, but when, later, it was shown
that chemical action took place, rapid progress was made in the
construction of voltaic cells. The next step after his pile was
constructed was to place pairs of strips of copper and zinc in cups
containing water or dilute acid. Volta received many honors for his
discovery, which contributed so much to the development of electrical
science and art--among them a call to Paris by Bonaparte to exhibit his
electrical experiments, and to receive a medal struck in his honor.

While Volta was being showered with honors, various scientific men with
great enthusiasm were entering new fields of research, among which was
the heating value of electric current and particularly of electric
sparks made by breaking a circuit. Late in 1800 Sir Humphrey Davy was
the first to use charcoal for the sparking points. In a lecture before
the Royal Society in the following year he described and demonstrated
that the "spark" passing between two pieces of charcoal was larger and
more brilliant than between brass spheres. Apparently, he was producing
a feeble arc, rather than a pure spark. In the years which immediately
followed many scientific men in England, France, and Germany were
publishing the results of their studies of electrical phenomena
bordering upon the arc.

By subscription among the members of the Royal Society, a voltaic
battery of two thousand cells was obtained and in 1808 Davy exhibited
the electric arc on a large scale. It is difficult to judge from the
reports of these early investigations who was the first to recognize the
difference between the spark and the arc. Certainly the descriptions
indicate that the simple spark was not being experimented with, but the
source of electric current available at that time was of such high
resistance that only feeble arcs could have been produced. In 1809 Davy
demonstrated publicly an arc obtained by a current from a Volta pile of
one thousand plates. This he described as "a most brilliant flame, of
from half an inch to one and a quarter inches in length."

In the library of the Royal Society, Davy's notes made during the years
of 1805 and 1812 are available in two large volumes. These were arranged
and paged by Faraday, who was destined to contribute greatly to the
future development of the science and art of electricity. In one of
these volumes is found an account of a lecture-experiment by Davy which
certainly is a description of the electric arc. An extract of this
account is as follows:

     The spark [presumably the arc], the light of which was so
     intense as to resemble that of the sun, ... produced a
     discharge through heated air nearly three inches in length, and
     of a dazzling splendor. Several bodies which had not been fused
     before were fused by this flame.... Charcoal was made to
     evaporate, and plumbago appeared to fuse in vacuo. Charcoal was
     ignited to intense whiteness by it in oxymuriatic acid, and
     volatilized by it, but without being decomposed.

From a consideration of his source of electricity, a voltaic pile of two
thousand plates, it is certain that this could not have been an electric
spark. Later in his notes Davy continued:

     ...the charcoal became ignited to whitness, and by withdrawing
     the points from each other, a constant discharge took place
     through the heated air, in a space at least equal to four
     inches, producing a most brilliant ascending arch of light,
     broad and conical in form in the middle.

This is surely a description of the electric arc. Apparently the
electrodes were in a horizontal position and the arc therefore was
horizontal. Owing to the rise of the heated air, the arc tended to rise
in the form of an arch. From this appearance the term "arc" evolved and
Davy himself in 1820 definitely named the electric flame, the "arc."
This name was continued in use even after the two carbons were arranged
in a vertical co-axial position and the arc no more "arched." An
interesting scientific event of 1820 was the discovery by Arago and by
Davy independently that the arc could be deflected by a magnet and that
it was similar to a wire carrying current in that there was a magnetic
field around it. This has been taken advantage of in certain modern
arc-lamps in which inclined carbons are used. In these arcs a magnet
keeps the arc in place, for without the magnet the arc would tend to
climb up the carbons and go out.

In 1838 Gassiot made the discovery that the temperature of the positive
electrode of an electric arc is much greater than that of the negative
electrode. This is explained in electronic theory by the bombardment of
the positive electrode by negative electrons or corpuscles of
electricity. This temperature-difference was later taken into account in
designing direct-current arc-lamps, for inasmuch as most of the light
from an ordinary arc is emitted by the end of the positive electrode,
this was placed above the negative electrode. In this manner most of the
light from the arc is directed downward where desired. In the few
instances in modern times where the ordinary direct-current arc has been
used for indirect lighting, in which case the arc is above an inverted
shade, the positive carbon is placed below the negative one. Gassiot
first proved that the positive electrode is hotter than the negative one
by striking an arc between the ends of two horizontal wires of the same
substance and diameter. After the arc operated for some time, the
positive wire was melted for such a distance that it bent downward, but
the negative remained quite straight.

Charcoal was used for the electrodes in all the early experiments, but
owing to the intense heat of the arc, it burned away rapidly. A
progressive step was made in 1843 when electrodes were first made by
Foucault from the carbon deposited in retorts in which coal was
distilled in the production of coal-gas. However, charcoal, owing to its
soft porous character, gives a longer arc and a larger flame. In 1877
the "cored" carbons were introduced. These consist of hard molded carbon
rods in which there is a core of soft carbon. In these are combined the
advantages of charcoal and hard carbon and the core in burning away more
rapidly has a tendency to hold the arc in the center. Modern carbons for
ordinary arc-lamps are generally made of a mixture of retort-carbon,
soot, and coal-tar. This paste is forced through dies and the carbons
are baked at a fairly high temperature. A variation in the hardness of
the carbons may be obtained as the requirements demand by varying the
proportions of soot and retort-carbon. Cored carbons are made by
inserting a small rod in the center of the die and the carbons are
formed with a hollow core. This may be filled with a softer carbon.

If two carbons connected to a source of electric current are brought
together, the circuit is completed and a current flows. If the two
carbons are now slightly separated, an arc will be formed. As the arc
burns the carbons waste away and in the case of direct current, the
positive decreases in length more rapidly than the negative one. This is
due largely to the extremely high temperature of the positive tip,
where the carbon fairly boils. A crater is formed at the positive tip
and this is always characteristic of the positive carbon of the ordinary
arc, although it becomes more shallow as the arc-length is increased.
The negative tip has a bright spot to which one end of the arc is
attached. By wasting away, the length of the arc increases and likewise
its resistance, until finally insufficient current will pass to maintain
the arc. It then goes out and to start it the carbons must be brought
together and separated. The mechanisms of modern arc-lamps perform these
functions automatically by the ingenious use of electromagnets.

The interior of the arc is of a violet color and the exterior is a
greenish yellow. The white-hot spot on the negative tip is generally
surrounded by a fringe of agitated globules which consist of tar and
other ingredients of carbons. Often material is deposited from the
positive crater upon the negative tip and these accretions may build up
a rounded tip. This deposit sometimes interferes with the proper
formation of the arc and also with the light from the arc. It is often
responsible for the hissing noise, although this hissing occurs with any
length of arc when the current is sufficiently increased. The hissing
seems to be due to the crater enlarging under excessive current until it
passes the confines of the cross-section of the carbon. It thus tends to
run up the side, where it comes in contact with oxygen of the air. In
this manner the carbon is directly burned instead of being vaporized, as
it is when the hot crater is small and is protected from the air by the
arc itself. The temperature of the positive crater is in the
neighborhood of 6000° to 7000°F. The brightness of the arc under
pressure is the greatest produced by artificial means and is very
intense. By putting the arc under high pressure, the brightness of the
sun may be attained. The temperature of the hottest spot on the negative
tip is about a thousand degrees below that of the positive.

No great demand arose for arc-lamps until the development of the Gramme
dynamo in 1870, which provided a practicable source of electric current.
In 1876 Jablochkov invented his famous "electric candle" consisting of
two rods of carbon placed side by side but separated by insulating
material. In this country Brush was the pioneer in the development of
open arc-lamps. In 1877 he invented an arc-lamp and an efficient form of
dynamo to supply the electrical energy. The first arc-lamps were
ordinary direct-current open arcs and the carbons were made from
high-grade coke, lampblack, and syrup. The upper positive carbon in
these lamps is consumed at a rate of one to two inches per hour.
Inasmuch as about 85 per cent. of the total light is emitted by the
upper (positive) carbon and most of this from the crater, the lower
carbon is made as small as possible in order not to obstruct any more
light than necessary. The positive carbon of the open arc is often cored
and the negative is a smaller one of solid carbon. This combination
operates quite satisfactorily, but sometimes solid carbons are used
outdoors. The voltage across the arc is about 50 volts.

In 1846 Staite discovered that the carbons of an arc enclosed in a glass
vessel into which the air was not freely admitted were consumed less
rapidly than when the arc operated in the open air. After the
appearance of the dynamo, when increased attention was given to the
development of arc-lamps, this principle of enclosing the arcs was again
considered. The early attempts in about 1880 were unsuccessful because
low voltages were used and it was not until the discovery was made that
the negative tip builds up considerably for voltages under 65 volts,
that higher voltages were employed. In 1893 marked improvements were
consummated and Jandus brought out a successful enclosed arc operating
at 80 volts. Marks contributed largely to the success of the enclosed
arc by showing that a small current and a high voltage of 80 to 85 volts
were the requisites for a satisfactory enclosed arc.

The principle of the enclosed arc is simple. A closely fitting glass
globe surrounds the arc, the fit being as close as the feeding of the
carbons will permit. When the arc is struck the oxygen is rapidly
consumed and the heated gases and the enclosure check the supply of
fresh air. The result is that the carbons are consumed about one tenth
as rapidly as in the open arc. There is no crater formed on the positive
tip and the arc wanders considerably. The efficiency of the enclosed arc
as a light-producer is lower than that of the open arc, but it found
favor because of its slow rate of consumption of the carbons and
consequent decreased attention necessary. This arc operates a hundred
hours or more without trimming, and will therefore operate a week or
more in street-lighting without attention. When it is considered that
open arcs for all-night burning were supplied with two pairs of
carbons, the second set going into use automatically when the first were
consumed, the value of the enclosed arc is apparent. However, the open
arc has served well and has given way to greater improvements. It is
rapidly disappearing from use.

The alternating-current arc-lamp was developed after the appearance of
the direct-current open-arc and has been widely used. It has no positive
or negative carbons, for the alternating current is reversing in
direction usually at the rate of 120 times per second; that is, it
passes through 60 complete cycles during each second. No marked craters
form on the tips and the two carbons are consumed at about the same
rate. The average temperature of the carbon tips is lower than that of
the positive tip of a direct-current arc, with the result that the
luminous efficiency is lower. These arcs have been made of both the open
and enclosed type. They are characterized by a humming noise due to the
effect of alternating current upon the mechanism and also upon the air
near the arc. This humming sound is quite different from the occasional
hissing of a direct-current arc. When soft carbons are used, the arc is
larger and apparently this mass of vapor reduces the humming
considerably. The humming is not very apparent for the enclosed
alternating-current arc. The alternating arc can easily be detected by
closely observing moving objects. If a pencil or coin be moved rapidly,
a number of images appear which are due to the pulsating character of
the light. At each reversal of the current, the current reaches zero
value and the arc is virtually extinguished. Therefore, there is a
maximum brightness midway between the reversals.

Various types of all these arcs have been developed to meet the
different requirements of ordinary lighting and to adapt this method of
light-production to the needs of projection, stage-equipment,
lighthouses, search-lights, and other applications.

Up to this point the ordinary carbon arc has been considered and it has
been seen that most of the light is emitted by the glowing end of the
positive carbon. In fact, the light from the arc itself is negligible. A
logical step in the development of the arc-lamp was to introduce salts
in order to obtain a luminous flame. This possibility as applied to
ordinary gas-flames had been known for years and it is surprising that
it had not been early applied to carbons. Apparently Bremer in 1898 was
the first to introduce fluorides of calcium, barium, and strontium. The
salts deflagrate and a luminous flame envelops the ordinary feeble
arc-flame. From these arcs most of the light is emitted by the arc
itself, hence the name "flame-arcs."

By the introduction of metallic salts into the carbons the possibilities
of the arc-lamp were greatly extended. The luminous output of such lamps
is much greater than that of an ordinary carbon arc using the same
amount of electrical energy. Furthermore, the color or spectral
character of the light may be varied through a wide range by the use of
various salts. For example, if carbons are impregnated with calcium
fluoride, the arc-flame when examined by means of a spectroscope will be
seen to contain the characteristic spectrum of calcium, namely, some
green, orange, and red rays. These combine to give to this arc a very
yellow color. As explained in a previous chapter, the salts for this
purpose may be wisely chosen from a knowledge of their fundamental or
characteristic flame-spectra.

These lamps have been developed to meet a variety of needs and their
luminous efficiencies range from 20 to 40 lumens per watt, being several
times that of the ordinary carbon open-arc. The red flame-arc owes its
color chiefly to strontium, whose characteristic visible spectrum
consists chiefly of red and yellow rays. Barium gives to the arc a
fairly white color. The yellow and so-called white flame-arcs have been
most commonly used. Flame-arcs have been produced which are close to
daylight in color, and powerful blue-white flame-arcs have satisfied the
needs of various chemical industries and photographic processes. These
arcs are generally operated in a space where the air-supply is
restricted similar to the enclosed-arc principle. Inasmuch as poisonous
fumes are emitted in large quantities from some flame-arcs, they are not
used indoors without rather generous ventilation. In fact, the
flame-arcs are such powerful light-sources that they are almost entirely
used outdoors or in very large interiors especially of the type of open
factory buildings. They are made for both direct and alternating current
and the mechanisms have been of several types. The electrodes are
consumed rather rapidly so they are made as long as possible. In one
type of arc, the carbons are both fed downward, their lower ends forming
a narrow V with the arc-flame between their tips. Under these
conditions the arc tends to travel vertically and finally to "stretch"
itself to extinction. However, the arc is kept in place by means of a
magnet above it which repels the arc and holds it at the ends of the

The chief objection to the early flame-arcs was the necessity for
frequent renewal of the carbons. This was overcome to a large extent in
the Jandus regenerative lamp in which the arc operates in a glass
enclosure surrounded by an opal globe. However, in addition to the inner
glass enclosure, two cooling chambers of metal are attached to it. Air
enters at the bottom and the fumes from the arc pass upward and into the
cooling chambers, where the solid products are deposited. The air on
returning to the bottom is thus relieved of these solids and the inner
glass enclosure remains fairly clean. The lower carbon is impregnated
with salts for producing the luminous flame and the upper carbon is
cored. The life of the electrodes is about seventy-five hours.

The next step was the introduction of the so-called "luminous-arc" which
is a "flame-arc" with entirely different electrodes. The lower
(negative) electrode consists of an iron tube packed chiefly with
magnetite (an iron oxide) and titanium oxide in the approximate
proportions of three to one respectively. The magnetite is a conductor
of electricity which is easily vaporized. The arc-flame is large and the
titanium gives it a high brilliancy. The positive electrode, usually the
upper one, is a short, thick, solid cylinder of copper, which is
consumed very slowly. This lamp, known as the magnetite-arc, has a
luminous efficiency of about 20 lumens per watt with a clear glass

The mechanisms which strike the arc and feed the carbons are ingenious
devices of many designs depending upon the kind of arc and upon the
character of the electric circuit to which it is connected. Late
developments in electric incandescent filament lamps have usurped some
of the fields in which the arc-lamp reigned supreme for years and its
future does not appear as bright now as it did ten years ago.
High-intensity arcs have been devised with small carbons for special
purposes and considered as a whole a great amount of ingenuity has been
expended in the development of arc-lamps. There will be a continued
demand for arc-lamps, for scientific developments are opening new fields
for them. Their value in photo-engraving, in the moving-picture
production studios, in moving-picture projection, and in certain aspects
of stage-lighting is firmly established, and it appears that they will
find application in certain chemical industries because the arc is a
powerful source of radiant energy which is very active in its effects
upon chemical reactions.

The luminous efficiencies of arc-lamps depend upon so many conditions
that it is difficult to present a concise comparison; however, the
following may suffice to show the ranges of luminous output per watt
under actual conditions of usage. These efficiencies, of course, are
less than the efficiencies of the arc alone, because the losses in the
mechanism, globes, etc., are included.

                                             Lumens per watt
     Open carbon arc                             4 to  8
     Enclosed carbon arc                         3 to  7
     Enclosed flame-arc (yellow or white)       15 to 25
     Luminous arc                               10 to 25

Another lamp differing widely in appearance from the preceding arcs may
be described here because it is known as the mercury-arc. In this lamp
mercury is confined in a transparent tube and an arc is started by
making and breaking a mercury connection between the two electrodes. The
arc may be maintained of a length of several feet. Perhaps the first
mercury-arc was produced in 1860 by Way, who permitted a fine jet of
mercury to fall from a reservoir into a vessel, the reservoir and
receiver being connected to the poles of a battery. The electric current
scattered the jet and between the drops arcs were formed. He exhibited
this novel light-source on the mast of a yacht and it received great
attention. Later, various investigators experimented on the production
of a mercury-arc and the first successful ones were made in the form of
an inverted U-tube with the ends filled with mercury and the remainder
of the tube exhausted.

Cooper Hewitt was a successful pioneer in the production of practicable
mercury-arcs. He made them chiefly in the form of straight tubes of
glass up to several feet in length, with enlarged ends to facilitate
cooling. The tubes are inclined so that the mercury vapor which
condenses will run back into the enlarged end, where a pool of mercury
forms the negative electrode. The arc may be started by tilting the tube
so that a mercury thread runs down the side and connects with the
positive electrode of iron. The heat of the arc volatilizes the mercury
so that an arc of considerable length is maintained. The tilting is done
by electromagnets. Starting has also been accomplished by means of a
heating coil and also by an electric spark. The lamps are stabilized by
resistance and inductance coils.

One of the defects of the light emitted by the incandescent vapor of
mercury is its paucity of spectral colors. Its visible spectrum consists
chiefly of violet, blue, green, and yellow rays. It emits virtually no
red rays, and, therefore, red objects appear devoid of red. The human
face appears ghastly under this light and it distorts colors in general.
However, it possesses the advantages of high efficiency, of reasonably
low brightness, of high actinic value, and of revealing detail clearly.
Various attempts have been made to improve the color of the light by
adding red rays. Reflectors of a fluorescent red dye have been used with
some success, but such a method reduces the luminous efficiency of the
lamp considerably. The dye fluoresces red under the illumination of
ultra-violet, violet, and blue rays; that is, it has the property of
converting radiation of these wave-lengths into radiant energy of longer
wave-lengths. By the use of electric incandescent filament lamps in
conjunction with mercury-arcs, a fairly satisfactory light is obtained.
Many experiments have been made by adding other substances to the
mercury, such as zinc, with the hope that the spectrum of the other
substance would compensate the defects in the mercury spectrum. However
no success has been reached in this direction.

By the use of a quartz tube which can withstand a much higher
temperature than glass, the current density can be greatly increased.
Thus a small quartz tube of incandescent mercury vapor will emit as much
light as a long glass tube. The quartz mercury-arc produces a light
which is almost white, but the actual spectrum is very different from
that of white sunlight. Although some red rays are emitted by the quartz
arc, its spectrum is essentially the same as that of the glass-tube arc.
Quartz transmits ultra-violet radiation, which is harmful to the eyes,
and inasmuch as the mercury vapor emits such rays, a glass globe should
be used to enclose the quartz tube when the lamp is used for ordinary
lighting purposes.

It is fortunate that such radically different kinds of light-sources are
available, for in the complex activities of the present time all are in
demand. The quartz mercury-arc finds many isolated uses, owing to its
wealth of ultra-violet radiation. It is valuable as a source of
ultra-violet for exciting phosphorescence, for examining the
transmission of glasses for this radiation, for sterilizing water, for
medical purposes, and for photography.



Prior to 1800 electricity was chiefly a plaything for men of scientific
tendencies and it was not until Volta invented the electric pile or
battery that certain scientific men gave their entire attention to the
study of electricity. Volta was not merely an inventor, for he was one
of the greatest scientists of his period, endowed with an imagination
which marked him as a genius in creative work. By contributing the
electric battery, he added the greatest impetus to research in
electrical science that it has ever received. As has already been shown,
there began a period of enthusiastic research in the general field of
heating effects of electric current. The electric arc was born in the
cradle of this enthusiasm, and in the heating of metals by electricity
the future incandescent lamp had its beginning.

Between the years 1841 and 1848 several inventors attempted to make
light-sources by heating metals. These crude lamps were operated by
means of Grove and Bunsen electric cells, but no practicable
incandescent filament lamps were brought out until the development of
the electric dynamo supplied an adequate source of electric current. As
electrical science progressed through the continued efforts of
scientific men, it finally became evident that an adequate supply of
electric current could be obtained by mechanical means; that is, by
rotating conductors in such a manner that current would be generated
within them as they cut through a magnetic field. Even the pioneer
inventors of electric lamps made great contributions to electrical
practice by developing the dynamo. Brush developed a satisfactory dynamo
coincidental with his invention of the arc-lamp, and in a similar
manner, Edison made a great contribution to electrical practice in
devising means of generating and distributing electricity for the
purpose of serving his filament lamp.


Most of the light being emitted by the positive (upper) electrode]

[Illustration: FLAME ARC

Most of the light being emitted by the flame]


Thousands of lamps are burned out for the sake of making improvements. The
electrical energy used is equivalent to that consumed by a city of 30,000

Edison in 1878 attacked the problem of producing light from a wire or
filament heated electrically. He used platinum wire in his first
experiments, but its volatility and low melting-point (3200°F.) limited
the success of the lamps. Carbon with its extremely high melting-point
had long attracted attention and in 1879 Edison produced a carbon
filament by carbonizing a strip of paper. He sealed this in a vessel of
glass from which the air was exhausted and the electric current was led
to the filament through platinum wires sealed in the glass. Platinum was
used because its expansion and contraction is about the same as glass.
Incidentally, many improvements were made in incandescent lamps and
thirty years passed before a material was found to replace the platinum
leading-in wires. The cost of platinum steadily increased and finally in
the present century a substitute was made by the use of two metals whose
combined expansion was the same as that of platinum or glass. In 1879
and 1880 Edison had succeeded in overcoming the many difficulties
sufficiently to give to the world a practicable incandescent filament
lamp. About this time Swan and Stearn in England had also produced a
successful lamp.

In Edison's early experiments with filaments he used platinum wire
coated with carbon but without much success. He also made thin rods of a
mixture of finely divided metals such as platinum and iridium mixed with
such oxides as magnesia, zirconia, and lime. He even coiled platinum
wire around a piece of one of these oxides, with the aim of obtaining
light from the wire and from the heated oxide. However, these
experiments served little purpose besides indicating that the filament
was best if it consisted solely of carbon and that it should be
contained in an evacuated vessel.

One of the chief difficulties was to make the carbon filaments. Some of
the pioneers, such as Sawyer and Mann, attempted to cut these from a
piece of carbon. However, Edison and also Swan turned their attention to
forming them by carbonizing a fiber of organic matter. Filaments cut
from paper and threads of cotton and silk were carbonized for this
purpose. Edison scoured the earth for better materials. He tried a
fibrous grass from South America and various kinds of bamboo from other
parts of the world. Thin filaments of split bamboo eventually proved the
best material up to that time. He made many lamps containing filaments
of this material, and even until 1910 bamboo was used to some extent in
certain lamps.

Of these early days, Edison said:

     It occurred to me that perhaps a filament of carbon could be
     made to stand in sealed glass vessels, or bulbs, which we were
     using, exhausted to a high vacuum. Separate lamps were made in
     this way independent of the air-pump, and, in October, 1879, we
     made lamps of paper carbon, and with carbons of common sewing
     thread, placed in a receiver or bulb made entirely of glass,
     with the leading-in wires sealed in by fusion. The whole thing
     was exhausted by the Sprengel pump to nearly one-millionth of
     an atmosphere. The filaments of carbon, although naturally
     quite fragile owing to their length and small mass, had a
     smaller radiating surface and higher resistance than we had
     dared hope. We had virtually reached the position and condition
     where the carbons were stable. In other words, the incandescent
     lamp as we still know it to-day [1904], in essentially all its
     particulars unchanged, had been born.

After Edison's later success with bamboo, Swan invented a process of
squirting filaments of nitrocellulose into a coagulating liquid, after
which they are carbonized. Very fine uniform filaments can be made by
this process and although improvements have been made from time to time,
this method has been employed ever since its invention. In these later
years cotton is dissolved in a suitable solvent such as a solution of
zinc chloride and this material is forced through a small diamond die.
This thread when hardened appears similar to cat-gut. It is cut into
proper lengths and bent upon a form. It is then immersed in plumbago and
heated to a high temperature in order to destroy the organic matter. A
carbon filament is the result. From this point to the finished lamp many
operations are performed, but a discussion of these would lead far
afield. The production of a high vacuum is one of the most important
processes and manufacturers of incandescent lamps have mastered the art
perhaps more thoroughly than any other manufacturers. At least, their
experience in this field made it possible for them to produce quickly
and on a large scale such devices as X-ray tubes during the recent war.

During the early years of incandescent lamps, improvements were made
from time to time which increased the life and the luminous efficiency
of the carbon filaments, but it was not until 1906 that any radical
improvement was achieved. In that year in this country a process was
devised whereby the carbon filament was made more compact. In fact, from
its appearance it received the name "metallized filament." These carbon
filaments are prepared in the same manner as the earlier ones but are
finally "treated" by heating in an atmosphere of hydrocarbons such as
coal-gas. The filament is heated by electric current and the heat breaks
down the hydrocarbons, with the result that carbon is deposited upon the
filament. This "treated" filament has a coating of hard carbon and its
electrical resistance is greater than that of the untreated filament.

The luminous efficiency of a carbon filament is a function of its
temperature and it increases very rapidly with increasing temperature.
For this reason it is a constant aim to reach high filament
temperatures. Of all the materials used in filaments up to the present
time, carbon possesses the highest melting-point (perhaps as high as
7000°F.), but the carbon filament as operated in practice has a lower
efficiency than any other filament. This is because the highest
temperature at which it can be operated and still have a reasonable life
is much lower than that of metallic filaments. The incandescent carbon
in the evacuated bulb sublimes or volatilizes and deposits upon the
bulb. This decreases the size of the filament eventually to the
breaking-point and the blackening of the bulb decreases the output of
light. The treated filament was found to be a harder form of carbon that
did not volatilize as rapidly as the untreated filament. It immediately
became possible to operate it at a higher temperature with a resulting
increase of luminous efficiency. This "graphitized" carbon filament lamp
became known as the gem lamp in this country and many persons have
wondered over the word "gem." The first two letters stand for "General
Electric" and the last for "metallized." This lamp was welcomed with
enthusiasm in its day, but the day for carbon filaments has passed. The
advent of incandescent lamps of higher efficiency has made it
uneconomical to use carbon lamps for general lighting purposes. Although
the treated carbon filament was a great improvement, its reign was cut
short by the appearance of metal filaments.

In 1803 a new element was discovered and named tantalum. It is a dark,
lustrous, hard metal. Pure tantalum is harder than steel; it may be
drawn into fine wire; and its melting-point is very high (about
5100°F.). It is seen to possess properties desirable for filaments, but
for some reason it did not attract attention for a long time. A century
elapsed after its discovery before von Bolton produced the first
tantalum filament lamp. Owing to the low electrical resistance of
tantalum, a filament in order to operate satisfactorily on a standard
voltage must be long and thin. This necessitates storing away a
considerable length of wire in the bulb without permitting the loops to
come into contact with each other. After the filaments have been in
operation for a few hundred hours they become brittle and faults
develop. When examined under a microscope, parts of the filament
operated on alternating current appear to be offset. The explanation of
this defect goes deeply into crystalline structure. The tantalum
filament was quickly followed by osmium and by tungsten in this country.

The osmium filament appeared in 1905 and its invention is due to
Welsbach, who had produced the marvelous gas-mantle. Owing to its
extreme brittleness, osmium was finely divided and made into a paste of
organic material. The filaments were squirted through dies and, after
being formed and dried, they were heated to a high temperature. The
organic matter disappeared and the fine metallic particles were
sintered. This made a very brittle lamp, but its high efficiency served
to introduce it.

In 1870 when Scheele discovered a new element, known in this country as
tungsten, no one realized that it was to revolutionize artificial
lighting and to alter the course of some of the byways of civilization.
This metal--which is known as "wolfram" in Germany, and to some extent
in English-speaking countries--is one of the heaviest of elements,
having a specific gravity of 19.1. It is 50 per cent. heavier than
mercury and nearly twice as heavy as lead. It was early used in German
silver to the extent of 1 or 2 per cent. to make platinoid, an alloy
possessing a high resistance which varies only slightly as the
temperature changes. This made an excellent material for electrical
resistors. The melting-point of tungsten is about 5350°F., which makes
it desirable for filaments, but it was very brittle as prepared in the
early experiments. It unites very readily with oxygen and with carbon at
high temperatures.

The first tungsten lamps appeared on the market in 1906, but these
contained fragile filaments made by the squirting process. When the
squirted filament of tungsten powder and organic matter was heated in an
atmosphere of steam and hydrogen to remove the binding material, a
brittle filament of tungsten was obtained. The first lamps were costly
and fragile. After years of organized research tungsten is now drawn
into the finest wires, possessing a tensile strength perhaps greater
than any other material. Filaments are now made into many shapes and the
greatest strides in artificial lighting have been due to scientific
research on a huge scale.

The achievements which combined to perfect the tungsten lamp to the
point where it has become the mainstay of electric lighting are not
attached to names in the Hall of Fame. Organization of scientific
research in the industrial laboratories is such that often many persons
contribute to the development of an improvement. Furthermore, time is
usually required for a full perspective of applications of scientific
knowledge. In the early days organized research was not practised and
the great developments of those days were the works of individuals.
To-day, even in pure science, some of the greatest contributions are
made by industrial laboratories; but sometimes these do not become known
to the public for many years. The whole scheme of scientific development
has changed materially. For example, the story of the development of
ductile tungsten, which has revolutionized lighting, is complex and more
or less shrouded in secrecy at the present time. Many men have
contributed toward this accomplishment and the public at the present
time knows little more than the fact that tungsten filaments, which were
brittle yesterday, are now made of ductile tungsten wire drawn into the
finest filaments.

The earlier tungsten filaments were made by three rival processes. By
the first, a deposit of tungsten was "flashed" on a fine carbon
filament, the latter being eliminated finally by heating in an
atmosphere of hydrogen and water-vapor. By the second, colloidal
tungsten was produced by operating an arc between tungsten electrodes
under water. The finely divided tungsten was gathered, partially dried,
and squirted through dies to form filaments. These were then sintered.
The third was the "paste" process already described. These methods
produced fragile filaments, but their luminous efficiency was higher
than that of previous ones. However, in this country ductile tungsten
was soon on its way. An ingot of tungsten is subjected to vigorous
swaging until it takes the form of a rod. This is finally drawn into

Much of this development work was done by the laboratories of the
General Electric Company and they were destined to contribute another
great improvement. The blackening of the lamp bulbs was due to the
evaporation of tungsten from the filament. All filaments up to this time
had been confined in evacuated bulbs and the low pressure facilitates
evaporation, as is well known. It had long been known that an inert gas
in the bulb would reduce the evaporation and remedy other defects;
however, under these conditions, there would be a considerable loss of
energy through conduction of heat by the gases. In the vacuum lamp
nearly all the electrical energy is converted into radiant energy, which
is emitted by the filament and any dissipation of heat is an energy
loss. A high vacuum was one of the chief aims up to this time, but a
radical departure was pending.

If an ordinary tungsten-lamp bulb be filled with an inert gas such as
nitrogen, the filament may be operated at a very much higher temperature
without any more deterioration than takes place in a vacuum at a lower
temperature. This gives a more efficient _light_ but a less efficient
_lamp_. The greater output of light is compensated by losses by
conduction of heat through the gas. In other words, a great deal more
energy is required by the filament in order to remain at a given
temperature in a gas than in a vacuum. However, elaborate studies of the
dependence of heat-losses upon the size and shape of the filament and of
the physics of conduction from a solid to a gas, established the
foundation for the gas-filled tungsten lamp. The knowledge gained in
these investigations indicated that a thicker filament lost a relatively
less percentage of energy by conduction than a thin one for equal
amounts of emitted light. However, a practical filament must have
sufficient resistance to be used safely on lighting circuits already
established and, therefore, the large diameter and high resistance were
obtained by making a helical coil of a fine wire. In fact, the
gas-filled tungsten lamp may be thought of as an ordinary lamp with its
long filament made into a short helical coil and the bulb filled with
nitrogen or argon gas.

This development was not accidental and from a scientific point of view
it is not spectacular. It did not mark a new discovery in the same sense
as the discovery of X-rays. However, it is an excellent example of the
great rewards which come to systematic, thorough study of rather
commonplace physical laws in respect to a given condition. Such
achievements are being duplicated in various lines in the laboratories
of the industries. Scientific research is no longer monopolized by
educational institutions. The most elaborate and best-equipped
laboratories are to be found in the industries sometimes surrounded by
the smoke and noise and vigorous activity which indicate that
achievements of the laboratory are on their way to mankind. The
smoke-laden industrial district, pulsating with life, is the proud
exhibit of the present civilization. It is the creation of those who
discover, organize, and apply scientific facts. But how many appreciate
the debt that mankind owes not only to the individual who dedicates his
life to science but to the far-sighted manufacturer who risks his money
in organized quest of new benefits for mankind? A glimpse into a vast
organization of research, which, for example, has been mainly
responsible for the progress of the incandescent lamp would alter the
attitude of many persons toward science and toward the large industrial

The progress in the development of electric incandescent lamps is shown
in the following table, where the dates and values are more or less
approximate. It should be understood that from 1880 to the present time
there has been a steady progress, which occasionally has been greatly
augmented by sudden steps.


                                                               Lumens per
     Date    Filament                      Temperature            watt
     1880    Carbon                          3300°F.              3.0
     1906    Carbon (graphitized)            3400                 4.5
     1905    Tantalum                        3550                 6.5
     1905    Osmium                          3600                 7.5
     1906    Tungsten (vacuum)               3700                 8.0
     1914    Tungsten (gas-filled)     up to 5300°F.           10 to 25

Throughout the development of incandescent filament lamps many ingenious
experiments were made which resulted usually in light-sources of
scientific interest but not of practical value. One of the latest is the
tungsten arc in an inert gas. By means of a heating coil, a small arc is
started between two electrodes consisting of tungsten, but this as yet
has not been shown to be practicable.

Another type of filament lamp was developed by Nernst in 1897. It was an
ingenious application of the peculiar properties of rare-earth oxides.
His first lamp consisted essentially of a slender rod of magnesia. This
substance does not conduct electricity at ordinary temperatures, but
when heated to incandescence it becomes conducting. Upon sufficient
heating of this filament by external means while a proper voltage is
impressed upon it, the electric current passes through it and thereafter
this current will maintain its temperature. Thus such a filament becomes
a conductor and will continue to glow brilliantly by virtue of the
electrical energy which it converts into heat. Later lamps consisted of
"glowers" about one inch long made from a mixture of zirconia and
yttria, and finally a mixture of ceria, thoria, and zirconia was used.
The glower is heated initially by a coil of platinum wire located near
it but not in contact with it. Owing to the fact that this glower
decreases rapidly in resistance as its temperature is increased, it is
necessary to place in series with it a substance which increases in
resistance with increasing current. This is called a "ballasting
resistance" and is usually an iron wire in a glass bulb containing
hydrogen. The heater is cut out by an electromagnet when the glower goes
into operation. This lamp is a marvel of ingenuity and when at its
zenith it was installed to a considerable extent. Its light is
considerably whiter than that of the carbon filament lamps. However, its
doom was sounded when metallic filament lamps appeared.

An interesting filament was developed by Parker and Clark by using as a
core a small filament of carbon. This flashed in an atmosphere
containing a vapor of a compound of silicon, became coated with silicon.
This filament was of high specific resistance and appeared to have
promise. It has not been introduced commercially and doubtless it cannot
compete with the latest tungsten lamps.

Electric incandescent lamps are the present mainstay of electric
illumination and, it might be stated, of progress in lighting. Wonderful
achievements have been accomplished in other modes of lighting and the
foregoing statement is not meant to depreciate those achievements.
However, the incandescent filament lamp has many inherent advantages.
The light-source is enclosed in an air-tight bulb which makes for a
safe, convenient lamp. The filament is capable of subdivision, with the
result that such lamps vary from the minutest spark of the smallest
miniature lamp to the enormous output of the largest gas-filled tungsten
lamp. The outputs of these are respectively a fraction of a lumen and
twenty-five thousand lumens; that is, the luminous intensity varies from
an equivalent of a small fraction of a standard candle to a single
light-source emitting light equivalent to two thousand standard candles.

Statistics are cold facts and are usually uninteresting in a volume of
this character, but they tell a story in a concise manner. The
development of the modern incandescent lamp has increased the intensity
of light available with a great decrease in cost, and this progressive
development is shown easily by tables. For example, since the advent of
the tungsten lamp the average candle-power and luminous efficiency of
all the lamps sold in this country has steadily increased, while the
average wattages of the lamps have remained virtually stationary.


     Year     Candle-power      Watts         per watt
     1907        18.0            53            3.33
     1908        19.0            53            3.52
     1909        21.0            52            3.96
     1910        23.0            51            4.42
     1911        25.0            51            4.82
     1912        26.0            49            5.20
     1913        29.4            47            6.13
     1914        38.2            48            7.80
     1915        42.2            47            8.74
     1916        45.8            49            9.60
     1917        48.7            51           10.56

It will be noted that the luminous intensity of incandescent filament
lamps has steadily increased since the carbon lamp was superseded, and
that in a period of ten years of organized research behind the tungsten
lamp the luminous efficiency (lumens per watt) has trebled. In other
words, everything else remaining unchanged, the cost of light in ten
years was reduced to one third. But the reduction in cost has been more
than this, as will be shown later. During the same span of years the
percentage of carbon filament lamps of the total filament lamps sold
decreased from 100 per cent. in 1907 to 13 per cent. in 1917. At the
same time the percentage of tungsten (Mazda) lamps increased from
virtually zero in 1907 to about 87 per cent. in 1917. The tantalum lamp
had no opportunity to become established, because the tungsten lamp
followed its appearance very closely. In 1910 the sales of the former
reached their highest mark, which was only 3.5 per cent. of all the
lamps sold in the United States. From a lowly beginning the number of
incandescent filament lamps sold for use in this country has grown
rapidly, reaching nearly two hundred million in 1919.



In viewing the development of artificial light and its manifold effects
upon the activities of mankind, it is natural to look into the future.
Jules Verne possessed the advantage of being able to write into fiction
what his riotous imagination dictated, and so much of what he pictured
has come true that his success tempts one to do likewise in prophesying
the future of lighting. Surely a forecast based alone upon the past
achievements and the present indications will fall short of the actual
realizations of the future! If the imagination is permitted to view the
future without restrictions, many apparently far-fetched schemes may be
devised. It may be possible to turn to nature's supply of daylight and
to place some of it in storage for night use. One millionth part of
daylight released as desired at night would illuminate sufficiently all
of man's nocturnal activities. The fictionist need not heed the
scientist's inquiry as to how this daylight would be bottled. Instead of
giving time to such inquiries he would pass on to another scheme,
whereby earth would be belted with optical devices so that day could
never leave. When the sun was shining in China its light would be
gathered on a large scale and sent eastward and westward in these great
optical "pipe-lines" to the regions of darkness, thus banishing night
forever. The writer of fiction need not bother with a consideration of
the economic situation which would demand such efforts. This line of
conjecture is interesting, for it may suggest possibilities toward which
the present trend of artificial lighting does not point; however, the
author is constrained to treat the future of light-production on a
somewhat more conservative basis.

At the present time the light-source of chief interest in electric
lighting is the incandescent filament lamp; but its luminous efficiency
is limited, as has been shown in a previous chapter. When light is
emitted by virtue of its temperature much invisible radiant energy
accompanies the visible energy. The highest luminous efficiency
attainable by pure temperature radiation will be reached when the
temperature of a normal radiator reaches the vicinity of 10,000°F. to
11,000°F. The melting-points of metals are much lower than this. The
tungsten filament in the most efficient lamps employing it is operating
near its melting-point at the present time. Carbon is a most attractive
element in respect to melting-point, for it melts at a temperature
between 6000°F. and 7000°F. Even this is far below the most efficient
temperature for the production of light by means of pure temperature
radiation. There are possibilities of higher efficiency being obtained
by operating arcs or filaments under pressure; however, it appears that
highly efficient light of the future will result from a radical

Scientists are becoming more and more intimate with the structure of
matter. They are learning secrets every year which apparently are
leading to a fundamental knowledge of the subject. When these mysteries
are solved, who can say that man will not be able to create elements to
suit his needs, or at least to alter the properties of the elements
already available? If he could so alter the mechanism of radiation that
a hot metal would radiate no invisible energy, he would have made a
tremendous stride even in the production of light by virtue of high
temperature. This property of selective radiation is possessed by some
elements to a slight degree, but if treatment could enhance this
property, luminous efficiency would be greatly increased. Certainly the
principle of selectivity is a byway of possibilities.

A careful study of commonplace factors may result in a great step in
light-production without the creation of new elements or compounds, just
as such a procedure doubled the luminous efficiency of the tungsten
filament when the gas-filled lamp appeared. There are a few elements
still missing, according to the Periodic Law which has been so valuable
in chemistry. When these turn up, they may be found to possess valuable
properties for light-production; but this is a discouraging byway.

It is natural to inquire whether or not any mode of light-production now
in use has a limiting luminous efficiency approaching the ultimate limit
which is imposed by the visibility of radiation. The eye is able to
convert radiant energy of different wave-lengths into certain fixed
proportions of light. For example, radiant energy of such a wave-length
as to excite the sensation of yellow-green is the most efficient and one
watt of this energy is capable of being converted by the visual
apparatus into about 625 lumens of light. Is this efficiency of
conversion of the visual apparatus everlastingly fixed? For the answer
it is necessary to turn to the physiologist, and doubtless he would
suggest the curbing of the imagination. But is it unthinkable that the
visual processes will always be beyond the control of man? However, to
turn again to the physics of light-production, there are still several
processes of producing light which are appealing.

Many years ago Geissler, Crookes, and other scientists studied the
spectra of gases excited to incandescence by the electric discharge in
so-called vacuum tubes. The gases are placed in transparent glass or
quartz tubes at rather low pressures and a high voltage is impressed
upon the ends of these tubes. When the pressure is sufficiently low, the
gases will glow and emit light. Twenty-eight years ago, D. McFarlan
Moore developed the nitrogen tube, which was actually installed in
various places. But there is such a loss of energy near the cathode that
short "vacuum" tubes of this character are very inefficient producers of
light. Efficiency is greatly increased by lengthening the tubes, so
Moore used tubes of great length and a rather high voltage. As a tube of
this sort is used, the gas gradually disappears and it must be
replenished. In order to replenish the gas, Moore devised a valve for
feeding gas automatically. An advantage of this mode of light-production
is that the color or quality of the light may be varied by varying the
gas used. Nitrogen yields a pinkish light; neon an orange light; and
carbon dioxide a white light. Moore's carbon-dioxide tube is an
excellent substitute for daylight and has been used for the
discrimination of colors where this is an important factor. However, for
this purpose devices utilizing color-screens which alter the light from
the tungsten lamp to a daylight quality are being used extensively.

The vacuum-tube method of producing light has an advantage in the
selection of a gas among a large number of possibilities, and some of
the color effects of the future may be obtained by means of it. Claude
has lately worked on light-production by vacuum tubes and has combined
the neon tube with the mercury-vapor tube. The spectrum of neon to a
large extent compensates for the absence of red light in the mercury
spectrum, with a result that the mixture produces a more satisfactory
light than that of either tube. However, this mode of light-production
has not proved practicable in its present state of development.
Fundamentally the limitations are those of the inherent spectral
characteristics of gases. Doubtless the possibilities of the mechanisms
of the tubes and of combining various gases have not been exhausted.
Furthermore, if man ever becomes capable of controlling to some extent
the structure of elements and of compounds, this method of
light-production is perhaps more promising than others of the present

There is another attractive method of producing light and it has not
escaped the writer of fiction. H. G. Wells, with his rare skill and with
the license so often envied by the writer of facts, has drawn upon the
characteristics of fluorescence and phosphorescence. In his story "The
First Men in the Moon," the inhabitants of the moon illuminate their
caverns by utilizing this phenomenon. A fluorescent liquid was prepared
in large quantities. It emitted a brilliant phosphorescent glow and when
it splashed on the feet of the earth-men it felt cold, but it glowed for
a long time. This is a possibility of the future and many have had
visions of such lighting. If the ceiling of a coal-mine was lined with
glowing fireflies or with phosphorescent material excited in some
manner, it would be possible to see fairly well with the dark-adapted

This leads to the class of phenomena included under the general term
"luminescence." The definition of this term is not thoroughly agreed
upon, but light produced in this manner does not depend upon temperature
in the sense that a glowing tungsten filament emits light because it is
sufficiently hot. A phosphorus match rubbed in the moist palm of the
hand is seen to glow, although it is at an ordinary temperature. This
may be termed "chemi-luminescence." Sidot blende, Balmain's paint, and
many other compounds, when illuminated with ordinary light, and
especially with ultra-violet and violet rays, will continue to glow for
a long time. Despite their brightness they will be cold to the touch.
This phenomenon would be termed "photo-luminescence," although it is
better known as "phosphorescence." It should be noted that the latter
term was carelessly originated, for phosphorus has nothing to do with
it. The glow of the Geissler tube or electrically excited gas at low
pressure would be an example of "electro-luminescence." The luminosity
of various salts in the Bunsen-flame is due to so-called luminescence
and there are many other examples of light-production which are included
in the same general class. Inasmuch as light is emitted from
comparatively cold bodies in these cases, it is popularly known as
"cold" light.

There are many instances of light being emitted without being
accompanied by appreciable amounts of invisible radiant energy and it is
natural to hope for practical possibilities in this direction. As yet
little is known regarding the efficiency of light-production by
phosphorescence. The luminous efficiency of the radiant energy emitted
by phosphorescent substances has been studied, but it seems strange that
among the vast works on phosphorescent phenomena, scarcely any mention
is made of the efficiency of producing light in this manner. For
example, assume that phosphorescent zinc sulphide is excited by the
light from a mercury-arc. All the energy falling upon it is not capable
of exciting phosphorescence, as may be readily shown. Assuming that a
known amount of radiant energy of a certain wave-length has been
permitted to fall upon the phosphorescent material, then in the dark the
latter may be seen to glow for a long time. An interesting point to
investigate is the relation of the output to input; that is, the ratio
of the total emitted light to the total exciting energy. This is a
neglected aspect in the study of light-production by this means.

The firefly has been praised far and wide as the ideal light-source. It
is an efficient radiator of light, for its light is "cold"; that is, it
does not appear to be accompanied by invisible radiant energy. But
little is said about its efficiency as a light-producer. Who knows how
much fuel its lighting-plant consumes? The chemistry of light-production
by living organisms is being unraveled and this part of the phenomenon
will likely be laid bare before long. For an equal amount of energy
radiated, the firefly emits a great many times more light than the most
efficient lamp in use at the present time, but before the firefly is
pronounced ideal, the efficiency of its light-producing process must be

There are many ways of exciting phosphorescence and fluorescence, the
latter being merely an unenduring phosphorescence, which ceases when the
exciting energy is cut off. Ultra-violet, violet, and blue rays are
generally the most effective radiant energy for excitation purposes.
X-rays and the high-frequency discharge are also powerful excitants. As
already stated, virtually nothing is known of the efficiency of this
mode of light-production or of the mechanism within the substance, but
on the whole it is a remarkable phenomenon.

Radium is also a possibility in light-production and in fact has been
practically employed for this purpose for several years. It or one of
its compounds is mixed with a phosphorescent substance such as zinc
sulphide and the latter glows continuously. Inasmuch as the life of some
of the radium products is very long, such a method of illuminating
watch-dials, scales of instruments, etc., is very practicable where they
are to be read by eyes adapted to darkness and consequently highly
sensitive to light. Whether or not radium will be manufactured by the
ton in the future can only conjectured.

Owing to the limitations imposed by physical laws of radiation and by
the physiological processes of vision the highest luminous efficiency
obtainable by heating solid materials is only about 15 per cent. of the
luminous efficiency of the most luminous radiant energy. At present
there are no materials available which may be operated at the
temperature necessary to reach even this efficiency. Great progress in
the future of light-production as indicated by present knowledge appears
to lie in the production of light which is unaccompanied by invisible
radiant energy. At present such phenomena as fluorescence,
phosphorescence, the light of the firefly, chemi-luminescence, etc., are
examples of this kind of light-production. Of course, if science ever
obtains control over the constitution of matter, many difficulties will
disappear; for then man will not be dependent upon the elements and
compounds now available but will be able to modify them to suit his



In this age of brilliantly lighted boulevards and "great white ways"
flooded with light from shop-windows, electric signs, and street-lamps,
it is difficult to visualize the gloom which shrouded the streets a
century ago. As the belated pedestrian walks along the suburban highways
in comparative safety under adequate artificial lighting, he will
realize the great influence of artificial light upon civilization if he
recalls that not more than two centuries ago in London

     it was a common practice ... that a hundred or more in a
     company, young and old, would make nightly invasions upon
     houses of the wealthy to the intent to rob them and that when
     night was come no man durst adventure to walk in the streets.

Inhabitants of the cities of the present time are inclined to think that
crime is common on the streets at night, but what would it be without
adequate artificial light? Two centuries ago in a city like London a
smoking grease-lamp, a candle, or a basket of pine knots here and there
afforded the only street-lighting, and these were extinguished by eleven
o'clock. Lawlessness was hatched and hidden by darkness, and even the
lantern or torch served more to mark the victim than to protect him. It
has been said in describing the conditions of the age of dark streets
that everybody signed his will and was prepared for death before he left
his home. By comparison with the present, one is again encouraged to
believe that the world grows better. Doubtless, artificial light
projected into the crannies has had something to do with this change.

Adequate street-lighting is really a product of the twentieth century,
but throughout the nineteenth century progress was steadily made from
the beginning of gas-lighting in 1807. In preceding centuries crude
lighting was employed here and there but not generally by the public
authorities. In the earliest centuries of written history little is said
of street-lighting. In those days man was not so much inclined to
improve upon nature, beyond protecting himself from the elements, and he
lighted the streets more as a festive outburst than as an economic
proposition. Nevertheless, in the early writings occasionally there are
indications that in the centers of advanced civilization some efforts
were made to light the streets.

The old Syrian city of Antioch, which in the fourth century of the
Christian era contained about four hundred thousand inhabitants, appears
to have had lighted streets. Libanius, who lived in the early years of
that century, wrote:

     The light of the sun is succeeded by other lights, which are
     far superior to the lamps lighted by Egyptians on the festival
     of Minerva of Sais. The night with us differs from the day only
     in the appearance of the light; with regard to labor and
     employment, everything goes on well.

Although apparently labor was not on a strike, the soldiers caused
disturbances, for in another passage he tells of riotous soldiers who

     cut with their swords the ropes from which were suspended the
     lamps that afforded light in the night-time, to show that the
     ornaments of the city ought to give way to them.

Another writer in describing a dispute between two religious adherents
of opposed creeds stated that they quarreled "till the streets were
lighted" and the crowd of onlookers broke up, but not until they "spat
in each other's face and retired." Thus it is seen that artificial light
and civilization may advance, even though some human traits remain
fundamentally unchanged.

Throughout the next thousand years there was little attempt to light the
streets. Iron baskets of burning wood, primitive oil-lamps, and candles
were used to some extent, but during all these centuries there was no
attempt on the part of the government or of individuals to light the
streets in an organized manner. In 1417 the Mayor of London ordained
"lanthorns with lights to bee hanged out on the winter evenings betwixt
Hallowtide and Candlemasse." This was during the festive season, so
perhaps street-lighting was not the sole aim. Early in the sixteenth
century, the streets of Paris being infested with robbers, the
inhabitants were ordered to keep lights burning in the windows of all
houses that fronted on the streets.

For about three centuries the citizens of London, and doubtless of Paris
and of other cities, were reminded from time to time in official
mandates "on pains and penalties to hang out their lanthorns at the
appointed time." The watchman in long coat with halberd and lantern in
hand supplemented these mandates as he made his rounds by,

    A light here, maids, hang out your lights,
    And see your horns be clear and bright,
    That so your candle clear may shine,
    Continuing from six till nine;
    That honest men that walk along
    May see to pass safe without wrong.

In 1668, when some regulations were made for improving the streets of
London, the inhabitants were ordered "for the safety and peace of the
city to hang out candles duly to the accustomed hour." Apparently this
method of obtaining lighting for the streets was not met by the
enthusiastic support of the people, for during the next few decades the
Lord Mayor was busy issuing threats and commands. In 1679 he proclaimed
the "neglect of the inhabitants of this city in hanging and keeping out
their lights at the accustomed hours, according to the good and ancient
usage of this City and Acts of the Common Council on that behalf." The
result of this neglect was "when nights darkened the streets then
wandered forth the sons of Belial, flown with insolence and wine."

In 1694 Hemig patented a reflector which partially surrounded the open
flame of a whale-oil lamp and possessed a hole in the top which aided
ventilation. He obtained the exclusive rights of lighting London for a
period of years and undertook to place a light before every tenth door,
between the hours of six and twelve o'clock, from Michaelmas to Lady
Day. His effort was a worthy one, but he was opposed by a certain
faction, which was successful in obtaining a withdrawal of his license
in 1716. Again the burden of lighting the streets was thrust upon the
residents and fines were imposed for negligence in this respect. But
this procedure after a few more years of desultory lighting was again
found to be unsatisfactory.

In 1729 certain individuals contracted to light the streets of London by
taxing the residents and paid the city for this monopoly. Householders
were permitted to hang out a lantern or a candle or to pay the company
for doing so. But robberies increased so rapidly that in 1736 the Lord
Mayor and Common Council petitioned Parliament to erect lamps for
lighting the city. An act was passed accordingly, giving them the
privilege to erect lamps where they saw fit and to burn them from sunset
to sunrise. A charge was made to the residents, on a sliding scale
depending upon the rate of rental of the houses. As a consequence five
thousand lamps were soon installed. In 1738 there were fifteen thousand
street lamps in London and they were burned an average of five thousand
hours annually.

In the annals of these early times street-lighting is almost invariably
the result of an attempt to reduce the number of robberies and other
crimes. In appealing for more street-lamps in 1744 the Lord Mayor and
aldermen of London in a petition to the king, stated

     that divers confederacies of great numbers of evil-disposed
     persons, armed with bludgeons, pistols, cutlasses, and other
     dangerous weapons, infest not only the private lanes and
     passages, but likewise the public streets and places of public
     concourse, and commit most daring outrages upon the persons of
     your Majesty's good subjects, whose affairs oblige them to pass
     through the streets, by terrifying, robbing and wounding them;
     and these facts are frequently perpetrated at such times as
     were heretofore deemed hours of security.

It has already been seen that gas-lighting was introduced in the streets
of London for the first time in 1807. This marks the real beginning of
public-service lighting companies. In the next decade interest in
street-lighting by means of gas was awakened on the Continent, and it
was not long before this new phase of civilization was well under way.
Although this first gas-lighting was done by the use of open flames, it
was a great improvement over all the preceding efforts. Lawlessness did
not disappear entirely, of course, and perhaps it never will, but it
skulked in the back streets. A controlling influence had now appeared.

But early innovations in lighting did not escape criticism and
opposition. In fact, innovations to-day are not always received by
unanimous consent. There were many in those early days who felt that
what was good for them should be good enough for the younger generation.
The descendants of these opponents are present to-day but fortunately in
diminishing numbers. It has been shown that in Philadelphia in 1833 a
proposal to install a gas-plant was met with a protest signed by many
prominent citizens. A few paragraphs of an article entitled "Arguments
against Light" which appeared in the Cologne _Zeitung_ in 1816 indicate
the character of the objections raised against street-lighting.

1  From the theological standpoint: Artificial illumination
     is an attempt to interfere with the divine
     plan of the world, which has preordained darkness
     during the night-time.

2  From the judicial standpoint: Those people who
     do not want light ought not to be compelled to pay
     for its use.

3  From the medical standpoint: The emanations of
     illuminating gas are injurious. Moreover, illuminated
     streets would induce people to remain later
     out of doors, leading to an increase in ailments
     caused by colds.

4  From the moral standpoint: The fear of darkness
     will vanish and drunkenness and depravity increase.

5  From the viewpoint of the police: The horses will
     get frightened and the thieves emboldened.

6  From the point of view of national economy: Great
     sums of money will be exported to foreign countries.

7  From the point of view of the common people: The
     constant illumination of streets by night will rob
     festive illuminations of their charm.

The foregoing objections require no comment, for they speak volumes
pertaining to the thoughts and activities of men a century ago. It is
difficult to believe that civilization has traveled so far in a single
century, but from this early beginning of street-lighting social
progress received a great impetus. Artificial light-sources were feeble
at that time, but they made the streets safer and by means of them
social intercourse was extended. The people increased their hours of
activity and commerce, industry, and knowledge grew apace.

The open gas-jet and kerosene-flame lamps held forth on the streets
until within the memory of middle-aged persons of to-day. The
lamplighter with his ladder is still fresh in memory. Many of the towns
and villages have never been lighted by gas, for they stepped from the
oil-lamp to the electric lamp. The gas-mantle has made it possible for
gas-lighting to continue as a competitor of electric-lighting for the

In 1877 Mr. Brush illuminated the Public Square of Cleveland with a
number of arc-lamps, and these met with such success that within a short
time two hundred and fifty thousand open-arc lamps were installed in
this country, involving an investment of millions of dollars. Adding to
this investment a much greater one in central-station equipment, a very
large investment is seen to have resulted from this single development
in lighting.

This open-arc lamp was the first powerful light-source available and,
appearing several years before the gas-mantle, it threatened to
monopolize street-lighting. It consumed about 500 watts and had a
maximum luminous intensity of about 1200 candles at an angle of about 45
degrees. Its chief disadvantage was its distribution of light, mainly at
this angle of 45 degrees, which resulted in a spot of light near the
lamp and little light at a distance. A satisfactory street-lighting unit
must emit its light chiefly just below the horizontal in those cases
where the lamps must be spaced far apart for economical reasons. On
referring to the chapter on the electric arc it will be seen that the
upper (positive) carbon of the open-arc emits most of the light. Thus
most of the light tends to be sent downward, but the lower carbon
obstructs some of this with a resulting dark spot beneath the lamp.

The gas-mantle followed closely after the arrival of the carbon arc and
is responsible for the existence of gas-lighting on the streets at the
present time. It is a large source of light and therefore its light
cannot be controlled by modern accessories as well as the light from
smaller sources, such as the arc or concentrated-filament lamp. As a
consequence, there is marked unevenness of illumination along the
streets unless the gas-mantle units are spaced rather closely. Even with
the open-arc, without special light-controlling equipment there is about
a thousand times the intensity near the lamps when placed on the corners
of the block as there is midway between them.

In 1879 the incandescent filament lamp was introduced and it began to
appear on the streets in a short time. It was a feeble, inefficient
light-source, compared with the arc-lamp, but it had the advantage of
being installed on a small bracket. As a consequence of simplicity of
operation, the incandescent lamp was installed to a considerable extent,
especially in the suburban districts.


In lobby of Madison Square Garden]



Tunnels of light boring through the darkness provide safe channels for
modern traffic]

The open-arc lamp possessed the disadvantage of emitting a very unsteady
light and of consuming the carbons so rapidly that daily trimming was
often necessary. In 1893 the enclosed arc appeared and although it
consumed as much electrical energy as the open-arc and emitted
considerably less light, it possessed the great advantage of operating a
week without requiring a renewal of carbons. By surrounding the arc
by means of a glass globe, little oxygen could come in contact with the
carbons and they were not consumed very rapidly. The light was fairly
steady and these arcs operated satisfactorily on alternating current.
The latter feature simplified the generating and distributing equipment
of the central station.

The magnetite or luminous arc-lamp next appeared and met with
considerable success. It was more efficient than the preceding lamps but
was handicapped by being solely a direct-current device. Those familiar
with the generation and distribution of electricity will realize this
disadvantage. However, its luminous intensity just below the horizontal
was about 700 candles and its general distribution of light was fairly
satisfactory. Later the flame-arcs began to appear and they were
installed to some extent. The arc-lamp has served well in
street-lighting from the year 1877, when the open-arc was introduced,
until the present time, when the luminous-arc is the chief survivor of
all the arc-lamps.

The carbon incandescent filament lamp was used extensively until 1909,
when the tungsten filament lamp began to replace it very rapidly.
However, it was not until 1914, when the gas-filled tungsten lamp
appeared, that this type of light-source could compete with arc-lamps on
the basis of efficiency. The helical construction of the filament made
it possible to confine the filament of a high-intensity tungsten lamp in
a small space and for the first time a high degree of control of the
light of street lamps was possible. Prismatic "refractors" were
designed, somewhat on the principle of the lighthouse refractor, so
that the light would be emitted largely just below the horizontal. This
type of distribution builds up the illumination at distant points
between successive street lamps, which is very desirable in
street-lighting. The incandescent filament lamp possesses many
advantages over other systems. It is efficient; capable of subdivision;
operates on direct and alternating current; requires little attention;
and is capable of most successful use with light-controlling apparatus.

According to the reports of the Department of Commerce the number of
electric arc-lamps for street-lighting supplied by public electric-light
plants decreased from 348,643 in 1912 to 256,838 in 1917, while the
number of electric incandescent filament lamps increased from 681,957 in
1912 to 1,389,382 in 1917.

Street-lighting is not only a reinforcement for the police but it
decreases accidents and has come to be looked upon as an advertising
medium. In the downtown districts the high-intensity "white-way"
lighting is festive. The ornamental street lamps have possibilities in
making the streets attractive and in illuminating the buildings.
However, it is to be hoped that in the present age the streets of cities
and towns will be cleared of the ragged equipment of the telephone and
lighting companies. These may be placed in the alleys or underground,
leaving the streets beautiful by day and glorified at night by the
torches of advanced civilization.



At the present time thousands of lighthouses, light-ships, and
light-buoys guide the navigator along the waterways and into harbors and
warn him of dangerous shoals. Many wonderful feats of engineering are
involved in their construction and in no field of artificial lighting
has more ingenuity been displayed in devising powerful beams of light.
Many of these beacons of safety are automatic in operation and require
little attention. It has been said that nothing indicates the
liberality, prosperity, or intelligence of a nation more clearly than
the facilities which it affords for the safe approach of the mariner to
its shores. Surely these marine lights are important factors in modern

The first "lighthouses" were beacon-fires of burning wood maintained by
priests for the benefit of the early commerce in the eastern part of the
Mediterranean Sea. As early as the seventh century before Christ these
beacon-fires were mentioned in writings. In the third century before the
Christian era a tower said to be of a great height was built on a small
island near Alexandria during the reign of Ptolemy II. The tower was
named Pharos, which is the origin of the term "pharology" applied to the
science of lighthouse construction. Cæsar, who visited Alexandria two
centuries later, described the Pharos as a "tower of great height, of
wonderful construction." Fire was kept burning in it night and day and
Pliny said of it, "During the night it appears as bright as a star, and
during the day it is distinguished by the smoke." Apparently this tower
served as a lighthouse for more than a thousand years. It was found in
ruins in 1349. Throughout succeeding centuries many towers were built,
but little attention was given to the development of light-sources and
optical apparatus.

The first lighthouse in the United States and perhaps on the Western
continents was the Boston Light, which was completed in 1716. A few days
after it was put into operation a news item in a Boston paper heralded
the noteworthy event as follows:

     By virtue of an Act of Assembly made in the First Year of His
     Majesty's Reign, For Building and Maintaining a Light House
     upon the Great Brewster (called Beacon-Island) at the Entrance
     of the Harbour of Boston, in order to prevent the loss of the
     Lives and Estates of His Majesty's Subjects; the said Light
     House has been built; and on Fryday last the 14th Currant the
     Light was kindled, which will be very useful for all Vessels
     going out and coming in to the Harbour of Boston, or any other
     Harbours in the Massachusetts Bay, for which all Masters shall
     pay to the Receiver of Impost, one Penny per Ton Inwards, and
     another Penny Outwards, except Coasters, who are to pay Two
     Shillings each, at their clearance Out, And all Fishing
     Vessels, Wood Sloops, etc. Five Shillings each by the Year.

This was the practical result of a petition of Boston merchants made
three years before. The tower was built of stone, at a cost of about
ten thousand dollars. Two years later the keeper and his family were
drowned and the catastrophe so affected Benjamin Franklin, a boy of
thirteen, that he wrote a poem concerning it. The lighthouse was badly
damaged during the Revolution, by raiding-parties, and in 1776, when the
British fleet left the harbor, a squad of sailors blew it up. It was
rebuilt in 1783 and has since been increased in height.

Apparently oil-lamps were used in it from the beginning, notwithstanding
the fact that candles and coal fires served for years in many
lighthouses of Europe. In 1789 sixteen lamps were used and in 1811
Argand lamps and reflectors were installed, with a revolving mechanism.
It now ceased to be a fixed light and the day of flashing lights had
arrived. At the present time the Boston Light emits a beam of 100,000
candle-power directed by modern lenses.

When the United States Government was organized in 1789 there were ten
lighthouses owned by the Colonies, but the Boston Light was in operation
thirty years before the others. Sandy Hook Light, New York Harbor, was
established in 1764 and its original masonry tower is still standing and
in use. It is the oldest surviving lighthouse in this country. It was
built with funds raised by means of two lotteries authorized by the New
York Assembly. A few days after it was lighted for the first time the
following news item appeared in a New York paper:

     On Monday evening last the New York Light-house erected at
     Sandy Hook was lighted for the first time. The House is of an
     Octagon Figure, having eight equal Sides; the Diameter at the
     Base 29 Feet; and at the top of the Wall, 15 Feet. The Lanthorn
     is 7 feet high; the Circumference 33 feet. The whole
     Construction of the Lanthorn is Iron; the Top covered with
     Copper. There are 48 Oil Blazes. The Building from the Surface
     is Nine Stories; the whole from Bottom to Top is 103 Feet.

From these early years the number of lighthouses has steadily grown,
until now the United States maintains lights along 50,000 miles of
coast-line and river channels, a distance equal to twice the
circumference of the earth. It maintains at the present time about
15,000 aids to navigation at an annual cost of about $5,000,000. In 1916
this country was operating 1706 major lights, 53 light-ships, and 512
light-buoys--a total of 5323.

The earliest lighthouses were equipped with braziers or grates in which
coal or wood was burned. These crude light-sources were used until after
the advent of the nineteenth century and in one case until 1846. In the
famous Eddystone tower off Plymouth, England, candles were used for the
first time. The first Eddystone tower was completed in 1698, but it was
swept away in 1703. Another was built and destroyed by fire in 1755.
Smeaton then built another in 1759. Inasmuch as Smeaton is credited with
having introduced the use of candles, this must have occurred in the
eighteenth century; still it appears that, as we have said, the Boston
Light, built in 1716, used oil-lamps from its beginning. However,
Smeaton installed twenty-four candles of rather large size each credited
with an intensity of 2.8 candles. The total luminous intensity of the
light-source in this tower was about 67 candles. Inasmuch as this was
before the use of efficient reflectors and lenses, it is obvious that
the early lighthouses were rather feeble beacons.

According to British records, oil-lamps with flat wicks were first used
in the Liverpool lighthouses in 1763. The Argand lamp, introduced in
about 1784, became widely used. The better combustion obtained with this
lamp having a cylindrical wick and a glass chimney greatly increased the
luminous intensity and general satisfactoriness of the oil-lamp. Later
Lange added an improvement by providing a contraction toward the upper
part of the chimney. Rumford and also Fresnel devised multiple-wick
burners, thus increasing the luminous intensity. In these early lamps
sperm-oil and colza-oil were burned and they continued to be until the
middle of the nineteenth century. Cocoanut-oil, lard-oil, and olive-oil
have also been used in lighthouses.

Naturally, mineral oil was introduced as soon as it was available, owing
to its lower cost; but it was not until nearly 1870 that a satisfactory
mineral-oil lamp was in operation in lighthouses. Doty is credited with
the invention of the first successful multiple-wick lighthouse lamp
using mineral oil, and his lamp and modifications of it were very
generally used until the latter part of the nineteenth century. These
lamps are of two types--one in which oil is supplied to the burner under
pressure and the other in which oil is maintained at a constant level.
In some of the smallest lamps the ordinary capillarity of the wick is
depended on to supply oil to the flame.

Coal-gas was introduced into lighthouses in about the middle of the
nineteenth century. Inasmuch as the gas-mantle had not yet appeared, the
gas was burned in jets. Various arrangements of the jets, such as
concentric rings forming a stepped cone, were devised. The gas-mantle
was a great boon to the mariner as well as to civilized beings in
general. It greatly increases the intensity of light obtainable from a
given amount of fuel and it is a fairly compact bright source which
makes it possible to direct the light to some degree by means of optical
systems. Owing to the elaborate apparatus necessary for making coal-gas,
several other gases have been more desirable fuels for lighthouse lamps.
Various simple gas-generators have been devised. Some of the high-flash
mineral-oils are vaporized and burned under a mantle. Acetylene, which
is so simply made by means of calcium carbide and water, has been a
great factor in lighting for navigation. By the latter part of the
nineteenth century lighthouses employing incandescent gas-burners were
emitting beams of light having luminous intensities as great as several
hundred thousand candles. These special gas-mantle light-sources have
brightness as high as several hundred candles per square inch.

Electric arc-lamps were first introduced into lighthouse service in
about 1860, but these lamps cannot be considered to have been really
practicable until about 1875. In 1883 the British lighthouse authorities
carried out an extensive investigation of arc-lamps. It was found that
the whiter light from these lamps suffered a greater absorption by the
atmosphere than the yellower light from oils, but the much greater
luminous intensity of the arc-lamp more than compensated for this
disadvantage. The final result of the investigation was the conclusion
that for ordinary lighthouse purposes the oil-and gas-lamps were more
suitable and economical than arc-lamps; but where great range was
desired, the latter were much more advantageous, owing to their great
luminous intensity. Electric incandescent filament lamps have been used
for the less important lights, and recently there has been some
application of the modern high-efficiency filament lamps.

Besides the high towers there are many minor beacons, light-ships, and
light-buoys in use. Many of these are untended and therefore must
operate automatically. The light-ship is used where it is impracticable
or too expensive to build a lighthouse. Inasmuch as it is anchored in
fairly deep water, it is safe in foggy weather to steer almost directly
toward its position as indicated by the fog-signal. Light-ships are more
expensive to maintain than lighthouses, but they have the advantages of
smaller cost and of mobility; for sometimes it may be desired to move
them. The first light-ship was established in 1732 near the mouth of the
Thames, and the first in this country was anchored in Chesapeake Bay
near Norfolk in 1820. The early ships had no mode of self-propulsion,
but the modern ones are being provided with their own power. Oil and gas
have been used as fuel for the light-sources and in 1892 the U. S.
Lighthouse Board constructed a light-ship with a powerful electric
light. Since that time several have been equipped with electric lights
supplied by electric generators and batteries.

Untended lights were not developed until about 1880, when Pintsch
introduced his welded buoys filled with compressed gas and thereby
provided a complete lighting-plant. With improvements in lamps and
controls the untended light-buoys became a success. The lights burn for
several months, and even for a year continuously; and the oil-gas used
appears to be very satisfactory. Recently some experiments have been
made with devices which would be actuated by sunlight in such a manner
that the light would be extinguished during the day excepting a small
pilot-flame. By this means a longer period of burning without attention
may be obtained. Electric filament lamps supplied by batteries or by
cables from the shore have been used, but the oil-gas buoy still remains
in favor. Acetylene has been employed as a fuel for light-buoys.
Automatic generators have been devised, but the high-pressure system is
more simple. In the latter case purified acetylene is held in solution
under high pressure in a reservoir containing an asbestos composition
saturated with acetone.

The light-sources of beacons have had the same history as those of other
navigation lights. Many of these are automatic in operation, sometimes
being controlled by clockwork. During the last twenty years the
gas-mantle has been very generally applied to beacon-lights. In the
latter part of the nineteenth century a mineral-oil lamp was devised
with a permanent wick made by forming upon a thick wick a coating of
carbon. The operation is such that this is not consumed and it prevents
further burning of the wick.

The optical apparatus of navigation lights has undergone many
improvements in the past century. The early lights were not equipped
with either reflecting or refracting apparatus. In 1824 Drummond devised
a scheme for reflecting light in order that a distant observer might
make a reading upon the point where the apparatus was being operated by
another person. He was led by his experiments to suggest the application
of mirrors to lighthouses. His device was essentially a parabolic mirror
similar to the reflectors now widely used in automobile head-lamps,
search-lights, etc. He employed the lime-light as a source of light and
was enthusiastic over the results obtained. His discussion published in
1826 indicates that little practical work had been done up to that time
toward obtaining beams or belts of light by means of optical apparatus.
However, lighthouse records show that as early as 1763 small silvered
plane glasses were set in plaster of Paris in such a manner as to form a
partially enveloping reflector. Spherical reflectors were introduced in
about 1780 and parabolic reflectors about ten years later.

All the earlier lights were "fixed," but as it is desirable that the
mariner be able to distinguish one light from another, the revolving
mechanism evolved. By its agency characteristic flashes are obtained and
from the time interval the light is recognized. The first revolving
mechanism was installed in 1783. The early flashing lights were obtained
by means of revolving reflectors which gathered the light and directed
it in the form of a beam or pencil. The type of parabolic reflector now
in use does not differ essentially from that of an automobile head-lamp,
excepting that it is larger.

Lenses appear to have been introduced in the latter part of the
nineteenth century. They were at first ground from a solid piece of
glass, in concentric zones, in order to reduce the thickness. They were
similar in principle to some of the tail-light lenses used at present on
automobiles. Later the lenses were built up by means of separate annular
rings. The name of Fresnel is permanently associated with lighthouse
lenses because in 1822 he developed an elaborate built-up lens of
annular rings. The centers of curvature of the different rings receded
from the axis as their distance from the center increased, in such a
manner as to overcome a serious optical defect known as spherical
aberration. Fresnel devised many improvements in which he used
refracting and reflecting prisms for the outer elements.

The optical apparatus of lighthouses usually aims (1) to concentrate the
rays of light into a pencil of light, (2) to concentrate them into a
belt of light, or (3) to concentrate the rays over a limited azimuth. In
the first case a single lens or a parabolic reflector suffices, but in
the second case a cylindrical lens which condenses the light vertically
into a horizontal sheet of light is essential. The third case is a
combination of the first two. The modern lighthouse lenses are very
elaborate in construction, being built up by means of many elements into
several sections. For example, the central section may consist of a
spherical lens ground with annular rings. In the next section refracting
prisms may be used and in the outer section reflecting glass prisms are
employed. The various elements are carefully designed according to the
laws of geometrical optics.

The flashing light has such advantages over the fixed that it is
generally used for important beacons. A variety of methods of obtaining
intermittent light have been employed, but they are not of particular
interest. Sometimes the lens or reflector is revolved and in other types
an opaque screen containing slits is revolved. In the larger lighthouses
the optical apparatus and its structure sometimes weigh several tons.
When it is necessary to revolve apparatus of this weight, the whole
mechanism is floated upon mercury contained in a cast-iron vessel of
suitable size, and by an ingenious arrangement only a small portion of
mercury is required.

The characteristics of navigation lights are varied considerably in
order to enable the mariner to distinguish them and thereby to learn
exactly where he is. The fixed light is liable to be confused with
others, so it has now become a minor light. Flashes of short duration
followed by longer periods of darkness are extensively used. The mariner
by timing the intervals is able to recognize the light. This method is
extended to groups of short flashes followed by longer intervals of
darkness. In fact, short flashes have been employed to indicate a
certain number so that a mariner could recognize the light by a number
rather than by means of his watch. However, a time element is generally
used. A combination of fixed light upon which is superposed a flash or a
group of flashes of white or of colored light has been used, but it is
in disrepute as being unreliable. A type known as "occulating lights"
consists of a fixed light which is momentarily eclipsed, but the
duration of the eclipse is usually less than that of the light.
Obviously, groups of eclipses may be used. Sometimes lights of different
colors are alternated without any dark intervals. The colored ones used
are generally red and green, but these are short-range lights at best.
Colored sectors are sometimes used over portions of the field, in order
to indicate dangers, and white light shows in the fairway. These are
usually fixed lights for marking the channel.

The distance at which a light may be seen at sea depends upon its
luminous intensity, upon its color or spectral composition, upon its
height and that of the observer's eyes above the sea-level, and upon the
atmospheric conditions. Assuming a perfectly clear atmosphere, the
visibility of a light-source apparently depends directly upon its
candle-power. The atmosphere ordinarily absorbs the red, orange, and
yellow rays less than the green, blue, and violet rays. This is
demonstrated by the setting sun, which as it approaches closer to the
horizon changes from yellow to orange and finally to red as the amount
of atmosphere between it and the eye increases. For this reason a red
light would have a greater range than a blue light of the same luminous

Under ordinary atmospheric conditions the range of the more powerful
light-sources used in lighthouses is greater than the range as limited
by the curvature of the earth. For the uncolored illuminants the range
in nautical miles appears to be at least equal to the square root of the
candle-power. A real practical limitation which still exists is the
curvature of the earth, and the distance an object may be seen by the
eye at sea-level depends upon the height of the object. The relation is
approximately expressed thus,--

Range in nautical miles = 8/7 square root of Height of object in
feet. For example, the top of a tower 100 feet high is visible to an eye
at sea-level a distance of 8/7 square root of 100 = 80/7 = 11.43
miles. Now if the eye is 49 feet above sea-level, a similar computation
will show how far away it may be seen by the original eye at sea-level.
This is 8/7 square root of 49 = 8 miles. Hence an eye 49 feet above
sea-level will be able to see the top of the 100-foot tower at a
distance of 11.43 + 8 or 19.43 nautical miles. Under these conditions an
imaginary line drawn from the top of the tower to the eye will be just
tangent to the spherical surface of the sea at a distance of 8 miles
from the eye and 11.43 miles from the tower.

The luminous intensity of a light-source or of the beam of light is
directly responsible for the range. The luminous intensity of the early
beacon-fires and oil-lamps was equivalent to a few candles. The
improvements in light-sources and also in reflecting and refracting
optical systems have steadily increased the candle-power of the beams,
until to-day the beams from gas-lamps have intensities as high as
several hundred thousand candle-power. The beams sent forth by modern
lighthouses equipped with electric lamps and enormous light-gathering
devices are rated in millions of candle-power. In fact, Navesink Light
at the entrance of New York Bay is rated as high as 60,000,000

Of course, light-production has increased enormously in efficiency in
the past century, but without optical devices for gathering the light,
the enormous beam intensity would not be obtained. For example, consider
a small source of light possessing a luminous intensity of one candle in
all directions. If all this light which is emitted in all directions is
gathered and sent forth in a beam of small angle, say one thousandth of
the total angle surrounding a point, the intensity of this beam would be
1000 candles. It is in this manner that the enormous beam intensities
are built up.

There is an interesting point pertaining to short flashes of light. To
the dark-adapted eye a brief flash is registered as of considerably
higher intensity than if the light remained constant. In other words,
the lookout on a vessel is adapted to darkness and a flash from a beam
of light is much brighter than if the same beam were shining steadily.
This is a physiological phenomenon which operates in favor of the
flashing light.





Doubtless, the reader has noted that reliability, simplicity, and low
cost of operation are the primary considerations for light-sources used
as aids to navigation. This accounts for the continued use of oil and
gas. From an optical standpoint the electric arc-lamps and
concentrated-filament lamps are usually superior to the earlier sources
of light, but the complexity of a plant for generating electricity is
usually a disadvantage in isolated places. The larger light-ships are
now using electricity generated by apparatus installed in the vessels.
There seems to be a tendency toward the use of more buoys and fewer
lighthouses, but the beam-intensities of the latter are increasing.

In the hundred years since the Boston Light was built the same great
changes wrought by the development of artificial light in other
activities of civilization have appeared in the beacons of the mariner.
The development of these aids to navigation has been wonderful, but it
must go on and on. The surface of the earth comprises 51,886,000 square
statute miles of land and 145,054,000 square miles of water. Three
fourths of the earth's surface is water and the oceans will always be
highways of world commerce. All the dangers cannot be overcome, but
human ingenuity is capable of great achievements. Wreckage will appear
along the shore-lines despite the lights, but the harvest of the shoals
has been much reduced since the time described by Robert Louis
Stevenson, when the coast people in the Orkneys looked upon wrecks as a
source of gain. He states:

     It had become proverbial with some of the inhabitants to
     observe that "if wrecks were to happen, they might as well be
     sent to the poor island of Sanday as anywhere else." On this
     and the neighboring island, the inhabitants have certainly had
     their share of wrecked goods. On complaining to one of the
     pilots of the badness of his boat's sails, he replied with some
     degree of pleasantry, "Had it been His [God's] will that you
     come na here wi these lights, we might a' had better sails to
     our boats and more o' other things."

     In the leasing of farms, a location with a greater probability
     of shipwreck on the shore brought a much higher rent.



When the recent war broke out science responded to the call and under
the stress of feverish necessity compressed the normal development of a
half-century into a few years. The airplane, in 1914 a doubtful
plaything of daredevils, emerged from the war a perfected thing of the
air. Lighting did not have the glamor of flying or the novelty of
chemical warfare, but it progressed greatly in certain directions and
served well. While artificial lighting conducted its unheralded
offensive by increasing production in the supporting industries and
helped to maintain liaison with the front-line trenches by lending eyes
to transportation, it was also doing its part at the battle front. Huge
search-lights revealed the submarine and the aërial bomber; flares
exposed the manoeuvers of the enemy; rockets brought aid to
beleaguered vessels and troops; pistol lights fired by the aërial
observer directed artillery fire; and many other devices of artificial
light were in the fray. Many improvements were made in search-lights and
in signaling devices and the elements of the festive fireworks of past
ages were improved and developed for the needs of modern warfare.

Night after night along the battle front flares were sent up to reveal
patrols and any other enemy activity. On the slightest suspicion great
swarms of these brilliant lights would burst forth as though flocks of
huge fireflies had been disturbed. They were even used as light
barrages, for movements could be executed in comparative safety when a
large number of these lights lay before the enemy's trenches sputtering
their brilliant light. The airman dropped flares to illuminate his
target or his landing field. The torches of past parades aided the
soldier in his night operations and rockets sent skyward radiated their
messages to headquarters in the rear. The star-shell had the same
missions as other flares, but it was projected by a charge of powder
from a gun. These and many modifications represent the useful
applications of what formerly were mere "fireworks." Those which are
primarily signaling devices are discussed in another chapter, but the
others will be described sufficiently to indicate the place which
artificial light played in certain phases of warfare.

The illuminating compounds used in these devices are not particularly
new, consisting essentially of a combustible powder and chemical salts
which make the flame luminous and give it color when desired. Among the
ingredients are barium nitrate, potassium perchlorate, powdered
aluminum, powdered magnesium, potassium nitrate, and sulphur. One of the
simplest mixtures used by the English is,

     Barium nitrate          37 per cent.
     Powdered magnesium      34 per cent.
     Potassium nitrate       29 per cent.

The magnesium is coated with hot wax or paraffin, which not only acts as
a binder for the mixture when it is pressed into its container but also
serves to prevent oxidation of the magnesium when the shells are stored.
The barium and potassium nitrates supply the oxygen to the magnesium,
which burns with a brilliant white flame. The potassium nitrate takes
fire more readily than the barium nitrate, but it is more expensive than
the latter.

Owing to the cost of magnesium, powdered aluminum has been used to some
extent as a substitute. Aluminum does not have the illuminating value of
magnesium and it is more difficult to ignite, but it is a good
substitute in case of necessity. An English mixture containing these
elements is,

     Barium nitrate       58 per cent.
     Magnesium            29 per cent.
     Aluminum             13 per cent.

Mixtures which are slow to ignite must be supplemented by a primary
mixture which is readily ignited. For obtaining colored lights it is
only necessary to add chemicals which will give the desired color. The
mixtures can be proportioned by means of purely theoretical
considerations; that is, just enough oxygen can be present to burn the
fuel completely. However, usually more oxygen is supplied than called
for by theory.

The illuminating shell is perhaps the most useful of these devices to
the soldier. It has been constructed with and without parachutes, the
former providing an intense light for a brief period because it falls
rapidly. These shells of the larger calibers are equipped with
time-fuses and are generally rather elaborate in construction. The shell
is of steel, and has a time-fuse at the tip. This fuse ignites a
charge of black powder in the nose of the shell and this explosion
ejects the star-shell out of the rear of the steel casing. At the same
time the black powder ignites the priming mixture next to it, which in
turn ignites the slow-burning illuminating compound. The star-shell has
a large parachute of strong material folded in the rear of the casing
and the cardboard tube containing the illuminating mixture is attached
to it. The time of burning varies, but is ordinarily less than a minute.
Certain structural details must be such as to endure the stresses of a
high muzzle velocity. Furthermore, a velocity of perhaps 1000 feet per
second still obtains when the star-shell with its parachute is ejected
at the desired point in the air.

The non-parachute illuminating shell is designed to give an intense
light for a brief interval and is especially applicable to defense
against air raids. Such a light aims to reveal the aircraft in order
that the gunners may fire at it effectively. These shells are fitted
with time-fuses which fire the charge of black powder at the desired
interval after the discharge of the shell from the gun. The contents of
the shell are thereby ejected and ignited. The container for the
illuminating material is so designed that there is rapid combustion and
consequently a brilliant light for about ten seconds. The enemy airman
in this short time is unable to obtain any valuable knowledge pertaining
to the earth below and furthermore he is likely to be temporarily
blinded by the brilliant light if it is near him.

The rifle-light which resembles an ordinary rocket, is fired from a
rifle and is designed for short-range use. It consists of a steel
cylindrical shell a few inches long fastened to a steel rod. A parachute
is attached to the cardboard container in which the illuminating mixture
is packed and the whole is stowed away in the steel shell. Shore
delay-fuses are used for starting the usual cycle of events after the
rifle-light has been fired from the gun. The steel rod is injected into
the barrel of a rifle and a blank cartridge is used for ejecting this
rocket-like apparatus. Owing to inertia the firing-pin in the shell
operates and the short delay-fuse is thus fired automatically an instant
after the trigger of the rifle is pulled.

Illuminating "bombs" of the same general principles are used by airmen
in search of a landing for himself or for a destructive bomb; in
signaling to a gunner, and in many other ways. They are simple in
construction because they need not withstand the stresses of being fired
from a gun; they are merely dropped from the aircraft. The mechanism of
ignition and the cycle of events which follow are similar to those of
other illuminating shells.

The value of such artificial-lighting devices depends both upon luminous
intensity and time of burning. Although long-burning is not generally
required in warfare, it is obvious that more than a momentary light is
usually needed. In general, high candle-power and long-burning are
opposed to each other, so that the most intense lights of this character
usually are of short duration. Typical performances of two flares of the
same composition are as follows:

                                    Flare No. 1  Flare No. 2
     Average candle-power            270,000       95,000
     Seconds of burning                10            35
     Candle-seconds                 2,700,000     3,325,000
     Cubic inches of compound           6             7
     Candle-seconds per cubic inch   450,000       475,000
     Candle-hours per cubic inch       125           132

The illuminating compound was the same in these two flares, which
differed only in the time allowed for burning. Of course, the
measurements of the luminous intensity of such flares is difficult
because of the fluctuations, but within the errors of the measurements
it is seen that the illuminating power of the compound is about the same
regardless of the time of burning. The light-source in the case of
burning powders is really a flame, and inasmuch as the burning end hangs
downward, more light is emitted in the lower hemisphere than in the
upper. The candle-power of the largest flares equals the combined
luminous intensities of 200 street arc-lamps or of 10,000 ordinary
40-watt tungsten lamps such as are used in residence lighting.

It is interesting to note the candle-hours obtained per cubic inch of
compound and to find that the cost of this light is less than that of
candles at the present time and only five or ten times greater than that
of modern electric lighting.

Illuminating shells in use during the recent war were designed for
muzzle velocities as high as 2700 feet per second and were gaged to
ignite at any distance from a quarter of a mile to several miles. The
maximum range of illuminating shells fired from rifles was about 200
yards; for trench mortars about one mile; and from field and naval guns
about four miles.

The search-light has long been a valuable aid in warfare and during the
recent conflict considerable attention was given to its development and
application. It is used chiefly for detecting and illuminating distant
targets, but this covers a wide range of conditions and requirements. In
order that a search-light may be effective at a great distance, as much
as possible of the light emitted by a source is directed into a beam of
light of as nearly parallel rays as can be obtained. Reflectors are
usually employed in military search-lights, and in order that the beam
may be as nearly parallel (minimum divergence) as possible, the light
must be emitted by the smallest source compatible with high intensity.
This source is placed at the proper point in respect to a large
parabolic reflecter which renders the rays parallel or nearly so.

Ever since its advent the electric arc has been employed in large
search-lights, with which the army and the navy were supplied; however,
the greatest improvements have been made under the stress of war. The
science of aëronautics advanced so rapidly during the recent war that
the necessity for powerful search-lights was greatly augmented and as
the conflict progressed the enemy airmen came to look upon the newly
developed ones with considerable concern. The rapidly moving aircraft
and its high altitude brought new factors into the design of these
lights. It now became necessary to have the most intense beam and to be
able to sweep the heavens with it by means of delicate controlling
apparatus, for the targets were sometimes minute specks moving at high
speed at altitudes as high as five miles. Furthermore, owing to the
shifting battle areas, mobile apparatus was necessary.

The control of light by means of reflectors has been studied for
centuries, but until the advent of the electric arc the light-sources
were of such large areas that effective control was impossible. Optical
devices generally are considered in connection with "point sources," but
inasmuch as no light can be obtained from a point, a source of small
dimensions and of high brightness is the most effective compromise.
Parabolic mirrors were in use in the eighteenth century and their
properties were known long before the first search-light worthy of the
name was made in 1825 by Drummond, who used as a source of light a piece
of lime heated to incandescence in a blast flame. He finally developed
the "lime-light" by directing an oxyhydrogen flame upon a piece of lime
and this device was adapted to search-lights and to indoor projection.
It is said that the first search-light to be used in warfare was a
Drummond lime-light which played a part in the attack on Fort Wagner at
Charleston in 1863.

In 1848 the first electric arc lamp used for general lighting was
installed in Paris. It was supplied with current by a large voltaic
cell, but the success of the electric arc was obliged to await the
development of a more satisfactory source of electricity. A score of
years was destined to elapse, after the public was amazed by the first
demonstration, before a suitable electric dynamo was invented. With the
advent of the dynamo, the electric arc was rapidly developed and thus
there became available a concentrated light-source of high intensity
and great brilliancy. Gradually the size was increased, until at the
present time mirrors as large as seven feet in diameter and electric
currents as great as several hundred amperes are employed. The beam
intensities of the most powerful search-lights are now as great as
several hundred million candles.

The most notable advance in the design of arc search-lights was achieved
in recent years by Beck, who developed an intensive flame carbon-arc.
His chief object was to send a much greater current through the arc than
had been done previously without increasing the size of the carbons and
the unsteadiness of the arc. In the ordinary arc excessive current
causes the carbons to disintegrate rapidly unless they are of large
diameter. Beck directed a stream of alcohol vapor at the arc and they
were kept from oxidizing. He thus achieved a high current-density and
much greater beam intensities. He also used cored carbons containing
certain metallic salts which added to the luminous intensity, and by
rotation of the positive carbon so that the crater was kept in a
constant position, greater steadiness and uniformity were obtained.
Tests show that, in addition to its higher luminous efficiency, an arc
of this character directs a greater percentage of the light into the
effective angle of the mirror. The small source results in a beam of
small divergence; in other words, the beam differs from a cylinder by
only one or two degrees. If the beam consisted entirely of parallel rays
and if there were no loss of light in the atmosphere by scattering or by
absorption, the beam intensity would be the same throughout its entire
length. However, both divergence and atmospheric losses tend to reduce
the intensity of the beam as the distance from the search-light

Inasmuch as the intensity of the beam depends upon the actual brightness
of the light-source, the brightness of a few modern light-sources are of
interest. These are expressed in candles per square inch of projected
area; that is, if a small hole in a sheet of metal is placed next to the
light-source and the intensity of the light passing through this hole is
measured, the brightness of the hole is easily determined in candles per
square inch.


     Kerosene flame                             5 to      10
     Acetylene                                 30 to      60
     Gas-mantle                                30 to     500
     Tungsten filament (vacuum) lamp          750 to   1,200
     Tungsten filament (gas-filled) lamp    3,500 to  18,000
     Magnetite arc                          4,000 to   6,000
     Carbon arc for search-lights          80,000 to  90,000
     Flame arc for search-lights          250,000 to 350,000
     Sun (computed mean)                     about 1,000,000

As the reflector of a search-light is an exceedingly important factor in
obtaining high beam-intensities, considerable attention has been given
to it since the practicable electric arc appeared. The parabolic mirror
has the property of rendering parallel, or nearly so, the rays from a
light-source placed at its focus. If the mirror subtends a large angle
at the light-source, a greater amount of light is intercepted and
rendered parallel than in the case of smaller subtended angles; hence,
mirrors are large and of as short focus as practicable. Search-light
projectors direct from 30 to 60 per cent. of the available light into
the beam, but with lens systems the effective angle is so small that a
much smaller percentage is delivered in the beam. Mangin in 1874 made a
reflector of glass in which both outer and inner surfaces were spherical
but of different radii of curvature, so that the reflector was thicker
in the middle. This device was "silvered" on the outside and the
refraction in the glass, as the light passed through it to the mirror
and back again, corrected the spherical aberration of the mirrored
surface. These have been extensively used. Many combinations of curved
surfaces have been developed for special projection purposes, but the
parabolic mirror is still in favor for powerful search-lights. The tip
of the positive carbon is placed at its focus and the effective angle in
which light is intercepted by the mirror is generally about 125 degrees.
Within this angle is included a large portion of the light emitted by
the light-source in the case of direct-current arcs. If this angle is
increased for a mirror of a given diameter by decreasing its focal
length, the divergence of the beam is increased and the beam-intensity
is diminished. This is due to the fact that the light-source now becomes
apparently larger; that is, being of a given size it now subtends a
larger angle at the reflector and departs more from the theoretical

When the recent war began the search-lights available were intended
generally for fixed installations. These were "barrel" lights with
reflectors several feet in diameter, the whole output sometimes weighing
as much as several tons. Shortly after the entrance of this country
into the war, a mobile "barrel" search-light five feet in diameter was
produced, which, complete with carriage, weighed only 1800 pounds. Later
there were further improvements. An example of the impetus which the
stress of war gives to technical accomplishments is found in the
development of a particular mobile searchlight. Two months after the War
Department submitted the problems of design to certain large industrial
establishments a new 60-inch search-light was placed in production. It
weighed one fifth as much as the previous standard; it had one twentieth
the bulk; it was much simpler; it could be built in one fourth the time;
and it cost half as much. Remote control of the apparatus has been
highly developed in order that the operator may be at a distance from
the scattered light near the unit. If he is near the search-light, this
veil of diffused light very seriously interferes with his vision.

Mobile power-units were necessary and the types developed used the
automobile engine as the prime mover. In one the generator is located in
front of the engine and supported beyond the automobile chassis. In
another type the generator is located between the automobile
transmission and the differential. A standard clutch and gear-shift
lever is employed to connect the engine either with the generator or
with the propeller shaft of the truck. The first type included a
115-volt, 15-kilowatt generator, a 36-inch wheel barrel search-light,
and 500 feet of wire cable. The second type included a 105-volt,
20-kilowatt generator, a 60-inch open searchlight, and 600 feet of
cable. This type has been extended in magnitude to include a 50-kilowatt
generator. When these units are moved, the search-light and its
carriage are loaded upon the rear of the mobile generating equipment. An
idea of the intensities obtainable with the largest apparatus is gained
from illumination produced at a given distance. For example, the
15-kilowatt search-light with highly concentrated beam, produced an
illumination at 930 feet of 280 foot-candles. At this point this is the
equivalent of the illumination produced by a source having a luminous
intensity of nearly 250,000,000 candles.

Of course, the range at which search-lights are effective is the factor
of most importance, but this depends upon a number of conditions such as
the illumination produced by the beam at various distances, the
atmospheric conditions, the position of the observer, the size, pattern,
color, and reflection-factor of the object, and the color, pattern, and
reflection-factor of the background. These are too involved to be
discussed here, but it may be stated that under ordinary conditions
these powerful lights are effective at distances of several miles.
According to recent work, it appears that the range of a search-light in
revealing a given object under fixed conditions varies about as the
fourth root of its intensity.

Although the metallic parabolic reflector is used in the most powerful
search-lights, there have been many other developments adapted to
warfare. Fresnel lenses have been used above the arc for search-lights
whose beams are directed upward in search of aircraft, thus replacing
the mirror below the arc, which, owing to its position, is always in
danger of deterioration by the hot carbon particles dropping upon it.
For short ranges incandescent filament lamps have been used with
success. Oxyacetylene equipment has found application, owing to its
portability. The oxyacetylene flame is concentrated upon a small pellet
of ceria, which provides a brilliant source of small dimensions. A tank
containing about 1000 liters of dissolved acetylene and another
containing about 1100 liters of oxygen supply the fuel. A beam having an
intensity of about 1,500,000 candles is obtained with a consumption of
40 liters of each of the gases per hour. At this rate the search-light
may be operated twenty hours without replenishing.

Although the beacon-light for nocturnal airmen is a development which
will assume much importance in peaceful activities, it was developed
chiefly to meet the requirements of warfare. These do not differ
materially from those which guide the mariner, except that the traveler
in the aërial ocean is far above the plane on which the beacon rests.
For this reason the lenses are designed to send light generally upward.
In foreign countries several types of beacons for aërial navigation have
been in use. In one the light from the source is freely emitted in all
upward directions, but the light normally emitted into the lower
hemisphere is turned upward by means of prisms. In a more elaborate
type, belts of lenses are arranged so as to send light in all directions
above the horizontal plane. A flashing apparatus is used to designate
the locality by the number or character of the flashes. Electric
filaments and acetylene flames have been used as the light-sources for
this purpose. In another type the light is concentrated in one azimuth
and the whole beacon is revolved. Portable beacons employing gas were
used during the war on some of the flying-fields near the battle front.

All kinds of lighting and lighting-devices were used depending upon the
needs and material available. Even self-luminous paint was used for
various purposes at the front, as well as for illuminating watch-dials
and the scales of instruments. Wooden buttons two or three inches in
diameter covered with self-luminous paint could be fixed wherever
desired and thus serve as landmarks. They are visible only at short
distances and the feebleness of their light made them particularly
valuable for various purposes at the battle front. They could be used in
the hand for giving optical signals at a short distance where silence
was essential. Self-luminous arrows and signs directed troops and trucks
at night and even stretcher-bearers have borne self-luminous marks on
their backs in order to identify them to their friends.

Somewhat analogous to this application of luminous paint is the use of
blue light at night on battle-ships and other vessels in action or near
the enemy. Several years ago a Brazilian battle-ship built in this
country was equipped with a dual lighting-system. The extra one used
deep-blue light, which is very effective for eyes adapted to darkness or
to very low intensities of illumination and is a short-range light.
Owing to the low luminous intensity of the blue lights they do not carry
far; and furthermore, it is well established that blue light does not
penetrate as far through ordinary atmosphere as lights of other colors
of the same intensity.

The war has been responsible for great strides in certain directions in
the development and use of artificial light and the era of peace will
inherit these developments and will adapt them to more constructive



From earliest times the beacon-fire has sent forth messages from
hilltops or across inaccessible places. In this country, when the Indian
was monarch of the vast areas of forest and prairie, he spread news
broadcast to roving tribesmen by means of the signal-fire, and he
flashed his code by covering and uncovering it. Castaways, whether in
fiction or in reality, instinctively turn to the beacon-fire as a mode
of attracting a passing ship. On every hand throughout the ages this
simple means of communication has been employed; therefore, it is not
surprising that mankind has applied his ingenuity to the perfection of
signaling by means of light, which has its own peculiar fields and
advantages. Of course, wireless telephony and telegraphy will replace
light-signaling to some extent, but there are many fields in which the
last-named is still supreme. In fact, during the recent war much use was
made of light in this manner and devices were developed despite the many
other available means of signaling. One of the chief advantages of light
as a signal is that it is so easily controlled and directed in a
straight line. Wireless waves, for example, are radiated broadcast to be
intercepted by the enemy.

The beginning of light-signaling is hidden in the obscurity of the past.
Of course, the most primitive light-signals were wood fires, but it is
likely that man early utilized the mirror to reflect the sun's image and
thus laid the foundation of the modern heliograph. The Book of Job,
which is probably one of the oldest writings available, mentions molten
mirrors. The Egyptians in the time of Moses used mirrors of polished
brass. Euclid in the third century before the Christian era is said to
have written a treatise in which he discussed the reflection of light by
concave mirrors. John Peckham, Archbishop of Canterbury in the
thirteenth century, described mirrors of polished steel and of glass
backed with lead. Mirrors of glass coated with an alloy of tin and
mercury were made by the Venetians in the sixteenth century. Huygens in
the seventeenth century studied the laws of refraction and reflection
and devised optical apparatus for various purposes. However, it was not
until the eighteenth century that any noteworthy attempts were made to
control artificial light for practical purposes. Dollond in 1757 was the
first to make achromatic lenses by using combinations of different
glasses. Lavoisier in 1774 made a lens about four feet in diameter by
constructing a cell of two concave glasses and filling it with water and
other liquids. It is said that he ignited wood and melted metals by
concentrating the sun's image upon them by means of this lens. About
that time Buffon made a built-up parabolic mirror by means of several
hundred small plane mirrors set at the proper angles. With this he set
fire to wood at a distance of more than two hundred feet by
concentrating the sun's rays. He is said also to have made a lens from a
solid piece of glass by grinding it in concentric steps similar to the
designs worked out by Fresnel seventy years later. These are examples of
the early work which laid the foundation for the highly perfected
control of light of the present time.

While engaged in the survey of Ireland, Thomas Drummond in 1826 devised
apparatus for signaling many miles, thus facilitating triangulation.
Distances as great as eighty miles were encountered and it appeared
desirable to have some method for seeing a point at these great
distances. Gauss in 1822 used the reflection of the sun's image from a
plane mirror and Drummond also tried this means. The latter was
successful in signaling 45 miles to a station which because of haze
could not be seen, or even the hill upon which it rested. Having
demonstrated the feasibility of the plan, he set about making a device
which would include a powerful artificial light in order to be
independent of the sun. In earlier geodetic surveys Argand lamps had
been employed with parabolic reflectors and with convex lenses, but
apparently these did not have a sufficient range. Fresnel and Arago
constructed a lens consisting of a series of concentric rings which were
cemented together, and on placing this before an Argand lamp possessing
four concentric wicks, they obtained a light which was observed at
forty-eight miles.

Despite these successes, Drummond believed the parabolic mirror and a
more powerful light-source afforded the best combination for a
signal-light. In searching for a brilliant light-source he experimented
with phosphorus burning in oxygen and with various brilliant
pyrotechnical preparations. However, flames were unsteady and generally
unsuitable. He then turned in the direction which led to his development
of the lime-light. In his first apparatus he used a small sphere of lime
in an alcohol flame and directed a jet of oxygen through the flame upon
the lime. He thereby obtained, according to his own description in 1826,

     a light so intense that when placed in the focus of a reflector
     the eye could with difficulty support its splendor, even at a
     distance of forty feet, the contour being lost in the
     brilliancy of the radiation.

He then continued to experiment with various oxides, including zirconia,
magnesia, and lime from chalk and marble. This was the advent of the
lime-light, which should bear Drummond's name because it was one of the
greatest steps in the evolution of artificial light.

By means of this apparatus in the survey, signals were rendered visible
at distances as great as one hundred miles. Drummond proposed the use of
this light-source in the important lighthouses at that time and foresaw
many other applications. The lime-light eventually was extensively used
as a light-signaling device. The heliograph, which utilizes the sun as a
light-source, has been widely used as a light-signaling apparatus and
Drummond perhaps was the first to utilize artificial light with it. The
disadvantage of the heliograph is the undependability of the sun. With
the adoption of artificial light, various optical devices have come into

Philip Colomb perhaps is deserving of the credit of initiating modern
signaling by flashing a code. He began work on such a system in 1858 and
as an officer in the British Navy worked hard to introduce it. Finally,
in 1867, the British Navy adopted the flashing-system, in which a
light-source is exposed and eclipsed in such a manner as to represent
dots and dashes analogous to the Morse code. At first the rate of
transmission of words was from seven to ten per minute. Recently much
more sensitive apparatus is available, and with such devices the rate is
limited only by the sluggishness of the visual process. This initial
system was very successful in the British Navy and it was soon found
that a fleet could be handled with ease and safety in darkness or in
fog. Inasmuch as the "dot-and-dash" system requires only two elements,
it may be transmitted by various means. A lantern may be swung in short
and long arcs or dipped accordingly.

The blinker or pulsating light-signal consists of a single light-source
mechanically occulted. It is controlled by means of a telegraph-key and
the code may be rapidly transmitted. The search-light affords a means
for signaling great distances, even in the daytime. The light is usually
mechanically occulted by a quick-acting shutter, but recently another
system has been devised. In the latter the light itself is controlled by
means of an electrical shunt across the arc. In this manner the light is
dimmed by shunting most of the current, thereby producing the same
effect as actually eclipsing the light with a mechanical shutter. By
means of the search-light signals are usually visible as far as the
limitations of the earth's curvature will permit. By directing the beam
against a cloud, signals have been observed at a distance of one hundred
miles from the search-light despite intervening elevated land or the
curvature of the ocean's surface. By means of small search-lights it is
easy to send signals ten miles.

This kind of apparatus has the advantage of being selective; that is,
the signals are not visible to persons a few degrees from the direction
of the beam. One of the most recent developments has been a special
tungsten filament in a gas-filled bulb placed at the focus of a small
parabolic mirror. The beam is directed by means of sights and the
flashes are obtained by interrupting the current by means of a
trigger-switch. The filament is so sensitive that signals may be sent
faster than the physiological process of vision will record. With the
advent of wireless telegraphy light-signaling for long distances was
temporarily eclipsed, but during the recent war it was revived and much
development work was prosecuted.

The Ardois system consists of four lamps mounted in a vertical line as
high as possible. Each lamp is double, containing a red and a white
light, and these lights are controlled from a keyboard. A red light
indicates a dot in the Morse code and a white light indicates a dash.
The keys are numbered and lettered, so that the system may be operated
by any one. Various other systems employing colored lights have been
used, but they are necessarily short-range signals. Another example is
the semaphore. When used at night, tungsten lamps in reflectors indicate
the positions of the arms. The advantage of these signals over the
flashing-system is that each signal is complete and easy to follow. The
flashing-system is progressive and must be carefully followed in order
to obtain the meaning of the dots and dashes.

Smaller signal-lamps using acetylene have been employed in the forestry
service and in other activities where a portable device is necessary. In
one type, a mixture-tank containing calcium carbide and water is of
sufficient capacity for three hours of signaling. A small pilot-light is
permitted to burn constantly and the flashes are obtained by operating a
key which increases the gas-pressure. The light flares as long as the
key is depressed. The range of this apparatus is from ten to twenty
miles. An electric lamp supplied from a storage battery has been
designed for geodetic operations in mountainous districts where it is
desired to send signals as far as one hundred miles. Tests show that
this device is a hundred and fifty times more powerful than the ordinary
acetylene signal-lamp, and it is thought that with this new electric
lamp haze and smoke will seldom prevent observations.

Certain fixed lights are required by law on a vessel at night. When it
is under way there must be a white light at the masthead, a starboard
green light, a port red light, a white range-light, and a white light at
the stern. The masthead light is designed to emit light through a
horizontal arc of twenty points of the compass, ten on each side of dead
ahead. This light must be visible at a distance of five miles. The port
and starboard lights operate through a horizontal arc of twenty points
of the compass, the middle of which is dead ahead. They are screened so
as not to be visible across the bow and they must be intense enough to
be visible two miles ahead. The masthead light is carried on the
foremast and the range-light on the mainmast, at an elevation fifteen
feet higher than the former. The range-light emits light toward all
points of the compass and must be intense enough to be seen at a
distance of three miles. The stern light is similar to the masthead, but
its light must not be visible forward of the beam. When a vessel is
towing another it must display two or three lights in a vertical line
with the masthead light and similar to it. The lights are spaced about
six feet apart, and two extra ones indicate a short tow and three a long
one. A vessel over a hundred and fifty feet long when at anchor is
required to display a white light forward and aft, each visible around
the entire horizon. These and many other specifications indicate how
artificial light informs the mariner and makes for order in shipping.
Without artificial light the waterways would be trackless and chaos
would reign.

The distress signals of a vessel are rockets, but any burning flame also
serves if rockets are unavailable. Fireworks were known many centuries
ago and doubtless the possibilities of signaling by means of rockets
have long been recognized. An early instance of scientific interest in
rockets and their usefulness is that of Benjamin Robins in 1749. While
he was witnessing a display of fireworks in London it occurred to him
that it would be of interest to measure the height to which the rockets
ascended and to determine the ranges at which they were visible. His
measurements indicated that the rockets ascended usually to a height of
440 yards, but some of them attained altitudes as high as 615 yards. He
then had some special ones made and despatched letters to friends in
three different localities, at distances as great as 50 miles, asking
them to observe at a certain time, when the rockets were to be sent up
in the outskirts of London. Some of these rockets rose to altitudes as
great as 600 yards and were distinctly seen by observers 38 miles away.
Later he made rockets which ascended as high as 1200 yards and concluded
that this was a practical means of signaling. Since that time and
especially during the recent war, rockets have served well in signaling

The self-propelled rockets have not been altered in essential features
since the remote centuries when the Chinese first used them in
celebrations. A cylindrical shell is mounted on a wooden stick and when
the powder in the shell burns the hot gases are ejected so violently
downward that the reaction drives the shell upward. At a certain point
in the air, various signals burst forth, which vary in character and
color. One of the advantages of the rocket is that it contains within
itself the force of propulsion; that is, no gun is necessary to project
it. The illuminating compounds and various details are similar to those
of the illuminating shells described in another chapter.

At present the rocket is not scientifically designed to obtain the
greatest efficiency of propulsion, but its simplicity in this respect is
one of its chief advantages. If the self-propelled rocket becomes the
projectile of the future, as some have ventured to predict, much
consideration must be given to the design of the orifice through which
the gases violently escape in order that the best efficiency of
propulsion may be attained. There are other details in which
improvements may be made. The combustion products of the black powder
which are not gaseous equal about one third the weight of the powder.
This represents inefficient propulsion. Furthermore, during recent years
much information has been gained pertaining to the air-resistance which
can be applied to advantage in designing the form of rockets.

Besides the various rockets, signal-lights have been constructed to be
fired from guns and pistols. During the recent war the airman in the
dark heights used the pistol signal-light effectively for communication.
These devices emitted stars either singly or in succession, and the
color of these stars as well as their number and sequence gave
significance to the signal. Some of these light-signals were provided
with parachutes and were long-burning; that is, light was emitted for a
minute or two. There are many variations possible and a great many
different kinds of light-signals of this character were used. In the
front-line trenches and in advances they were used when telephone
service was unavailable. The airman directed artillery fire by means of
his pistol-light. Rockets brought aid to the foundered ship or to the
life-boats. The signal-tube which burned red, green, or white was held
in the hand or laid on the ground and it often told its story. For many
years such a device dropped from the rear of the railroad train has kept
the following train at a safe distance. A device was tried out in the
trenches, during the war, which emitted a flame. This could be varied in
color to serve as a signal and the apparatus had sufficient capacity for
thirty hours' burning. This could also be used as a weapon, or when
reduced in intensity it served as a flash-light.

For many years experiments have been made upon the use of the invisible
rays which accompany visible rays. The practicability of signaling with
invisible rays depends upon producing them efficiently in sufficient
quantity and upon separating them from the visible rays which accompany
them. Some successful results were obtained with a 6-volt electric lamp
possessing a coiled filament at the focus of a lens three inches in
diameter and twelve inches in focal length. This gave a very narrow beam
visible only in the neighborhood of the observation post to which the
signals were directed. The beam was directed by telescopic sights.
During the day a deep red filter was placed over the lamp and the light
was invisible to an observer unless he was equipped with a similar red
screen to eliminate the daylight. It is said that signals were
distinguished at a distance of six miles. By night a screen was used
which transmitted only the ultraviolet rays, and the observer's
telescope was provided with a fluorescent screen in its focal plane. The
ultraviolet rays falling upon this screen were transformed into visible
rays by the phenomenon of fluorescence. The range of this device was
about six miles. For naval convoys lamps are required to radiate toward
all points of the compass. For this purpose a quartz mercury-arc which
is rich in ultraviolet rays was surrounded with a chimney which
transmitted the ultraviolet rays efficiently and absorbed all visible
rays excepting violet light. The lamp appeared a deep violet color at
close range, but the faintly visible light which it transmitted was not
seen at a distance. A distant observer picks up the invisible
ultraviolet "light" by means of a special optical device having a
fluorescent screen of barium-platino-cyanide. This device had a range of
about four miles.

Light-signals are essential for the operation of railways at night and
they have been in use for many years. In this field the significance of
light-signals is based almost universally on color. The setting of a
switch is indicated by the color of the light that it shows. With the
introduction of the semaphore system, in which during the day the
position of the arm is significant, colored glasses were placed on the
opposite end of the arm in such a manner that a certain colored glass
would appear before the light-source for a certain position of the arm.
A kerosene flame behind a glass lens was the lamp used, and, for
example, red meant "Stop," green counseled "Caution," and clear or white
indicated "All clear." For many years the kerosene lamp has been used,
but recently the electric filament lamp is being installed to some
extent for this purpose. In fact, on one railroad at least, tungsten
lamps are used for light-signals by day as well as by night. Three
signals--red, green, and white--are placed in a vertical line and behind
each lens are two lamps, one operating at high efficiency and one at low
efficiency to insure against the failure of the signal. The normal
daylight range is about three thousand feet and under the worst
conditions when opposed to direct sunlight, the range is not less than
two thousand feet. It is said that these lights are seen more easily
than semaphore arms under all circumstances and that they show two or
three times as far as the latter during a snow-storm.

The standard colors for light-signals as adopted by the Railway Signal
Association are red, yellow, green, blue, purple, and lunar white. These
are specified as to the amount of the various spectral colors which they
transmit when the light-source is the kerosene flame. Obviously, the
colors generally appear different when another illuminant is used. The
blue and purple are short-range signals, but the effective range of the
best railway signal employing a kerosene flame is only about four miles.

It has been shown that the visibility of point sources of white light in
clear atmosphere, for distances up to a mile at least, is proportional
to their candle-power and inversely proportional to the square of the
distance. Apparently the luminous intensities of signal-lamps required
in clear weather in order that they may be visible must be 0.43 candles
for one nautical mile, 1.75 candles for two nautical miles, and 11
candles for five nautical miles. From the data available it appears that
a red or a white signal-light will be easily visible at a distance in
nautical miles equal to the square root of its candle-power in that
direction. The range in nautical miles of a green light apparently is
proportional to the cube root of the candle-power. Whether or not these
relations between the range in miles and the luminous intensity in
candles hold for greater distances than those ordinarily encountered has
not been determined, but it is interesting to note that the square root
of the luminous intensity of the Navesink Light at the entrance to New
York Harbor is about 7000. Could this light be seen at a distance of
seven thousand miles through ordinary atmosphere?

The most distinctive colored lights are red, yellow, green, and blue. To
these white (clear) and purple have been added for signaling-purposes.
Yellow is intense, but it may be confused with "white" or clear. Blue
and purple as obtained from the present practicable light-sources are of
low intensity. This leaves red, green, and clear as the most generally
satisfactory signal-lights.

There are numerous other applications, especially indoors. Some of these
have been devised for special needs, but there are many others which are
general, such as for elevators, telephones, various call systems, and
traffic signals. Light has the advantages of being silent and
controllable as to position and direction, and of being a visible signal
at night. Thus, in another field artificial light has responded to the
demands of civilization.



Artificial light is so superior to natural light in many respects that
mankind has acquired the habit of retiring many hours after darkness has
fallen, a result of which has brought forth the issue known as "daylight
saving." Doubtless, daylight should be used whenever possible, but there
are two sides to the question. In the first place, it costs something to
bring daylight indoors. The architectural construction of windows and
skylights increases the cost of daylight. Light-courts, by sacrificing
valuable floor-area, add to the expense. The maintenance of windows and
sky lights is an appreciable item. Considering these and other factors,
it can be seen that daylight indoors is expensive; and as it is also
undependable, a supplementary system of artificial lighting is generally
necessary. In fact, it is easy to show in some cases that artificial
lighting is cheaper than natural lighting.

The average middle-class home is now lighted artificially for about
$15.00 to $25.00 per year, with convenient light-sources which are
available at all times. There is no item in the household budget which
returns as much satisfaction, comfort, and happiness in proportion to
its cost as artificial light. It is an artistic medium of great
potentiality, and light in a narrow utilitarian sense is always a
by-product of artistic lighting. The insignificant cost of modern
lighting may be emphasized in many ways. The interest on the investment
in a picture or a vase which cost $25.00 will usually cover the cost of
operating any decorative lamp in the home. A great proportion of the
investment in personal property in a home is chargeable to an attempt to
beautify the surroundings. The interest on only a small portion of this
investment will pay for artistic and utilitarian artificial lighting in
the home. The cost of washing the windows of the average house may be as
great as the cost of artificial lighting and is usually at least a large
fraction of the latter. It would become monotonous to cite the various
examples of the insignificant cost of artificial light and its high
return to the user. The example of the home has been chosen because the
reader may easily carry the analysis further. The industries where costs
are analyzed are now looking upon adequate and proper lighting as an
asset which brings in profits by increasing production, by decreasing
spoilage, and by decreasing the liability of accidents.

Inasmuch as daylight saving became an issue during the recent war and is
likely to remain a matter of concern, its history is interesting. One of
the outstanding differences between primitive and civilized beings is
their hours of activities. The former automatically adjusted themselves
to daylight, but as civilization advanced, the span of activities began
to extend more and more beyond the coming of darkness. Finally in many
activities the work-day was extended to twenty-four hours. There can be
no insurmountable objection to working at night with a proper
arrangement of the periods of work; in fact, the cost of living would
be greatly increased if the overhead charges represented by such items
as machinery and buildings were allowed to be carried by the decreased
products of a shortened period of production. There cannot be any basic
objection to artificial lighting, because most factories, for example,
may be better illuminated by artificial than by natural light.

Of course, the lag of comfortable temperature behind daylight is
responsible to some extent for a natural shifting of the ordinary
working-day somewhat behind the sun. The chill of dawn tends to keep
mankind in bed and the cheer of artificial light and the period of
recreation in the evening tends to keep the civilized races out of bed.
There are powerful influences always at work and despite the desirable
features of daylight-saving, mankind will always tend to lag. As years
go by, doubtless it will be necessary to make the shift again and again.
It seems certain that throughout the centuries thoughtful persons have
seen the difficulty of rousing man from his warm bed in the early
morning and have recognized a simple solution in turning the hands of
the clock ahead. Among the earliest advocates of daylight saving during
modern times, when it became important enough to be considered as an
economic issue, was Benjamin Franklin. In 1784 he wrote a masterful
serio-comic essay entitled "An Economical Project" which was published
in the _Journal_ of Paris. The article, which appeared in the form of a
letter, began thus:

     MESSIEURS: You often entertain us with accounts of
     new discoveries. Permit me to communicate to the public through
     your paper one that has lately been made by myself and which I
     conceive may be of great utility.

     I was the other evening in a grand company where the new lamp
     of Messrs. Quinquet and Lange was introduced and much admired
     for its splendor; but a general inquiry was made whether the
     oil it consumed was not in exact proportion to the light it
     afforded, in which case there would be no saving in the use of
     it. No one present could satisfy us on that point, which all
     agreed ought to be known, it being a very desirable thing to
     lessen, if possible, the expense of lighting our apartments,
     when every other article of family expense was so much
     augmented. I was pleased to see this general concern for
     economy, for I love economy exceedingly.

     I went home, and to bed, three or four hours after midnight,
     with my head full of the subject. An accidental sudden noise
     waked me about 6 in the morning, when I was surprised to find
     my room filled with light, and I imagined at first that a
     number of those lamps had been brought into it; but, rubbing my
     eyes, I perceived the light came in at the windows. I got up
     and looked out to see what might be the occasion of it, when I
     saw the sun just rising above the horizon, from whence he
     poured his rays plentifully into my chamber, my domestic having
     negligently omitted the preceding evening to close the

     I looked at my watch, which goes very well, and found that it
     was but 6 o'clock; and, still thinking it something
     extraordinary that the sun should rise so early, I looked into
     the almanac, where I found it to be the hour given for his
     rising on that day. I looked forward, too, and found he was to
     rise still earlier every day till toward the end of June, and
     that at no time in the year he retarded his rising so long as
     till 8 o'clock.

     Your readers who, with me, have never seen any signs of sunshine
     before noon, and seldom regard the astronomical part of the
     almanac, will be as much astonished as I was when they hear of
     his rising so early, and especially when I assure them that he
     gives light as soon as he rises. I am convinced of this. I am
     certain of my fact. One cannot be more certain of any fact. I saw
     it with my own eyes. And, having repeated this observation the
     three following mornings, I found always precisely the same

He then continues in the same vein to show that learned persons did not
believe him and to point out the difficulties which the pioneer
encounters. He brought out the vital point by showing that if he had not
been awakened so early he would have slept six hours longer by the light
of the sun and in exchange he would have lived six hours the following
night by candle-light. He then mustered "the little arithmetic" he was
master of and made some serious computations. He assumed as the basis of
his computations that a hundred thousand families lived in Paris and
each used a half-pound of candles nightly. He showed that between March
20th and September 20th, 64,000,000 pounds of wax and tallow could be
saved, which was equivalent to $18,000,000.

After these serious computations he amusingly proposed the means for
enforcing the daylight saving. Obviously, it was necessary to arouse the
sluggards and his proposals included the use of cannons and bells.
Besides, he proposed that each family be restricted to one pound of
candles per week, that coaches would not be allowed to pass after sunset
except those of physicians, etc., and that a tax be placed upon every
window which had shutters. His closing paragraph was as follows:

     For the great benefit of this discovery, thus freely
     communicated and bestowed by me on the public, I demand neither
     place, pension, exclusive privilege, nor any other regard
     whatever. I expect only to have the honor of it. And yet I know
     there are little, envious minds who will, as usual, deny me
     this and say that my invention was known to the ancients, and
     perhaps they may bring passages out of the old books in proof
     of it. I will not dispute with these people that the ancients
     knew not the sun would rise at certain hours; they possibly
     had, as we have, almanacs that predicted it; but it does not
     follow thence that they knew he gave light as soon as he rose.
     That is what I claim as my discovery. If the ancients knew it,
     it might have been long since forgotten; for it certainly was
     unknown to the moderns, at least to the Parisians, which to
     prove I need use but one plain simple argument. They are as
     well instructed, judicious and prudent a people as exist
     anywhere in the world, all professing, like myself, to be
     lovers of economy, and, for the many heavy taxes required from
     them by the necessities of the State have surely an abundant
     reason to be economical. I say it is impossible that so
     sensible a people, under such circumstances, should have lived
     so long by the smoky, unwholesome and enormously expensive
     light of candles, if they had really known that they might have
     had as much pure light of the sun for nothing.

Franklin's amusing letter had a serious aim, for in 1784 family expenses
were much augmented and adequate lighting by means of candles was very
costly in those days. However, conditions have changed enormously in the
past hundred and thirty-five years. A great proportion of the population
lives in the darker cities. The wheels of progress must be kept going
continuously in order to curb the cost of living, which is constantly
mounting higher owing to the addition of conveniences and luxuries.
Furthermore, the cost of light has so diminished that it is not only a
minor factor at present but in many cases is actually paying dividends
in commerce and industry. It is paying dividends of another kind in the
social and educational aspects of the home, library, church, and art
museum. Daylight saving has much to commend it, but the cost of daylight
and the value of artificial light are important considerations.

The cost of fuels for lighting purposes cannot be thoroughly compared
throughout a span of years without regard to the fluctuating purchasing
power of money, which would be too involved for consideration here.
However, it is interesting to make a brief survey throughout the past
century. From 1800 until 1845 whale-oil sold for about $.80 per gallon,
but after this period it increased in value, owing apparently to its
growing scarcity, until it reached a price of $1.75 per gallon in 1855.
Fortunately, petroleum was discovered about this time, so that the
oil-lamp did not become a luxury. From 1800 to 1850 tallow-candles sold
at approximately 20 cents a pound. There being six candles to the pound,
and inasmuch as each candle burned about seven hours, the light from a
candle cost about 1/2 cent per hour. From 1850 to 1875 tallow-candles
sold at an average price of approximately 25 cents a pound. It may be
interesting to know that a large match emits about as much light as a
burning candle and a so-called safety match about one third as much.

A candle-hour is the total amount of light emitted by a standard candle
in one hour, and candle-hours in any case are obtained by multiplying
the candle-power of the source by the hours of burning. In a similar
manner, lumens output multiplied by hours of operation give the
lumen-hours. A standard candle may be considered to emit an amount of
light approximately equal to 10 lumens. A wax-candle will emit about as
much light as a sperm candle but will consume about 10 per cent. less
weight of material. A tallow candle will emit about the same amount of
light with a consumption about 50 per cent. greater. The tallow-candle
has disappeared from use.

With the appearance of kerosene distilled from petroleum the camphene
lamp came into use. The kerosene cost about 80 cents per gallon during
the first few years of its introduction. The price of kerosene averaged
about 55 cents a gallon between 1865 and 1875. During the next decade it
dropped to about 22 cents a gallon and between 1885 and 1895 it sold as
low as 13 cents.

Artificial gas in 1865 sold approximately at $2.50 per thousand cubic
feet; between 1875 and 1885 at $2.00; between 1885 and 1895 at $1.50.

The combined effect of decreasing cost of fuel or electrical energy for
light-sources and of the great improvements in light-production gave to
the householder, for example, a constantly increasing amount of light
for the same expenditure. For example, the family which a century ago
spent two or three hours in the light of a single candle now enjoys many
times more light in the same room for the same price. It is interesting
to trace the influence of this greatly diminishing cost of light in the
home. For the sake of simplicity the light of a candle will be retained
as the unit and the cost of light for the home will be considered to
remain approximately the same throughout the period to be considered. In
fact, the amount of money that an average householder spends for
lighting has remained fairly constant throughout the past century, but
he has enjoyed a longer period of artificial light and a greater amount
of light as the years advanced. The following is a table of approximate
values which shows the lighting obtainable for $20.00 per year
throughout the past century exclusive of electricity:

              Hours       Equivalent of          Candle-hours
     Year   per night    light in candles    per night     per year
     1800       3               5               15            5,500
     1850       3               8               24            8,700
     1860       3              11               33           12,000
     1870       3              22               66           24,000
     1880       3.5            36              126           46,000
     1890       4              50              200           73,000
     1900       5             154              770          280,000

It is seen from the foregoing that in a century the candle-equivalent
obtainable for the same cost to the householder increased at least
thirty times, while the hours during which this light is used have
nearly doubled. In other words, in the nineteenth century the
candle-hours obtainable for $20.00 per year increased about fifty
times. Stated in another manner, the cost of light at the end of the
century was about one fiftieth that of candle light at the beginning of
the century. One authority in computing the expense of lighting to the
householder in a large city of this country has stated that

     coincident with an increase of 1700 per cent. in the amount of
     night lighting of an American family, in average circumstances,
     using gas for light, there has come a reduction in the cost of
     the year's lighting of 34 per cent. or approximately $7.50 per
     year; and that the cost of lighting per unit of light--the
     candle-hour--is now but 2.8 per cent. of what it was in the
     first half of the nineteenth century. No other necessity of
     household use has been so cheapened and improved during the
     last century.

In general, the light-user has taken advantage of the decrease by
increasing the amount of light used and the period during which it is
used. In this manner the greatly diminished cost of light has been a
marked sociological and economic influence.

After Murdock made his first installation of gas-lighting in an
industrial plant early in the nineteenth century, he published a
comparison of the expense of operation with that of candle-lighting. He
arrived at the costs of light equivalent to 1000 candle-hours as

                                                 1000 candle-hours
     Gas-lighting at a rate of two hours per day     $1.95
          "        " "  "   "  three "    "   "       1.40
     Candle-lighting                                  6.50

It is seen that the longer hours of burning reduce the cost of
gas-lighting by reducing the percentage of overhead charges. There are
no such factors in lighting by candles because the whole "installation"
is consumed. This is an early example of which an authentic record is
available. At the present time a certain amount of light obtained for
$1.00 with efficient tungsten filament lamps, costs $2.00 if obtained
from kerosene flames and about $50.00 if obtained by burning candles.

In order to obtain the cost of an equivalent amount of light throughout
the past century a great many factors must be considered. Obviously, the
results obtained by various persons will differ owing to the unavoidable
factor of judgment; however, the following list of approximate values
will at least indicate the trend of the price of light throughout the
century or more of rapid developments in light-production. A fair
average of the retail values of fuels and of electrical energy and an
average luminous efficiency of the light-sources involved have been used
in making the computations. The figures apply particularly to this


                                               Per 1000
     1800 to 1850, sperm-oil                     $2.40
                   tallow candle                  5.00
     1850 to 1865, kerosene                       1.65
                   tallow candle                  6.85
     1865 to 1875, kerosene                        .75
                   tallow candle                  6.25
                   gas, open-flame                 .90
     1875 to 1885, kerosene                        .25
                   gas, open-flame                 .60
     1885 to 1895, kerosene                        .15
                   gas, open-flame                 .40
     1895 to 1915, gas mantle                      .07
                   carbon filament                 .38
                   metallized filament             .28
                   tungsten filament (vacuum)      .12
                   tungsten filament (gas-filled)  .07

In these days the cost of living has claimed considerable attention and
it is interesting to compare that of lighting. In the following table
the price of food and of electric lighting are compared for twenty years
preceding the recent war. The great disturbance due to the war is
thereby eliminated from consideration, but it should be noted that since
1914 the price of food has greatly increased but that of electric
lighting has not changed materially. The cost of each commodity is taken
as one hundred units for the year 1894 but, of course, the actual cost
of living for the householder is perhaps a hundred times greater than
the cost of electric lighting.

     Year         Food    Electric lighting
     1894         100            100
     1896          80             92
     1898          92             90
     1900         100             85
     1902         113             77
     1904         110             77
     1906         115             57
     1908         128             30
     1910         138             28
     1912         144             23
     1914         145             17

One feature of electric lighting which puzzles the consumer and which
gives the politicians an opportunity for crying "discrimination" and
"injustice" at the public-service company is the great variation in
rates. There is no discrimination or injustice when the householder, for
example, must pay more for his lighting than a factory pays. The rates
are not only affected by "demand" but by the period in which the demand
comes. Residence lighting is chiefly confined to certain hours from 5 to
9 P. M. and there is a great "peak" of demand at this time. The
central-stations must have equipment available for this short-time
demand and much of the capacity of the equipment is unused during the
remainder of the day. The factory which uses electricity throughout the
day or night or both is helping to keep the central-station operating
efficiently. The equipment necessary to supply electricity to the
factory is operating long hours. Not only is this overhead charge much
less for factories and many other consumers than for the householder,
but the expense of accounting, of reading meters, etc., is about the
same for all classes of consumers. Therefore, this is an appreciable
item on the bill of the small consumer.

Doubtless, the public does not realize that the enormous decrease in the
cost of lighting during the past century is due largely to the fact that
the lighting industry has grown large. Increased production is
responsible for some of this decrease and science for much of it. The
latter, having been called to the aid of the manufacturers, who are
better able by virtue of their magnitude to spend time and resources
upon scientific developments, has responded with many improvements which
have increased the efficiency of light-production. Some figures of the
Census Bureau may be of interest. These are given for 1914 in order that
the abnormal conditions due to the recent war may be avoided. The
figures pertaining to the manufacture of gas for sale which do not
include private plants are as follows for the year 1914 for this

     Number of establishments                          1,284
     Capital                                  $1,252,421,584
     Value of products (gas, coke, tar, etc.)   $220,237,790
     Cost of materials                           $76,779,288
     Value added by manufacture                 $143,458,502
     Value of gas                               $175,065,920
     Coal used (tons)                              6,116,672
     Coke used (tons)                                964,851
     Oil used (gallons)                          715,418,623
     Length of gas mains (miles)                      58,727
         Manufactured products sold
     Total gas (cubic feet)                  203,639,260,000
     Straight coal gas (cubic feet)           10,509,946,000
     Carbureted water gas (cubic feet)        90,017,725,000
     Mixed coal- and water-gas (cubic feet)   86,281,339,000
     Oil gas (cubic feet)                     16,512,274,000
     Acetylene (cubic feet)                      136,564,000
     Other gas, chiefly gasolene (cubic feet)    181,412,000
     Coke (bushels)                              114,091,753
     Tar (gallons)                               125,938,607
     Ammonia liquors (gallons)                    50,737,762
     Ammonia, sulphate (pounds)                    6,216,618

Of course, only a small fraction of the total gas manufactured is used
for lighting.

According to the U. S. Geological Survey, the quantities of gas sold in
this country in the year 1917 were as follows:

     Coal-gas        42,927,728,000 cubic feet
     Water-gas      153,457,318,000   "    "
     Oil-gas         14,739,508,000   "    "
     Byproduct gas  131,026,575,000   "    "
     Natural gas    795,110,376,000   "    "

In 1914 there were 38,705,496 barrels (each fifty gallons) of
illuminating oils refined in this country and the value was $96,806,452.
About half of this quantity was exported. In 1914 the value of all
candles manufactured in this country was about $2,000,000, which was
about half that of the candles manufactured in 1909 and in 1904. In 1914
the value of the matches manufactured in this country was $12,556,000.
This has increased steadily from $429,000 in 1849. In 1914 the glass
industries in this country made 7,000,000 lamps, 70,000,000 chimneys,
16,300,000 lantern globes, 24,000,000 shades, globes, and other gas
goods. Many millions of other lighting accessories were made, but
unfortunately they are not classified.

Some figures pertaining to public electric light and power stations of
the United States for the years 1907 and 1917 are as follows:

                                                  1917            1907
     Number of  establishments                     6,541            4,714
       Commercial                                  4,224            3,462
       Municipal                                   2,317            1,562
     Income                                 $526,886,408     $175,642,338
     Total horse-power of plants              12,857,998        4,098,188
       Steam engines                           8,389,389        2,693,273
       Internal combustion engines               217,186           55,828
       Water-wheels                            4,251,423        1,349,087
     Kilowatt capacity of generators           9,001,872        2,709,225
     Output in millions of kilowatt-hours         25,438            5,863
     Motors served (horse-power)               9,216,323        1,649,026
     Electric-arc street-lamps served            256,838           ....
     Electric-filament street-lamps served     1,389,382           ....

In general, there is a large increase in the various items during the
decade represented. The output of the central stations doubled in the
five years from 1907 to 1912, and doubled again in the next five years
from 1912 to 1917. Street lamps were not reported in 1907, but in 1912
there were 348,643 arc-lamps served by the public companies. The number
of arc-lamps decreased to 256,838 in 1917. On the other hand, there were
681,957 electric filament street lamps served in 1912, which doubled in
number to 1,389,382 in 1917. The cost of construction and equipment of
these central stations totaled more than $3,000,000,000 in 1917.

Although there is no immediate prospect of the failure of the coal and
oil supplies, exhaustion is surely approaching. And as the supplies of
fuel for the production of gas and electricity diminish, the cost of
lighting may advance. The total amount of oil available in the known
oil-fields of this country at the present time has been estimated by
various experts between 5,000,000,000 and 20,000,000,000 barrels, the
best estimate being about 7,000,000,000. The annual consumption is now
about 400,000,000 barrels. These figures do not take into account the
oil which may be distilled from the rich shale deposits. Apparently this
source will yield a hundred billion barrels of oil. In a similar manner
the coal-supply is diminishing and the consumption is increasing. In
1918 more than a half-billion tons of coal were shipped from the mines.
The production of natural gas perhaps has reached its peak, and, owing
to its relation to the coal and oil deposits, its supply is limited.

Although only a fraction of the total production of gas, oil, and coal
is used in lighting, the limited supply of these products emphasizes the
desirability of developing the enormous water-power resources of this
country. The present generation will not be hard pressed by the
diminution of the supply of gas, oil, and coal, but it can profit by
encouraging and even demanding the development of water-power.
Furthermore, it is an obligation to succeeding generations to harness
the rivers and even the tides and waves in order that the other
resources will be conserved as long as possible. Science will continue
to produce more efficient light-sources, but the cost of light finally
is dependent upon the cost of the energy supplied to these lamps. At the
present time water-power is the anchor to the windward.



It is established that outdoors life and property are at night safer
under adequate lighting than they are under inadequate lighting. Police
departments in the large cities will testify that street-lighting is a
powerful ally and that crime is fostered by darkness. But in reckoning
the cost of street-lighting to-day how many take into account the value
of safety to life and property and the saving occasioned by the
reduction in the police-force necessary to patrol the cities and towns?
Owing to the necessity of darkening the streets in order to reduce the
hazards of air-raids, London experienced a great increase in accidents
on the streets, which demonstrated the practical value of
street-lighting from the standpoint of accident prevention.

During the war, when dastardly traitors and agents of the enemy were
striking at industry, the value of lighting was further recognized by
the industries, with the result that flood-lighting was installed to
protect them. By common consent this new phase was termed "protective
lighting." Soon after the entrance of this country into the recent war,
the U. S. Military Intelligence established a Section of Plant Protection
which had thirty-three district offices during the war and gave
attention to thirty-five thousand industrial plants engaged in
production of war materials. Protective lighting was early recognized by
this section as a very potential agency for defense, and extensive use
was made of it. For example, Edmund Leigh, chief of the section, in
discussing the value of outdoor lighting stated:

     An illustration of our work in this connection is the case of
     an $80,000,000 powder plant of recent construction. We arranged
     to have all wires buried. In addition to the ordinary lighting
     on an adjacent hill there is a large searchlight which will
     command any part of the buildings and grounds. Every three
     hundred yards there is a watch-tower with a searchlight on top.
     These searchlights are for use only in emergency. Each tower
     has a telephone service, one connected with the other. The men
     in the towers have a view of the building exteriors, which are
     all well lighted, and the men in the buildings look across the
     yard to the lighted fence line and so get a silhouette of
     persons or objects in between. The most vital parts of the
     buildings are surrounded by three fences. In the near-by woods
     the underbrush has been cleared out and destroyed. The trunks
     and limbs of trees have been whitewashed. No one can walk among
     these trees or between the trees and the plant without being
     seen in silhouette.... I say flatly that I know nothing that is
     so potential for good defense as good illumination and at the
     same time so little understood.

Without such protective lighting an army of men would have been required
to insure the safety of this one vital plant; still it is obvious that
the cost of the protective lighting was an insignificant part of the
value of the plant which it insured against damage and destruction.

The United States participated for nineteen months in the recent war and
during that time about 400,000 casualties were suffered by its forces.
This was at the rate of about 250,000 per year, which included
casualties in battle, at sea, and from sickness, wounds, and accidents.
Every one has felt the magnitude of this rate of casualties because
either his home or that of a friend was blighted by one or more of these
tragedies in the nineteen months. However, R. E. Simpson of the Travelers
Insurance Company has stated that:

     During a one-year period in this country the number of
     accidents due to inadequate or improper lighting exceeds the
     yearly rate of our war casualties.

This is a startling comparison, which emphasizes a phase of lighting
that has long been recognized by experts but has been generally ignored
by the industries and by the public. The condition doubtless is due
largely to a lag in the proper utilization of artificial lighting behind
the rapid increase in congestion in the industries and in public places.

Accident prevention is an important phase of modern life which must
receive more attention. From published statistics and conservative
estimates it has been concluded that there are approximately 25,000
persons killed or permanently disabled, 500,000 seriously injured, and
1,000,000 slightly injured each year in this country. Translating these
figures by means of the accident severity rates, Mr. Simpson has found
that there is a total of 180,000,000 days of time lost per year. This is
equivalent to the loss of services of 600,000 men for a full year of 300
work-days. This loss is distributed over the entire country and
consequently its magnitude is not demonstrated excepting by statistics.
Of course, the causes of the accidents are numerous, but, among the
means of prevention, proper lighting is important.

According to some authorities at least 18 per cent. of these accidents
are due to defects in lighting. On this basis the services of 108,000
men as producers and wage-earners are continually lost at the present
time because the lighting is not sufficient or proper for the safety of
workers. If the full year's labor of 108,000 men could be applied to the
mining of coal, 130,000,000 million tons of coal would be added to the
yearly output; and only 10,000 tons would be necessary to supply
adequate lighting for this army of men working for a full year for ten
hours each day.

Statistics obtained under the British workmen's compensation system show
that 25 per cent. of the accidents were caused by inadequate lighting of
industrial plants.

Much has been said and actually done regarding the saving of fuel by
curtailing lighting, but the saving may easily be converted into a great
loss. For example, a 25-watt electric lamp may be operated ten hours a
day for a whole year at the expense of one eighth of a ton of coal.
Suppose this lamp to be over a stairway or at any vital point and that
by extinguishing it there occurs a single accident which involves the
loss of only one day's work on the part of the worker. If this one day's
time could have produced coal, there would have been enough coal mined
in the ten hours to operate the lamp for thirty-two years. The
insignificant cost of lighting is also shown by the distribution of the
consumption of fuel for heating, cooking, and lighting in the home. Of
the total amount of fuel consumed in the home for these purposes, 87 per
cent. is for heating, 11 per cent. for cooking and 2 per cent. for
lighting. The amount of coal used for lighting purposes in general is
about 2.5 per cent. of the total consumption of coal, so it is seen that
the curtailment of lighting at best cannot save much fuel; and it may
actually result in a great economic loss. By replacing inefficient lamps
and accessories with efficient lighting-equipment and by washing windows
and artificial lighting devices, a real saving can be realized.

Improper lighting may be as productive of accidents as inadequate
lighting, and throughout the industries and upon the streets the misuse
of light is in evidence. The blinding effect of a brilliant light-source
is easily proved by looking at the sun. After a few moments great
discomfort is experienced, and on looking away from this brilliant
source the eyes are temporarily blinded by the after-images. When this
happens in a factory as the result of gazing into an unshielded
light-source, the workman may be injured by moving machinery, by
stumbling over objects, and in many other ways. Unshaded light-sources
are too prevalent in the industries. Improper lighting is likely to
cause deep shadows wherein many dangers may be hidden. On the street the
glare from automobile head-lamps is very prevalent and nearly everybody
may testify from experience to the dangers of glare. Even the glaring
locomotive head-lamp has been responsible for many casualties.

Unfortunately, natural lighting outdoors has not been under the control
of man and he has accepted it as it is. The sky is a harmless source of
light when viewed outdoors and the sun is in such a position that it is
usually easy to avoid looking at it. It is so intensely glaring that man
unconsciously avoids looking directly at it. These conditions are
responsible to an extent for man's indifference and even ignorance of
the rudiments of safe lighting. When he has artificial light, over which
he may exercise control, he either ignores it or owing to the less
striking glare he misuses it and his eyesight without realizing it. A
great deal of eye-strain and permanent eye trouble arises from the abuse
of the eyes by improper lighting. For example, near-sightedness is often
due to inadequate illumination, which makes it necessary for the eyes to
be near the work or the reading-page. Improper or inadequate lighting
especially influences eyes that are immature in growth and in function,
and it has been shown that with improvements in lighting the percentage
of short-sightedness has decreased in the schools. Furthermore, it has
been shown that where no particular attention has been given to lighting
and vision, the percentage of short-sightedness has increased with the
grade. There are twenty million school children in this country whose
future eyesight is in the hands of those who have jurisdiction over
lighting and vision. There are more than a hundred million persons in
this country whose eyes are daily subjected to improper
lighting-conditions, either through their own indifference or through
the negligence of others.

Of a certain group of 91,000 purely industrial accidents in the year
1910, Mr. Simpson has stated that 23.8 per cent. were due, directly or
indirectly, to the lack of proper illumination. These may be further
divided into two approximately equal groups, one of which comprises the
accidents due to inadequate illumination and the other to those toward
which improper lighting was a contributing cause. The seasonal variation
of these accidents is given in the following table, both for those due
directly or indirectly to inadequate and improper lighting and those due
to other causes.


                            Percentage due to
                    Lighting conditions  Other causes

     July                      4.8           5.9
     August                    5.2           6.2
     September                 6.1           6.9
     October                   8.6           8.5
     November                 10.9          10.5
     December                 15.6          12.2
     January                  16.1          11.9
     February                 10.0          10.5
     March                     7.6           8.8
     April                     6.1           6.9
     May                       5.2           5.8
     June                      3.8           5.9

The figures in one column have no direct relation to those in the other;
that is, each column must be considered by itself. It is seen from the
foregoing that about half the number of the accidents due to poor
illumination occurred in the months of November, December, January, and
February. These are the months of inadequate illumination unless
artificial lighting has been given special attention. The same general
type of seasonal distribution of accidents due to other causes is seen
to exist but not so prominently. The greatest monthly rate of accidents
during the winter season is nearly four times the minimum monthly rate
during the summer for those accidents due to lighting conditions. This
ratio reduces to about twice in the case of accidents due to other
causes. Looking at the data from another angle, it may be considered
that the likelihood of an accident being caused by lighting conditions
is about twice as great in any of the four "winter" months as in any of
the remaining eight months. Doubtless, this may be explained largely
upon the basis of morale. The winter months are more dreary than those
of summer and the workman's general outlook is different in winter than
in summer. In the former season he goes back and forth to work in the
dark, or at best, in the cold twilight. He is not only more depressed
but he is clumsier in his heavier clothing. If the enervating influence
of these factors is combined with a greater clumsiness due to cold and
perhaps to colds, it is not difficult to account for this type of
seasonal distribution of accidents. A study of the accidents of 1917
indicated that 13 per cent. occurred between 5 and 6 P. M. when
artificial lighting is generally in use to help out the failing
daylight. Only 7.3 per cent. occurred between 12 M. and 1 P. M.







There is another aspect of the subject which deals particularly with the
safety of the light-source or method of lighting. As each innovation
in lighting appeared during the past century there immediately arose the
question of safety. The fire-hazard of open flames received attention in
early days, and when gas-lighting appeared it was condemned as a poison
and an explosive. Mineral-oil lamps introduced the danger of explosions
of the vapors produced by evaporation. When electric lighting appeared
it was investigated thoroughly. The result of all this has been an
effort to make lamps and methods safe. Insurance companies have the
relative safety of these systems established to their satisfaction and
to-day little fire-hazard is attached to the present modes of general
lighting if proper precautions have been taken.

When electric lighting was first introduced the public looked upon
electricity as dangerous and naturally many questions pertaining to
hazards arose. The distribution of electricity has been so highly
perfected that little is heard of the hazards which were so magnified in
the early years. Data gathered between 1884 and 1889 showed that about
13,000 fires took place in a certain district. Of these, 42 were
attributed to electric wires; 22 times as many to breakage and explosion
of kerosene lamps; and ten times as many through carelessness with
matches. These figures cannot be taken at their face value because of
the absence of data showing the relative amount of electric and kerosene
lighting; nevertheless they are interesting because they represent the
early period.

There are industries where unusual care must be exercised in regard to
the lighting. In certain chemical industries no lamps are used excepting
the incandescent lamp and this is enclosed in an air-tight glass globe.
Even a public-service gas company cautions its employees and patrons
thus: "_Do not look for a gas-leak with a naked light! Use electric
light._" The coal-mine offers an interesting example of the precautions
necessary because the same type of problems are found in it as in
industries in general, with the additional difficulties attending the
presence or possible presence of explosive gas. The surroundings in a
coal-mine reflect a small percentage of the light, so that much light is
wasted unless the walls are whitewashed. This is a practical method for
increasing safety in coal-mines. However, the most dangerous feature is
the light-source itself. According to the Bureau of Mines during the
years 1916 and 1917 about 60 per cent. of the fatalities due to gas and
coal-dust explosions were directly traceable to the use of defective
safety lamps and to open flames.

In the early days of coal-mining it was found that the flame of a candle
occasionally caused explosions in the mines. It was also found that
sparks of flint and steel would not readily ignite the gas or coal-dust
and this primitive device was used as a light-source. Of course,
statistics are unavailable concerning the casualties in coal-mines
throughout the past centuries, but with the accidents not uncommon in
this scientific age, with its elaborate organizations striving to stamp
out such casualties, there is good reason to believe that previous to a
century or two ago the risks of coal-mining must have been great. Open
flames have been widely used in this industry, but there has always been
the risk of the presence or the appearance of gas or explosive dust.

The early open-flame lamps not only were sources of danger but their
feeble varying intensity caused serious damage to the eyesight of
miners. This factor is always present in inadequate and improper
lighting, but its influence is noticeable in coal-mining in the nervous
disease affecting the eyes which is known as nystagmus. The symptoms of
the disease are inability to see at night and the dazzling effect of
ordinary lamps. Finally objects appear to the sufferer to dance about
and his vision is generally very much disturbed.

The oil-lamps used in coal-mining have a luminous intensity equivalent
to about one to four candles, but owing to the atmospheric conditions in
the mines a flame does not burn as brightly as in the fresh air. The
possibility of explosion due to the open flame was eliminated by
surrounding it with a metal gauze. Davy was the inventor of this device
and his safety lamp introduced about a hundred years ago has been a boon
to the coal-miner. Various improvements have been devised, but Davy's
lamp contained the essentials of a safety device. The flame is
surrounded by a cylinder of metal gauze which by forming a much cooler
boundary prevents the mine-gas from becoming heated locally by the lamp
flame to a sufficient temperature to ignite and consequently to explode.
This device not only keeps the flame from igniting the gas but it also
serves as an indicator of the amount of gas present, by the variation in
the size and appearance of the tip of the flame. However, the gauze
reduces the luminous output, and as it accumulates soot and dust the
light is greatly diminished. One of these lamps is about as luminous as
a candle, initially, but its intensity is often reduced by accumulations
upon the gauze to only one fifth of the initial value.

The acetylene lamp is the best open-flame light-source available to the
miner, for several reasons. It is of a higher candle-power than the
others and as it is a burning gas, there is not the danger of flying
sparks as in the case of burning wicks. The greater intensity of
illumination affords a greater safety to the miner by enabling him to
detect loose rock which may be ready to fall upon him. However, this
lamp may be a source of danger, owing to the fact that it will burn more
brilliantly in a vitiated atmosphere than other flame-lamps. Another
disadvantage is the possibility of calcium carbide accidentally spilt
coming in contact with water and thereby causing the generation of
acetylene gas. If this is produced in the mine in sufficient quantities
it is a danger which may not be suspected. If ignited it will explode
and may also cause severe burns.

The electric lamp, being an enclosed light-source capable of being
subdivided and fed by a small portable battery, early gave promise of
solving the problem of a safe mine-lamp of adequate candle-power. Much
ingenuity has been applied to the development of a portable electric
safety mine-lamp, and several such lamps are now approved by the Bureau
of Mines. Two general types are being manufactured, the cap outfit and
the hand outfit. They consist essentially of a lamp in a reflector whose
aperture is closed with a sheet or a lens of clear glass. The battery
may be of the "dry" or "storage" type and in the case of the cap outfit
the battery is carried on the back. The specifications for these lamps
demand that a luminous intensity averaging at least 0.4 candle be
maintained throughout twelve consecutive hours of operation. At no time
during this period shall the output of light fall below 1.25 lumens for
a cap-lamp and below 3 lumens for a hand-lamp. Inasmuch as these are
equipped with reflectors, the specifications insist that a circle of
light at least seven feet in diameter shall be cast on a wall twenty
inches away. It appears that a portable lamp is an economic necessity in
the coal-mines, on account of the expense, inconvenience, and possible
dangers introduced by distribution systems such as are used in most

Although the major defects in lighting are due to absence of light in
dangerous places, to glare, and to other factors of improper lighting,
there are many minor details which may contribute to safety. For
example, low lamps are useful in making steps in theaters and in other
places, in drawing attention to entrances of elevators, in lighting the
aisles of Pullman cars, under hand-rails on stairways, and in many other
vital places. A study of accidents indicates that simple expedients are
effective preventives.



A comparison of the civilization of the present with that of a century
ago reveals a startling difference in the standards of living. To-day
mankind enjoys conveniences and luxuries that were undreamed of by the
past generations. For example, a certain town in Iowa, a score of years
ago, was appraised for a bond-issue and it was necessary to extend its
limits considerably in order to include a valuation of one half million
dollars required by the underwriters. On a summer's evening at the
present time a thousand "pleasure" automobiles may be found parked along
its streets and these exceed in valuation that of the entire town only
twenty years ago and equal it to-day. There are economists who would
argue that the automobile has paid for itself by its usefulness, but the
fact still exists that a great amount of labor has been diverted from
producing food, clothing, and fuel to the production of "pleasure"
automobiles. And this is the case with many other conveniences and
luxuries. It is admitted that mankind deserves these refinements of
modern civilization, but he must expect the cost of living to increase
unless counteracting measures are taken.

The economics of the increasing cost of living and the analysis of the
relations of necessities, conveniences, and luxuries are too complex to
be thoroughly discussed here. In fact, the most expert economists would
disagree on many points. However, it is certain that the cost of living
has steadily increased during the past century and it is reasonably
certain that the standards of the present civilization are responsible
for some if not all of the increase. Increased production is an anchor
to the windward. It may drag and give way to some extent, but it will
always oppose the course of the cost of living.

When the first industrial plant was lighted by gas, early in the
nineteenth century, the aim was merely to reinforce daylight toward the
end of the day. Continuous operation of industrial plants was not
practised in those days, excepting in a very few cases where it was
essential. To-day some industries operate continuously, but most of them
do not. In the latter case the consumer pays more for the product
because the percentage of fixed or overhead charge is greater.
Investment in ground, buildings, and equipment exacts its toll
continuously and it is obvious that three successive shifts producing
three times as much as a single day shift, or as much as a trebled day
shift, will produce the less costly product. In the former case the
fixed charge is distributed over the production of continuous operation,
but in the latter case the production of a single day shift assumes the
entire burden. Of course, there are many factors which enter into such a
consideration and an important one is the desirability of working at
night. It is not the intention to touch upon the psychological and
sociological aspects but merely to look coldly upon the facts pertaining
to artificial light and production.

In the first place, it has been proved that in factories proper lighting
as obtained by artificial means is generally more satisfactory than the
natural lighting. Of course, a narrow building with windows on two sides
or a one-story building with a saw-tooth roof of best design may be
adequately illuminated by natural light, but these buildings are the
exception and they will grow rarer as industrial districts become more
congested. Artificial light may be controlled so that light of a
satisfactory quality is properly directed and diffused. Sufficient
intensities of illumination may be obtained and the failure of
artificial light is a remote possibility as compared with the daily
failure of natural light. With increasing cost of ground space,
factories are built of several stories and with less space given to
light courts, with the result that the ratio of window area to that of
the floor is reduced. These tendencies militate against satisfactory
daylighting. In the smoky congested industrial districts the period of
effective daylight is gradually diminishing and artificial lighting is
always essential at least as a reinforcement for daylight. It has been
proved that proper artificial lighting--and there is no excuse for
improper artificial lighting--is superior to most interior daylighting




Although it is difficult to present figures in a brief discussion of
this character, it may be stated that, in general, the cost of adequate
artificial light is about 2 per cent. of the pay-roll of the workers;
about 10 per cent. of the rental charges; and only a fraction of 1 per
cent. of the cost of the manufactured products. These figures vary
considerably, but they represent conservative average estimates. From
these it is seen that artificial lighting is a small factor in adding to
the cost of the product. But does artificial lighting add to the cost of
a product? Many examples could be cited to prove that proper artificial
lighting may be responsible for an actual reduction in the cost of the

In a certain plant it was determined that the workmen each lost an
appreciable part of an hour per day because of inadequate lighting. A
properly designed and maintained lighting-system was installed and the
saving in the wages previously lost, more than covered the
operating-expense of the artificial lighting. Besides really costing the
manufacturer less than nothing, the new artificial lighting system was
responsible for better products, decreased spoilage, minimized
accidents, and generally elevated spirits of the workmen. In some cases
it is only necessary to save one minute per hour per workman to offset
entirely the cost of lighting. The foregoing and many other examples
illustrate the insignificance of the cost of lighting.

The effectiveness of artificial lighting in reducing the cost of living
is easily demonstrated by comparing the output of a factory operating on
one and two shifts per day respectively. In a well-lighted factory which
operated day and night shifts, the cost of adequate lighting was 7 cents
per square foot per year. If this factory, operating only in the
daytime, were to maintain the same output, it would be necessary to
double its size. In order to show the economic value of artificial
lighting it is only necessary to compare the cost of lighting with the
rental charge of the addition and of its equipment. A fair rental value
for plant and equipment is 50 cents per square foot per year; but of
course this varies considerably, depending upon the type of plant and
the character of the equipment. An investigation showed that this value
varies usually between 30 to 70 cents per square foot per year. Using
the mean value, 50 cents, it is seen that the rental charge is about
seven times the cost of lighting. Furthermore, there is a saving of 43
cents per square foot per year during the night operation by operating
the night shift. Of course, this is not strictly true because a
depreciation of machinery during the night shift should be allowed for.
These fixed charges would average slightly more than half as much in the
case of the two-shift factory as in the case of the same output from a
factory twice as large but operating only a day shift. Incidentally, the
two-shift factory need not be a hardship for the workers, for, if the
eight-hour shifts are properly arranged, the worker on the night shift
may be in bed by midnight and the objection to a disturbance of ordinary
hours of sleep is virtually eliminated.

In a discussion of light and safety presented in another chapter the
startling industrial losses due to accidents are shown to be due
partially to inadequate or improper lighting. About one fourth of the
total number of accidents may be charged to defective lighting. The
consumer bears the burden of the support of an unproducing army of idle
men. According to some experts an average of about 150,000 men are
continuously idle in this country owing to inadequate and improper

This is an appreciable factor in the cost of living, but the greatest
effectiveness of artificial lighting in curtailing costs is to be found
in reducing the fixed charges borne by the product through the operation
of two shifts and by directly increasing production owing to improved
lighting. The standard of artificial-lighting intensity possessed by the
average person at the present time is an inheritance from the past. In
those days when artificial light was much more costly than at present
the tendency naturally was to use just as little light as necessary.
That attitude could not have been severely criticized in those early
days of artificial lighting, but it is inexcusable to-day. Eyesight and
greater safety from accidents are in themselves valuable enough to
warrant adequate lighting, but besides these there is the appeal of
increased production.

Outdoors on a clear summer day at noon the intensity of daylight
illumination at the earth's surface is about 10,000 foot-candles; in
other words, it is equal to the illumination on a surface produced by a
light-source equivalent to 10,000 candles at a distance of one foot from
the surface. This will be recognized as an enormous intensity of
illumination. On a cloudy day the intensity of illumination at the
earth's surface may be as high as 3000 foot-candles and on a "gloomy"
day the illumination at the earth's surface may be 1000 foot-candles.
When it is considered that mankind works under artificial light with an
intensity of only a few foot-candles, the marvels of the visual
apparatus are apparent. But it should be noted that the eyes of the
human race evolved under natural light. They have been used to great
intensities when called upon for their greatest efforts. The human being
is wonderfully adaptive, but it could scarcely be hoped that the eyes
could readjust themselves in a few generations to the changed conditions
of low-intensity artificial lighting. There is no complaint against the
range of intensities to which the eye responds, for in range of
sensibility it is superior to any man-made device.

For extremely low brightnesses another set of physiological processes
come into play. Based purely upon the physiological laws of vision it
seems reasonable to conclude that mankind should not work under
artificial illumination as low as has been considered necessary owing to
the cost in the past. With this principle of vision as a foundation,
experiments have been made with greater intensities of illumination in
the industries and elsewhere and increased production has been the
result. In a test in a factory where an adequate record of production
was in effect it was found that an increase in the intensity of
illumination from 4 to 12 foot-candles increased the production in
various operations. The lowest increase in production was 8 per cent.,
the highest was 27 per cent., and the average was 15 per cent. The
original lighting in this case was better than that of the typical
industrial conditions, so that it seems reasonable to expect a greater
increase in production when a change is made from the average inadequate
lighting of a factory to a well-designed lighting-system giving a high
intensity of illumination.

In another test the production under a poor system of lighting by means
of bare lamps on drop-cords was compared with that of an excellent
system in which well-designed reflectors were used. The intensity of
illumination in the latter case was twenty-five times that of the former
and the production was increased in various operations from 30 per cent.
for the least increase to 100 per cent. for the greatest increase.
Inasmuch as the energy consumption in the latter case was increased
seven times and the illumination twenty-five times, it is seen that the
increase in intensity of illumination was due largely to the use of
proper reflectors and to the general layout of the new lighting-system.

In another case a 10 per cent. increase in production was obtained by
increasing the intensity of illumination from 3 foot-candles to about 12
foot-candles. This increase of four times in the intensity of
illumination involved an increase in consumption of electrical energy of
three times the original amount at an increase in cost equal to 1.2 per
cent. of the pay-roll. In another test an increase of 10 per cent. in
production was obtained at an increase in cost equal to less than 1 per
cent. of the payroll. The efficiency of well-designed lighting
installations is illustrated in this case, for the illumination
intensity was increased six times by doubling the consumption of
electrical energy.

Various other tests could be cited, but these would merely emphasize the
same results. However, it may be stated that the factory
superintendents involved are convinced that adequate and proper
artificial lighting is a great factor in increasing production. Mr. W. A.
Durgin, who conducted the tests, has stated that the average result of
increasing the intensity of illumination and of properly designing the
lighting installations in factories will be at least a 15 per cent.
increase in production at an increased cost of not more than 5 per cent.
of the pay-roll. This is apparently a conservative statement. When it is
considered that generally the cost of lighting is only a fraction of 1
per cent. of the cost of products to the consumer, it is seen that the
additional cost of obtaining an increase of 15 per cent. in production
is inappreciable.

Industrial superintendents are just beginning to see the advantage of
adequate artificial lighting, but the low standards of lighting which
were inaugurated when artificial light was much more costly than it is
to-day persist tenaciously. When high intensities of proper illumination
are once tried, they invariably prove successful in the industries. Not
only does the worker see all his operations better, but there appears to
be an enlivening effect upon individuals under the higher intensities of
illumination. Mankind chooses a dimly lighted room in which to rest and
to dream. A room intensely lighted by means of well-designed units which
are not glaring is comfortable but not conducive to quiet contemplation.
It is a place in which to be active. This is perhaps one of the factors
which makes for increased production under adequate lighting.

Civilization has just passed the threshold of the age of adequate
artificial lighting and only a small percentage of the industries have
increased their lighting standards commensurately to the possibilities
of the present time. If high-intensity artificial lighting was installed
in all the industries and a 15 per cent. increase in production
resulted, as tests appear to indicate, the increased production would be
equal to that of nearly two million workers. This great increase in
output is brought about by lighting at an insignificant increase in cost
but without the additional consumption of food or clothing. Besides this
increase in production there is the decrease in spoilage. The saving
possible in this respect through adequate lighting has been estimated
for the industries of this country at $100,000,000. If mankind is to
have conveniences and luxuries, efficiency in production must be
practised to the utmost and in the foregoing a proved means has been

There are many other ways in which artificial light may serve in
increasing production. Man has found that eight hours of sleep is
sufficient to keep him fit for work if he has a sufficient amount of
recreation. Before the advent of artificial light the activities of the
primitive savage were halted by darkness. This may have been Nature's
intention, but civilized man has adapted himself to the changed
conditions brought about by efficient and adequate artificial light.
There appears to be no fundamental reason for not imposing an artificial
day upon plants, animals, chemical processes, etc.; and, in fact,
experiments are being prosecuted in these directions.

The hen, when permitted to follow her natural course, rises with the
sun and goes to roost at sunset. During the winter months she puts in
short days off the roost. It has been shown that an artificial day, made
by piecing out daylight by means of artificial light, might keep the hen
scratching and feeding longer, with an increased production of eggs as a
result. Many experiments of this character have been carried out, and
there appears to be a general conclusion that the use of artificial
light for this purpose is profitable.

Experiments conducted recently by the agricultural department of a large
university indicate that in poultry husbandry, when artificial light is
applied to the right kind of stock with correct methods of feeding, the
distribution of egg-production throughout the whole year can be
radically changed. The supply of eggs may be increased in autumn and
winter and decreased in spring and summer. Data on the amount of
illumination have not been published, but it is said that the most
satisfactory results have been obtained when the artificial illumination
is used from sunset until about 9 P. M. throughout the year.

An increase of 30 to 40 per cent. in the number of eggs laid on a
poultry-farm in England as the result of installing electric lamps in
the hen-houses was reported in 1913. On this farm there were nearly 200
yards of hen-houses containing about 6000 hens, and the runs were
lighted on dark mornings and early nights of the year preceding the
report. About 300 small lamps varying from 8 to 32 candle-power were
used in the houses. It was found that an imitation of sunset was
necessary by switching off the 32 candle-power lamps at 6 P. M.
and the 16 candle-power lamps at 9:30. This left only the 8
candle-power lamps burning, and in the faint illumination the hens
sought the roosting-places. At 10 P. M. the remaining lights
were extinguished. It was found that if all the lights were extinguished
suddenly the fowls went to sleep on the ground and thus became a prey to
parasites. The increase in production of eggs is brought about merely by
keeping the fowls awake longer. On the same farm the growth of chicks
incubated during the winter months increased by one third through the
use of electric light which kept them feeding longer.

Many fishermen will testify that artificial light seems to attract fish,
and various reports have been circulated regarding the efficacy of using
artificial light for this purpose on a commercial scale. One report
which bears the earmarks of authenticity is from Italy, where it is said
that electric lights were successfully used as "bait" to augment the
supply of fish during the war. The lamps were submerged to a
considerable depth and the fish were attracted in such large numbers
that the use of artificial light was profitable. The claims made were
that the supply of fish was not only increased by night fishing but that
a number of fishermen were thereby released for national service during
the war. An interesting incident pertaining to fish, but perhaps not an
important factor in production, is the use of electric lights in the
summer over the reservoirs of a fish hatchery. These lights, which hang
low, attract myriads of bugs, many of which fall in the water and
furnish natural and inexpensive food for the fish.

Many experiments have been carried out in the forcing of plants by
means of artificial light. Some of these were conducted forty years ago,
when artificial light was more costly than at the present time. Of
course, it is well known that light is essential to plant life and in
general it is reasonable to believe that daylight is the most desirable
quality of light for plants. In greenhouses the forcing of plants is
desirable, owing to the restricted area for cultivation. It has been
established that some of the ultra-violet rays which are absorbed or not
transmitted by glass are harmful to growing plants. For this reason an
arc-lamp designed for forcing purposes should be equipped with a glass
globe. F. W. Rane reported in 1894 upon some experiments with electric
carbon-filament lamps in greenhouses in which satisfactory results were
obtained by using the artificial light several hours each night. Prof.
L. H. Bailey also conducted experiments with the arc-lamp and concluded
that there were beneficial results if the light was filtered through
clear glass. Without considering the details of the experiment, we find
some of Rane's conclusions of interest, especially when it is remembered
that the carbon-filament lamps used at that time were of very low
efficiency compared with the filament lamps at the present time. Some of
his conclusions were as follows:

     The incandescent electric light has a marked effect upon
     greenhouse plants.

     The light appears to be beneficial to some plants grown for
     foliage, such as lettuce. The lettuce was earlier, weighed more
     and stood more erect.

     Flowering plants blossomed earlier and continued to bloom
     longer under the light. The light influences some plants, such
     as spinach and endive, to quickly run to seed, which is
     objectionable in forcing these plants for sale.

     The stronger the candle-power the more marked the results,
     other conditions being the same.

     Most plants tended toward a taller growth under the light.

     It is doubtful whether the incandescent light can be used in
     the greenhouse from a practical and economic standpoint on
     other plants than lettuce and perhaps flowering plants; and at
     present prices (1894) it is a question if it will pay to employ
     it even for these.

     There are many points about the incandescent electric light
     that appear to make it preferable to the arc light for
     greenhouse use.

     Although we have not yet thoroughly established the economy and
     practicability of the electric light upon plant growth, still I
     am convinced that there is a future in it.

These are encouraging conclusions, considering the fact that the cost of
light from incandescent lamps at the present time is only a small
fraction of its cost at that time.

In an experiment conducted in England in 1913 mercury glass-tube arcs
were used in one part of a hothouse and the other part was reserved for
a control test. The same kind of seeds were planted in the two parts of
the hothouse and all conditions were maintained the same, excepting that
a mercury-vapor lamp was operated a few hours in the evening in one of
them. Miss Dudgeon, who conducted the test, was enthusiastic over the
results obtained. Ordinary vegetable seeds and grains germinated in
eight to thirteen days in the hothouse in which the artificial light was
used to lengthen the day. In the other, germination took place in from
twelve to fifty-seven days. In all cases at least several days were
saved in germination and in some cases several weeks. Flowers also
increased in foliage, and a 25 per cent. increase in the crop of
strawberries was noted. Seedlings produced under the forcing by
artificial light needed virtually no hardening before being planted in
the open. Professor Priestley of Bristol University said of this work:

     The light seems to have been extraordinarily efficacious,
     producing accelerated germination, increased growth, greater
     depth of color, and more important still, no signs of lanky,
     unnatural extension of plant usually associated with forcing.
     Rather the plants exposed to the radiation seem to have grown
     if anything more sturdy than the control plants. A structural
     examination of the experimental and control plants carried out
     by means of the microscope fully confirmed Miss Dudgeon's
     statements both as to depth of color and greater sturdiness of
     the treated plants.

Unfortunately there is much confusion amid the results of experiments
pertaining to the effects of different rays, including ultra-violet,
visible and infra-red, upon plant growth. If this aspect was thoroughly
established, investigations could be outlined to greater advantage and
efficient light-sources could be chosen with certainty. There is the
discouraging feature that the average intensity of daylight illumination
from sunrise to sunset in the summer-time is several thousand
foot-candles. The cost of obtaining this great intensity by means of
artificial light would be prohibitive. However, the daylight
illumination in a greenhouse in winter is very much less than the
intensity outdoors in summer. Indeed, this intensity perhaps averages
only a few hundred foot-candles in winter. There is encouragement in
this fact and there is hope that a little light is relatively much more
effective than a great amount. Expressed in another manner, it is
possible that a little light is much more effective than no light at
all. Experiments with artificial light indicate very generally an
increased growth.

Recently Hayden and Steinmetz experimented with a plot of ground 5 feet
by 9 feet, over which were hung five 500-watt gas-filled tungsten lamps
3 feet above the ground and 17 inches apart. The lamps were equipped
with reflectors and the resulting illumination was 700 foot-candles.
This is an extremely high intensity of artificial illumination and is
comparable with daylight in greenhouses. The only seeds planted were
those of string beans and two beds were carried through to maturity, one
lighted by daylight only and the other by daylight and artificial light,
the latter being in operation twenty-fours hours per day. The plants
under the additional artificial light grew more rapidly than the others,
and of the various records kept the gain in time was in all cases about
50 per cent. From the standpoint of profitableness the artificial
lighting was not justified. However, there are several points to be
brought out before considering this conclusion too seriously. First, it
appears unwise to use the artificial light during the day; second, it
appears possible that a few hours of artificial light in the evening
would suffice for considerable forcing; third, it is possible that a
much lower intensity of artificial light might be more effective per
lumen than the great intensity used; fourth, it is quite possible that
some other efficient light-source may be more effective in forcing the
growth of plants. These and many other factors must be carefully
determined before judgment can be passed on the efficacy of artificial
light in reducing the cost of living in this direction. Certainly,
artificial light has been shown to increase the growth of plants and it
appears probable that future generations at least will find it
profitable to use the efficient light-producers of the coming ages in
this manner.

Many other instances could be cited in which artificial light is very
closely associated with the cost of living. Overseas shipment of fruit
from the Canadian Northwest is responsible for a decided innovation in
fruit-picking. In searching for a cause of rotting during shipment it
was finally concluded that the temperature at the time of picking was
the controlling factor. As a consequence, daytime was considered
undesirable for picking and an electric company supplied electric
lighting for the orchards in order that the picking might be done during
the cool of night. This change is said to have remedied the situation.
Cases of threshing and other agricultural operations being carried on at
night are becoming more numerous. These are just the beginnings of
artificial light in a new field or in a new relation to civilization.
Its economic value has been demonstrated in the ordinary fields of
lighting and these new applications are merely the initial skirmishes
which precede the conquest of new territory. The modern illuminants have
been developed so recently that the new possibilities have not yet been
established. However, artificial light is already a factor on the side
of the people in the struggle against the increasing cost of living, and
its future in this direction is still more promising.



Some one in an early century was the first to notice that the sun's rays
tanned the skin, and this unknown individual made the initial discovery
in what is now an extensive branch of science known as photo-chemistry.
The fading of dyes, the bleaching of textiles, the darkening of silver
salts, the synthesis and decomposition of compounds are common examples
of chemical reactions induced by light. There are thousands of other
examples of the chemical effects of light some of which have been
utilized by mankind. Others await the development of more efficient
light-sources emitting greater quantities of active rays, and many still
remain interesting scientific facts without any apparent practical
applications at the present time. Visible and ultra-violet rays are the
radiations almost entirely responsible for photochemical reactions, but
the most active of these are the blue, violet, and ultra-violet rays.
These are often designated chemical or actinic rays in order to
distinguish the group as a whole from other groups such as ultra-violet,
visible, and infra-red. Light is a unique agent in chemical reactions
because it is not a material substance. It neither contaminates nor
leaves a residue. Although much information pertaining to photochemistry
has been available for years, the absence of powerful light-sources
emitting so-called chemical rays in large quantities inhibited the
practical development of the science of photochemistry. Even to-day,
with vast applications of light in this manner, mankind is only
beginning to utilize its chemical powers.

[Illustration: In a moving-picture studio

In a portrait studio


[Illustration: Swimming pool

City waterworks


Although it appears that the chemical action of light was known to the
ancients, the earliest photochemical investigations which could be
considered scientific and systematic were those of K. W. Scheele in 1777
on silver salts. An extract from his own account is as follows:

     I precipitated a solution of silver by sal-ammoniac; then I
     edulcorated (washed) it and dried the precipitate and exposed
     it to the beams of the sun for two weeks; after which I stirred
     the powder and repeated the same several times. Hereupon I
     poured some caustic spirit of sal-ammoniac (strong ammonia) on
     this, in all appearance, black powder, and set it by for
     digestion. This menstruum (solvent) dissolved a quantity of
     luna cornua (horn silver), though some black powder remained
     undissolved. The powder having been washed was, for the greater
     part, dissolved by a pure acid of nitre (nitric acid), which,
     by the operation, acquired volatility. This solution I
     precipitated again by means of sal-ammoniac into horn silver.
     Hence it follows that the blackness which the luna cornua
     acquires from the sun's light, and likewise the solution of
     silver poured on chalk, is _silver by reduction_. I mixed so
     much of distilled water with the well-washed horn silver as
     would just cover this powder. The half of this mixture I poured
     into a white crystal phial, exposed it to the beams of the sun,
     and shook it several times each day; the other half I set in a
     dark place. After having exposed the one mixture during the
     space of two weeks, I filtrated the water standing over the
     horn silver, grown already black; I let some of this water fall
     by drops in a solution of silver, which was immediately
     precipitated into horn silver.

This extract shows that Scheele dealt with the reducing action of light.
He found that silver chloride was decomposed by light and that there was
a liberation of chlorine. However, it was learned later that dried
silver chloride sealed in a tube from which the air was exhausted is not
discolored by light and that substances must be present to absorb the
chlorine. Scheele's work aroused much interest in photochemical effects
and many investigations followed. In many of these the superiority of
blue, violet, and ultra-violet rays was demonstrated. In 1802 the first
photograph was made by Wedgwood, who copied paintings upon glass and
made profiles by casting shadows upon a sensitive chemical compound.
However, he was not able to fix the image. Much study and
experimentation were expended upon photochemical effects, especially
with silver compounds, before Niepce developed a method of producing
pictures which were subsequently unaffected by light. Later Daguerre
became associated with Niepce and the famous daguerreotype was the
result. Apparently the latter was chiefly responsible for the
development of this first commercial process, the products of which are
still to be found in the family album. A century has elapsed since this
earliest period of commercial photography, and during each year progress
has been made, until at the present time photography is thoroughly woven
into the activities of civilized mankind.

In those earliest years a person was obliged to sit motionless in the
sun for minutes in order to have his picture taken. The development of a
century is exemplified in the "snapshot" of the present time.
Photographic exposures outdoors at present are commonly one thousandth
of a second, and indoors under modern artificial light miles of
"moving-picture" film are made daily in which the individual exposures
are very small fractions of a second. Artificial light is playing a
great part in this branch of photochemistry, and the development of
artificial light for the various photographic needs is best emphasized
by reminding the reader that the sources must be generally comparable
with the sun in actinic or chemical power. The intensity of illumination
due to sunlight on a clear day when the sun is near the zenith is
commonly 10,000 foot-candles on a surface perpendicular to the direct
rays. This is equivalent to the illumination due to a source 90,000
candle-power at a distance of three feet. The sun delivers about
200,000,000,000 horse-power to the earth continuously, which is
estimated to be about one million times the amount of power generated
artificially on the earth. Of this inconceivable quantity of energy a
small part is absorbed by vegetation, some is reflected and radiated
back into space, and the balance heats the earth. To store some of this
energy so that it may be utilized at will in any desired form is one of
the dreams of science. However, artificial light-sources are depended
upon at present in many photographic and other chemical processes.

Although two illuminants may be of the same luminous intensity, they may
differ widely in actinic value. It is impossible to rate the different
illuminants in a general manner as to actinic value because the various
photochemical reactions are not affected to the same extent by rays of a
given wave-length. Nearly all human eyes see visible rays in
approximately the same manner, but the multitude of chemical reactions
show a wide variation in sensitivity to the various rays. For example,
one photographic emulsion may be sensitive only to ultra-violet, violet,
and blue rays and another to all these rays and also to the green,
yellow, and red. Therefore, one illuminant may be superior to another
for one photochemical reaction, while the reverse may be true in the
case of another reaction. In general, it may be said that the arc-lamps
including the mercury-arcs provide the most active illuminants for
photochemical processes; however, a large number of electric
incandescent filament lamps are used in photographic work.

The photo-engraver has been independent of sunlight since the practical
development of his art. In fact, the printer could not depend upon
sunlight for making the engravings which are used to illustrate the
magazines and newspapers. The newspaper photographer may make a
"flashlight" exposure, develop his negative, and make a print from it
under artificial light. He may turn this over to the photo-engraver who
carries out his work by means of powerful arc-lamps and in an hour or
two after the original exposure was made the newspaper containing the
illustration is being sold on the streets.

The moving-picture studio is independent of daylight in indoor settings
and there is a tendency toward the exclusive use of artificial light.
In this field mercury-vapor lamps, arc-lamps, and tungsten photographic
lamps are used. Similarly, in the portrait studio there is a tendency
for the photographer to leave the skylighted upper floors and to utilize
artificial light. In this field the tungsten photographic lamp is
gaining in popularity, owing to its simplicity and to other advantages.
Artificial light in general is more satisfactory than natural light for
many kinds of photographic work because through the ease of controlling
it a greater variety of more artistic effects may be obtained. In
ordinary photographic printing tungsten lamps are widely used, but in
blue-printing the white flame-arc and the mercury-vapor lamp are
generally employed. Not many years ago the blue-printer waited for the
sun to appear in order to make his prints, but to-day large machines
operate continuously under the light of powerful artificial sources. How
many realize that the blue-print is almost universally at the foundation
of everything at the present time? Not only are products made from
blue-prints but the machinery which makes the products is built from
blue-prints. Even the building which houses the machinery is first
constructed from blue-prints. They form an endless chain in the
activities of present civilization.

Artificial light has been a great factor in the practical development of
photography and it is looked upon for aid in many other directions.
Although there is a multitude of reactions in photographic processes
which are brought about by exposure to light, these represent relatively
few of the photochemical reactions. In general, it may be stated that
light is capable of causing nearly every type of reaction. The chemical
compounds which are photo-sensitive are very numerous. Many of the
compounds of silver, gold, platinum, mercury, iron, copper, manganese,
lead, nickel, and tin are photo-sensitive and these have been widely
investigated. Light and oxygen cause many oxidation reactions and, on
the other hand, light reduces many compounds such as silver salts, even
to the extent of liberating the metal. Oxygen is converted partially
into ozone under the influence of certain rays and there are many
examples of polymerization caused by light.

Various allotropic changes of the elements are due to the influence of
light; for example, a sulphur soluble in carbon disulphide is converted
into sulphur which is insoluble, and the rate of change of yellow
phosphorus into the red variety is greatly accelerated by light.
Hydrogen and chlorine combine under the action of light with explosive
rapidity to form hydrochloric acid and there are many other examples of
the synthesizing action of light. Carbon monoxide and chlorine combine
to form phosgene and the combination of chlorine, bromine, and iodine,
with organic compounds, is much hastened by exposing the mixture to
light. In a similar manner many decompositions are due to light; for
example, hydrogen peroxide is decomposed into water and oxygen. This
suggests the reason for the use of brown bottles as containers for many
chemical compounds. Such glass does not transmit appreciably the
so-called actinic or chemical rays.

There is a large number of reactions due to light in organic chemistry
and one of fundamental importance to mankind is the effect of light on
the chlorophyll, the green coloring matter in vegetation. No permanent
change takes place in the chlorophyll, but by the action of light it
enables the plant to absorb oxygen, carbon dioxide, and water and to use
these to build up the complex organic substances which are found in
plants. Radiant energy or light is absorbed and converted into chemical
energy. This use of radiant energy occurs only in those parts of the
plant in which chlorophyll is present, that is, in the leaves and stems.
These parts absorb the radiant energy and take carbon dioxide from the
air through breathing openings. They convert the radiant energy into
chemical energy and use this energy in decomposing the carbon dioxide.
The oxygen is exhausted and the carbon enters into the structure of the
plant. The energy of plant life thus comes from radiant energy and with
this aid the simple compounds, such as the carbon dioxide of the air and
the phosphates and nitrates of the soil, are built into complex
structures. Thus plants are constructive and synthetic in operation. It
is interesting to note that the animal organism converts complex
compounds into mechanical and heat energy. The animal organism depends
upon the synthetic work of plants, consuming as food the complex
structures built by them under the action of light. For example, plants
inhale carbon dioxide, liberate the oxygen, and store the carbon in
complex compounds, while the animal uses oxygen to burn up the complex
compounds derived from plants and exhales carbon dioxide. It is a
beautiful cycle, which shows that ultimately all life on earth depends
upon light and other radiant energy associated with it. Contrary to most
photochemical reactions, it appears that plant life utilize yellow, red,
and infra-red energy more than the blue, violet, and ultra-violet.

In general, great intensities of blue light and of the closely
associated rays are necessary for most photochemical reactions with
which man is industrially interested. It has been found that the white
flame-arc excels other artificial light-sources in hastening the
chlorination of natural gas in the production of chloroform. One
advantage of the radiation from this light-source is that it does not
extend far into the ultra-violet, for the ultra-violet rays of short
wave-lengths decompose some compounds. In other words, it is necessary
to choose radiation which is effective but which does not have rays
associated with it that destroy the desired products of the reaction. By
the use of a shunt across the arc the light can be gradually varied over
a considerable range of intensity. Another advantage of the flame-arc in
photochemistry is the ease with which the quality or spectral character
of the radiant energy may be altered by varying the chemical salts used
in the carbons. For example, strontium fluoride is used in the red
flame-arc whose radiant energy is rich in red and yellow. Calcium
fluoride is used in the carbons of the yellow flame-arc which emits
excessive red and green rays causing by visual synthesis the yellow
color. The radiant energy emitted by the snow-white flame-arc is a close
approximation to average daylight both as to visible and to ultra-violet
rays. Its carbons contain rare-earths. The uses of the flame-arcs are
continually being extended because they are of high intensity and
efficiency and they afford a variety of color or spectral quality. A
million white flame-carbons are being used annually in this country for
various photochemical processes.

Of the hundreds of dyes and pigments available many are not permanent
and until recent years sunlight was depended upon for testing the
permanency of coloring materials. As a consequence such tests could not
be carried out very systematically until a powerful artificial source of
light resembling daylight was available. It appears that the white
flame-arc is quite satisfactory in this field, for tests indicate that
the chemical effect of this arc in causing dye-fading is four or five
times as great as that of the best June sunlight if the materials are
placed within ten inches of a 28-ampere arc. It has been computed that
in several days of continuous operation of this arc the same fading
results can be obtained as in a year's exposure to daylight in the
northern part of this country. Inasmuch as the fastness of colors in
daylight is usually of interest, the artificial illuminant used for
color-fading should be spectrally similar to daylight. Apparently the
white flame-arc fulfils this requirement as well as being a powerful

Lithopone, a white pigment consisting of zinc sulphide and barium
sulphate, sometimes exhibits the peculiar property of darkening on
exposure to sunlight. This property is due to an impurity and apparently
cannot be predicted by chemical analysis. During the cloudy days and
winter months when powerful sunlight is unavailable, the manufacturer is
in doubt as to the quality of his product and he needs an artificial
light-source for testing it. In such a case the white flame-arc is
serving satisfactorily, but it is not difficult to obtain effects with
other light-sources in a short time if an image of the light-source is
focused upon the material by means of a lens. In fact, a darkening of
lithopone may be obtained in a minute by focusing upon it the image of a
quartz mercury-arc by means of a quartz lens. In special cases of this
sort the use of a focused image is far superior to the ordinary
illumination from the light-source, but, of course, this is
impracticable when testing a large number of samples simultaneously.
Incidentally, lithopone which turns gray or nearly black in the sunlight
regains its whiteness during the night.

An amusing incident is told of a young man who painted his boat one
night with a white paint in which lithopone was the pigment. On
returning home the next afternoon after the boat had been exposed to
sunlight all day, he was astonished to see that it was black. Being very
much perturbed, he telephoned to the paint store, but the proprietor
escaped a scathing lecture by having closed his shop at the usual hour.
The young man telephoned in the morning and told the proprietor what had
happened, but on being asked to make certain of the facts he went to the
window and looked at his boat and behold! it was white. It had regained
whiteness during the night but would turn black again during the day.
Although pigments and dyes are not generally as peculiar as lithopone,
much uncertainty is eliminated by systematic tests under constant,
continuous, and controllable artificial light.

The sources of so-called chemical rays are numerous for laboratory work,
but there is a need for highly efficient powerful producers of this kind
of energy. In general the flame-arcs perhaps are foremost sources at the
present time, with other kinds of carbon arcs and the quartz mercury-arc
ranking next. One advantage of the mercury-arc is its constancy.
Furthermore, for work with a single wave-length it is easy to isolate
one of the spectral lines. The regular glass-tube mercury-arc is an
efficient producer of the actinic rays and as a consequence has been
extensively used in photographic work and in other photochemical
processes. An excellent source for experimental work can be made easily
by producing an arc between two small iron rods. The electric spark has
served in much experimental work, but the total radiant energy from it
is small. By varying the metals used for electrodes a considerable
variety in the radiant energy is possible. This is also true of the
electric arcs, and the flame-arcs may be varied widely by using
different chemical compounds in the carbons.

There are other effects of light which have found applications but not
in chemical reactions. For example, selenium changes its electrical
resistance under the influence of light and many applications of this
phenomenon have been made. Another group of light-effects forms a branch
of science known as photo-electricity. If a spark-gap is illuminated by
ultra-violet rays, the resistance of the gap is diminished. If an
insulated zinc plate is illuminated by ultra-violet or violet rays, it
will gradually become positively charged. These effects are due to the
emission of electrons from the metal. Violet and ultra-violet rays will
cause a colorless glass containing manganese to assume a pinkish color.
The latter is the color which manganese imparts to glass and under the
influence of these rays the color is augmented. Certain ultra-violet
rays also ionize the air and cause the formation of ozone. This can be
detected near a quartz mercury-arc, for example, by the characteristic

The foregoing are only a few of the multitude of photochemical reactions
and other effects of radiant energy. The development of this field
awaits to some extent the production of so-called actinic rays more
efficiently and in greater quantities, but there are now many practical
applications of artificial light for these purposes. In the extensive
fields of photography various artificial light-sources have served for
many years and they are constantly finding more applications. Artificial
light is now used to a considerable extent in the industries in
connection with chemical processes, but little information is available,
owing to the secrecy attending these new developments in industrial
processes. However, this brief chapter has been introduced in order to
indicate another field of activity in which artificial light is serving.
It is agreed by scientists that photochemistry has a promising future.
Mankind harnesses nature's forces and produces light and this light is
put to work to exert its influence for the further benefit of mankind.
Science has been at work systematically for only a century, but the
accomplishments have been so wonderful that the imagination dares not
attempt to prophesy the achievements of the next century.



The human being evolved without clothing and the body was bathed with
light throughout the day, but civilization has gone to the other extreme
of covering the body with clothing which keeps most of it in darkness.
Inasmuch as light and the invisible radiant energy which is associated
with it are known to be very influential agencies in a multitude of
ways, the question arises: Has this shielding of the body had any marked
influence upon the human organism? Although there is a vast literature
upon the subject of light-therapy, the question remains unanswered,
owing to the conflicting results and the absence of standardization of
experimental details. In fact, most investigations are subject to the
criticism that the data are inadequate. Throughout many centuries light
has been credited with various influences upon physiological processes
and upon the mind. But most of the early applications had no foundation
of scientific facts. Unfortunately, many of the claims pertaining to the
physiological and psychological effects of light at the present time are
conflicting and they do not rest upon an established scientific
foundation. Furthermore some of them are at variance with the
possibilities and an unprejudiced observer must conclude that much
systematic work must be done before order may arise from the present
chaos. This does not mean that many of the effects are not real, for
radiant energy is known to cause certain effects, and viewing the
subject broadly it appears that light is already serving humanity in
this field and that its future is promising.

The present lack of definite data pertaining to the effects of radiation
is due to the failure of most investigators to determine accurately the
quantities and wave-lengths of the rays involved. For example, it is
easy to err by attributing an effect to visible rays when the effect may
be caused by accompanying invisible rays. Furthermore, it may be
possible that certain rays counteract or aid the effective rays without
being effective alone. In other words, the physical measurements have
been neglected notwithstanding the fact that they are generally more
easily made than the determinations of curative effects or of germicidal
action. Radiant energy of all kinds and wave-lengths has played a part
in therapeutics, so it is of interest to indicate them according to
wave-length or frequency. These groups vary in range of wave-length, but
the actual intervals are not particularly of interest here. Beginning
with radiant energy of highest frequencies of vibration and shortest
wave-lengths, the following groups and subgroups are given in their
order of increasing wave-length:

     Röntgen or X-rays, which pass readily through many substances
     opaque to ordinary light-rays.

     Ultra-violet rays, which are divided empirically into three
     groups, designated as "extreme," "middle," and "near" in
     accordance with their location in respect to the visible

     Visible rays producing various sensations of color, such as
     violet, blue, green, yellow, orange, and red.

     Infra-red or the invisible rays bordering on the red rays.

     An unknown, unmeasured, or unfilled region between the
     infra-red and the "electric" waves.

     Electric waves, which include a class of electromagnetic
     radiant energy of long wave-length. Of these the Herzian waves
     are of the shortest wave-length and these are followed by
     "wireless" waves. Electric waves of still greater wave-length
     are due to the slower oscillations in certain electric circuits
     caused by lightning discharges, etc.

The Röntgen rays were discovered by Röntgen in 1896 and they have been
studied and applied very widely ever since. Their great use has been in
X-ray photography, but they are also being used in therapeutics. The
extreme ultra-violet rays are not available in sunlight and are
available only near a source rich in ultra-violet rays, such as the
arc-lamps. They are absorbed by air, so that they are studied in a
vacuum. These are the rays which convert oxygen into ozone because the
former strongly absorbs them. The middle ultra-violet rays are not found
in sunlight, because they are absorbed by the atmosphere. They are also
absorbed by ordinary glass but are freely transmitted by quartz. The
nearer ultra-violet rays are found in sunlight and in most artificial
illuminants and are transmitted by ordinary glass. Next to this region
is the visible spectrum with the various colors, from violet to red,
induced by radiant energy of increasing wave-length. The infra-red rays
are sometimes called heat-rays, but all radiant energy may be converted
into heat. Various substances transmit and absorb these rays in general
quite differently from the visible rays. Water is opaque to most of the
infra-red rays. Next there is a region of wave-lengths or frequencies
for which no radiant energy has been found. The so-called electric waves
vary in wave-length over a great range and they include those employed
in wireless telegraphy. All these radiations are of the same general
character, consisting of electromagnetic energy, but differing in
wave-length or frequency of vibration and also in their effects. In
effect they may overlap in many cases and the whole is a chaos if the
physical details of quantity and wave-length are not specified in
experimental work.

[Illustration: In art work

In a haberdashery


[Illustration: In an underground tunnel

In an art gallery


It has been conclusively shown that radiant energy kills bacteria. The
early experiments were made with sunlight and the destruction of
micro-organisms is generally attributed to the so-called chemical rays,
namely, the blue, violet, and ultra-violet rays. It appears in general
that the middle ultra-violet rays are the most powerful destroyers. It
is certainly established that sunlight sterilizes water, for example,
and the quartz mercury-lamp is in daily use for this purpose on a
practicable scale. However, there still appears to be a difference of
opinion as to the destructive effect of radiant energy upon bacteria in
living tissue. It has been shown that the middle ultra-violet rays
destroy animal tissue and, for example, cause eye-cataracts. It appears
possible from some experiments that ultra-violet rays destroy bacteria
in water and on culture plates more effectively in the absence of
visible rays than when these attend the ultra-violet rays as in the case
of sunlight. This is one of the reasons for the use of blue glass in
light-therapy, which isolates the blue, violet, and near ultra-violet
rays from the other visible rays. If the infra-red rays are not
desired they can be readily eliminated by the use of a water-cell.

There is a vast amount of testimony which proves the bactericidal action
of light. Bacteria on the surface of the body are destroyed by
ultra-violet rays. Typhus and tubercle bacilli are destroyed equally
well by the direct rays from the sun and from the electric arcs.
Cultures of diphtheria develop in diffused daylight but are destroyed by
direct sunlight. Lower organisms in water are readily killed by the
radiation from any light-source emitting ultra-violet rays comparable
with those in direct sunlight. From the great amount of data available
it appears reasonable to conclude that radiant energy is a powerful
bactericidal agency but that the action is due chiefly to ultra-violet
rays. It appears also that no bacteria can resist these rays if they are
intense enough and are permitted to play upon the bacteria long enough.
The destruction of these organisms appears to be a phenomenon of
oxidation, for the presence of oxygen appears to be necessary.

The foregoing remarks about the bactericidal action of radiant energy
apply only to bacteria in water, in cultures, and on the surface of the
body. There is much uncertainty as to the ability of radiant energy to
destroy bacteria within living tissue. The active rays cannot penetrate
appreciably into such tissue and many authorities are convinced that no
direct destruction takes place. In fact, it has been stated that the
so-called chemical rays are more destructive to the tissue cells than to
bacteria. Finsen, a pioneer in the use of radiant energy in the
treatment of disease, effected many wonderful cures and believed that
the bacteria were directly destroyed by the ultra-violet rays. However,
many have since come to the conclusion that the beneficent action of the
rays is due to the irritation which causes an outflow of serum, thus
bringing more antibodies in contact with the bacilli, and causing the
destruction of the latter. Hot applications appear to work in the same

Primitive beings of the tropics are known to treat open wounds by
exposing them to the direct rays of the sun without dressings of any
kind. These wounds are usually infected and the sun's rays render them
aseptic and they heal readily. Many cases of sores and surgical wounds
have been quickly healed by exposure to sunlight. Even red light has
been effective, so it has been concluded by some that rays of almost any
wave-length, if intense enough, will effect a cure of this character by
causing an effusion of serum. It has also been stated that the chemical
rays have anæsthetic powers and have been used in this rôle for many
minor operations.

It is said that the Chinese have used red light for centuries in the
treatment of smallpox and throughout the Middle Ages this practice was
not uncommon. In the oldest book on medicine written in English there is
an account of a successful treatment of the son of Edward I for smallpox
by means of red light. It is also stated that this treatment was
administered throughout the reigns of Elizabeth and of Charles II.
Another account states that a few soldiers confined in dark dungeons
recovered from smallpox without pitting. Finsen also obtained excellent
results in the treatment of this disease by means of red light.
However, in this case it appears that the exclusion of the so-called
chemical rays favors healing of the postules of smallpox and that the
use of red light is therefore a negative application of light-therapy.
In other words, the red light plays no part except in furnishing a light
which does not inhibit healing.

Although the so-called actinic rays have curative value in certain
cases, there are some instances where light-baths are claimed to be
harmful. It is said that sun-baths to the naked body are not so popular
as they were formerly, except for obesity, gout, rheumatism, and
sluggish metabolism, because it is felt that the shorter ultra-violet
rays may be harmful. These rays are said to increase the pulse,
respiration, temperature, and blood-pressure and may even start
hemorrhages and in excessive amounts cause headache, palpitation,
insomnia, and anemia. These same authorities condemn sun-baths to the
naked body of the tuberculous, claiming that any cures effected are
consummated despite the injury done by the energy of short wave-length.
There is no doubt that these rays are beneficial in local lesions, but
it is believed that the cure is due to the irritation caused by the rays
and the consequent bactericidal action of the increased flow of serum,
and not to any direct beneficial result on the tissue-cells. Others
claim to cure tuberculosis by means of powerful quartz mercury-arcs
equipped with a glass which absorbs the ultra-violet rays of shorter
wave-lengths. These conclusions by a few authorities are submitted for
what they are worth and to show that this phase of light-therapy is also

Any one who has been in touch with light-therapy in a scientific rôle is
bound to note that much ignorance is displayed in the use of light in
this manner. In fact, it appears safe to state that light-therapy often
smacks of quackery. Very mysterious effects are sometimes attributed to
radiant energy, which occasionally border upon superstition.
Nevertheless, this kind of energy has value, and notwithstanding the
chaos which still exists, it is of interest to note some of the
equipment which has been used. Some practitioners have great confidence
in the electric bath, and elaborate light-baths have been devised. In
the earlier years of this kind of treatment the electric arc was
conspicuous. Electrodes of carbon, carbon and iron, and iron have been
used when intense ultra-violet rays were desired. The quartz mercury-arc
of later years supplies this need admirably. Dr. Cleaves, after many
years of experience with the electric-arc bath, has stated:

     From the administration of an electric-arc bath there is
     obtained an action upon the skin, the patient experiences a
     pleasant and slightly prickly sensation. There is produced,
     even from a short exposure, upon the skin of some patients a
     slight erythema, while with others there is but little such
     effect even from long exposures. The face assumes a normal rosy
     coloring and an appearance of refreshment and repose on
     emerging from the bath is always observed. From the
     administration of the electric-arc bath there is also noted the
     establishment of circulatory changes with a uniform regulation
     of the heart's action, as evidenced by improved volume and
     slower pulse rate, the augmentation of the temperature,
     increased activity of the skin, fuller and slower respiration,
     gradually increased respiratory capacity, and diminished
     irritability of the mucous membrane in tubercular, bronchitic,
     or asthmatic patients. There is also lessened discharge in
     those patients suffering from catarrhal conditions of the nasal
     passages. In diseases of the respiratory system, a soothing
     effect upon the mucous membranes is always experienced, while
     cough and expectoration are diminished.

The cabinet used by Dr. Cleaves was large enough to contain a cot upon
which the patient reclined. An arc-lamp was suspended at each of the two
ends of the cabinet and a flood of light was obtained directly and by
reflection from the white inside surfaces of the cabinet. By means of
mirrors the light from the arcs could be concentrated upon any desired
part of the patient.

Finsen, who in 1895 published his observations upon the stimulating
action of light, is considered the pioneer in the use of so-called
chemical rays in the treatment of disease. He had a circular room about
thirty-seven feet in diameter, in which two powerful 100-ampere
arc-lamps about six feet from the floor were suspended from the ceiling.
Low partitions extended radially from the center, so that a number of
patients could be treated simultaneously. The temperature of the room
was normal, so that the treatment was essentially by radiant energy and
not by heat. The chemical action upon the skin was said to be quite as
strong as under sunlight. The exposures varied from ten minutes to an

Light-baths containing incandescent filament lamps are also used. In
some cases the lamp, sometimes having a blue bulb, is merely contained
as a reflector and the light is applied locally as desired.
Light-cabinets are also used, but in these there is considerable effect
due to heat. The ultra-violet rays emitted by the small electric
filament lamps used in these cabinets are of very low intensity and the
bactericidal action of the light must be feeble. The glass bulbs do not
transmit the extreme ultra-violet rays responsible for the production of
ozone, or the middle ultra-violet rays which are effective in destroying
animal tissue. The cabinets contain from twenty to one hundred
incandescent filament lamps of the ordinary sizes, from 25 to 60 watts.
In the days of the carbon filament lamp the 16-candle-power lamp was
used. Certainly the heating effect has advantages in some cases over
other methods of heating. The light-rays penetrate the tissue and are
absorbed and transformed into heat. Other methods involve conduction of
heat from the hot air or other hot applications. Of course, it is also
contended that the light-rays are directly beneficial.

Light is also concentrated upon the body by means of lenses and mirrors.
For this purpose the sun, the arc, the quartz mercury-arc, and the
incandescent lamp have been used. Besides these, vacuum-tube discharges
and sparks have been utilized as sources for radiant energy and
"electrical" treatment. Röntgen rays and radium have also figured in
recent years in the treatment of disease.

The quartz mercury-arc has been extensively used in the past decade for
the treatment of skin diseases and there appears to be less uncertainty
about the efficacy of radiant energy for the treatment of surface
diseases than of others. Herod related that the Egyptians treated
patients by exposure to direct sunlight and throughout the centuries and
among all types of civilization sunlight has been recognized as having
certain valuable healing or purifying properties. Finsen in his early
experiments cured a case of lupus, a tuberculous skin disease, by means
of the visible and near ultra-violet rays in sunlight. He demonstrated
that these were the effective rays by using only the radiant energy
which passed through a water-cell made by using a convex lens for each
end of the cell and filling the intervening space with water. This was
really a lens made of glass and water. The glass absorbed the
ultra-violet rays of shorter wave-length and the water absorbed the
infra-red rays. Thus he was able to concentrate upon the diseased skin
radiant energy consisting of visible and near ultra-violet rays.

The encouraging results which Finsen obtained in the treatment of skin
diseases led him to become independent of sunlight by equipping a
special arc-lamp with quartz lenses. This gave him a powerful source of
so-called chemical rays, which could be concentrated wherever desired.
However, when science contributed the mercury-vapor arc, developments
were immediately begun which aimed to utilize this artificial source of
steady powerful ultra-violet rays in light-therapy. As a consequence,
there are now available very compact quartz mercury-arcs designed
especially for this purpose. Apparently their use has been very
effective in curing many skin diseases. Certainly if radiant energy is
effective, it has a great advantage over drugs. An authority has stated
in regard to skin diseases that,

     treatment with the ultra-violet rays, especially in conjunction
     with the Röntgen rays, radium and mesothorium is that treatment
     which in most instances holds rank as the first, and in many as
     the only and often enough the most effective mode of handling
     the disease.

Sterilization by means of the radiation from the quartz mercury-arc has
been practised successfully for several years. Compact apparatus is in
use for the sterilization of water for drinking, for surgical purposes,
and for swimming-pools, and the claims made by the manufacturers of the
apparatus apparently are substantiated. One type of apparatus withstands
a pressure of one hundred pounds per square inch and may be connected in
series with the water-main. The water supplied to the sterilizer should
be clear and free of suspended matter, in order that the radiant energy
may be effective. Such apparatus is capable of sterilizing any quantity
of water up to a thousand gallons an hour, and the lamp is kept burning
only when the water is flowing. It is especially useful in hotels,
stores, factories, on ships, and in many industries where sterile water
is needed.

Water is a vital necessity in every-day life, whether for drinking,
cooking, or industrial purposes. It is recognized as a carrier of
disease and the purification of water-supply in large cities is an
important problem. Chlorination processes are in use which render the
treated water disagreeable to the taste and filtration alone is looked
upon with suspicion. The use of chemicals requires constant analysis,
but it is contended that the bactericidal action of ultra-violet rays is
so certain and complete that there is never any doubt as to the
sterilization of the water if it is clear, or if it has been properly
filtered before treating. The system of sterilization by ultra-violet
rays is the natural way, for the sun's rays perform this function in
nature. Apparatus for sterilization of water by means of ultra-violet
rays is built for public plants in capacities up to ten million gallons
per day and these units may be multiplied to meet the needs of the
largest cities. Large mechanical filters are used in conjunction with
these sterilizers, and thus mankind copies nature's way, for natural
supplies of pure water have been filtered through sand and have been
exposed to the rays of the sun which free it from germ life.

Some sterilizers of this character are used at the place where a supply
of pure water is desired or at a point where water is bottled for use in
various parts of a factory, hospital, store, or office building. These
were used in some American hospitals during the recent war, where they
supplied sterilized water for drinking and for the antiseptic bathing of
wounds. In warfare the water supply is exceedingly important. For
example, the Japanese in their campaign in Manchuria boiled the water to
be used for drinking purposes. The mortality of armies in many previous
wars was often much greater from preventable diseases than from bullets,
but the Japanese in their war with Russia reversed the mortality
statistics. Of a total mortality of 81,000 more than 60,000 died of
casualties in battle.

The sterilization of water for swimming-pools is coming into vogue.
Heretofore it was the common practice to circulate the water through a
filter, in order to remove the impurities imparted to it by the bathers
and to return it to the pool. It is insisted by the adherents of
sterilization that filtration of this sort is likely to leave harmful
bacteria in the water. Sterilizers in which ultra-violet rays are the
active rays are now in use for this purpose, being connected beyond the
outflow from the filter. The effectiveness of the apparatus has been
established by the usual method of counting the bacteria. Near the
outlet of the ordinary filter a count revealed many thousand bacteria
per cubic inch of water and among these there were bacteria of
intestinal origin. Then a sterilizer was installed in which the
effective elements were two quartz mercury-lamps which consumed 2.2
amperes each at 220 volts. A count of bacteria in the water leaving the
sterilizer showed that these organisms had been reduced to 5 per cent.
and finally to a smaller percentage of their original value, and that
all those of intestinal origin had been destroyed. In fact, the water
which was returned to the pool was better than that which most persons
drink. Radiant energy possesses advantages which are unequaled by other
bactericidal agents, in that it does not contaminate or change the
properties of the water in any way. It does its work of destroying
bacteria and leaves the water otherwise unchanged.

These glimpses of the use of the radiant energy as a means of regaining
and retaining good health suggest greater possibilities when the facts
become thoroughly established and correlated. The sun is of primary
importance to mankind, but it serves in so many ways that it is
naturally a compromise. It cannot supply just the desired radiant
energy for one purpose and at the same time serve for another purpose in
the best manner. It is obscured on cloudy days and disappears nightly.
These absences are beneficial to some processes, but man in the highly
organized activity of present civilization desires radiant energy of
various qualities available at any time. In this respect artificial
light is superior to the sun and is being improved continually.



In a single century science has converted the dimly lighted nights with
their feeble flickering flames into artificial daytime. In this brief
span of years the production of light has advanced far from the
primitive flames in use at the beginning of the nineteenth century, but,
as has been noted in another chapter, great improvements in
light-production are still possible. Nevertheless, the wonderful
developments in the last four decades, which created the arc-lamps, the
gas-mantle, the mercury-vapor lamps, and the series of electric
incandescent-filament lamps, have contributed much to the efficiency,
safety, health, and happiness of mankind.

A hundred years ago civilization was more easily satisfied and an
improvement which furnished more light at the same cost was all that
could be desired. To-day light alone is not sufficient. Certain kinds of
radiant energy are required for photography and other photochemical
processes and a vast array of colored light is demanded for displays and
for effects upon the stage. Man now desires lights of various colors for
their expressive effects. He is no longer satisfied with mere light in
adequate quantities; he desires certain qualities. Furthermore, he no
longer finds it sufficient to be independent of daylight merely in
quantity of light. In fact, he has demanded artificial daylight.

Doubtless the future will see the production of efficient light of many
qualities or colors, but to-day many of the demands must be met by
modifying the artificial illuminants which are available. Vision is
accomplished entirely by the distinction of brightness and color. An
image of any scene or any object is focused upon the retina as a
miniature map in light, shade, and color. Although the distinction of
brightness is a more important function in vision than the ability to
distinguish colors, color-vision is far more important in daily life
than is ordinarily appreciated. One may go through life color-blind
without suffering any great inconvenience, but the divine gift of
color-vision casts a magical drapery over all creation. Relatively few
are conscious of the wonderful drapery of color, except for occasional
moments when the display is unusual. Nevertheless a study of vision in
nearly all crafts reveals the fact that the distinction of colors plays
an important part.

In the purchase of food and wearing-apparel, in the decoration of homes
and throughout the arts and industries, mankind depends a great deal
upon the appearance of colors. He depends upon daylight in this respect
and unconsciously often, when daylight fails, ceases work which depends
upon the accurate distinction of colors. His color-vision evolved under
daylight; arts and industries developed under daylight; and all his
associations of color are based primarily upon daylight. For these
reasons, adequate artificial illumination does not make mankind
independent of daylight in the practice of arts and crafts and in many
minor activities. In quality or spectral character, the unmodified
illuminants used for general lighting purposes differ from daylight and
therefore do not fully replace it. Noon sunlight contains all the
spectral colors in approximately the same proportions, but this is not
true of these artificial illuminants. For these reasons there is a
demand for artificial daylight.

The "vacuum" tube affords a possibility of an extensive variety of
illuminants differing widely in spectral character or color. Every gas
when excited to luminescence by an electric discharge in the "vacuum"
tube (containing the gas at a low pressure) emits light of a
characteristic quality or color. By varying the gas a variety of
illuminants can be obtained, but this means of light-production has not
been developed to a sufficiently practicable state to be satisfactory
for general lighting. Nitrogen yields a pinkish light and the nitrogen
tube as developed by Dr. Moore was installed to some extent a few years
ago. Neon yields an orange light and has been used in a few cases for
displays. Carbon dioxide furnishes a white light similar to daylight and
small tubes containing this gas are in use to-day where accurate
discrimination of color is essential.

The flame-arcs afford a means of obtaining a variety of illuminants
differing in spectral character or color. By impregnating the carbons
with various chemical compounds the color of the flame can be widely
altered. The white flame-arc obtained by the use of rare-earth compounds
in the carbons provides an illuminant closely approximating average
daylight. By using various substances besides carbon for the
electrodes, illuminants differing in spectral character can be
obtained. These are usually rich in ultra-violet rays and therefore have
their best applications in processes demanding this kind of radiant
energy. The arc-lamp is limited in its application by its unsteadiness,
its bulkiness, and the impracticability of subdividing it into
light-sources of a great range of luminous intensities.

The most extensive applications of artificial daylight have been made by
means of the electric incandescent filament lamp, equipped with a
colored glass which alters the light to the same quality as daylight.
The light from the electric filament lamp is richer in yellow, orange,
and red rays than daylight, and by knowing the spectral character of the
two illuminants and the spectral characteristics of colored glasses in
which various chemicals have been incorporated, it is possible to
develop a colored glass which will filter out of the excess of yellow,
orange, and red rays so that the transmitted light is of the same
spectral character as daylight. Thousands of such artificial daylight
units are now in use in the industries, in stores, in laboratories, in
dye-works, in print-shops, and in many other places. Currency and
Liberty Bonds have been made under artificial daylight and such units
are in use in banks for the detection of counterfeit currency. The
diamond expert detects the color of jewels and the microscopist is
certain of the colors of his stains under artificial daylight. The dyer
mixes his dyes for the coloring of tons of valuable silk and the artist
paints under this artificial light. These are only a few of a vast
number of applications of artificial daylight, but they illustrate that
mankind is independent of natural light in another respect.

There are various kinds of daylight, two of which are fairly constant in
spectral character. These are noon sunlight and north skylight. The
former may be said to be white light and its spectrum indicates the
presence of visible radiant energy of all wave-lengths in approximately
equal proportions. North skylight contains an excess of violet, blue,
and blue-green rays and as a consequence is a bluish white. Noon
sunlight on a clear day is fairly constant in spectral character, but
north skylight varies somewhat depending upon the absence or presence of
clouds and upon the character of the clouds. If large areas of sunlit
clouds are present, the light is largely reflected sunlight. If the sky
is overcast, the north skylight is a result of a mixture of sunlight and
blue skylight filtered through the clouds and is slightly bluish. If the
sky is clear, the light varies from light blue to deep blue.



The daylight which enters buildings is often considerably altered in
color by reflection from other buildings and from vegetation, and after
it enters a room it is sometimes modified by reflection from colored
surroundings. It may be commonly noted that the light reflected from
green grass through a window to the upper part of a room is very much
tinted with green and the light reflected from a yellow brick building
is tinted yellow. Besides these alterations, sunlight varies in color
from the yellow or red of dawn through white at noon to orange or red at
sunset. Throughout the day the amount of light from the sky does not
change nearly as much as the amount of sunlight, so there is a
continual variation in the proportion of direct sunlight and skylight
reaching the earth. This is further varied by the changing position of
the sun. For example, at a north window in which the direct sunlight may
not enter throughout the day, the amount of sunlight which enters by
reflection from adjacent buildings and other objects may vary greatly.
Thus it is seen that daylight not only varies in quantity but also in
quality, and an artificial daylight, which is based upon an extensive
analysis, has the advantage of being constant in quantity and quality as
well as correct in quality. Modern artificial-daylight units which have
been scientifically developed not only make mankind independent of
daylight in the discrimination of colors but they are superior to

Although there are many expert colorists who require an accurate
artificial daylight, there are vast fields of lighting where a less
accurate daylight quality is necessary. The average eyes are not
sufficiently skilled for the finest discrimination of colors and
therefore the Mazda "daylight" lamp supplies the less exacting
requirements of color matching. It is a compromise between quality and
efficiency of light and serves the purpose so well that millions of
these lamps have found applications in stores, offices, and industries.
In order to make an accurate artificial north skylight for color-work by
means of colored glass, from 75 to 85 per cent. of the light from a
tungsten lamp must be filtered out. This absorption in a broad sense
increases the efficiency of the light, for the fraction that remains is
now satisfactory, whereas the original light is virtually useless for
accurate color-discrimination. About one third of the original light is
absorbed by the bulb of the tungsten "daylight" lamp, with a resultant
light which is an approximation to average daylight.

Old illuminants such as that emitted by the candle and oil-lamp were
used for centuries in interiors. All these illuminants were of a warm
yellow color. Even the earlier modern illuminants were not very
different in color, so it is not surprising that there is a deeply
rooted desire for artificial light in the home and in similar interiors
of a warm yellow color simulating that of old illuminants. The
psychological effect of warmth and cheerfulness due to such illuminants
or colors is well established. Artificial light in the home symbolizes
independence of nature and protection from the elements and there is a
firm desire to counteract the increasing whiteness of modern illuminants
by means of shades of a warm tint. The white light is excellent for the
kitchen, laundry, and bath-room, and for reading-lamps, but the warm
yellow light is best suited for making cozy and cheerful the environment
of the interiors in which mankind relaxes. An illuminant of this
character can be obtained efficiently by using a properly tinted bulb on
tungsten filament lamps. By absorbing about one fourth to one third of
the light (depending upon the temperature of the filament) the color of
the candle flame may be simulated by means of a tungsten filament lamp.
Some persons are still using the carbon-filament lamp despite its low
efficiency, because they desire to retain the warmth of tint of the
older illuminants. However, light from a tungsten lamp may be filtered
to obtain the same quality of light as is emitted by the carbon
filament lamp by absorbing from one fifth to one fourth of the light.
The luminous efficiency of the tungsten lamp equipped with such a tinted
bulb is still about twice as great as that of the carbon-filament lamp.
Thus the high efficiency of the modern illuminants is utilized to
advantage even though their color is maintained the same as the old

All modern illuminants emit radiant energy, which does not affect the
ordinary photographic plate. This superfluous visible energy merely
contributes toward glare or a superabundance of light in photographic
studios. A glass has been developed which transmits virtually all the
rays that affect the ordinary photographic plate and greatly reduces the
accompanying inactive rays. Such a glass is naturally blue in color,
because it must transmit the blue, violet, and near ultra-violet rays.
Its density has been so determined for use in bulbs for the
high-efficiency tungsten lamps that the resultant light appears
approximately the color of skylight without sacrificing an appreciable
amount of the value of the radiant energy for ordinary photography. This
glass, it is seen, transmits the so-called chemical rays and is useful
in other activities where these rays alone are desired. It is used in
light-therapy and in some other activities in which the chemical effects
of these rays are utilized.

In the photographic dark-room a deep red light is safe for all emulsions
excepting the panchromatic, and lamps of this character are standard
products. An orange light is safe for many printing papers. Panchromatic
plates and films are usually developed in the dark where extreme safety
is desired, but a very weak deep red light is not unsafe if used
cautiously. However, many photographic emulsions of this character are
not very sensitive to green rays, so a green light has been used for
this purpose.

A variety of colored lights are in demand for theatrical effects,
displays, spectacular lighting, signaling, etc., and there are many
superficial colorings available for this purpose. Few of these show any
appreciable degree of permanency. Permanent superficial colorings have
recently been developed, but these are secret processes unavailable for
the market. For this reason colored glass is the only medium generally
available where permanency is desired. For permanent lighting effects,
signal glasses, colored caps, and sheets of colored glass may be used.
Tints may be obtained by means of colored reflectors. Other colored
media are dyes in lacquers and in varnishes, colored inks, colored
textiles, and colored pigments.

Inasmuch as colored glass enters into the development of permanent
devices, it may be of interest to discuss briefly the effects of various
metallic compounds which are used in glass. The exact color produced by
these compounds, which are often oxides, varies slightly with the
composition of the glass and method of manufacture, but this phase is
only of technical interest. The coloring substances in glass may be
divided into two groups. The first and largest group consists of those
in which the coloring matter is in true solution; that is, the coloring
is produced in the same manner as the coloring of water in which a
chemical salt is dissolved. In the second group the coloring substances
are present in a finely divided or colloidal state; that is, the
coloring is due to the presence of particles in mechanical suspension.
In general, the lighter elements do not tend to produce colored glasses,
but the heavier elements in so far as they can be incorporated into
glass tend to produce intense colors. Of course, there are exceptions to
this general statement.

The alkali metals, such as sodium, potassium, and lithium, do not color
glass appreciably, but they have indirect effects upon the colors
produced by manganese, nickel, selenium, and some other elements. Gold
in sufficient amounts produces a red in glass and in low concentration a
beautiful rose. It is present in the colloidal state. In the manufacture
of "gold" red glass, the glass when first cooled shows no color, but on
reheating the rich ruby color develops. The glass is then cooled slowly.
The gold is left in a colloidal state. Copper when added to a glass
produces two colors, blue-green and red. The blue-green color, which
varies in different kinds of glasses, results when the copper is fully
oxidized, and the red by preventing oxidation by the presence of a
reducing agent. This red may be developed by reheating as in the case of
making gold ruby glass. Selenium produces orange and red colors in

Silver when applied to the surface of glass produces a beautiful yellow
color and it has been widely used in this manner. It has little coloring
effect in glass, because it is so readily reduced, resulting in a
metallic black. Uranium produces a canary yellow in soda and potash-lime
glasses, which fluoresce, and these glasses may be used in the
detection of ultra-violet rays. The color is topaz in lead glass. Both
sulphur and carbon are used in the manufacture of pale yellow glasses.
Antimony has a weak effect, but in the presence of much lead it is used
for making opaque or translucent yellow glasses. Chromium produces a
green color, which is reddish in lead glass, and yellowish in soda, and
potash-lime glasses.

Iron imparts a green or bluish green color to glass. It is usually
present as an impurity in the ingredients of glass and its color is
neutralized by adding some manganese, which produces a purple color
complementary to the bluish green. This accounts for the manganese
purple which develops from colorless glass exposed to ultra-violet rays.
Iron is used in "bottle green" glass. Its color is greenish blue in
potash-lime glass, bluish green in soda-lime glass, and yellowish green
in lead glass.

Cobalt is widely used in the production of blue glasses. It produces a
violet-blue in potash-lime and soda-lime glasses and a blue in lead
glasses. It appears blue, but it transmits deep red rays. For this
reason when used in conjunction with a deep red glass, a filter for only
the deepest red rays is obtained. Nickel produces an amethyst color in
potash-lime glass, a reddish brown in soda-lime glass, and a purple in
lead glass. Manganese is used largely as a "decolorizing" agent in
counteracting the blue-green of iron. It produces an amethyst color in
potash-lime glass and reddish violet in soda-lime and lead glasses.

These are the principal coloring ingredients used in the manufacture of
colored glass. The staining of glass is done under lower temperatures,
so that a greater variety of chemical compounds may be used. The
resulting colors of metals and metallic oxides dissolved in glass depend
not only upon the nature of the metal used, but also partly upon the
stage of oxidation, the composition of the glass and even upon the
temperature of the fusion.

In developing a glass filter the effects of the various coloring
elements are determined spectrally and the various elements are varied
in proper proportions until the glass of desired spectral transmission
is obtained. It is seen that the coloring elements are limited and the
combination of these is further limited by chemical considerations. In
combining various colored glasses or various coloring elements in the
same glass the "subtractive" method of color-mixture is utilized. For
example, if a green glass is desired, yellowish green chromium glass may
be used as a basis. By the addition of some blue-green due to copper,
the yellow rays may be further subdued so that the resulting color is

The primary colors for this method of color-mixture are the same as
those of the painter in mixing pigments--namely, purple, yellow, and
blue-green. Various colors may be obtained by superposing or intimately
mixing the colors. The resulting transmission (reflection in the case of
reflecting media such as pigments) are those colors commonly transmitted
by all the components of a mixture. Thus,

     Purple and yellow     = red
     Yellow and blue-green = green
     Blue-green and purple = blue

The colors produced by adding lights are based not on the "subtractive"
method but on the actual addition of colors. These primaries are red,
green, and blue and it will be noted that they are the complementaries
of the "subtractive" primaries. By the use of red, green, and blue
lights in various proportions, all colors may be obtained in varying
degrees of purity. The chief mixtures of two of the "additive" primaries
produce the "subtractive" primaries. Thus,

     Red and blue    = purple
     Red and green   = yellow
     Green and blue  = blue-green

Although the coloring media which are permanent under the action of
light, heat, and moisture are relatively few, by a knowledge of their
spectral characteristics and other principles of color the expert is
able to produce many permanent colors for lighting effects. The additive
and subtractive methods are chiefly involved, but there is another
method which is an "averaging" additive one. For example, if a warm tint
of yellow is desired and only a dense yellow glass is available, the
yellow glass may be cut into small pieces and arranged upon a colorless
glass in checker-board fashion. Thus a great deal of uncolored light
which is transmitted by the filter is slightly tinted by the yellow
light passing through the pieces of yellow glass. If this light is
properly mixed by a diffusing glass the effect is satisfactory. These
are the principal means of obtaining colored light by means of filters
and by mixing colored lights. By using these in conjunction with the
array of light-sources available it is possible to meet most of the
growing demands. Of course, the ideal solution is to make the colored
light directly at the light-source, and doubtless future developments
which now appear remote or even impossible will supply such colored
illuminants. In the meantime, much is being accomplished with the means



Artificial light is a natural agency for producing spectacular effects.
It is readily controlled and altered in color and the brightness which
it lends to displays outdoors at night renders them extremely
conspicuous against the darkness of the sky. It surpasses other
decorative media by the extreme range of values which may be obtained.
The decorator and painter are limited by a range of values from black to
white pigments, which ordinarily represents an extreme contrast of about
one to thirty. The brightnesses due to light may vary from darkness to
those of the light-sources themselves. The decorator deals with
secondary light--that is, light reflected by more or less diffusely
reflecting objects. The lighting expert has at his command not only this
secondary light but the primary light of the sources. Lighting effects
everywhere attract attention and even the modern merchant testifies that
adequate lighting in his store is of advertising value. In all the field
of spectacular lighting the superiority of artificial light over natural
light is demonstrated.

Light is a universal medium with which to attract attention and to
enthrall mankind. The civilizations of all ages have realized this
natural power of light. It has played a part in the festivals and
triumphal processions from time immemorial and is still the most
important feature of many celebrations. In the early festivals fires,
candles, and oil-lamps were used and fireworks were invented for the
purpose. Even to-day the pyrotechnical displays against the dark depths
of the night sky hold mankind spellbound. But these evanescent notes of
light have been improved upon by more permanent displays on a huge
scale. Thirty years before the first practical installation of
gas-lighting an exhibition of "Philosophical Fireworks" produced by the
combustion of inflammable gases was given in several cities of England.

It is a long step from the array of flickering gas-flames with which the
fronts of the buildings of the Soho works were illuminated a century ago
to the wonderful lighting effects a century later at the Panama-Pacific
Exposition. Some who saw that original display of gas-jets totaling a
few hundred candle-power described it as an "occasion of extraordinary
splendour." What would they have said of the modern spectacular lighting
at the Exposition where Ryan used in a single effect forty-eight large
search-lights aggregating 2,600,000,000 beam candle-power! No other
comparison exemplifies more strikingly the progress of artificial
lighting in the hundred years which have elapsed since it began to be

The nature of the light-sources in the first half of the nineteenth
century did not encourage spectacular or display lighting. In fact, this
phase of lighting chiefly developed along with electric lamps. Of
course, occasionally some temporary effect was attempted as in the case
of illuminating the dome of St. Paul's Cathedral in London in 1872, but
continued operation of the display was not entertained. In the case of
lighting this dome a large number of ship's lanterns were used, but the
result was unsatisfactory. After this unsuccessful attempt at lighting
St. Paul's, a suggestion was made of "flooding it with electric light
projected from various quarters." Spectacular lighting outdoors really
began in earnest in the dawn of the twentieth century.

Although some of the first attempts at spectacular lighting outdoors
were made with search-lights, spectacular lighting did not become
generally popular until the appearance of incandescent filament lamps of
reasonable efficiency and cost. The effects were obtained primarily by
the use of small electric filament lamps draped in festoons or installed
along the outlines and other principal lines of buildings and monuments.
The effect was almost wholly that of light, for the glare from the
visible lamps obscured the buildings or other objects. The method is
still used because it is simple and the effects may be permanently
installed without requiring any attention excepting to replace
burned-out lamps. However, the method has limitations from an artistic
point of view because the artistic effects of painting, sculpture, and
architecture cannot be combined with it very effectively. For example,
the details of a monument or of a building cannot be seen distinctly
enough to be appreciated. The effect is merely that of outlines or lines
and patterns of points of light and is usually glaring.

The next step was to conceal these lamps behind the cornices or other
projections or in nooks constructed the purpose. Light now began to
mold and to paint the objects. The structures began to be visible; at
least the important cornices and other details were no longer mere
outlines. The introduction of the drawn-wire tungsten lamp is
responsible for an innovation in spectacular lighting of this sort, for
now it became possible to make concentrated light-sources so essential
to projectors. Furthermore, these lighting units require very little
attention after once being located. With the introduction of
electric-filament lamps of this character small projectors came into
use, and by means of concentrated beams of light whole buildings and
monuments could be flooded with light from remote positions. The effects
obtained by concealing lamps behind cornices had demonstrated that the
lighting of the surfaces was the object to be realized in most cases,
and when small projectors not requiring constant attention became
available, a great impetus was given to flood-lighting.

When France gave to this country the Bartholdi Statue of Liberty there
was no thought of having this emblem visible at night excepting for the
torch held the hand of Liberty. This torch was modified at the time of
the erection of the statue to accommodate the lamps available, with the
result that it was merely a lantern containing a number of electric
lamps. At night it was a speck of light more feeble than many
surrounding shore lights. The statue had been lighted during festivals
with festoons and outlines of lamps, but in 1915, when the freedom of
the generous donor of the statue appeared to be at stake, a movement was
begun which culminated in a fund for flood-lighting Liberty. The broad
foundation of the statue made the lighting comparatively easy by means
of banks of incandescent filament search-lights. About 225 of these
units were used with a total beam candle-power of about 20,000,000. The
original idea of an imitation flame for the torch was restored by
building this from pieces of yellow cathedral glass of three densities.
About six hundred pieces of glass were used, the upper ones being
generally of the lighter tints and the lower ones of the darker tints. A
lighthouse lens was placed in this lantern so that an intense beam of
light would radiate from it. The flood-lighted Statue of Liberty is now
visible by night as well as by day and it has a double significance at
night, for light also symbolizes independence.

Just as the Statue of Liberty stands alone in the New York Harbor so
does the Woolworth Building reign supreme on lower Manhattan. Liberty
proclaims independence from the bondage of man and the Woolworth Tower
stands majestically in defiance of the elements as a symbol of man's
growing independence of nature. This building with its cream terra-cotta
surface and intricate architectural details touched here and there with
buff, blue, green, red, and gold, rises 792 feet or sixty stories above
the street and typifies the American spirit of conceiving and of
executing great undertakings. In it are blended art, utility, and
majesty. Viewed by multitudes during the day, it is a valuable
advertisement for the name which stands for a national institution. But
by day it shares attention with its surroundings. If lighted at night it
would stand virtually alone against the dark sky and the investment
would not be wholly idle during the evening hours.

Mr. H. H. Magdsick, who designed the lighting for Liberty, planned the
lighting for the Woolworth Tower, which rises 407 feet or thirty-one
stories above the main building. Five hundred and fifty projectors
containing tungsten filament lamps were distributed about the base of
the tower and among some of the architectural details. The main
architectural features of the mansard roof extending from the
fifty-third to the fifty-seventh floor, the observation balcony at the
fifty-eighth and the lantern structures at the fifty-ninth and sixtieth
floors are covered with gold-leaf. By proper placing of the projectors a
glittering effect is obtained from these gold surfaces. The crowning
features of the lighting effect are the lanterns in the crest of the
spire. Twenty-four 1000-watt tungsten lamps were placed behind crystal
diffusing glass, which transmits the light predominantly in a horizontal
direction. Thus at long distances, from which the architectural details
cannot be distinguished, the brilliant crowning light is visible. An
automatic dimmer was devised so that the effect of a huge varying flame
was obtained. At close range, owing to the nature of the glass panels,
this portion is not much brighter than the remainder of the surfaces.
When the artificial lighting is in operation the tower becomes a
majestic spire of light and this magnificent Gothic structure projecting
defiantly into the depths of darkness is in more than one sense a torch
of modern civilization.

Many prominent buildings and monuments have burst forth in a flood of
light, and their beauty and symbolism have been appreciated at night by
many persons who do not notice them by day. Not only are the beautiful
structures of man lighted permanently but many temporary effects are
devised. Artificial lighting effects have become a prominent part in
outdoor festivals, pageants, and theatricals. Candles have been
associated with Christmas trees ever since the latter came into use and
naturally artificial light has been a feature in the community Christmas
trees which have come into vogue in recent years. The Municipal
Christmas Tree in Chicago in 1916 was ninety feet high and was lighted
with projectors. Thousands of gems taken from the Tower of Jewels at the
San Francisco Exposition added life and sparkle to that of the other

[Illustration: The Capitol flooded with light

Luna Park, Coney Island, studded with 60,000 incandescent
filament lamps



After the close of the recent war artificial light played a prominent
part throughout the country in the joyful festivals. A jeweled arch
erected in New York in honor of the returning soldiers rivaled some of
the spectacles of the Panama-Pacific Exposition. The arch hung like a
gigantic curtain of jewels between two obelisks, which rose to a height
of eighty feet and were surmounted by jeweled forms in the shape of
sunbursts. Approximately thirty thousand jewels glittered in the beams
of batteries of arc-projectors. Many of the signs and devices which
played a part in the "Welcome Home" movement were of striking nature and
of a character to indicate permanency. The equipment of a large building
consisted of more than five thousand 10-watt lamps, the entire building
being outlined with stars consisting of eleven lamps each. The "Brighten
Up" campaign spread throughout the country. The lighting and
installation of signs and special patriotic displays, the flooding of
streets and shop-windows with light without stint, produced an inspiring
and uplifting effect which did much to restore cheerfulness and
optimism. A glowing example was set in Washington, where the
flood-lighting of the Capitol, discontinued shortly after our entrance
into the war, was resumed.

In Chicago a "Victory Way" was established, with street-lighting posts
on both sides of the street equipped with red, white, and blue globes
surmounted by a golden goddess of Victory. One hundred and seventy-five
projectors were installed along the way on the roofs and in the windows
of office buildings. A brilliant, scintillating "Altar of Victory" was
erected at the center of the Way. It was composed of two enormous
candelabra erected one on each side of a platform ninety feet high.
These were studded with jewels and supported a curtain of jewels
suspended from the altar. In the center of the curtain was a huge
jeweled eagle bearing the Allied flags. This was illuminated by
arc-projectors which delivered 200,000,000 beam candle-power. In
addition to these there were many smaller projectors. In the top of each
candelabra six large red-and-orange lamps were installed in reflectors.
These illuminated live steam which issued from the top. Surmounting the
whole was a huge luminous fan formed by beams from large arc
search-lights. These are only a few of the many lighting effects which
welcomed the returning soldiers, but they illustrate how much modern
civilization depends upon artificial light for expressing its feelings
and emotions. Throughout all these festivals light silently symbolized
happiness, freedom, and advancement.

Projectors were used on a large scale in several cases before the advent
of the concentrated filament lamp. W. D'A. Ryan, the leader in
spectacular lighting, lighted the Niagara Falls in 1907 with batteries
of arc-projectors aggregating 1,115,000,000-beam candle-power. In 1908
he used thirty arc-projectors to flood the Singer Tower in New York with
light and projected light to the flag on top by means of a search-light
thirty inches in diameter. Many flags waved throughout the war in the
beams of search-lights, symbolizing a patriotism fully aroused. The
search-light beam as it bores through the atmosphere at night is usually
faintly bright, owing to the small amount of fog, dust, and smoke in the
air. By providing more "substance" in the atmosphere, the beams are made
to appear brighter. Following this reasoning, Ryan developed his
scintillator consisting of a battery of search-light beams projected
upward through clouds of steam which provided an artificial fog. This
was first displayed at the Hudson-Fulton celebration with a battery of
arc search-lights totaling 1,000,000,000-candle-power.

All these effects despite their magnitude were dwarfed by those at the
Panama-Pacific Exposition, and inasmuch as this up to the present time
represents the crowning achievement in spectacular lighting, some of the
details worked out by Ryan may be of interest. In general, the lighting
effects departed from the bizarre outline lighting in which glaring
light-sources studded the structures. The radiant grandeur and beauty
of flood-lighting from concealed light-sources was the key-note of the
lighting. In this manner wonderful effects were obtained, which not only
appealed to the eye and to the artistic sensibility but which were free
from glare. By means of flood-lighting and relief-lighting from
concealed light-sources the third dimension or depth was obtained and
the architectural details and colorings were preserved. A great many
different kinds of devices and lamps were used to make the night effects
superior in grandeur to those of daytime. The Zone or amusement section
was lighted with bare lamps in the older manner and the glaring bizarre
effects contrasted the spectacular lighting of the past with the
illumination of the future.

In another section the visitor was greeted with a gorgeous display of
carnival spirit. Beautifully colored heraldic shields on which were
written the early history of the Pacific coast were illuminated by
groups of luminous arc-lamps on standards varying from twenty-five to
fifty-five feet in height. The Tower of Jewels with more than a hundred
thousand dangling gems was flood-lighted, and the myriads of minute
reflected images of light-sources glittering against the dark sky
produced an effect surpassing the dreams of imagination. Shadows and
high-lights of striking contrasts or of elusive colors greeted the
visitor on every hand. Individual isolated effects of light were to be
found here and there. Fire hissed from the mouths of serpents and cast
the spell of mobile light over the composite Spanish-Gothic-Oriental
setting. A colored beam of a search-light played here and there.
Mysterious vapors rising from caldrons were in reality illuminated
steam. Symbolic fountain groups did not escape the magic touch of the
lighting wizard.

In the Court of the Universe great areas were illuminated by two
fountains rising about a hundred feet above the sunken gardens. One of
these symbolized the setting sun, the other the rising sun. The shaft
and ball at the crest of each fountain were glazed with heavy opal glass
imitating travertine marble and in these were installed incandescent
lamps of a total candle-power of 500,000. The balustrade seventy feet
above the sunken gardens was surmounted by nearly two hundred
incandescent filament search-lights. Light was everywhere, either
varying in color into a harmonious scene or changing in light and shadow
to mold the architecture and sculpture. The enormous glass dome of the
Palace of Horticulture was converted into an astronomical sphere by
projecting images upon it in such a manner that spots of light revolved;
rings and comets which appeared at the horizon passed on their way
through the heavens, changing in color and disappearing again at the
horizon. All these effects and many more were mirrored in the waters of
the lagoons and the whole was a Wonderland indeed.

The scintillator consisted of 48 arc search-lights three feet in
diameter totaling 2,600,000,000 beam candle-power. The lighting units
were equipped with colored screens and the beams which radiated upward
were supplied with an artificial fog by means of steam generated by a
modern express locomotive. The latter was so arranged that the wheels
could be driven at a speed of sixty miles per hour under brake, thereby
emitting great volumes of steam and smoke, which when illuminated with
various colors produced a magnificent spectacle. Over three hundred
scintillator effects were worked out and this feature of fireless
fireworks was widely varied. The aurora borealis and other effects
created by this battery of search-lights extended for many miles. The
many effects regularly available were augmented on special occasions and
it is safe to state that this apparatus built upon a huge scale provided
a flexibility of fireless fireworks never attained even with small-scale

The lighting of the exposition can barely be touched upon in a few
paragraphs and it would be difficult to describe in words even if space
were unlimited. It represented the power of light to beautify and to
awe. It showed the feebleness of the decorator's media in comparison
with light pulsating with life. It consisted of a great variety of
direct, masked, concealed, and projected effects, but these were blended
harmoniously with one another and with the decorative and architectural
details of the structures. It was a crowning achievement of a century of
public lighting which began with Murdock's initial display of a hundred
flickering gas-jets. It demonstrated the powers of science in the
production of light and of genius and imagination in the utilization of
light. It was a silent but pulsating display of grandeur dwarfing into
insignificance the aurora borealis in its most resplendent moments.



From an esthetic or, more broadly, a psychological point of view no
medium rivals light in expressiveness. Not only is light allied with
man's most important sense but throughout long ages of associations and
uses mankind has bestowed upon it many attributes. In fact, it is
possible that light, color, and darkness possess certain fundamentally
innate powers; at least, they have acquired expressive and impressive
powers through the many associations in mythology, religion, nature, and
common usage. Besides these attributes, light possesses a great
advantage over the media of decoration in obtaining brightness and color
effects. For example, the landscape artist cannot reproduce the range of
values or brightnesses in most of nature's scenes, for if black is used
to represent a deep shadow, white is not bright enough to represent the
value of the sky. In fact, the range of brightnesses represented by the
deep shadow and the sky extends far beyond the range represented by
black and white pigments. The extreme contrast ordinarily available by
means of artist's colors is about thirty to one, but the sky is a
thousand times brighter than a shadow, a sunlit cloud is thousands of
times brighter than the deep shadows of woods, and the sun is millions
of times brighter than the shadows in a landscape.

The range of brightnesses obtainable by means of light extends from
darkness or black throughout the range represented by pigments under
equal illumination and beyond these through the enormous range
obtainable by unequal illumination of surfaces to the brightnesses of
the light-sources themselves. In the matter of purity of colors, light
surpasses reflecting media, for it is easy to obtain approximately pure
hues by means of light and to obtain pure spectral hues by resorting to
the spectrum of light. It is impossible to obtain pure hues by means of
pigments or of other reflecting media. These advantages of light are
very evident on turning to spectacular lighting effects, and even the
lighting of interiors illustrates a potentiality in light superior to
other media. For example, in a modern interior in which concealed
lighting produces brilliantly illuminated areas above a cornice and dark
shadows on the under side, the range in values is often much greater
than that represented by black and white, and still there remains the
possibility of employing the light-sources themselves in extending the
scale of brightness. Superposing color upon the whole it is obvious that
the combination of "primary" light with reflected light possesses much
greater potentiality than the latter alone. This potentiality of light
is best realized if lighting is regarded as "painting with light" in a
manner analogous to the decorator's painting with pigments, etc.

The expressive possibilities of lighting find extensive applications in
relation to painting, sculpture, and architecture. A painting is an
expression of light and the sculptor's product finally depends upon
lighting for its effectiveness. Lighting is the master painter and
sculptor. It may affect the values of a painting to some extent and it
is a great influence upon the colors. It molds the model from which the
sculptor works and it molds the completed work. The direction,
distribution, and quality of light influence the appearance of all
objects and groups of them. Aside from the modeling of ornament, the
light and shade effects of relatively large areas in an interior such as
walls and ceiling, the contrasts in the brightnesses of alcoves with
that of the main interior, and the shadows under cornices, beams, and
arches are expressions of light.

The decorator is able to produce a certain mood in a given interior by
varying the distribution of values and the choice of colors and the
lighting artist is able to do likewise, but the latter is even able to
alter the mood produced by the decorator. For example, a large interior
flooded with light from concealed sources has the airiness and
extensiveness of outdoors. If lighted solely by means of sources
concealed in an upper cornice, the ceiling may be bright and the walls
may be relatively dark by contrast. Such a lighting effect may produce a
feeling of being hemmed in by the walls without a roof. If the room is
lighted by means of chandeliers hung low and equipped with shades in
such a manner that the lower portions of the walls may be light while
the upper portions of the interior may be ill defined, the feeling
produced may be that of being hemmed in by crowding darkness. Thus
lighting is productive of moods and illusions ranging from the mystery
of crowding darkness to the extensiveness of outdoors.

Future lighting of interiors doubtless will provide an adequacy of
lighting effects which will meet the respective requirements of various
occasions. A decorative scheme in which light and medium grays are
employed produces an interior which is very sensitive to lighting
effects. To these light-and-shade effects colored light may add its
charming effectiveness. Not only are colored lighting effects able to
add much to the beauty of the setting but they possess certain other
powers. Blue tints produce a "cold" effect and the yellow and orange
tints a "warm" effect. For example, a room will appear cooler in the
summer when illuminated by means of bluish light and a practical
application of this effect is in the theater which must attract
audiences in the summer. How tinted illuminants fit the spirit of an
occasion or the mood of a room may be fully appreciated only through
experiments, but these are so effective that the future of lighting will
witness the application of the idea of "painting with light" to its
fullest extent. Color is demanded in other fields, and, considering its
effectiveness and superiority in lighting, it will certainly be demanded
in lighting when its potentiality becomes appreciated and readily

The expressiveness of light is always evident in a landscape. On a sunny
day the mood of a scene varies throughout the day and it grows more
enticing and agreeable as the shadows lengthen toward evening. The
artist in painting a desert scene employs short harsh shadows if he
desires to suggest the excessive heat. These shadows suggest the
relentless noonday sun. The overcast sky is universally depressing and
it has been found that on a sunny day most persons experience a slight
depression when a cloud obscures the sun. Nature's lighting varies from
moment to moment, from day to day, and from season to season. It
presents the extremes of variation in distributions of light from
overcast to sunny days and in the latter cases the shadows are
continually shifting with the sun's altitude. They are harshest at noon
and gradually fade as they lengthen, until at sunset they disappear. The
colors of sunlit surfaces and of shadows vary from sunrise to sunset.
These are the fundamental variations in the lighting, but in the various
scenes the lighting effects are further modified by clouds and by local
conditions or environment. The vast outdoors provides a fruitful field
for the study of the expressiveness of light.

Having become convinced of this power of light, the lighting expert may
turn to artificial light, which is so easily controlled in direction,
distribution, and color, and draw upon its potentiality. Not only is it
easy to provide a lighting suitable to the mood or to the function of an
interior but it is possible to obtain some variety in effect so that the
lighting may always suit the occasion. A study of nature's lighting
reveals one great principle, namely, variety. Mankind demands variety in
most of his activities. Work is varied and alternated with recreation.
Meals are not always the same. Clothing, decorations, and furnishings
are relieved of monotony. One of the most potent features of artificial
light is the ease with which variety may be obtained. In obtaining
relief from the monotony of decorations and furnishings, considerable
expense and inconvenience are inevitably encountered. With an adequate
supply of outlets, circuits, and controls a wide variety of lighting
effects may be obtained with perhaps an insignificant increase in the
initial investment. Variety is the spice of lighting as well as of life.

These various principles of lighting are readily exemplified in the
lighting of the home, which is discussed in another chapter. The church
is even a better example of the expressive possibilities of lighting.
The architectural features are generally of a certain period and first
of all it is essential to harmonize the lighting effect with that of the
architectural and decorative scheme. Obviously, the dark-stained ceiling
of a certain type of church would not be flooded with light. The fact
that it is made dark by staining precludes such a procedure in lighting.
The characteristics of creeds are distinctly different and these are to
some extent exemplified by the lines of the architecture of their
churches. In the same way the lighting effect may be harmonized with the
creed and the spirit of the interior. The lighting may always be
dignified, impressive, and congruous. Few churches are properly lighted
with a high intensity of illumination; moderate lighting is more
appropriate, for it is conducive to the spirit of worship. In some
creeds a dominant note is extreme penitence and severity. The
architecture may possess harsh outlines, and this severity or extreme
solemnity may be expressed in lighting by harsher contrasts, although
this does not mean that the lighting must be glaring. On the other hand,
in a certain modern creed the dominant note appears to be cheerfulness.
The spacious interiors of the churches of this creed are lacking in
severe lines and the walls and ceilings are highly reflecting. Adequate
illumination by means of diffused light without the production of severe
contrasts expresses the creed, modernity, and enlightenment. On the
altar of certain churches the expressiveness of light is utilized in the
ceremonial uses which vary with the creed. Even the symbolism of color
may be appropriately woven into the lighting of the church.

The expressiveness of light and color originated through the contact of
primitive man with nature. Sunlight meant warmth and a bountiful
vegetation, but darkness restricted his activities and harbored manifold
dangers. Many associations thus originated and they were extended
through ignorance and superstition. Yellow is naturally emblematical of
the sun and it became the symbol of warmth. Brown as the predominant
color of the autumn foliage became tinctured with sadness because the
decay of the vegetation presaged the death of the year and the cold
dreary months of winter. The first signs of green vegetation in the
spring were welcomed as an end of winter and a beginning of another
bountiful summer; hence green symbolized youth and hope. It became
associated with the springtime of life and thus signified inexperience,
but as the color of vegetation it also meant life itself and became a
symbol of immortality. Blue acquired certain divine attributes because,
as the color of the sky, it was associated with the abode of the gods or
heaven. Also a blue sky is the acme of serenity and this color acquired
certain appropriate attributes.

Associations of this character became woven into mythology and thus
became firmly established. Poets have felt these influences of light
and color in nature and have given expression to them in words. They
also have entwined much of the mythology of past civilizations and these
repetitions have helped to establish the expressiveness of light and
color. Early ecclesiasts employed these symbolisms in religious
ceremonies and dictated the garbs of saints and other religious
personages in the paintings which decorated their edifices. Thus there
were many influences at work during the early centuries when intellects
were particularly susceptible through superstition and lack of
knowledge. The result has been an extensive symbolism of light, color,
and darkness.

At the present time it is difficult to separate the innate appeal of
light, color, and darkness from those attributes which have been
acquired through associations. Possibly light and color have no innate
powers but merely appear to have because the acquired attributes have
been so thoroughly established through usage and common consent. Space
does not permit a discussion of this point, but the chief aim is
consummated if the existence of an expressiveness and impressiveness of
light is established. There are many other symbolisms of color and light
which have arisen in various ways but it is far beyond the scope of this
book to discuss them.

Psychological investigations reveal many interesting facts pertaining to
the influence of light and color upon mankind. When choosing color for
color's sake alone, that is, divorced from any associations of usage,
mankind prefers the pure colors to the tints and shades. It is
interesting to note that this is in accord with the preference
exhibited by uncivilized beings in their use of colors for decorating
themselves and their surroundings. Civilized mankind chooses tints and
shades predominantly to live with, that is, for the decoration of his
surroundings. However, civilized man and the savage appear to have the
same fundamental preference for pure colors and apparently culture and
refinement are responsible for their difference in choice of colors to
live with. This is an interesting discovery and it has its applications
in lighting, especially in spectacular and stage-lighting.

It appears to be further established that when civilized man chooses
color for color's sake alone he not only prefers the pure colors but
among these he prefers those near the ends of the spectrum, such as red
and blue. Red is favored by women, with blue a close second, but the
reverse is true for men. It is also thoroughly established that red,
orange, and yellow exert an exciting influence; yellow-green, green, and
blue-green, a tranquilizing influence, and blue and violet a subduing
influence upon mankind. All these results were obtained with colors
divorced from surroundings and actual usage. In the use of light and
color the laws of harmony and esthetics must be obeyed, but the
sensibility of the lighting artist is a satisfactory guide. Harmonies
are of many varieties, but they may be generally grouped into two
classes, those of analogy and those of contrast. The former includes
colors closely associated in hue and the latter includes complementary
colors. No rules in simplified form can be presented for the production
of harmonies in light and color. These simplifications are made only by
those who have not looked deeply enough into the subject through
observation and experiment to see its complexity.

The expressiveness of light finds applications throughout the vast field
of lighting, but the stage offers great opportunities which have been
barely drawn upon. When one has awakened to the vast possibilities of
light, shade, and color as a means of expression it is difficult to
suppress a critical attitude toward the crudity of lighting effects on
the present stage, the lack of knowledge pertaining to the latent
possibilities of light, and the superficial use of this potential
medium. The crude realism and the almost total absence of deep insight
into the attributes of light and color are the chief defects of
stage-lighting to-day. One turns hopefully toward the gallant though
small band of stage artists who are striving to realize a harmony of
lighting, setting, and drama in the so-called modern theater.
Unappreciated by a public which flocks to the melodramatic movie, whose
scenarios produced upon the legitimate stage would be jeered by the same
public, the modern stage artist is striving to utilize the potentiality
of light. But even among these there are impostors who have never
achieved anything worth while and have not the perseverance to learn to
extract some of the power of light and to apply it effectively. Lighting
suffers in the hands of the artist owing to the absence of scientific
knowledge and it is misused by the engineer who does not possess an
esthetic sensibility. Science and art must be linked in lighting.

The worthy efforts of stage artists in some of the modern theaters lack
the support of the producers, who cater to the taste of the public which
pays the admission fees. Apparently the modern theater must first pass
through a period in which financial support must be obtained from those
who are able to give it, just as the symphony orchestra has been
supported for the sake of art. Certainly the time is at hand for
philanthropy to come to the aid of worthy and capable stage artists who
hope to rescue theatrical production from the mire of commercialism.

Those who have not viewed stage-lighting from behind the scenes would
often be surprised at the crudity of the equipment, and especially at
the superficial intellects which are responsible for some of the
realistic effects obtained. But these are the result usually of
experiment, not of directed knowledge. Furthermore, little thought is
given to the emotional value of light, shade, and color. The flood of
light and the spot of light are varied with gaudy color-effects, but how
seldom is it possible to distinguish a deep relation between the
lighting and the dramatic incidents!

[Illustration: Soldiers' and Sailors' Monument

Jeweled portal welcoming returned soldiers




In much of the foregoing discussion the present predominating theatrical
productions are not considered, for the lighting effects are good enough
for them. Many ingenious tricks and devices are resorted to in these
productions, and as a whole lighting is serving effectively enough. But
in considering the expressiveness of light the deeper play is the medium
necessary for utilizing the potentiality of light. These are rare and
unfortunately the stage artist appreciative of the significations and
emotional value of light and color is still rarer.

The equipment of the present stage consists of footlights, side-lights,
border-lights, flood-lights, spot-lights, and much special apparatus.
One of the severest criticisms of stage-lighting from an artistic point
of view may be directed against the use of footlights for obtaining the
dominant light. This is directed upward and the effect is an unnatural
and even a grotesque modeling of the actors' features. The shadows
produced are incongruous, for they are opposed to the other real and
painted effects of light and shade. The only excuse for such lighting is
that it is easily done and that proper lighting is difficult to obtain,
owing to the fact that it involves a change in construction. By no means
should the footlights be abandoned, for they would still be invaluable
in obtaining diffused light even when the dominant light is directed
from above the horizontal. In the present stage-lighting, in which the
footlights generally predominate, the expressiveness of light is not
satisfactory. Perhaps they are a necessary compromise, but inasmuch as
their effect is unnatural they should not be accepted until it is
thoroughly proved that ingenuity cannot eliminate the present defects.

The stage as a whole is a mobile picture in light, shade, and color with
the addition of words and music. Excepting the latter, it is an
expression of light worthy of the same care and consideration that the
painting, which is also an expression of light, receives from the
artist. The scenery and costumes should be considered in terms of the
lighting effects because they are affected by changes in the color of
the light. In fact, the author showed a number of years ago that by
carefully relating the colors of the light with the colors used in
painting the scenery, a complete change of scene can be obtained by
merely changing the color of the light. Rather wonderful dissolving
effects can be produced in this manner without shifting scenery. For
example, a warm summer scene with trees in full foliage under a yellow
light may be changed under a bluish light to a winter scene with ground
covered with snow and trees barren of leaves. But before such
accomplishments can be realized upon the stage, scientific knowledge
must be available behind the scenes.

The art museum affords a multitude of opportunities for utilizing the
expressiveness of light. This is more generally true of sculptured
objects than of paintings because the latter may be treated as a whole.
The artist almost invariably paints a picture by daylight and unless it
is illuminated by daylight it is altered in appearance, that is, it
becomes another picture. The great difference in the appearance of a
painting under daylight and ordinary artificial light is quite
startling, when demonstrated by means of apparatus in which the two
effects may be rapidly alternated. Art museums are supposed to exhibit
the works of artists and, therefore, no changes in these works should be
tolerated if they can be avoided. The modern artificial-daylight lamps
make it possible to illuminate galleries with light at night which
approximates daylight. A further advantage of artificial light is that
it may be easily controlled and a more satisfactory lighting may be
obtained than with natural light. Considering the cost of daylight in
museums and its disadvantages it appears possible that artificial
daylight with its advantages may replace it eventually in the large
galleries. If the works of artists are really prized for their
appearance, the lighting of them is very important.

Sculpture is modeled by light and although it is impossible to ascertain
the lighting under which the sculptor viewed his completed work with
pride and satisfaction, it is possible to give the best consideration to
its lighting in its final place of exhibition. The appearance of a
sculpture depends upon the dominant direction of the light, the
solid-angle subtended by the light-source (skylight, area of sky, etc.)
and the amount of scattered light. The direction of dominant light
determines the general direction of the shadows; the solid-angle of the
light-source affects the character of the edges of the shadows; and the
scattered light accounts for the brightness of the shadows. It should be
obvious that variations of these factors affect the appearance or
expression of three-dimensional objects. Therefore the position of a
sculptured object with respect to the window or other skylight and the
amount of light reflected from the surroundings are important. Visits to
art museums with these factors in mind reveal a gross neglect in the
lighting of objects of art which are supposed to appeal by virtue of
their appearances, for they can arouse the emotions only through the
doorway of vision.

A century ago mankind gave no thought to utilizing the expressive and
impressive powers of light except in religious ceremonies. It was not
practicable to utilize light from the feeble flames of those days in the
elaborate manner necessary to draw upon these powers. Man was concerned
with the more pressing needs. He wanted enough light to make the winter
evenings endurable and the streets reasonably safe. The artists of those
days saw the wonderful expressions of light exhibited by Nature, but
they dared not dream of rivaling these with artificial light. To-day
Nature surpasses man in the production of lighting effects only in
magnitude. Man surpasses her artistically. In fact, the artist becomes a
master only when he can improve upon her settings; when he is able by
rare judgment in choosing and in eliminating and by skill and ingenuity
to substitute a complete harmony for her incomplete and unsatisfactory
reality. But everywhere Nature is the great teacher, for her world is
full of an everchanging infinitude of expressions of light. Mankind
needs only to study these with an attuned sensibility to be able
eventually to play the music of light for those who are blessed with an
esthetic sense.



In the home artificial light exerts its influence upon every one.
Without artificial lighting the family circle may not have become the
important civilizing influence that it is to-day. Certainly civilized
man now shudders at the thought of spending his evenings in the light of
the fire upon the hearth or of a burning splinter.

The importance of artificial light is emphatically impressed upon the
householder when he is forced temporarily to depend upon the primitive
candle through the failure of the modern system of lighting. He flees
from his home to that of his more fortunate neighbor, or he retires in
his helplessness to awaken in the morning with a blessing for daylight.
He cannot conceive of happiness and recreation in the homes of a century
or two ago, when a few candles or an oil-lamp or two were the sole
sources of light. But when the electric or gas service is again restored
he relapses shortly into his former placid indifference toward the
wonderfully efficient and adequate artificial light of the present age.

Until recently artificial light was costly and the householder in common
with other users of light did not concern himself with the question of
adequate and artistic lighting. His chief aim was to utilize as little
as possible, for cost was always foremost in his mind. The development
of the science of light-production has been so rapid during the past
generation that adequate, efficient, and cheap artificial light finds
mankind unconsciously viewing lighting with the same attitude as he
displays toward his food and fuel bills. Another consequence of this
rapid development is that mankind does not know how to extract the joy
from modern artificial light. This is readily demonstrated by analyzing
the lighting of middle-class homes.

The cost of light has been discussed in another chapter and it has been
shown that it has decreased enormously in a century. It is now the most
potential agency in the home when viewed from the standpoint of cost.
The average householder pays less than twenty dollars per year for
ever-ready light throughout his home. For about five cents per day the
average family enjoys all the blessings of modern lighting, which is
sufficient proof that cost is an insignificant item.

In order to simplify the discussion of lighting the home the terminology
of electric-lighting will be used. The principles expounded apply as
well to gas as to electricity, and owing to the ingenuity of the
gas-lighting experts, the possibilities of gas-lighting are extensive
despite its handicaps. There are some places in the home, such as the
kitchen and basement, where lighting is purely utilitarian in the narrow
sense, but in most of the rooms the esthetic or, more broadly, the
psychological aspects of lighting should dominate. Pure utility is
always a by-product of artistic lighting and furthermore, the lighting
effects will be without glare when they satisfy all the demands of

In dealing with lighting in the home the householder should concentrate
his attention upon lighting effects. Unfortunately, he is not taught to
do so, for everywhere he turns for help he finds the discussion directed
toward fixtures and lamps instead of toward lighting effects. However,
these are merely links in the chain from the meter to the eye. Lamps are
of interest from the standpoint of quantity and quality of light, and
fixtures are of importance chiefly as distributers of light. These
details are merely means to an end and the end is the lighting effect.
Of course, the fixtures are more important as objects than the wires
because they are visible and should harmonize with the general
decorative and architectural scheme.

The home is the theater of life full of various moods and occasions;
hence the lighting of a home should be flexible. A degree of variety
should be possible. Controls, wiring, outlets, and fixtures should
conspire to provide this variety. At the present time the average
householder does not give much attention to lighting until he purchases
fixtures. It is probable that he thought of it when he laid out or
approved the wiring, but usually he does not consider it seriously until
he visits the fixture-dealer to purchase fixtures. And then
unfortunately the fixture-dealer does not light his home; he does not
sell the householder lighting-effects designed to meet the requirements
of the particular home; he sells merely fixtures.

Unfortunately there are few fixtures available which have definite aims
in lighting as demanded by the home. Of the great variety of fixtures
available there are many artistic objects, but it is obvious that little
attention is given to their design from the standpoint of lighting.
That the fixture-dealer usually thinks of fixtures as objects and gives
little or no thought to lighting effects is apparent from his
conversation and from his display. He exhibits fixtures usually en masse
and seldom attempts to illustrate the lighting effects produced in the

The foregoing criticisms are presented to emphasize the fact that
throughout the field of lighting the great possibilities which have been
opened by modern light-sources are not fully appreciated. The point at
which to begin to design the lighting for a home is the wiring.
Unfortunately this is too often done by a contractor who has given no
special thought to the possibilities of lighting and to the requirements
in wiring and switches necessary in order to realize them. At this point
the householder should attempt to form an opinion as to the relative
values. Is artificial lighting important enough to warrant an
expenditure of two per cent. of the total investment in the home and its
furnishings? The answer will depend upon the extent to which artificial
light is appreciated. It appears that four or five per cent. is not too
much if it is admitted that the artificial lighting system ranks next to
the heating plant in importance and that these two are the most
important features of an interior of a residence. A switch or a
baseboard outlet costs an insignificant sum but either may pay for
itself many times in the course of a few years through its utility or

It appears best to take up this subject room by room because the
requirements vary considerably, but in order to be specific in the
discussions, a middle-class home will be chosen. The more important
rooms will be treated first and various simple details will be touched
upon because, after all, the proper lighting of a home is realized by
attention to small details.

The living-room is the scene of many functions. It serves at times for
the quiet gathering of the family, each member devoted to reading. At
another time it may contain a happy company engaged at cards or in
conversation. The lighting requirements vary from a spot or two of light
to a flood of light. Excepting in the small living-rooms there does not
appear to be a single good reason for a ceiling fixture. It is nearly
always in the field of vision when occupants are engaged in
conversation, and for reading purposes the portable lamp of satisfactory
design has no rival. Wall brackets cannot supply general lighting
without being too bright for comfort. If they are heavily shaded they
may still emit plenty of light upward, but the adjacent spots on the
walls or ceiling will generally be too bright. Wall brackets may be
beautiful ornaments and decorative spots of light and have a right to
exist as such, but they cannot be safely depended upon for adequate
general lighting on those occasions which demand such lighting.

As a general principle, it is well to visualize the furniture in the
room when looking at the architect's drawings and it is advantageous
even to cut out pieces of paper representing the furniture in scale. By
placing these on the drawings the furnished room is readily visualized
and the locations of baseboard outlets become evident. It appears that
the best method of lighting a living-room is by means of decorative
portable lamps. Such lamps are really lighting-furniture, for they aid
in decorating and in furnishing the room at all times. A number of these
lamps in the living-room insures great flexibility in the lighting, and
the light may be kept localized if desired so that the room is restful.
A room whose ceiling and walls are brilliantly illuminated is not so
comfortable for long periods as one in which these areas are dimly
lighted. Furthermore, the latter is more conducive to reading and to
other efforts at concentration. The furniture may be readily shifted as
desired and the portable lamps may be rearranged.

Such lighting serves all the purposes of the living-room excepting those
requiring a flood of light, but it is easy to conceal elaborate lighting
mechanisms underneath the shades of portable lamps. Several types of
portable lamps are available which supply an indirect component as well
as direct light. The former illuminates the ceiling with a flood of
light without any discomforting glare. Such a lighting-unit is one of
the most satisfactory for the home, for two distinct effects and a
combination of these introduce a desirable element of variety into the
lighting. Not less than four and preferably six baseboard outlets should
be provided in a living-room of moderate size. One outlet on the mantel
is also to be desired for connecting decorative candlesticks, and
brackets above the fireplace are of ornamental value. Although the
absence of ceiling fixtures improves the appearance of the room, wiring
may be provided for ceiling outlets in new houses as a matter of
insurance against the possible needs of the future. When ceiling
fixtures are not used, switches may be provided for the mantel brackets
or certain baseboard outlets in order that light may be had upon
entering the room.

The merits of a portable lamp may be ascertained before purchasing by
actual demonstration. Some of them are not satisfactory for
reading-lamps, owing to the shape of the shade or to the position of the
lamps. The utility of a table lamp may be determined by placing it upon
a table and noting the spread of light while seated in a chair beside
it. A floor lamp may also be tested very easily. A miniature floor lamp
about four feet in height with an appropriate shade provides an
excellent lamp for reading purposes because it may be placed by the side
of a chair or moved about independent of other furniture. A tall floor
lamp often serves for lighting the piano, but small piano lamps may be
found which are decorative as well as serviceable in illuminating the
music without glare.

The dining-room presents an entirely different problem for the setting
is very definite. The dining-table is the most important area in the
room and it should be the most brilliantly illuminated area in the room.
A demonstration of this point is thoroughly convincing. The decorator
who designs wall brackets for the dining-room is interested in beautiful
objects of art and not in a proper lighting effect. The fixture-dealer,
having fixtures to sell and not recognizing that he could fill a crying
need as a lighting specialist, is as likely to sell a semi-indirect or
an indirect lighting fixture as he is to provide a properly balanced
lighting effect with the table brightly illuminated. The indirect and
semi-indirect units illuminate the ceiling predominantly with the
result that this bright area distracts attention from the table. A
brightly illuminated table holds the attention of the diners. Light
attracts and a semi-darkness over the remainder of the room crowds in
with a result that is far more satisfactory than that of a dining-room
flooded with light.

The old-fashioned dome which hung over the dining-table has served well,
for it illuminated the table and left the remainder of the room dimly
lighted. But its wide aperture made it necessary to suspend it rather
low in order that the lamps within should not be visible. It is an
obtrusive fixture and despite its excellent lighting effect, it went out
of style. But satisfactory lighting principles never become antiquated,
and as taste in fixtures changes the principles may be retained in new
fixtures. Modern domes are available which are excellent for the
dining-room if the lamps are well concealed. The so-called showers are
satisfactory if the shades are dense and of such shape as to conceal the
lamps from the eyes. Various modifications readily suggest themselves to
the alert fixture-designer. Even the housewife can do much with silk
shades when the principle of lighting the dining-table is understood.
The so-called candelabra have been sold extensively for dining-rooms and
they are fairly satisfactory if equipped with shades which reflect much
of the light downward. Semi-indirect and indirect fixtures have many
applications in lighting, but they do not provide the proper effect for
a dining-room.

It is easy to make a special fixture which will send a component of
light downward to the table and will permit a small amount of diffused
light to the ceiling and walls. If a daylight lamp is used for the
direct component, the table will appear very beautiful. Under this light
the linen and china are white, flowers and decorations on the china
appear in their full colors, the silver is attractive, and the various
color-harmonies such as butter, paprika, and baked potato are enticing.
This is an excellent place for a daylight lamp if diffused light
illuminating the remainder of the room and the faces of the diners is of
a warm tone obtained by warm yellow lamps or by filtering these
components of the light through orange shades. The ceiling fixture
should be provided with two circuits and switches. In some cases it is
easy to provide a dangling plug for connecting such electric equipment
as a toaster, percolator, or candlesticks. Two candlesticks are
effective on the buffet, but usually the smallest normal-voltage lamps
available give too much light. Miniature lamps may be used with a small
transformer, or two regular lamps may be connected in series. At least
two baseboard outlets are convenient.

The foregoing deals with the more or less essential lighting of a
dining-room, but there are various practicable additional lighting
effects which add much charm to certain occasions. Colored light of low
intensity obtained from a cove or from "flower-boxes" fastened upon the
wall is very pleasing. If a cove is provided around the room, two
circuits containing orange and blue lamps respectively will supply two
colors widely differing in effect. By mixing the two a beautiful rose
tint may be obtained. This equipment has been installed with much
satisfaction. A simpler method of obtaining a similar effect is to use
imitation flower-boxes plugged into wall outlets. Artificial foliage
adds to the charm of these boxes. The colored light is merely to add
another effect on special occasions and its intensity should never be
high. In the dining-room such unusual effects are not out of place and
they need not be garish.

The sun-room partakes of the characteristics of the living-room to some
extent, but, it being smaller, a semi-indirect fixture may be
satisfactory for general illumination. However, a portable lamp which
supplies an indirect component of light besides the direct light serves
admirably for reading as well as for flooding the room with light when
necessary. Two or three baseboard outlets are desirable for attaching
decorative or even purely utilitarian lamps. The sun-room is an
excellent place for utilizing "flower-box" fixtures decorated with
artificial foliage. In fact, a central fixture may assume the appearance
of a "hanging basket" of foliage. The library and den offer no problems
differing from those already discussed in the living-room. A careful
consideration of the disposition of the furniture will reveal the best
positions for the outlets. In a small library wall brackets may serve as
decorative spots of light and if the shades are pendent they may serve
as lamps for reading purposes. In both these rooms an excellent
reading-lamp is desired, but it may be decorative as well. Wall outlets
may be desired for decorative portable lamps upon the bookcases.

The sleeping-room, which commonly is also a dressing-room, often
exhibits the errors of a lack of foresight in lighting. In most rooms of
this character there is one best arrangement of furniture and if this
is determined it is easy to ascertain where the windows and outlets
should be located. The windows may usually be arranged for twin beds as
well as for a single one with obvious advantages of flexibility in
arrangement. With the position of the bureau determined it is easy to
locate outlets for two wall brackets, one on each side, about sixty-six
inches above the floor and about five feet apart. When the brackets are
equipped with dense upright shades, the figure before the mirror is well
illuminated without glare and sufficient light reaches the ceiling to
illuminate the whole room.

A baseboard outlet should be available for small portable lamps which
may be used upon the bureau or for electric heating devices. The same is
true for the dressing-table; indeed, two small decorative lamps on the
table serve better than high wall brackets owing to the fact that the
user is seated. A baseboard outlet near the head of the bed or between
the beds is convenient for a reading-lamp and for other purposes. An
outlet in the center of the ceiling controlled by a convenient switch
may be installed on building, as insurance against future needs or
desires. But a single lighting-unit in the center of the ceiling does
not serve adequately the needs at the bureau and dressing-table. In
fact, two wall brackets properly located with respect to the bureau
afford a lighting much superior for all purposes in the bedroom to that
produced by a ceiling fixture.

In the bath-room the principal problem is to illuminate the person,
especially the face, before the mirror. Many mistakes are made at this
point, despite the simplicity of the solution. In order to see the
image of an object in a mirror, the object must be illuminated. It is
best to do this in a straightforward manner by means of a small
lighting-unit on each side of the mirror at a height of five feet. Both
sides of the face will be well illuminated and the light-sources are low
enough to eliminate objectionable shadows. The units may be merely
pull-chain sockets containing frosted or opal lamps. A center bracket or
a single unit suspended from the ceiling is not as satisfactory as the
two brackets. These afford enough light for the entire bath-room. A
baseboard or wall outlet is convenient for connecting a heater,
curling-iron, and other electrically heated devices.

The sewing-room, which in the middle-class home is usually a small room,
is sometimes used as a bedroom. A ceiling fixture will supply adequate
general lighting, but a baseboard outlet should be available for a short
floor lamp or a table lamp for sewing purposes. An intense local light
is necessary for this occupation, which severely taxes the eyes. A
so-called daylight lamp serves very well in this case.



Towering shafts of light defy the darkness and thousands of lighted
windows symbolize man's successful struggle against nature]

In the kitchen the wall brackets are easily located after the positions
of the range, work-table, sink, etc., are determined. A bracket for each
is advisable unless they are so located that one will serve two
purposes. It is customary to have a combination fixture for gas and
electricity. This is often suspended from the center of the ceiling, but
inasmuch as the gas-light cannot be close to the ceiling, the fixture
extends so far downward as to become a nuisance. Furthermore, a
light-source hung low from the center of the ceiling is in such a
position that the worker in the kitchen usually works in his shadow. If
a ceiling outlet is used it should be an electrical socket at the
ceiling. The combination fixture is best placed on the wall as a
bracket. The so-called daylight lamps are valuable in the kitchen.

In the basement a generous supply of ceiling outlets adds much to the
satisfaction of a basement. One in each locker, one before the furnace,
and a large daylight lamp above but to one side of the laundry trays are
worth many times their cost. Furthermore, a wall socket for the electric
iron and washing-machine is a convenience very much appreciated.

In the stairways convenient three-way switches for each of the ceiling
fixtures represents the best practice. A baseboard outlet in the upper
hall affords a connection for a decorative lamp and pays for itself many
times as a place to attach the vacuum-cleaner from which all the rooms
on that floor may be served. In vestibules and on porches ceiling
fixtures controlled by means of convenient switches are satisfactory.
The entrance hall may be made to express hospitality by means of
lighting which should be adequate and artistic.

An adequate supply of outlets and wall switches is not costly and they
pay generous dividends. With a scanty supply of these, the possibilities
of lighting are very much curtailed. There is nothing intricate about
locating switches and outlets, so the householder may do this himself,
or he may view critically the plans as submitted. The chief difficulties
are to throw aside his indifference and to readjust his ideas and
values. It may be confidently stated that the possibilities of lighting
far outrank most of the features which contribute to the cost of a house
and of its furnishings.

After considering the requirements and decorative schemes of the various
rooms the householder should be competent to judge the appropriateness
of the lighting effects obtained from fixtures which the dealer
displays, but he should insist upon a demonstration. If the dealer is
not equipped with a room for this purpose, he should be asked to
demonstrate in the rooms to be lighted. If the fixture-dealer does not
realize that he should be selling lighting effects, the householder
should make him understand that lighting effects are of primary
importance and the fixtures themselves are of secondary interest in most
cases. The unused outlets that have been installed for possible future
needs may be sealed in plastering if the positions are marked so that
they may be found when desired.

An advantage of portable lamps is that they may be taken away on moving.
In fact, when lighting is eventually considered a powerful decorative
medium, as it should be, it is probable that fixtures will be personal
property attached to ceiling, wall, and floor outlets by means of plugs.

A variety of incandescent lamps are available. For the home, opal,
frosted, or bowl-frosted lamps are usually more satisfactory than clear
lamps. Bare filaments should not be visible, for they not only cause
discomfort and eye-strain but they spoil what might otherwise be an
artistic effect. Lamps with diffusing bulbs do much toward eliminating
harsh shadows cast by the edges of the shades, by the chains of the
fixtures, etc. These lamps are available in many shapes and sizes and
the householder should make a record of voltage, wattage, and shape of
the lamps which he finds satisfactory in the various fixtures. The Mazda
daylight lamp has several places in the home and the Mazda white-glass
and other high-efficiency lamps supply many needs better than the vacuum
lamps. In brackets and other purely decorative lighting-units small
frosted lamps are usually the most satisfactory. There is a general
desire for the warm yellowish light of the candle-flame, and this may be
obtained by a tinted shade but usually more satisfactorily by means of a
tinted lamp.

The householder will find it interesting to become intimate with
lighting, for it can serve him well. The housewife will often find much
interest in making shades of textiles and of parchment. Charming
glassware in appropriate tints and painted designs is available for all
rooms. In the bedchamber and the nursery some of these painted designs
are exceedingly effective. Fixtures should shield the lamps from the
eyes, and the diffusing media whether glass or textile should be dense
enough to prevent glare. No fixture can be beautiful and no lighting
effect can be artistic if glare is present. If the architect and the
householder will realize that light is a medium comparable with the
decorator's media, better lighting will result. Light has the great
advantage of being mobile and with adequate outlets and controls
supplemented by fixtures from which different effects are available, the
householder will find in lighting one of the most fruitful sources of
interest and pleasure. It can do much toward expressing the taste of
the householder or if neglected it can undo much of the effect of
excellent decoration and furnishing. Artificial lighting, softly
diffused and properly localized, is one of the most important factors in
making a house a home.



In the preceding chapters the progress of light has been sketched from
its obscure infancy to its vigorous youth of the present time. It has
been seen that progress was slow until the beginning of the nineteenth
century, after which it began to gain momentum until the present century
has witnessed tremendous advances. Until the latter part of the
nineteenth century artificial light was considered an expensive utility,
but as modern lamps appeared which supplied adequate light at reasonable
cost attention began to be centered upon utilization, and the lighting
engineer was born. Gradually it is being realized that artificial light
is no longer a luxury, that it may be used in great quantity, and that
it may be directed, diffused, and altered in color as desired. Although
the potentiality of light has been barely drawn upon, the present usages
surpass the most extravagant dreams of civilized beings a half-century
ago. Mere light of that time was changed into more light as gas-lighting
developed, and more light has increased to adequate light of the present
time through the work of scientists.

It is apparent that a sudden enforced reversion to the primitive flames
of fifty years ago would paralyze many activities. Much of interest and
beauty would be blotted out of this brilliant, pulsating, productive
age. It is startling to note that almost the entire progress in
artificial lighting has taken place during the past hundred years and
that most of it has been crowded into the latter part of this period. In
fact, its development since it began in earnest has gone forward with
ever-increasing momentum. On viewing the wonders of modern artificial
lighting on every hand it is not difficult to muster the courage
necessary to venture into its future.

The lighting engineer has been a natural evolution of the present age,
for the economic aspects of lighting have demanded attention. He is
increasing the safety, efficiency, and happiness of mankind and
civilization is beginning to feel his influence economically. However,
with the advent of adequate, efficient, and controllable light, the
potentiality of light as an artistic medium may be drawn upon and the
lighting artist with a deep insight into the possibilities of artificial
light now has his opportunity. But the artist who believes that a new
art may be evolved to perfection in a few years is doomed to
disappointment, for it is necessary only to view retrospectively such
arts as painting and music to be convinced that understanding and
appreciation develop slowly through centuries of experiment and contact.

Will lighting ever become a fine art? Will it ever be able alone to
arouse emotional man as do the fine arts? Are the powers of light
sufficiently great to enthrall mankind without the aid of form, music,
action, or spoken words? It is safer to answer "yes" than "no" to these
questions. Painting has reached a high place as an art and this art is
the expressiveness of secondary or reflected light reinforced by
imitation forms, which by a combination of light and drawing comprise
the "subjects." A painting is a momentary expression of light, a
cross-section of something mobile, such as nature, thought, or action.
Light has the essential qualifications of painting with the advantages
of a greater range of brightness, of greater purity of colors, and the
great potentiality of mobility. If lighting becomes a fine art it will
doubtless be related to painting somewhat in the same manner that
architecture is akin to sculpture. With the introduction of mobility it
will borrow something from the arts of succession and especially from

The art of lighting in its present infancy is leaning upon established
arts, just as the infant learns to walk alone by first depending upon
support. The use of color in painting developed slowly, being supported
for centuries by the strength of drawing or subject. The landscapes of a
century ago were dull, for color was employed hesitatingly and
sparingly. The colors in the portraits of the past merely represented
the gorgeous dress of bygone days. But the painter of the present shows
that color is beginning to be used for itself and that the painter is no
longer hesitant concerning its power to go hand in hand with drawing.
Drafting and coloring are now in partnership, the former having given up
guardianship when the latter reached maturity.

Lighting is now an accompaniment of the drama, of the dance, of
architecture, of decoration, and of music. It has been a background or a
part of the "atmosphere" excepting occasionally when some one with
imagination and daring has given it the leading rôle. Even in its
infancy it has on occasions performed admirably almost without any aid.
The bursting rocket, the marvelous effects at the Panama-Pacific
Exposition, and some of the exhibitions on the theatrical stage are
glimpses of the potentiality of light. To fall back upon the terminology
of music, these may be glimmerings of light-symphonies.

Harmony is simultaneity and a painting in this respect is a chord--a
momentary expression fixed in material media. A melody of light requires
succession just as the melody in music. The restless colors of the opal
comprise a light melody like the songs of birds. The gorgeous splendor
of the sunset compares in magnitude and in its various moods with the
symphony orchestra and its powers. Throughout nature are to be found
gentle chords, beautiful melodies and powerful symphonies of light and
this music of light exhibits the complexity and structure analogous to
music. There is no physical relation between music, poetry, and light,
but it is easy to lean upon the established terminology for purposes of
discussion. Those who would build color-music identical to sound music
are making the mistake of starting with a physical foundation instead of
basing the art of light-expression upon psychological effects of light.
In other words, a relation between light and music can exist only in the
psychological realm.

These melodies and symphonies of light in nature are admittedly pleasing
or impressive as the case may be, but are they as appealing as music,
poetry, painting, or sculpture? The consensus of opinion of a large
group of average persons might indicate a negative reply, but the
combined opinion of this group is not so valuable as the opinion of a
colorist or of an artist who has sensed the wonders of light. The
unprejudiced opinion of artists is that light is a powerfully expressive
and impressive medium. The psychologist will likely state that the
emotive value of light or color is not comparable to the appeal of an
excellent dinner or of many other commonplace things. But he has
experimented only with single colors or with simple patterns and his
subjects are selected more or less at random from the multitude. What
would be his conclusion if he examined painters and others who have
developed their sensibilities to a deep appreciation of light and color?
It is certain that the painter who picks up a purple petal fallen from a
rose and places it upon a green leaf is as thrilled by the powerful
vibrant color-chord as the musician who hears an exquisite harmony of

Music has been presented to civilized mankind in an organized manner for
ages and the fundamental physical basis of modern music is a thousand
years old. Would the primitive savage appreciate the modern symphony
orchestra? Even the majority of civilized beings prefer the modern
ragtime or jazz to the exquisite art of the symphony. An appreciation of
the opera and the symphony is reached by educational methods extending
over long periods. An appreciation of the expressiveness of light cannot
be expected to be realized by any short-cut. Most persons to-day enjoy
the melodramatic "movie" more than the drama and relatively few
experience the deep appeal of the fine arts. Surely the symphony of
light cannot be justly condemned because of a lack of appreciation and
understanding of it, for it has not been introduced to the public.
Furthermore, the expressiveness of music is still indefinite at best
despite the many centuries of experimenting on the part of musicians.

If poetry is to be believed, the symphonies of light as rendered by
nature in the sunsets, in the aurora borealis, and in other sky-effects
of great magnitude have deeply impressed the poet. If his descriptions
are to be accepted at their face-value, the melodies of light rendered
in the precious stone, in the ice-crystal, and in the iridescence of
bird-plumage please his finer sensibilities. If he is sincere, mobile
light is a seductive agency.

The painter has contributed little of direct value in developing the
music of light. He is concerned with an instantaneous expression. He
waits for it patiently and, while waiting, learns to appreciate the
fickleness of mood in nature, but when he fixes one of these moods he
has contributed very little to the art of mobile light. Unfortunately
the art schools teach the student little or nothing pertaining to color
for color's sake. When the student is capable of drawing fairly well and
is acquainted with a few stereotyped principles of color-harmony he is
sent forth to follow in the footsteps of past masters. He may be seen at
the art museum faithfully copying a famous painting or out in the fields
stalking a tree with the hopes of an embryo Corot. The world moves and
has only a position in the rank and file for imitators. Occasionally an
artist goes to work with a vim and indulges in research, thereby
demonstrating originality in two respects. Painting is just as much a
field for research as light-production.

Recently experiments are being made in the production of color-harmonies
devoid of form. Surely there is a field for pure color-composition and
this the field of the painter which leads toward the art of mobile
light. Many of the formless paintings of the present day which pass
under the banner of this _ism_ or that are merely experiments in the
expressiveness of light. Being formless, they are devoid of subject in
the ordinary sense and cannot be more or less than a fixed expression of
light. Naturally they have received much criticism and have been
ridiculed, but they can expect nothing else until they are understood.
They cannot be understood until mankind learns their language and then
they must be understandable. In other words, there are impostors
gathered around the sincere research-artist because the former have
neither the ability to paint for a living nor the inclination to forsake
the comparative safety of the mystery of art for the practical world
where their measure would be quickly taken. This army of camp-followers
will not advance the art of mobile light, but the sincere seekers after
the principles of light-expression who form the foundation of the
various _isms_ may contribute much.

The painter will always be available with his finer sensibility to
appreciate and to aid in developing the art of mobile light, but his
direct contribution appears most likely to come from the present chaos
of experiments in pure color-composition, in the psychology of light,
or, more broadly, in the expressiveness of light. The decorator and the
designer of gowns and costumes do not arrogate to themselves the name
"artist," but they are daily creating something which is leading toward
a fuller appreciation of the expressiveness of light. If they do not
contribute directly to the development of the art of mobile light, they
are at least aiding in developing what may eventually be an appreciative

The artist paints a "still-life," the decorator creates a color-harmony
of abstract or conventional forms, and the costumer produces a
color-composition in textiles. The decorator and costumer approach
closer to pure color-composition than the artist in his still-life. The
latter is a grouping of objects primarily for their color-notes. Why
bother with a banana when a yellow-note is desired? Why utilize the
abstract or conventional forms of the decorator? Why not follow this
lead further to the less definite forms employed by the costumer? Why
not eliminate form even more completely? This is an important point and
an interesting lead, for to become rid of form has been one of the
perplexing problems encountered by those who have dreamed of an art of
mobile light.

The painter who uses line and color imitatively has perhaps acquired
skill in depicting objects and more or less appreciation of the
beautiful. But if he is to be creative and to produce a higher art he
must be able to use line and color without reference to objects. He thus
may aid in the development of an abstract art which is the higher art
and at the same time aid in educating the public to appreciate pure
color-harmonies. From these momentary expressions of light and from the
experience gained, the mobile colorist would receive material aid and
his productions would be viewed by a more receptive audience or rather
"optience" as it may be called. The development of taste for abstract
art is needed in order that the art of mobile light may develop and,
incidentally, an appreciation of the abstract in art is needed in all

Science has contributed much by way of clearing the decks. It has
produced the light-sources and the apparatus for controlling light. It
has analyzed the physical aspects of color-mixture and has accumulated
extensive data pertaining to color-vision. It has pointed out pitfalls
and during recent years has been delving further by investigating the
psychology of light and color. The latter field is looked to for
valuable information, but, after all, there is one way of making
progress in the absence of data and that is to make attempts at the
production of impressive effects of mobile light. Some of these have
been made, but unfortunately they have been heralded as finished

Perhaps the most general mistake made is in relating sounds and colors
by stressing a mere analogy too far. Notwithstanding the vibratory
nature of the propagation of sound and light, this is no reason for
stressing a helpful analogy. After all it is the psychological effect
that is of importance and it is absurd to attribute any connection
between light-waves and sound-waves based upon a relation of physical
quantities. No space will be given to such a relation because it is so
absurdly superficial; however, the language of music will be borrowed
with the understanding that no relation is assumed.

A few facts pertaining to vision will indicate the trend of developments
necessary in the presentation of mobile light. The visual process
synthesizes colors and at this point departs widely from the auditory
process. The sensation of white may be due to the synthesis of all the
spectral colors in the proportions in which they exist in noon sunlight
or it may be due to the synthesis of proper proportions of yellow and
blue, of red, green, and blue, of purple and green, and a vast array of
other combinations. A mixture of red and green lights may produce an
exact match for a pure yellow. Thus it is seen that the mixture of
lights will cause some difficulty. For example, the components of a
musical chord may be picked out one by one by the trained ear, but if
two or more colored lights are mixed they are merged completely and the
resultant color is generally quite different from any of the components.
In music of light, the components of color-chords must be kept
separated, for if they are intermingled like those of musical chords
they are indistinguishable. Therefore, the elements of harmony in mobile
light must be introduced by giving the components different spatial

The visual process is more sluggish than the auditory process; that is,
lights must succeed each other less rapidly than musical notes if they
are to be distinguished separately. The ear can follow the most rapid
execution of musical passages, but there is a tendency for colors to
blend if they follow one another rapidly. This critical frequency or
rate at which successive colors blend decreases with the brightness of
the components. If red and green are alternated at a rate exceeding the
critical frequency, a sensation of yellow will result; that is, neither
component will be distinguishable and a steady yellow or a yellow of
flickering brightness will be seen. The hues blend at a lower frequency
than the brightness components of colors; hence there may be a blend of
color which still flickers in brightness. Many weird results may be
obtained by varying the rate of succession of colors. If this rate is so
low that the colors do not tend to merge, they are much enriched by
successive contrast. It is known that juxtaposed colors generally enrich
one another and this phenomenon is known as simultaneous contrast.
Successive contrast causes a similar effect of heightened color.

An effect analogous to dynamic contrast in music may be obtained with
mobile light by varying the intensity of the light or possibly the area.
Melody may be simply obtained by mere succession of lights. Tone-quality
has an analogy in the variation of the purity of color. For example, a
given spectral hue may be converted into a large family of tints by the
addition of various amounts of white light. Rhythm is as easily applied
to light as to music, to poetry, to pattern, or to the dance, but in
mobile lights its limitations already have been suggested. However, it
is bound to play an important part in the art of mobile light because
rhythmic experiences are much more agreeable than those which are
non-rhythmic. Rhythm abounds everywhere and nothing so stirs mankind
from the lowliest savage to the highly cultivated being as rhythmic

Many psychological effects of light have been recorded from experiment
and observation and affective values of light have been established in
various other byways. It is possible that the degree of pleasure
experienced by most persons on viewing a color-harmony or the delightful
color-melody of a sunlit opal may be less than that experienced on
listening to the rendition of music. However, if this were true it would
offer no discouragement, because absolute values play a small part in
life. Two events when directly compared apparently may differ enormously
in their ability to arouse emotions, but the human organism is so
adaptive that each in its proper environment may powerfully affect the
emotions. For example, those who have sported in aërial antics in the
heights of cloudland or have stormed the enemy's trench are still
capable of enjoying a sunset or the call of a bird to its mate at dusk.
The wonderful adaptability of the inner being is the salvation of art as
well as of life.

In the rendition of mobile light it is fair to give the medium every
advantage. Sometimes this means to eliminate competitors and sometimes
it means to remove handicaps. On the stage light has had competitors
which are better understood. For example, in the drama words and action
are easily understood, and regardless of the effectiveness of light it
would not receive much credit for the emotive value of the production.
In the wonderful harmony of music, dance, and light in certain recent
exhibitions, the dance and music overpowered the effects of lights
because they speak familiar languages.

[Illustration: A community Christmas tree

A community song-festival



Artificial light not only reveals the beauty of decoration and
architecture but enthralls mankind with its own unlimited powers]

A number of attempts have been made to utilize light as an accompaniment
of music and some of them on a small scale have been sincere and
creditable, but a much-heralded exhibition on a large scale a few
years ago was not the product of deep thought and sincere effort. For
example, colored lights thrown upon a screen having an area of perhaps
twenty square feet were expected to compete with a symphony orchestra in
Carnegie Hall. The music reached the most distant auditor in sufficient
volume, but the lighting effect dwindled to insignificance. Without
entering into certain details which condemned the exhibition in advance,
the method of rendition of the light-accompaniment revealed a lack of
appreciation of the problems involved on the part of those responsible.

Incidentally, it has been shown that the composer of this particular
musical selection with its light accompaniment was psychologically
abnormal; that is, he was affected with colored audition. It is not yet
established to what extent normal persons are similarly affected by
light and color. Certainly there is no similarity among the abnormal and
none between the abnormal and normal.

If light is to be used as an accompaniment to music, it must be given an
opportunity to supply "atmosphere." This it cannot do if confined to an
insignificant spot; it must be given extensity. Furthermore, by the use
of diaphanous hangings, form will be minimized and the evanescent
effects surely can be charming. But finally the lighting effects must
fill the field of vision just as the music "fills the field of audition"
in order to be effective. There are fundamental objections to the use of
mobile light as an accompaniment to music and therefore the future of
the art of mobile light must not be allowed to rest upon its success
with music. If it progresses through its relation with music, so much
is gained; if not, the relation may be broken for music is quite capable
of standing alone.

There is a tendency on the part of some revolutionary stage artists to
give to lighting an emotional part in the play, or, in other words, to
utilize lighting in obtaining the proper mood for the action of the
play. Color and purely pictorial effect are the dominant notes of some
of them. All of these modern stage-artists are abandoning the
intricately realistic setting, and, as a consequence, light is enjoying
a greater opportunity. In the more common and shallow theatrical
production, lighting and color effects have many times saved the day,
and, although these effects are not of the deeper emotional type, they
may add a spectacular beauty which brings applause where the singing is
mediocre and the comedy isn't comedy. The potentiality of lighting
effects for the stage has been barely drawn upon, but as the
expressiveness of light is more and more utilized on the stage, the art
of mobile light will be advanced just so much more. Light, color, and
darkness have many emotional suggestions which are easily understood and
utilized, but the blending of mobile light with the action is difficult
because its language is only faintly understood.

It is futile to attempt to describe a future composition of mobile
light. Certainly there is an extensive variety of possibilities. A
sunset may be compressed into minutes or an opalescent sky may be a
motif. Varying intensities of a single hue or of allied hues may serve
as a gentle melody. Realistic effects may be introduced. The
expressiveness of individual colors may be taken as a basis for
constructing the various motifs. These may be woven into melody in which
rhythm both in time and in intensity may be introduced. Action may be
easily suggested and the number of different colors, in a broad sense,
which are visible is comparable to the audible tones. Shading is as
easily accomplished as in music and the development of this art need not
be inhibited by a lack of mechanical devices and light-sources. The
tools will be forthcoming if the conscientious artist requests them.

Whatever the future of the art of mobile light may be, it is certain
that the utilization of the expressiveness of light has barely begun. It
may be that light-music must pass through the "ragtime" stage of
fireworks and musical-revue color-effects. If so, it is gratifying to
know that it is on its way. Certainly it has already served on a higher
level in some of the artistic lighting effects in which mobility has
featured to some extent.

If the art does not develop rapidly it will be merely following the
course of other arts. A vast amount of experimenting will be necessary
and artists and public alike must learn. But if it ever does develop to
the level of a fine art its only rival will be music, because the latter
is the only other abstract art. Material civilization has progressed far
and artificial light has been a powerful influence. May it not be true
that artificial light will be responsible for the development of
spiritual civilization to its highest level? If mobile light becomes a
fine art, it will be man's most abstract achievement in art and it may
be incomparably finer and more ethereal than music. If this is realized,
artificial light in every sense may well deserve to be known as the
torch of civilization.


No attempt will be made to give a pretentious bibliography of the
literature pertaining to the various aspects of artificial lighting, for
there are many articles widely scattered through many journals. _The
Transactions of the Illuminating Engineering Society_ afford the most
fruitful source of further information; the _Illuminating Engineer_
(London), contains much of interest; and _Zeitschrift für
Beleuchtungswesen_ deals with lighting in Germany. H. R. D'Allemagne has
compiled an elaborate "Historie du Luminaire" which is profusely
illustrated, and L. von Benesch in his "Beleuchtungswesen" has presented
many elaborate charts. In both these volumes lighting devices and
fixtures from the early primitive ones to those of the nineteenth
century are illustrated. A few of the latest books on lighting, in the
English language, are "The Art of Illumination," by Bell; "Modern
Illuminants and Illuminating Engineering," by Gaster and Dow;
"Radiation, Light and Illumination," by Steinmetz; "The Lighting Art,"
by Luckiesh; "Illuminating Engineering Practice," consisting of a course
of lectures presented by various experts under the joint auspices of the
University of Pennsylvania and the Illuminating Engineering Society;
"Lectures on Illuminating Engineering," comprising a series of lectures
presented under the joint auspices of Johns Hopkins University and the
Illuminating Engineering Society; and "The Range of Electric Searchlight
Projectors," by Rey; "The Electric Arc," by Mrs. Ayrton; "Electric Arc
Lamps," by Zeidler and Lustgarten, and "The Electric Arc," by Child
treat the scientific and technical aspects of the arc. G. B. Barham has
furnished a book on "The Development of the Incandescent Electric Lamp."
"Color and Its Applications," and "Light and Shade and Their
Applications," are two books by Luckiesh which deal with lighting from
unique points of view. "The Language of Color," by Luckiesh, aims to
present what is definitely known regarding the expressiveness and
impressiveness of color. W. P. Gerhard has supplied a volume on "The
American Practice of Gaspiping and Gas Lighting in Buildings," and Leeds
and Butterfield one on "Acetylene." A recent book in French by V.
Trudelle treats "Lumière Electrique et ses différentes Applications au
Théatre." Many books treat of photometry, power-plants, etc., but these
are omitted because they deal with phases of light which have not been
discussed in the present volume. "Light Energy," by Cleaves, is a large
volume devoted to light-therapy, germicidal action of radiant energy,
etc. References to individual articles will often be found in the
various indexes of publications.



Aaron, 43

Accidents: 8;
  street-lighting in relation to, 225 _et seq._;
  percentage (table) of, due to improper lighting, 231

Acetylene: 62;
  light-yield of, 106, 107, 170, 187, 191

Actinic rays: effect of, upon human organism, 275

Africa, public lighting in ancient, 31

Agni, god of fire, 40

Air-pump, 130

Air-raids, 225

Alaska, 18, 29

Alchemy, 20

Aleutians, 18

Alexandria, 43, 163

Allylene, 106

Aluminum, 108, 179, 180

Amiens, Treaty of, 69

Amylene, 106

Aniline dyes, 106

Animal: distinction between, and human being, 3; 15;
  production of light, 24 _et seq._;
  sources of light, 30, 31;
  oils, 51

Antimony, 294

Antioch, 153

Arago, 114, 196

Archbishop of Canterbury, 49

Archimedes, 19

Arc: lamps, 69, 89;
  electric, 111 _et seq._;
  distinction between spark and, 112;
  Davy's notes on electric, 113;
  formation of, 115, 116;
  Staite and enclosed, 117, 118;
  principle of enclosed, 118, 119;
  types of, 120;
  flame-, 121, 122;
  luminous, 122;
  electric, 127;
  luminous efficiency of electric (table), 124; 160 _et seq._;
  -lamp in lighthouses, 168 _et seq._;
  magnetite-, 187; 261

Ardois system of signaling, 199

Argand, Ami: 52;
  inaugurates new era in artificial lighting, 53, 54; 63, 70, 76, 77, 78,
    97, 167, 196

Argon, 137

Aristophanes, "The Clouds," 19

Art Museums, 9, 13, 322, 323

Asbestos, 170

Asia: public lighting in ancient, 31, 39

Automobiles, 238

Babylon, 39

Bacteria: effect of artificial light upon, 272 _et seq._; 281, 282

Bailey, Prof. L. H., 250

Baltimore, 98

Bamboo: carbon filaments, 169

Bartholdi, 302, 303

Beacons. _See_ Lighthouses.

Beck, 186

Beecher, 72

Beeswax, 35, 51

Benzene, 106

Bible, cited on importance of artificial light, 42-44

"Bluebird, The," Maeterlinck, 9

Blue-prints, 261

Bollman, 98

Bolton, von, 132, 133

Bombs, illuminating, 182 _et seq._

Boston Light, 164, 165, 166, 177

Bowditch, production of regenerative lamp by, 78, 79

Boy Scouts, 17

Bremer, 120

Bristol University, 252

Brush, 68, 159

Building, 8

Bunsen, 81, 85, 89, 148, 149

Bureau of Mines: cited on open flames, 234; 236

Burning-glasses, 19, 20.
  _See also_ Lenses.

Butylene, 106

Byzantium, 34

Cæsar, 163

Canada, 254

Candle-hour, defined, 215

Candles: progress and, 7; 25, 28, 29, 30, 33;
  religious uses of, 34, 35;
  as a modern light-source, 36, 37;
  ceremonial uses of, 38 _et seq._; 44, 48, 57, 82, 97, 222, 299, 304

Calcium, 107, 108

Carbolic acid, 106

Carbon: 53, 80, 81;
  physical characteristics of, 80, 81; 90, 104, 105, 128, 129, 144, 170

Carbon filament: 127 _et seq._;
  preparation of, 129, 130, 131;
  luminous efficiency of, 131, 132;
  lamps, 161;
  lamps in greenhouses, 250 _et seq._

Carbons, formation of, 115, 116

Carbureted hydrogen, 75

Carcel, invention of clockwork lamp by, 54, 55

Cat-gut, 130

Ceria, 85, 101

Charleston, S. C., 185

Charcoal: 113;
  uses of, for electrodes, 115

Chartered Gas Light and Coke Co., London, 74

Chemistry: artificial light and, 256-268

Chicago, 62, 304, 305

Chimneys, 54, 60, 62

China, 19, 31, 32

Chlorate of potash, 22

Christ, 33, 46, 47

Christians, "children of light," 42

Christmas trees, 43, 304

Chromium, 294

Church of England, 49

Cities: economy of artificial lighting in congested, 13

Civilization: effect of artificial light upon, 4 _et seq._;
  fire and, 15

Clark, Parker and, 139

Clayton, Dr.: invention of portable gas-light by, 64;
  quoted, 64, 65;
  experiments of, with coal-gas, 67

Claude, 147

Cleaves, Dr., quoted, 276, 277

Clegg, Samuel: 74;
  gas-lighting accomplishments of, 75, 76

Cleveland, 159

"Clouds, The," Aristophanes, 19

Coal: 32;
  as a light-source, 55;
  supply, 223; 228

Coal-gas: 63 _et seq._;
  public lighting by, developed, 70 _et seq._;
  analytical production of, 103, 104;
  yield of, retort (table), 105;
  analysis of, 106

Coal-mines, 234 _et seq._

Cobalt, 294

Coke, 68, 105

Cologne, 157, 158

Colomb, Philip, 197

Color: 9;
  relation of artificial light to, 284 _et seq._

Colza, 31, 52, 167

Combustion, 82 _et seq._

Commerce, 8, 97

Constantine, 42

Copper, 262, 295

Cornwall, 63

Cotton: 101;
  carbon filaments, 129, 130

Cromartie, 78

Crookes, 90, 146

Crosley, Samuel, improvement of gas-meter by, 76

Crusies, 32

Daguerre, 258

Dancing, 346

Davy, Sir Humphrey: 33, 68, 73;
  first use by, of charcoal for sparking points, 112;
  notes of, on electric arc, 113; 114

Daylight, artificial, 12: 284 _et seq._;
  application of, 287

Daylighting, 12-14

Dollond, 195

Doty, 61, 167

Drake, Col. E. L., discovery of oil in Pennsylvania by, 56

Drummond, Thomas: 171, 185, 196;
  quoted on signaling, 197

Dudgeon, Miss, 251, 252

Dyes, 256, 265

East Indies, 29

Eddystone Light, 166, 167

Edison: and problem of electric incandescent filament lamps, 128 _et seq._;
  quoted on birth of incandescent lamp, 130

Edward I, 274

Edward VI, 49

Efficiency, effect of artificial light upon, 14

Eggs: relation of artificial light to production of, 247, 248

Egypt: 31;
  sacredness of light in ancient, 39; 153, 195

Electric filament: 81, 127 _et seq._:
  approximate value of, lamps (table), 138

Electric pile: construction of, 111; 127

Electricity: 13, 22;
  as a light-source, 57;
  for home-lighting, 62, 84; 87, 89;
  ignition of gas by, 102;
  lighting by, 109 _et seq._

Electromagnetic waves, 68, 86, 87

Electromagnets, 114, 116

Electrodes, 113, 114, 115 _et seq._;
  life of, 122

Elizabeth, Queen, 274

England: 32;
  petroleum discovered in, 56;
  gas-lighting in, 63 _et seq._; 166, 251, 274

Erbia, 85

Esquimaux: 18;
  use of artificial light by, 31

Ethylene, 106

Factories: 13;
  artificial light in, 239 _et seq._

Faraday, 113

Filaments, carbon, 129 _et seq._

Finsen: 273, 274, 275;
  on stimulating action of artificial light, 277; 279, 280

Fire: importance of, to man, 5 _et seq._;
  man's dependence upon, 15;
  mythical origin of, 16;
  making, 17 _et seq._;
  production of, in the stone age, 18;
  in early civilization, 19;
  ancient worship of, 29, 299

Fireflies: 24, 81, 96, 148, 149, 150

"First Men in the Moon, The," H. G. Wells, cited, 148

Fish: artificial light as bait for, 249

Flame-arcs, 120, 121, 122, 187

Flames: 86, 88, 89;
  open, 233, 234 _et seq._

Flint, 33

Fool's gold, 18

Fort Wagner, 185

France: lamps in, 55;
  early gas-light in, 72

Franchot, invention of moderator lamps by, 55

Frankland, 77

Franklin, Benjamin: 165;
  quoted, 210-212; 213

Fresnel, 167, 196

Friction, 16, 17

Gas: 13, 22;
  discovery of coal, 32, 33;
  early uses of, as light-source, 63 _et seq._;
  installment of, pipes in England, 63, 64;
  Shirley's report on Natural, 66, 67;
  first public display of, lighting, 69;
  cost of, lighting, 71;
  first attempt at industrial, lighting, 72;
  first English, company, 74;
  first, explosion, 75;
  house, lighting, 76, 77; 80, 82;
  spectrum of, 90;
  modern, lighting industry, 97 _et seq._;
  origin of lighting by, 98;
  first, works in America, 98;
  growth of, consumption in United States, 99;
  electrical ignition applied to, lighting, 102;
  pressure, 102, 103;
  water, 105;
  carbons in, 106;
  production of Pintsch, 109, 110;
  salts applied to, flames, 120; 157;
  Census Bureau figures on cost of, plants, 221, 222; 224, 341

Gas-burners: 63, 64, 77;
  candle-power of pioneer (table), 79;
  improvements in, 84

Gas-mantle: 61, 81;
  influence of, 99;
  characteristics of, 100 _et seq._; 187

Gas-meter, Clegg's, 76

Gasolene: lamps, 55; 57

Gassiot, 114

Gauss, 196

Geissler, 146

General Electric Company, 132, 135, 136

Germany: development of lamps in, 56;
  early gas-lighting in, 72

Glass, 195, 290 _et seq._

Glowers, 139

Glow-worms, 24

Glycerides, 52

Gold, 293

Gout, 275

Gramme dynamo, 117

Grass: 18;
  carbon filaments, 129

Greece: 39;
  sacred lamps in ancient, 41; 42

Greenhouses, carbon-filament lamps in, 250 _et seq._

Hall of Fame, 134

Happiness, effect of artificial light upon, 14
Hayden and Steinmetz, 253

Health, artificial light in relation to, 269-283

Helium, 89

Hemig, 155

Hemp, 21

Henry, William, 75

Herodotus, 56

Hertz, 68

Hertzian waves, 271

Hewitt, Cooper, produces mercury-arcs, 124, 125

Home: artificial light in relation to, 6;
  lighting, 325 _et seq._

Hindu: light in, ceremonials, 40

Hudson-Fulton Celebration, 306

Huygens, 195

Hydrocarbons, 82

Hydrogen, 81

Illiteracy, artificial light and, 9

Invention, 7, 97

Iowa, 238

Iridium, 129

Iron, 18, 262, 294

Iron pyrites, 18

Italy, 249

Jablochkov: electric candle of, 117

Jamaica, 19

Jandus, 118, 122

Japan: 19;
  use of oil in, 30; 281

Jerusalem, 43

Jews: artificial light among, 40

_Journal_, Paris, quoted, 210-212

Kerosene: 57;
  weight of, lumens, 60; 62, 187, 233

Kitson, platinum-gauze mantle applied by, 61

Laboratories: achievements of, 137

Lamps: 16, 25;
  Roman, 30; 31;
  invention of safety, 33;
  ancient funereal, 39;
  sacred, of antiquity, 41;
  ceremonial, 44;
  scientific development of oil, 51 _et seq._;
  Holliday, 55;
  Carcel, 54, 55;
  Franchot's moderator, 55;
  gasolene, 55;
  development of, in Germany, 56;
  air pressure, 61;
  supremacy of oil, ends, 62;
  Bowditch's, 77, 78; 80, 97;
  mercury-arc, 126;
  electric incandescent filament, 127 _et seq._;
  gem, 132;
  tungsten, 133 _et seq._;
  luminous efficiency (table) of incandescent filament, 141; 299;
  in home, 328-333

Lange, 167

Lard-oil, 51

Lavoisier, 195

Lead, 262, 294

Le Bon, 72

"Legend of Montrose, The," Scott, cited on primitive lighting, 27

Leigh, Edmund, quoted, 226

Lenses, 20, 171 _et seq._

Libanius, quoted, 153, 154

Liberty, Statue of, 301, 302, 303

Libraries, 9

Light: relation of artificial, to progress, 3 _et seq._;
  as a civilizing agency, 3-14;
  primitive man and artificial, 4;
  Milton, quoted on importance of, 5;
  artificial, and science, 7;
  artificial, and industrial development, 8;
  Maeterlinck's tribute to, 9;
  Lincoln's debt to artificial, 9;
  symbolism of, 9, 10;
  therapy, 10;
  in war, 11;
  adaptations of, 12; 13;
  mythical origin of artificial, 16;
  earliest source of, 16;
  production of, in stone age, 18;
  matches as source of, 21;
  animals as, sources, 24, 25;
  primitive sources of, 24-37;
  evolution of artificial, sources, 24-37;
  development, 28 _et seq._;
  early outdoor use of artificial, 28;
  Roman uses of artificial, 30;
  beginning of scientific, 33, 34;
  candles as modern, source, 36, 37;
  symbolism and religious uses of, 38 _et seq._;
  Bible cited on artificial, 42-44;
  in relation to worship, 43, 45, 46;
  Argand's contribution to, 53, 54;
  coal as, source, 55;
  early uses of gas as, source, 63 _et seq._;
  as a public utility, 70;
  first installation of industrial gas, 72;
  science of, production, 80 _et seq._;
  causes of, radiation, 80, 81; 83;
  lime, 84; electric, 89 _et seq._;
  principle of, production, 90, 91;
  sources, 93;
  various gas-burners', supply, 95;
  relative efficiency of, sources, 95, 96;
  in the home, 97;
  influence of, upon science, invention, and commerce, 97 _et seq._;
  yield of acetylene, 106, 107;
  electric, 109;
  influence of gas upon development of artificial, 110;
  development of artificial, 111 _et seq._;
  efforts to improve color of mercury-arc, 125;
  electric-incandescent-filament, 127 _et seq._;
  effect of tungsten, upon, 133 _et seq._;
  of the future, 143-152;
  in warfare, 178-193;
  signaling, 194-207;
  cost of, 208-224;
  and safety, 225 _et seq._;
  improper use of, 229, 230;
  comparison of daylight and artificial, 240;
  reducing action of, 258;
  bactericidal action of, 272 _et seq._;
  modifying, 284 _et seq._;
  spectacular uses of, 298-309;
  expressiveness of, 310-324;
  utility of modern, 325-340;
  evolution of the art of applying, 341-356;
  mobile, 347, 348, 349, 350;
  psychological effect of, 351 _et seq._;
  as an accompaniment to music, 352-354

Light-buoys, 10, 169

Lighthouses: 10, 163-177;
  optical apparatus of, 172 _et seq._

Light-ships, 10, 169

Lighting-systems: comparison of, 12-14

Lime, 84, 107, 108, 294

Lincoln, Abraham, 9

Linen, 18

Link-buoys, 28

Lithopone, 265, 266

Liverpool, 167

Living: comparison of, standards, 238 _et seq._

London, 152, 154, 155, 156, 157, 202

London Gas Light and Coke Company, 74

Lucigen, 61

Lumen-hour: defined, 215

Lumens: 60, 94, 215

Lutheran Church, 49

Lyceum Theatre, London, 73

Maeterlinck, Maurice, 9

Magazines, 8

Magdsick, H. H., 303

Magnesia: 84;
  Nernst's application of, 138

Magnesium, 179, 180

Magnetite arc, 187

Man: distinction between, and animal, 3;
  artificial light and early, 4;
  light-sources of primitive, 25

Manganese, 262, 268, 294

Mangin, 188

Mann, 129

Mantles, 95

Manufacturing, 8

Marconi, 68

Marks, 118

Matches: as light-sources, 21; 22, 82

Maxwell, 68

Mazda lamps, 289, 339

Mecca, 40

Mediterranean Sea, 163

Mercury-arc: Way's, 124; 125, 126;
  quartz, 125, 126;
  attempts to improve color of, light, 125

Middle Ages, 46, 47, 474

Milton, quoted, 5

Mirror, 19

Mohammedans, 40

Moore, Dr. McFarlan, 146, 147

Morality, effect of light upon, 9

Morse code: application of, to light-signaling, 198, 199

Moses, 195

Moving-pictures, 9, 260, 261

Munich, 72

Murdock, William: installment of gas-pipes by, 63; 68, 69, 70;
  quoted on industrial use of artificial, 71; 72, 73, 74, 76, 78, 217, 309

Museums: 13;
  utilization of artificial light by, 322, 323

Music: light as an accompaniment to, 352-354

Mythology, 16

Nantes, 85

Napoleon, 111

Napthalene, 106

National Heat and Light Co., 72, 74

Natural gas, 99

Navesink Light, 206

Nernst, 138, 139

Newspapers, 8

Newton, Sir Isaac: 7;
  quoted on discovery of visible spectrum, 87; 88

New York, 98, 165, 166, 206, 302, 304

Niagara Falls, 108, 306

Nickel, 262

Nielson, 77

Niepce, 258

Niter, 21

Nitrogen, 137

Norfolk, 169

Obesity, 275

Offices, 13

Oil: as a light-source, 29 _et seq._;
  development of, lamps, 51 _et seq._; 155;
  in lighthouse, 165 _et seq._; 222, 224, 299

O'Leary, Mrs., and her lamp, 62

Olive-oil, 51, 52, 167

Orkney Islands, 29, 177

Osmium, 133

Oxygen: relative consumption of, by oil-lamps, 58, 59; 262

Ozone, 262

Painting, 342, 343, 347, 348, 349

Pall Mall, 74

Panama-Pacific Exposition: 304;
  artificial lighting of, 306, 307, 308, 309

Paper: 18;
  carbon filaments, 129, 130

Paraffin, 35, 57

Parker and Clark, 139

Paris: experimental gas-lighting in, 83, 84;
  Volta in, 111; 154, 185, 210, 212, 213

Peckham, John, 195

Pennsylvania: discovery of oil in, 56

Periodic Law, 145

Petroleum: 35, 51, 55;
  discovery of, 56;
  constitution of crude, 57; 58, 214

Pharos, 163

Philadelphia, 98, 99, 157

Phillips and Lee, 70, 72

"Philosophical Transactions of the Royal Society of London," 33;
  quoted on industrial lighting, 63;
  Shirley's report on natural gas in, 66, 67;
  quoted, 87

Phoenicians, 34, 39

Phosphorus, 21

Photo-micrography, 12

Photography: 126;
  early experiments in, 258;
  development of, 259; 291, 292

Picric acid, 106

Pigments, 265

Pintsch: production of, gas, 109, 110, 170

Pitch, 106

Plant-growth: artificial light and, 11, 249 _et seq._

Platinum, 85, 128, 129, 262

Plumbago, 113, 130

Plymouth, 166

Poetry, 346

Police, 162

Potash, chlorate of, 22

Priestley, Professor, quoted, 252

Printing, 8

Progress: influence of fire upon, 15 _et seq._

Prometheus, 16, 41

Propylene, 106

Ptolemy II, 163

Quartz: 18, 19;
  mercury-arcs, 125;
  uses of, 126;
  in skin diseases, 278, 279

Radiators, energy, 88 _et seq._

Radium, 150

Railway Signal Association, 205

Railways: light-signaling applied to, 205

Ramie fiber, 101

Rane, 250, 251

Rare-earth oxides: 85;
  properties of, 88, 99

Recreation, 9

Redruth, 63

Reformation: ceremonial uses of light during the, 48, 49

Rheumatism, 275

Robins, Benjamin, 201

Rome, 30, 32, 34, 39, 41, 42, 44

Röntgen, 270, 280.
  _See also_ X-ray.

Royal Society of London: 33, 63, 66, 67, 70, 73;
  and first gas explosion, 75, 111, 112

Rumford, 167

Rushlights, 28, 33

Russia, 281

Ryan, W. D'A., 306

Safety: artificial light in relation to, 14, 225 _et seq._

Salts: chemical, 88, 89;
  metallic, 120;
  silver, 257, 258

Sandy Hook Light, 165, 166

San Francisco, 304, 306-309

Savages, 3, 15, 17

Sawyer, 129

Scheele, K. W., 133;
  quoted, 257, 258

Schools, 9

Science: light and, 6, 7; 97;
  systematized, 268

Scotland: 26, 31, 32, 48;
  oil industry in, 56

Scott, Sir Walter, cited, 27, 98

Sculpture: artificial light in relation to, 184

Search-lights, 11, 169

Section of Plant Protection, 225, 226

Selenium, 267, 293

Semaphore, 199

Shells: illuminating, 179 _et seq._

Shirley, Thomas: quoted on natural gas, 66, 67

Siemens, 78

Signaling, 194-207

Silicon: filament, 140

Silk: artificial, 101;
  carbon-filaments, 129

Simpson, R. E., 227, 231

Silver, 258, 293

Skin diseases: treatment of, 278, 279, 280

Skylights, 13

Sleep, 8

Smallpox, 274, 275

Smeaton, 166

Soho, 69, 72

South Africa, 129

Sparks: 33, 125

Spectrum: visible, 86;
  Newton quoted on, 87;
  of elements, 89;
  of gases, 90; 120, 121;
  mercury, 124-126

Sperm, 31, 51, 52, 167

Spermaceti, 35, 51

Splinter-holders, 27, 28

Stage: and artificial light, 319 _et seq._; 343

Staite, 117, 118

Stearine, 35, 52

Stearn, 129

Steel, 18, 33

Steinmetz, Hayden and, 253

Sterilization: quartz-mercury-arc and, 280, 281, 282

Stevenson, Robert Louis, quoted, 177

Stores, 13

St. Paul, 43

St. Paul's Cathedral, 300

Street-lighting: development of, 152-162

Sugar, 22

Sulphide of iron, 18

Sulphur, 18, 21, 179, 180, 294

Sulphuric acid, 21, 22

Sun, 8, 16, 19, 20

Swan, 129

Syracuse, 19

Syria, 153

Tallow, 34, 35, 51, 52

Tantalum: 132;
  filament lamps, 133

Tar, 68, 106

Telegraphy, 195

Telephony, 194

Textiles, 256

Thames, 169

Theaters, 9, 319 _et seq._

Thoria, 85

Tin, 262

Tinder-boxes, 18, 19, 22

Travelers Insurance Company, 227

Trees, 26

Troy, 42

Tuberculosis, 273

Tungsten lamp, 161 _et seq._, 187, 261, 290, 303

Typhus, 273

Ultra-violet rays: 126, 150;
  in photographic electricity, 267, 268; 270, 272, 294

United States: petroleum in, 57;
  gas-consumption in, 99; 164, 165, 166

United States Geological Survey, cited on sale of gas, 222

United States Military Intelligence, 225, 226

Vacuum tubes, 81, 286

Venetians, 195

Ventilation, 13

Verne, Jules, 143

Vestal Virgins, 42

Volcanoes, 166

Volta, 111, 112, 127

Voltaic pile: construction of, 111, 127

Von Bolton. _See_ Bolton.

War: and artificial light, 11, 178-193

Washington, 305

Water: sterilization of, by artificial light, 280 _et seq._

Watson, Dr. Richard, 67, 68

Watt, 94

Waves: electro-magnetic, 68, 86, 125 _et seq._

Wax, 34, 46, 51

Way: mercury-arc produced by, 124

Wells, 61

Wells, H. G., cited, 148

Welsbach, Auer von: 61;
  invention of mantle by, 99, 100, 133

Wenham, 78

West Indies, 25

Whale-oil, 31

Wicks, 35, 36, 53, 54, 58, 59

Winsor, 72, 73.
  _See also_ Winzler.

Winzler. _See_ Winsor.

_Wolfram._ _See_ Tungsten.

Wood, 26, 27, 28

Woolworth Building, 302, 303

Wounds: treatment of, by artificial light, 10

X-ray: production of, tubes during War, 131; 137, 150, 270, 280

Young, James: discovers petroleum, 56

Yttria, 85

_Zeitung_, Cologne: 157;
   extract from, on street-lighting, 158

Zinc, 125, 130, 267

Zirconia, 84, 85

Transcriber's List of Corrections


Chapter II
         and similiar material
                  and similar material

Chapter XIII
         as a constant level
                  at a constant level

Chapter XIV
         the carbons to distintegrate
                  the carbons to disintegrate

Chapter XV
         John Pechham
                  John Peckham
         coated with an allow
                  coated with an alloy
         with various billiant
                  with various brilliant
         key in depressed
                  key is depressed

Chapter XVI
         has nearly doubled
                  have nearly doubled

Chapter XVII
         this own indifference
                  their own indifference

Chapter XXIII
         Nature's lighting varied
                  Nature's lighting varies

Chapter XXIV
         so-called cadelabra
                  so-called candelabra

         ...Applications an Théatre."
                  ...Applications au Théatre."


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