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Title: Artificial Light: Its Influence upon Civilization

Author: Matthew Luckiesh

Release date: January 29, 2006 [eBook #17625]

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK ARTIFICIAL
LIGHT: ITS INFLUENCE UPON CIVILIZATION ***

Transcriber's Notes:

1. Inconsistent hyphenation of words preserved.
2. Several misprints corrected. Hover over underlined word
in the text to see the corrections made. A full list of
corrections can be found at the end of the text.

3. On page 19, Aristophanes's period is noted as (488-385
b. c.); Aristophanes was born circa 448 b. c.

LIGHT AND LIBERTY

The Century Books of Useful Science

Artificial Light
ITS INFLUENCE UPON CIVILIZATION

BY

M. LUCKIESH
DIRECTOR OF APPLIED SCIENCE. NELA
RESEARCH LABORATORY, NATIONAL LAMP
WORKS OF GENERAL ELECTRIC COMPANY
Author of "Color and Its Applications," "Light
and Shade and Their Applications," "The Lighting
Art," "The Language of Color," etc.

ILLUSTRATED WITH PHOTOGRAPHS

NEW YORK
THE CENTURY CO.
1920

Copyright, 1920, by
The Century Co.

DEDICATED

TO THOSE WHO HAVE ENCOURAGED
ORGANIZED SCIENTIFIC RESEARCH FOR
THE ADVANCEMENT OF CIVILIZATION

PREFACE
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 mankind.
M. Luckiesh.

ACKNOWLEDGMENTS
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.

CONTENTS
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
V Oil-Lamps of the Nineteenth Century 51
VI Early Gas-Lighting 63
VII The Science of Light-Production 80
VIII Modern Gas-Lighting 97
IX The Electric Arcs 111
X The Electric Incandescent Filament Lamps 127
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
XIX Artificial Light and Chemistry 256
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

LIST OF ILLUSTRATIONS

Light and Liberty Frontispiece
FACING
PAGE
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
129
filament lamps
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
233
modern lighting
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
288
Celebration
Fireworks exhibition on May Day at Panama-Pacific
289
Exposition
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
336
which supplies direct and indirect components of light
The lights of New York City 337
Artificial light in community affairs 352
Panama-Pacific Exposition 353

ARTIFICIAL LIGHT

I

LIGHT AND PROGRESS
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 failed.
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 outdoors.
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 light.
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.

II

THE ART OF MAKING FIRE
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 mankind.
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
PRIMITIVE FIRE-BASKETS
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 fire.

CRUDE SPLINTER-HOLDERS

EARLY OPEN-FLAME OIL AND GREASE LAMPS

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 procedure.
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 light-source.
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 composition.
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 ignition.

III

PRIMITIVE LIGHT-SOURCES
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 A TYPICAL METAL MULTIPLE-WICK OPEN-FLAME OIL-LAMP
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.

A GROUP OF OIL-LAMPS OF TWO CENTURIES AGO

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 follows:

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 Phœnicians. It is known that the
Romans used them, especially the wax-candles, in religious ceremonies. The
Phœnicians introduced them into Byzantium, but they disappeared under the
Turkish rule and did not come into use again until the twelfth century.
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 trimming.
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.

IV

THE CEREMONIAL USE OF LIGHT
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 Phœnicians 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 daytime.
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.

V

OIL-LAMPS OF THE NINETEENTH CENTURY
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.

LAMPS OF A CENTURY OR TWO AGO

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 CnH2n+2 and the
individual members of this
series vary from CH4 (methane)
to C15H32 (pentadecane),
although the solid hydrocarbons
are still more complex.
Petroleum is found in many
countries and the United States
is particularly blessed with great
ELABORATE FIXTURES OF THE AGE OF CANDLES 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.

VI

EARLY GAS-LIGHTING
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 Oil.
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:

Candle-power
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.

VII

THE SCIENCE OF LIGHT-PRODUCTION
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 made.
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 light.
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, violet.
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 4p 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 ideal.
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.

Efficiency
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.

VIII

MODERN GAS-LIGHTING
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 market.

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 retorts.
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 C2H4 crotonylene C4H6
propylene C3H6 benzene C6H6
butylene C4H8 toluene C7H8
amylene C5H10 xylene C8H10
acetylene C2H2 methane C H4
allylene C3H4 ethane C2H6

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,

CaC2 + H2O = C2H2 + 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.

IX

THE ELECTRIC ARCS
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 carbons.
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 globe.
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 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.

X

THE ELECTRIC INCANDESCENT FILAMENT
LAMPS
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.
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
DIRECT CURRENT ARC
improvements were
Most of the light being emitted by the positive (upper) electrode 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.

FLAME ARC
Most of the light being emitted by the flame

ON THE TESTING-RACKS OF THE MANUFACTURER OF INCANDESCENT FILAMENT
LAMPS
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 inhabitants

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
wire.
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 companies.
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.
Approximate Values

Date Filament Temperature Lumens per 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.
Average Candle-Power, Watts, and Efficiency of All the Lamps Sold in
This Country

Lumens
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 52 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.

XI

THE LIGHT OF THE FUTURE
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 departure.
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 day.

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 eyes.
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 known.
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 needs.

XII

LIGHTING THE STREETS
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 streets.
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.

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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.

MODERN STREET LIGHTING
Tunnels of light boring through the darkness provide safe channels for modern traffic

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.

XIII

LIGHTHOUSES
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 navigation.
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 intensity.
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 √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 √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 √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 A. A COMPLETED LIGHTHOUSE LENS
candles. The improvements in light- B. TORRO POINT LIGHTHOUSE, PANAMA CANAL
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
candle-power.
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.

AMERICAN SEARCH-LIGHT POSITION ON WESTERN FRONT IN 1919

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.

AMERICAN STANDARD FIELD SEARCH-LIGHT AND POWER UNIT

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.

XIV

ARTIFICIAL LIGHT IN WARFARE
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
manœuvers 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 increases.
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.
Brightness of Light-Sources 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 point.

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 purposes.

XV

SIGNALING
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 use.
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
messages.
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.

XVI

THE COST OF LIGHT
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 shutters.
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 result.

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:

Equivalent of Candle-hours
Year Hours 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 follows:

1000 candle-hours
Gas-lighting at a rate of two hours per day $1.95
Gas-lighting at a rate of three hours per day 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 country.
Table Showing the Approximate Total Cost of 1000 Candle-Hours for Various
Periods

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

Electric
Year Food lighting
1894 100 100

Electric
Year Food lighting
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 country:

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.

XVII

LIGHT AND SAFETY
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.
Seasonal Distribution of Industrial Accidents Due to Lighting Conditions and 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.

SIGNAL-LIGHT FOR AIRPLANE TRENCH LIGHT-SIGNALING OUTFIT

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.

AVIATION FIELD LIGHT-SIGNAL PROJECTOR SIGNAL SEARCH-LIGHT FOR AIRPLANE

UNSAFE, UNPRODUCTIVE LIGHTING WORTHY OF THE DARK AGES

THE SAME FACTORY MADE SAFE, CHEERFUL, AND MORE PRODUCTIVE BY MODERN LIGHTING

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 places.
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.

XVIII

THE COST OF LIVING
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.

LOCOMOTIVE ELECTRIC HEADLIGHT

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 conditions.

SEARCH-LIGHT ON A FIRE-BOAT

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 product.

BUILDING SHIPS UNDER ARTIFICIAL LIGHT AT HOG ISLAND SHIPYARD

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 lighting.
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 discussed.
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.
ARTIFICIAL LIGHT IN PHOTOGRAPHY

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

eco
no
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val
ue
has
bee
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de
mo
nst
rat
ed
in
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ina
In a moving-picture studio ry In a portrait studio
fiel
ds
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.

XIX

ARTIFICIAL LIGHT AND CHEMISTRY
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.

Swimming pool

City waterworks
STERILIZING WATER WITH RADIANT ENERGY FROM QUARTZ MERCURY-ARCS

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
source.
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 odor.
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.

XX

LIGHT AND HEALTH
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 region.
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.

In art work

In a haberdashery
JUDGING COLOR UNDER ARTIFICIAL DAYLIGHT

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.

In an underground tunnel

In an art gallery
ARTIFICIAL DAYLIGHT

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 manner.
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 unsettled.
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 hour.
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.

XXI

MODIFYING ARTIFICIAL LIGHT
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.

FIREWORKS AND ILLUMINATED BATTLE-FLEET AT HUDSON-FULTON CELEBRATION

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.

FIREWORKS EXHIBITION ON MAY DAY AT PANAMA-PACIFIC EXPOSITION

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 daylight.
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 illuminants.
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 glass.

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 green.
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 available.

XXII

SPECTACULAR LIGHTING
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 developed.
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 decorations.

The Capitol flooded with light

Luna Park, Coney Island, studded with 60,000 incandescent filament lamps
THE NEW FLOOD LIGHTING CONTRASTED WITH THE OLD OUTLINE LIGHTING

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.

NIAGARA FALLS FLOODED WITH LIGHT

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 devices.
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.

XXIII

THE EXPRESSIVENESS OF LIGHT
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 utilized.
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.

Soldiers' and Sailors' Monument

Jeweled portal welcoming returned soldiers
ARTIFICIAL LIGHT HONORING THOSE WHO FELL AND THOSE WHO RETURNED

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!

THE EXPRESSIVENESS OF LIGHT IN CHURCHES

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.

XXIV

LIGHTING THE HOME
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