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+The Project Gutenberg EBook of Artificial Light, by M. Luckiesh
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Artificial Light
+       Its Influence upon Civilization
+
+Author: M. Luckiesh
+
+Release Date: January 29, 2006 [EBook #17625]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ARTIFICIAL LIGHT ***
+
+
+
+
+Produced by K.D. Thornton, Karina Aleksandrova and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+Transcriber's Notes:
+
+1. Subscripts have been marked with an underscore character in front
+   with text surrounded in curly braces, for example: H_{2}O (formula
+   of water).
+
+2. Inconsistent hyphenation of words preserved.
+
+3. Several misprints fixed. A full list of corrections can be found at
+   the end of the text.
+
+
+
+[Illustration: 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 filament lamps                            129
+
+Carbon-dioxide tube for accurate color-matching        160
+
+The Moore nitrogen tube                                160
+
+Modern street lighting                                 161
+
+A completed lighthouse lens                            176
+
+Torro Point Lighthouse, Panama Canal                   176
+
+American search-light position on Western Front in
+1919                                                   177
+
+American standard field search-light and power unit    177
+
+Signal-light for airplane                              232
+
+Trench light-signaling outfit                          232
+
+Aviation field light-signal projector                  232
+
+Signal search-light for airplane                       232
+
+Unsafe, unproductive lighting worthy of the dark ages  233
+
+The same factory made safe, cheerful, and more
+productive by modern lighting                          233
+
+Locomotive electric headlight                          240
+
+Search-light on a fire-boat                            240
+
+Building ships under artificial light at Hog Island
+Shipyard                                               241
+
+Artificial light in photography                        256
+
+Sterilizing water with radiant energy from quartz
+mercury-arcs                                           257
+
+Judging color under artificial daylight                272
+
+Artificial daylight                                    273
+
+Fireworks and illuminated battle-fleet at
+Hudson-Fulton Celebration                              288
+
+Fireworks exhibition on May Day at Panama-Pacific
+Exposition                                             289
+
+The new flood lighting contrasted with the old
+outline lighting                                       304
+
+Niagara Falls flooded with light                       305
+
+Artificial light honoring those who fell and those
+who returned                                           320
+
+The expressiveness of light in churches                321
+
+Obtaining two different moods in a room by a portable
+lamp which supplies direct and indirect components
+of light                                               336
+
+The lights of New York City                            337
+
+Artificial light in community affairs                  352
+
+Panama-Pacific Exposition                              353
+
+
+
+
+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 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.
+
+[Illustration: PRIMITIVE FIRE-BASKETS]
+
+[Illustration: CRUDE SPLINTER-HOLDERS]
+
+[Illustration: 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 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.
+
+[Illustration: A TYPICAL METAL MULTIPLE-WICK OPEN-FLAME OIL-LAMP]
+
+[Illustration: 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 Phoenicians. It is known that the
+Romans used them, especially the wax-candles, in religious ceremonies.
+The Phoenicians introduced them into Byzantium, but they disappeared
+under the Turkish rule and did not come into use again until the twelfth
+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 Phoenicians and Romans apparently continued
+the custom, but no traces of it have been found in Greece and Egypt.
+
+Fire and light have been closely associated in various religious creeds
+and their ceremonies. The Hindu festival in honor of the goddess of
+prosperity is attended by the burning of many lamps in the temples and
+homes. The Jewish synagogues have their eternal lamps and in their
+rituals fire and light have played prominent rôles. The devout Brahman
+maintains a fire on the hearth and worships it as omniscient and divine.
+He expects a brand from this to be used to light his funeral pyre, whose
+fire and light will make his spirit fit to enter his heavenly abode. He
+keeps a fire burning on the altar, worships Agni, the god of fire, and
+makes fire sacrifices on various occasions such as betrothals and
+marriages. To the Mohammedans lighted lamps symbolize holy places, and
+the Kaaba at Mecca, which contains a black stone supposed to have been
+brought from heaven, is illuminated by thousands of lamps. Many of the
+uses to which light was put in ancient times indicate its rarity and
+sacred nature. Doubtless, the increasing use of artificial light at
+festivals and celebrations of the present time is partly the result of
+lingering customs of bygone centuries and partly due to a recognition of
+an innate appeal or attribute of light. Certainly nothing is more
+generally appropriate in representing joy and prosperity.
+
+Throughout all countries ancient races had woven natural light and fire
+into their rites and customs, so it became a natural step to utilize
+artificial light and fire in the same manner. It would be tedious and
+monotonous to survey the vast field of ancient worship of light, for the
+underlying ideas are generally similar. The mythology of the Greeks is
+illustrative of the importance attached to fire and light by the
+cultivated peoples of ancient times. The myth of Prometheus emphasizes
+the fact that in those remote periods fire and light were regarded as of
+prime importance. According to this myth, fire and light were contained
+in heaven and great cunning and daring were necessary in order to obtain
+it. Prometheus stole this heavenly fire, for which act he was chained to
+the mountain and made to suffer. The Greeks mark this event as the
+beginning of human civilization. All arts are traced to Prometheus, and
+all earthly woe likewise. As past history is surveyed it appears natural
+to think of scientific men who have become martyrs to the quest of
+hidden secrets. They have made great sacrifices for the future benefit
+of civilization and not a few of them have endured persecution even in
+recent times. The Greeks recognized that a new era began with the
+acquisition of artificial light. Its divine nature was recognized and it
+became a phenomenon for worship and a means for representing divine
+presence. The origin of fire and light made them holy. The fire on the
+altar took its place in religious rites and there evolved many
+ceremonial uses of lamps, candles, and fire.
+
+The Greeks and Romans burned sacred lamps in the temples and utilized
+light and fire in many ceremonies. The torch-race, in which young men
+ran with lighted torches, the winner being the one who reached the goal
+first with his torch still alight, originated in a Grecian ceremony of
+lighting the sacred fire. There are many references in ancient Roman and
+Grecian literature to sacred lamps burning day and night in sanctuaries
+and before statues of gods and heroes. On birthdays and festivals the
+houses of the Romans were specially ornamented with burning lamps. The
+Vestal Virgins in Rome maintained the sacred fire which had been brought
+by fugitives from Troy. In ancient Rome when the fire in the Temple of
+Vesta became extinguished, it was rekindled by the rubbing of a piece of
+wood upon another until fire was obtained. This was carried into the
+temple by the Vestal Virgin and the sacred fire was rekindled. The fire
+produced in this manner, for some reason, was considered holy.
+
+The early peoples displayed many lamps on feast-days and an example of
+extravagance in this respect is an occasion when King Constantine
+commanded that the entire city of Constantinople be illuminated by
+wax-candles on Christmas Eve. Candelabra, of the form of the branching
+tree, were commonly in use in the Roman temples.
+
+The ceremonial use of light in the Christian church evolved both from
+adaptations of pagan customs and of the natural symbolisms of fire and
+light. However, these acquired a deeper meaning in Christianity than in
+early times because they were primarily visible representations or
+manifestations of the divine presence. The Bible contains many
+references to the importance and symbolisms of light and fire. According
+to the First Book of Moses, the achievement of the Creator immediately
+following the creation of "the heavens and the earth" was the creation
+of light. The word "light" is the forty-sixth word in Genesis. Christ is
+"the true light" and Christians are "children of light" in war against
+the evil "powers of darkness." When St. Paul was converted "there
+shined about him a great light from heaven." The impressiveness and
+symbolism of fire and light are testified to in many biblical
+expressions. Christ stands "in the midst of seven candle-sticks" with
+"his eyes as a flame of fire." When the Holy Ghost appeared before the
+apostles "there appeared unto them cloven tongues of fire." When St.
+Paul was preaching the gospel of Christ at Alexandria "there were many
+lights" suggesting a festive illumination.
+
+According to the Bible, the perpetual fire which came originally from
+heaven was to be kept burning on the altar. It was holy and those whose
+duty it was to keep it burning were guilty of a grave offense if they
+allowed it to be extinguished. If human hands were permitted to kindle
+it, punishment was meted out. The two sons of Aaron who "offered strange
+fire before the Lord" were devoured by "fire from the Lord." The
+seven-branched candlestick was lighted eternally and these burning
+light-sources were necessary accompaniments of worship.
+
+The countless ceremonial uses of fire and light which had evolved in the
+past centuries were bound to influence the rites and customs of the
+Christian church. The festive illumination of pagan temples in honor of
+gods was carried over into the Christian era. The Christmas tree of
+to-day is incomplete without its many lights. Its illumination is a
+homage of light to the source of light. The celebration of Easter in the
+Church of the Holy Sepulchre in Jerusalem is a typical example of
+fire-worship retained from ancient times. At the climax of the services
+comes the descent of the Holy Fire. The central candelabra suddenly
+becomes ablaze and the worshipers, each of whom carries a wax taper,
+light their candles therefrom and rush through the streets. The fire is
+considered to be of divine origin and is a symbol of resurrection. The
+custom is similar in meaning to the light which in older times was
+maintained before gods.
+
+During the first two or three centuries of the Christian era the
+ceremonial use of light does not appear to have been very extensive.
+Writings of the period contain statements which appear to ridicule this
+use to some extent. For example, one writer of the second century states
+that "On days of rejoicing ... we do not encroach upon daylight with
+lamps." Another, in the fourth century, refers with sarcasm to the
+"heathen practice" in this manner: "They kindle lights as though to one
+who is in darkness. Can he be thought sane who offers the light of lamps
+and candles to the Author and Giver of all light?"
+
+That candles were lighted in cemeteries is evidenced by an edict which
+forbade their use during the day. Lamps of the early centuries of the
+Christian era have been found in the catacombs of Rome which are thought
+to have been ceremonial lamps, for they were not buried with the dead.
+They were found only in niches in the walls. During these same centuries
+elaborate candelabra containing hundreds of candles were kept burning
+before the tombs of saints. Notwithstanding the doubt that exists as to
+the extent of ceremonial lighting in the early centuries of the
+Christian era, it is certain that by the beginning of the fifth century
+the ceremonial use of light in the Christian church had become very
+extensive and firmly established. That this is true and that there were
+still some objections is indicated by many controversies. Some thought
+that lamps before tombs were ensigns of idolatry and others felt that no
+harm was done if religious people thus tried to honor martyrs and
+saints. Some early writings convey the idea that the ritualistic use of
+lights in the church arose from the retention of lights necessary at
+nocturnal services after the hours of worship had been changed to
+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.
+
+[Illustration: LAMPS OF A CENTURY OR TWO AGO]
+
+[Illustration: ELABORATE FIXTURES OF THE AGE OF CANDLES]
+
+The crude petroleum, of course, is not fit for illuminating purposes,
+but it contains components which are satisfactory. The various
+components are sorted out by fractional distillation and the oil for
+burning in lamps is selected according to its volatility, viscosity,
+stability, etc. It must not be so volatile as to have a dangerously
+low flashing-point, nor so stable as to hinder its burning well. In this
+fractional distillation a vast variety of products are now obtained.
+Gasolene is among the lighter products, with a density of about 0.65;
+kerosene has a density of about 0.80; the lubricating-oils from 0.85 to
+0.95; and there are many solids such as vaseline and paraffin which are
+widely used for many purposes. This process of refining oils is now the
+source of paraffin for making candles, in which it is usually mixed with
+substances like stearin in order to raise its melting-point.
+
+Crude petroleum possesses a very repugnant odor; it varies in color from
+yellow to black; and its specific gravity ranges from about 0.80 to
+1.00, but commonly is between 0.80 and 0.90. Its chemical constitution
+is chiefly of carbon and hydrogen, in the approximate ratio of about six
+to one respectively. It is a mixture of paraffin hydrocarbons having the
+general formula of C_{n}H_{2n+2} and the individual members of this
+series vary from CH_{4} (methane) to C_{15}H_{32} (pentadecane),
+although the solid hydrocarbons are still more complex. Petroleum is
+found in many countries and the United States is particularly blessed
+with great stores of it.
+
+The ordinary lamp consisting of a wick which draws up the mineral oil
+and feeds it to a flame is efficient and fairly free from danger. It
+requires care and may cause disaster if it is upset, but it has been
+blamed unjustly in many accidents. A disadvantage of the kerosene lamp
+over electric lighting, for example, is the relatively greater
+possibility of accidents through the carelessness of the user. This
+point is brought out in statistics of fire-insurance companies, which
+show that the fires caused by kerosene lamps are much more numerous than
+those from other methods of lighting. If in a modern lamp of proper
+construction a close-fitting wick is used and the lamp is extinguished
+by turning down and blowing across the chimney, there is little danger
+in its use excepting accidental breakage or overturning.
+
+In oil-lamps at the present time mineral oils are used which possess
+flashing-points above 75°F. The highly volatile components of petroleum
+are dangerous because they form very explosive mixtures with air at
+ordinary temperatures. A mineral oil like kerosene, to be used with
+safety in lamps, should not be too volatile. It is preferable that an
+inflammable vapor should not be given off at temperatures under 120°F.
+The oil must be of such physical characteristics as to be drawn up to
+the burner by capillarity from the reservoir which is situated below. It
+is volatilized by the heat of the flame into a mixture of hydrogen and
+hydrocarbon gases and these are consumed under the heat of the process
+of consumption by the oxygen in the air. The resulting products of this
+combustion, if it is complete, are carbon dioxide and water-vapor. For
+each candle-power of light per hour about 0.24 cubic foot of carbon
+dioxide and 0.18 cubic foot of water-vapor are formed by a modern
+oil-lamp. That an open flame devours something from the air is easily
+demonstrated by enclosing it in an air-tight space. The flame gradually
+becomes feeble and smoky and finally goes out. It will be noted that a
+burning lamp will vitiate the atmosphere of a closed room by consuming
+the oxygen and returning in its place carbon dioxide. This is similar to
+the vitiation of the atmosphere by breathing persons and tests indicate
+that for each two candle-power emitted by a kerosene flame the vitiation
+is equal to that produced by one adult person. Inasmuch as oil-lamps are
+ordinarily of 10 to 20 candle-power, it is seen that one lamp will
+consume as much oxygen as several persons.
+
+In order that oil-lamps may produce a brilliant light free from smoke,
+combustion must be complete. The correct quantity of oil must be fed to
+the burner and it must be properly vaporized by heat. If insufficient
+oil is fed, the intensity of the light is diminished and if too much is
+available at the burner, smoke and other products of incomplete
+combustion will be emitted. The wick is an important factor, for,
+through capillarity, it feeds oil forcefully to the burner against the
+action of gravity. This action of a wick is commonly looked upon with
+indifference but in reality it is caused by an interesting and really
+wonderful phenomenon. Wicks are usually made of high-grade cotton fiber
+loosely spun into coarse threads and these are woven into a loose plait.
+The wick must be dry before being inserted into the burner; and it is
+desirable that it be considerably longer than is necessary merely to
+reach the bottom of the reservoir. A flame burning in the open will
+smoke because insufficient oxygen is brought in contact with it. The
+injurious products of this incomplete combustion are carbon monoxide and
+oil vapors, which are a menace to health.
+
+To supply the necessary amount of oxygen (air) to the flame, a forced
+draft is produced. Chimneys are simple means of accomplishing this, and
+this is their function whether on oil-lamps or factories. Other means of
+forced draft have been used, such as small fans or compressed air. In
+the railway locomotive the short smoke-stack is insufficient for
+supplying large quantities of air to the fire-box so the exhausted steam
+is allowed to escape into the stack. With each noisy puff of smoke a
+quantity of air is forcibly drawn into the fire-box through the burning
+fuel. In the modern oil-lamp the rush of air due to the "pull" of the
+chimney is broken and the air is diffused by the wire gauze or holes at
+the base of the burner. These metal parts, being hot, also serve to warm
+the oil before it reaches the burning end of the wick, thus serving to
+aid vaporization and combustion.
+
+The consumption of oil per candle-power per hour varies considerably
+with the kind of lamp and with the character of the oil. The average
+consumption of oil-lamps burning a mineral oil of about 0.80 specific
+gravity and a rather high flashing-point is about 50 to 60 grams of oil
+per candle-power per hour for well-designed flame-lamps. Kerosene weighs
+about 6.6 pounds per gallon; therefore, about 800 candle-power hours per
+gallon are obtained from modern lamps employing wicks. Kerosene lamps
+are usually of 10 to 20 candle-power, although they are made up to 100
+candle-power. These luminous intensities refer to the maximum horizontal
+candle-power. The best practice now deals with the total light output,
+which is expressed in lumens, and on this basis a consumption of one
+gallon of kerosene per hour would yield about 8000 lumens.
+
+Oil-lamps have been devised in which the oil is burned as a spray
+ejected by air-pressure. These burn with a large flame; however, a
+serious feature is the escape of considerable oil which is not burned.
+These lamps are used in industrial lighting, especially outdoors, and
+possess the advantage of consuming low-grade oils. They produce about
+700 to 800 candle-power hours per gallon of oil. Lamps of this type of
+the larger sizes burn with vertical flames two or three feet high. The
+oil is heated as it approaches the nozzle and is fairly well vaporized
+on emerging into the air. The names of Lucigen, Wells, Doty, and others
+are associated with this type of lamp or torch, which is a step in the
+direction of air-gas lighting.
+
+During the latter part of the nineteenth century numerous developments
+were made which paralleled the progress in gas-lighting. Experiments
+were conducted which bordered closely upon the next epochal event in
+light-production--the appearance of the gas mantle. One of these was the
+use of platinum gauze by Kitson. He produced an apparatus similar to the
+oil-spray lamp, on a small and more delicate scale. The hot blue flame
+was not very luminous and he attempted to obtain light by heating a
+mantle of fine platinum gauze. Although these mantles emitted a
+brilliant light for a few hours, their light-emissivity was destroyed by
+carbonization. After the appearance of the Welsbach mantle, Kitson's
+lamp and others met with success by utilizing it. From this point,
+attention was centered upon the new wonder, which is discussed in a
+later chapter after certain scientific principles in light-production
+have been discussed.
+
+The kerosene or mineral-oil lamp was a boon to lighting in the
+nineteenth century and even to-day it is a blessing in many homes,
+especially in villages, in the country, and in the remote districts of
+civilization. Its extensive use at the present time is shown by the fact
+that about eight million lamp-chimneys are now being manufactured yearly
+in this country. It is convenient and safe when carelessness is avoided,
+and is fairly free from odor. Its vitiation of the atmosphere may be
+counteracted by proper ventilation and there remains only the
+disadvantage of keeping it in order and of accidental breakage and
+overturning. The kerosene lantern is widely used to-day, but the danger
+due to accident is ever-present. The consequences of such accidents are
+often serious and are exemplified in the terrible conflagration in
+Chicago in 1871, when Mrs. O'Leary's cow kicked over a lantern and
+started a fire which burned the city. Modern developments in lighting
+are gradually encroaching upon the territory in which the oil-lamp has
+reigned supreme for many years. Acetylene plants were introduced to a
+considerable extent some time ago and to-day the self-contained
+home-lighting electric plant is being installed in large numbers in the
+country homes of the land.
+
+
+
+
+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 4 pi or 12.57 square feet;
+therefore, a light-source having a luminous intensity of one candle in
+all directions emits 12.57 lumens. This is the satisfactory unit, for it
+measures total quantity of light, and luminous efficiencies may be
+expressed in terms of lumens per watt, lumens per cubic foot of gas per
+hour, etc.
+
+Of course, the efficiencies of light-sources are usually of interest to
+the consumer if they are expressed in terms of cost. But from a
+practical point of view there are many elements which combine to make
+another important factor, namely, satisfactoriness. Therefore, the
+efficiency of artificial lighting from the standpoint of the consumer
+should be the ratio of satisfactoriness to cost. However, the scientist
+is interested chiefly in the efficiency of the light-source which may be
+expressed in lumens per watt, or the amount of light obtained from a
+given rate of consumption or of emission of energy. This method of
+rating light-sources penalizes those radiating considerable energy which
+does not produce the sensation of light or which at best is of
+wave-lengths that are inefficient in this respect. That radiant energy
+which is wholly of a wave-length of maximum visibility, or, in other
+words, excites the sensation of yellow-green, is the most efficient in
+producing luminous sensation. Of course, no illuminants are available
+which approach this theoretical ideal and it is not likely that this
+would be a practical ideal. Under monochromatic yellow-green light the
+magical drapery of color would disappear and the surroundings would be a
+monochrome of shades of this hue. Having no colors with which to
+contrast this color, the world would be colorless. This should be
+obvious when it is considered that an object which is red under an
+illuminant containing all colors such as sunlight would be black or dark
+gray under monochromatic yellow-green light. The red under present
+conditions is kept alive by contrast with other colors, because the
+latter live by virtue of the fact that most of our present illuminants
+contain their hues. It is assumed that the reader knows that a red
+object, for example, appears red because it reflects (or transmits) red
+rays and absorbs the other rays in the illuminant. In other words, color
+is due to selective absorption reflection, or transmission.
+
+Perhaps the ideal illuminant, which is most generally satisfactory for
+general activities, is a white light corresponding to noon sunlight. If
+this is chosen as the scientific ideal, the illuminants of the present
+time are much more "efficient" than if the most efficient light is the
+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    C_{2}H_{4}    crotonylene  C_{4}H_{6}
+     propylene   C_{3}H_{6}    benzene      C_{6}H_{6}
+     butylene    C_{4}H_{8}    toluene      C_{7}H_{8}
+     amylene     C_{5}H_{10}   xylene       C_{8}H_{10}
+     acetylene   C_{2}H_{2}    methane      C H_{4}
+     allylene    C_{3}H_{4}    ethane       C_{2}H_{6}
+
+A gas which has played a prominent part in lighting is acetylene,
+produced by the interaction of water and calcium carbide. No other gas
+easily produced upon a commercial scale yields as much light, volume for
+volume, as acetylene. It has the great advantage of being easily
+prepared from raw material whose yield of gas is considerably greater
+for a given amount than the raw materials which are used in making other
+illuminating gases. The simplicity of the manufacture of acetylene from
+calcium carbide and water gives to this gas a great advantage in some
+cases. It has served for individual lighting in houses and in other
+places where gas or electric service was unavailable. Where space is
+limited it also had an advantage and was adopted to some extent on
+automobiles, motor-boats, ships, lighthouses, and railway cars before
+electric lighting was developed for these purposes.
+
+The color of the acetylene flame is satisfactory and it is extremely
+brilliant compared with most flames. An interesting experiment is found
+in placing a spark-gap in the flame and sending a series of sparks
+across it. If the conditions are proper the flame will became very much
+brighter. When the gas issues from a proper jet under sufficient
+pressure, the flame is quite steady. Its luminous efficiency gives it an
+advantage over other open gas-flames in lighting rooms, because for the
+same amount of light it vitiates the air and exhausts the oxygen to a
+less degree than the others. Of course, in these respects the gas-mantle
+is superior.
+
+The reaction which takes place when water and calcium carbide are
+brought together is a double decomposition and is represented by,
+
+     CaC_{2} + H_{2}O = C_{2}H_{2} + CaO
+
+It will be seen that the products are acetylene gas and calcium oxide or
+lime. The lime, being hydroscopic and being in the presence of water or
+water-vapor in the acetylene generator, really becomes calcium hydroxide
+Ca(OH)_{2}, commonly called slaked lime. If there are impurities in the
+calcium carbide, it is sometimes necessary to purify the gas before it
+may be safely used for interior lighting.
+
+The burners and mantles used in acetylene lighting are essentially the
+same as those for other gas-lighting, excepting, of course, that they
+are especially adapted for it in minor details.
+
+The chief source of calcium carbide in this country is the electric
+furnace. Cheap electrical energy from hydro-electric developments, such
+as the Niagara plants, have done much to make the earth yield its
+elements. Aluminum is very prevalent in the soil of the earth's surface,
+because its oxide, alumina, is a chief constituent of ordinary clay. But
+the elements, aluminum and oxygen, cling tenaciously to each other and
+only the electric furnace with its excessively high temperatures has
+been able to separate them on a large commercial scale. Similarly,
+calcium is found in various compounds over the earth's surface.
+Limestone abounds widely, hence the oxide and carbonate of lime are
+wide-spread. But calcium clings tightly to the other elements of its
+compounds and it has taken the electric furnace to bring it to
+submission. The cheapness of calcium carbide is due to the development
+of cheap electric power. It is said that calcium carbide was discovered
+as a by-product of the electric furnace by accidentally throwing water
+upon the waste materials of a furnace process. The discovery of a
+commercial scale of manufacture of calcium carbide has been a boon to
+isolated lighting. Electric lighting has usurped its place on the
+automobile and is making inroads in country-home lighting. Doubtless,
+acetylene will continue to serve for many years, but its future does not
+appear as bright as it did many years ago.
+
+The Pintsch gas, used to some extent in railroad passenger-cars in this
+country, is an oil-gas produced by the destructive distillation of
+petroleum or other mineral oil in retorts heated externally. The product
+consists chiefly of methane and heavy hydrocarbons with a small amount
+of hydrogen. In the early days of railways, some trains were not run
+after dark and those which were operated were not always lighted. At
+first attempts were made at lighting railway cars with compressed
+coal-gas, but the disadvantage of this was the large tank required.
+Obviously, a gas of higher illuminating-value per volume was desired
+where limited storage space was available, and Pintsch turned his
+attention to oil-gas. Gas suffers in illuminating-value upon being
+compressed, but oil-gas suffers only about half the loss that coal-gas
+does. In about 1880 Pintsch developed a method of welding cylinders and
+buoys which satisfied lighthouse authorities and he was enabled to
+furnish these filled with compressed gas. Thus the buoy was its own
+gas-tank. He devised lanterns which would remain lighted regardless of
+wind and waves and thus gained a start with his compressed-gas systems.
+He compressed the gas to a pressure of about one hundred and fifty
+pounds per square inch and was obliged to devise a reducer which would
+deliver the gas to the burner at about one pound per square inch. This
+regulator served well throughout many years of exacting service. The
+system began to be adopted on ships and railroads in 1880 and for many
+years it has served well.
+
+Although gas-lighting has affected the activities of mankind
+considerably by intensifying commerce and industry and by advancing
+social progress, the illuminants which eventually took the lead have
+extended the possibilities and influences of artificial light. In the
+brief span of a century civilized man is almost totally independent of
+natural light in those fields over which he has control. What another
+century will bring can be predicted only from the accomplishments of the
+past. These indicate possibilities beyond the powers of imagination.
+
+
+
+
+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                         3 to  7
+     Enclosed flame-arc (yellow or white)       15 to 25
+     Luminous arc                               10 to 25
+
+Another lamp differing widely in appearance from the preceding arcs may
+be described here because it is known as the mercury-arc. In this lamp
+mercury is confined in a transparent tube and an arc is started by
+making and breaking a mercury connection between the two electrodes. The
+arc may be maintained of a length of several feet. Perhaps the first
+mercury-arc was produced in 1860 by Way, who permitted a fine jet of
+mercury to fall from a reservoir into a vessel, the reservoir and
+receiver being connected to the poles of a battery. The electric current
+scattered the jet and between the drops arcs were formed. He exhibited
+this novel light-source on the mast of a yacht and it received great
+attention. Later, various investigators experimented on the production
+of a mercury-arc and the first successful ones were made in the form of
+an inverted U-tube with the ends filled with mercury and the remainder
+of the tube exhausted.
+
+Cooper Hewitt was a successful pioneer in the production of practicable
+mercury-arcs. He made them chiefly in the form of straight tubes of
+glass up to several feet in length, with enlarged ends to facilitate
+cooling. The tubes are inclined so that the mercury vapor which
+condenses will run back into the enlarged end, where a pool of mercury
+forms the negative electrode. The arc may be started by tilting the tube
+so that a mercury thread runs down the side and connects with the
+positive electrode of iron. The heat of the arc volatilizes the mercury
+so that an arc of considerable length is maintained. The tilting is done
+by electromagnets. Starting has also been accomplished by means of a
+heating coil and also by an electric spark. The lamps are stabilized by
+resistance and inductance coils.
+
+One of the defects of the light emitted by the incandescent vapor of
+mercury is its paucity of spectral colors. Its visible spectrum consists
+chiefly of violet, blue, green, and yellow rays. It emits virtually no
+red rays, and, therefore, red objects appear devoid of red. The human
+face appears ghastly under this light and it distorts colors in general.
+However, it possesses the advantages of high efficiency, of reasonably
+low brightness, of high actinic value, and of revealing detail clearly.
+Various attempts have been made to improve the color of the light by
+adding red rays. Reflectors of a fluorescent red dye have been used with
+some success, but such a method reduces the luminous efficiency of the
+lamp considerably. The dye fluoresces red under the illumination of
+ultra-violet, violet, and blue rays; that is, it has the property of
+converting radiation of these wave-lengths into radiant energy of longer
+wave-lengths. By the use of electric incandescent filament lamps in
+conjunction with mercury-arcs, a fairly satisfactory light is obtained.
+Many experiments have been made by adding other substances to the
+mercury, such as zinc, with the hope that the spectrum of the other
+substance would compensate the defects in the mercury spectrum. However
+no success has been reached in this direction.
+
+By the use of a quartz tube which can withstand a much higher
+temperature than glass, the current density can be greatly increased.
+Thus a small quartz tube of incandescent mercury vapor will emit as much
+light as a long glass tube. The quartz mercury-arc produces a light
+which is almost white, but the actual spectrum is very different from
+that of white sunlight. Although some red rays are emitted by the quartz
+arc, its spectrum is essentially the same as that of the glass-tube arc.
+Quartz transmits ultra-violet radiation, which is harmful to the eyes,
+and inasmuch as the mercury vapor emits such rays, a glass globe should
+be used to enclose the quartz tube when the lamp is used for ordinary
+lighting purposes.
+
+It is fortunate that such radically different kinds of light-sources are
+available, for in the complex activities of the present time all are in
+demand. The quartz mercury-arc finds many isolated uses, owing to its
+wealth of ultra-violet radiation. It is valuable as a source of
+ultra-violet for exciting phosphorescence, for examining the
+transmission of glasses for this radiation, for sterilizing water, for
+medical purposes, and for photography.
+
+
+
+
+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.
+
+[Illustration: DIRECT CURRENT ARC
+
+Most of the light being emitted by the positive (upper) electrode]
+
+[Illustration: FLAME ARC
+
+Most of the light being emitted by the flame]
+
+[Illustration: 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]
+
+Edison in 1878 attacked the problem of producing light from a wire or
+filament heated electrically. He used platinum wire in his first
+experiments, but its volatility and low melting-point (3200°F.) limited
+the success of the lamps. Carbon with its extremely high melting-point
+had long attracted attention and in 1879 Edison produced a carbon
+filament by carbonizing a strip of paper. He sealed this in a vessel of
+glass from which the air was exhausted and the electric current was led
+to the filament through platinum wires sealed in the glass. Platinum was
+used because its expansion and contraction is about the same as glass.
+Incidentally, many improvements were made in incandescent lamps and
+thirty years passed before a material was found to replace the platinum
+leading-in wires. The cost of platinum steadily increased and finally in
+the present century a substitute was made by the use of two metals whose
+combined expansion was the same as that of platinum or glass. In 1879
+and 1880 Edison had succeeded in overcoming the many difficulties
+sufficiently to give to the world a practicable incandescent filament
+lamp. About this time Swan and Stearn in England had also produced a
+successful lamp.
+
+In Edison's early experiments with filaments he used platinum wire
+coated with carbon but without much success. He also made thin rods of a
+mixture of finely divided metals such as platinum and iridium mixed with
+such oxides as magnesia, zirconia, and lime. He even coiled platinum
+wire around a piece of one of these oxides, with the aim of obtaining
+light from the wire and from the heated oxide. However, these
+experiments served little purpose besides indicating that the filament
+was best if it consisted solely of carbon and that it should be
+contained in an evacuated vessel.
+
+One of the chief difficulties was to make the carbon filaments. Some of
+the pioneers, such as Sawyer and Mann, attempted to cut these from a
+piece of carbon. However, Edison and also Swan turned their attention to
+forming them by carbonizing a fiber of organic matter. Filaments cut
+from paper and threads of cotton and silk were carbonized for this
+purpose. Edison scoured the earth for better materials. He tried a
+fibrous grass from South America and various kinds of bamboo from other
+parts of the world. Thin filaments of split bamboo eventually proved the
+best material up to that time. He made many lamps containing filaments
+of this material, and even until 1910 bamboo was used to some extent in
+certain lamps.
+
+Of these early days, Edison said:
+
+     It occurred to me that perhaps a filament of carbon could be
+     made to stand in sealed glass vessels, or bulbs, which we were
+     using, exhausted to a high vacuum. Separate lamps were made in
+     this way independent of the air-pump, and, in October, 1879, we
+     made lamps of paper carbon, and with carbons of common sewing
+     thread, placed in a receiver or bulb made entirely of glass,
+     with the leading-in wires sealed in by fusion. The whole thing
+     was exhausted by the Sprengel pump to nearly one-millionth of
+     an atmosphere. The filaments of carbon, although naturally
+     quite fragile owing to their length and small mass, had a
+     smaller radiating surface and higher resistance than we had
+     dared hope. We had virtually reached the position and condition
+     where the carbons were stable. In other words, the incandescent
+     lamp as we still know it to-day [1904], in essentially all its
+     particulars unchanged, had been born.
+
+After Edison's later success with bamboo, Swan invented a process of
+squirting filaments of nitrocellulose into a coagulating liquid, after
+which they are carbonized. Very fine uniform filaments can be made by
+this process and although improvements have been made from time to time,
+this method has been employed ever since its invention. In these later
+years cotton is dissolved in a suitable solvent such as a solution of
+zinc chloride and this material is forced through a small diamond die.
+This thread when hardened appears similar to cat-gut. It is cut into
+proper lengths and bent upon a form. It is then immersed in plumbago and
+heated to a high temperature in order to destroy the organic matter. A
+carbon filament is the result. From this point to the finished lamp many
+operations are performed, but a discussion of these would lead far
+afield. The production of a high vacuum is one of the most important
+processes and manufacturers of incandescent lamps have mastered the art
+perhaps more thoroughly than any other manufacturers. At least, their
+experience in this field made it possible for them to produce quickly
+and on a large scale such devices as X-ray tubes during the recent war.
+
+During the early years of incandescent lamps, improvements were made
+from time to time which increased the life and the luminous efficiency
+of the carbon filaments, but it was not until 1906 that any radical
+improvement was achieved. In that year in this country a process was
+devised whereby the carbon filament was made more compact. In fact, from
+its appearance it received the name "metallized filament." These carbon
+filaments are prepared in the same manner as the earlier ones but are
+finally "treated" by heating in an atmosphere of hydrocarbons such as
+coal-gas. The filament is heated by electric current and the heat breaks
+down the hydrocarbons, with the result that carbon is deposited upon the
+filament. This "treated" filament has a coating of hard carbon and its
+electrical resistance is greater than that of the untreated filament.
+
+The luminous efficiency of a carbon filament is a function of its
+temperature and it increases very rapidly with increasing temperature.
+For this reason it is a constant aim to reach high filament
+temperatures. Of all the materials used in filaments up to the present
+time, carbon possesses the highest melting-point (perhaps as high as
+7000°F.), but the carbon filament as operated in practice has a lower
+efficiency than any other filament. This is because the highest
+temperature at which it can be operated and still have a reasonable life
+is much lower than that of metallic filaments. The incandescent carbon
+in the evacuated bulb sublimes or volatilizes and deposits upon the
+bulb. This decreases the size of the filament eventually to the
+breaking-point and the blackening of the bulb decreases the output of
+light. The treated filament was found to be a harder form of carbon that
+did not volatilize as rapidly as the untreated filament. It immediately
+became possible to operate it at a higher temperature with a resulting
+increase of luminous efficiency. This "graphitized" carbon filament lamp
+became known as the gem lamp in this country and many persons have
+wondered over the word "gem." The first two letters stand for "General
+Electric" and the last for "metallized." This lamp was welcomed with
+enthusiasm in its day, but the day for carbon filaments has passed. The
+advent of incandescent lamps of higher efficiency has made it
+uneconomical to use carbon lamps for general lighting purposes. Although
+the treated carbon filament was a great improvement, its reign was cut
+short by the appearance of metal filaments.
+
+In 1803 a new element was discovered and named tantalum. It is a dark,
+lustrous, hard metal. Pure tantalum is harder than steel; it may be
+drawn into fine wire; and its melting-point is very high (about
+5100°F.). It is seen to possess properties desirable for filaments, but
+for some reason it did not attract attention for a long time. A century
+elapsed after its discovery before von Bolton produced the first
+tantalum filament lamp. Owing to the low electrical resistance of
+tantalum, a filament in order to operate satisfactorily on a standard
+voltage must be long and thin. This necessitates storing away a
+considerable length of wire in the bulb without permitting the loops to
+come into contact with each other. After the filaments have been in
+operation for a few hundred hours they become brittle and faults
+develop. When examined under a microscope, parts of the filament
+operated on alternating current appear to be offset. The explanation of
+this defect goes deeply into crystalline structure. The tantalum
+filament was quickly followed by osmium and by tungsten in this country.
+
+The osmium filament appeared in 1905 and its invention is due to
+Welsbach, who had produced the marvelous gas-mantle. Owing to its
+extreme brittleness, osmium was finely divided and made into a paste of
+organic material. The filaments were squirted through dies and, after
+being formed and dried, they were heated to a high temperature. The
+organic matter disappeared and the fine metallic particles were
+sintered. This made a very brittle lamp, but its high efficiency served
+to introduce it.
+
+In 1870 when Scheele discovered a new element, known in this country as
+tungsten, no one realized that it was to revolutionize artificial
+lighting and to alter the course of some of the byways of civilization.
+This metal--which is known as "wolfram" in Germany, and to some extent
+in English-speaking countries--is one of the heaviest of elements,
+having a specific gravity of 19.1. It is 50 per cent. heavier than
+mercury and nearly twice as heavy as lead. It was early used in German
+silver to the extent of 1 or 2 per cent. to make platinoid, an alloy
+possessing a high resistance which varies only slightly as the
+temperature changes. This made an excellent material for electrical
+resistors. The melting-point of tungsten is about 5350°F., which makes
+it desirable for filaments, but it was very brittle as prepared in the
+early experiments. It unites very readily with oxygen and with carbon at
+high temperatures.
+
+The first tungsten lamps appeared on the market in 1906, but these
+contained fragile filaments made by the squirting process. When the
+squirted filament of tungsten powder and organic matter was heated in an
+atmosphere of steam and hydrogen to remove the binding material, a
+brittle filament of tungsten was obtained. The first lamps were costly
+and fragile. After years of organized research tungsten is now drawn
+into the finest wires, possessing a tensile strength perhaps greater
+than any other material. Filaments are now made into many shapes and the
+greatest strides in artificial lighting have been due to scientific
+research on a huge scale.
+
+The achievements which combined to perfect the tungsten lamp to the
+point where it has become the mainstay of electric lighting are not
+attached to names in the Hall of Fame. Organization of scientific
+research in the industrial laboratories is such that often many persons
+contribute to the development of an improvement. Furthermore, time is
+usually required for a full perspective of applications of scientific
+knowledge. In the early days organized research was not practised and
+the great developments of those days were the works of individuals.
+To-day, even in pure science, some of the greatest contributions are
+made by industrial laboratories; but sometimes these do not become known
+to the public for many years. The whole scheme of scientific development
+has changed materially. For example, the story of the development of
+ductile tungsten, which has revolutionized lighting, is complex and more
+or less shrouded in secrecy at the present time. Many men have
+contributed toward this accomplishment and the public at the present
+time knows little more than the fact that tungsten filaments, which were
+brittle yesterday, are now made of ductile tungsten wire drawn into the
+finest filaments.
+
+The earlier tungsten filaments were made by three rival processes. By
+the first, a deposit of tungsten was "flashed" on a fine carbon
+filament, the latter being eliminated finally by heating in an
+atmosphere of hydrogen and water-vapor. By the second, colloidal
+tungsten was produced by operating an arc between tungsten electrodes
+under water. The finely divided tungsten was gathered, partially dried,
+and squirted through dies to form filaments. These were then sintered.
+The third was the "paste" process already described. These methods
+produced fragile filaments, but their luminous efficiency was higher
+than that of previous ones. However, in this country ductile tungsten
+was soon on its way. An ingot of tungsten is subjected to vigorous
+swaging until it takes the form of a rod. This is finally drawn into
+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
+
+                                                               Lumens per
+     Date    Filament                      Temperature            watt
+     1880    Carbon                          3300°F.              3.0
+     1906    Carbon (graphitized)            3400                 4.5
+     1905    Tantalum                        3550                 6.5
+     1905    Osmium                          3600                 7.5
+     1906    Tungsten (vacuum)               3700                 8.0
+     1914    Tungsten (gas-filled)     up to 5300°F.           10 to 25
+
+Throughout the development of incandescent filament lamps many ingenious
+experiments were made which resulted usually in light-sources of
+scientific interest but not of practical value. One of the latest is the
+tungsten arc in an inert gas. By means of a heating coil, a small arc is
+started between two electrodes consisting of tungsten, but this as yet
+has not been shown to be practicable.
+
+Another type of filament lamp was developed by Nernst in 1897. It was an
+ingenious application of the peculiar properties of rare-earth oxides.
+His first lamp consisted essentially of a slender rod of magnesia. This
+substance does not conduct electricity at ordinary temperatures, but
+when heated to incandescence it becomes conducting. Upon sufficient
+heating of this filament by external means while a proper voltage is
+impressed upon it, the electric current passes through it and thereafter
+this current will maintain its temperature. Thus such a filament becomes
+a conductor and will continue to glow brilliantly by virtue of the
+electrical energy which it converts into heat. Later lamps consisted of
+"glowers" about one inch long made from a mixture of zirconia and
+yttria, and finally a mixture of ceria, thoria, and zirconia was used.
+The glower is heated initially by a coil of platinum wire located near
+it but not in contact with it. Owing to the fact that this glower
+decreases rapidly in resistance as its temperature is increased, it is
+necessary to place in series with it a substance which increases in
+resistance with increasing current. This is called a "ballasting
+resistance" and is usually an iron wire in a glass bulb containing
+hydrogen. The heater is cut out by an electromagnet when the glower goes
+into operation. This lamp is a marvel of ingenuity and when at its
+zenith it was installed to a considerable extent. Its light is
+considerably whiter than that of the carbon filament lamps. However, its
+doom was sounded when metallic filament lamps appeared.
+
+An interesting filament was developed by Parker and Clark by using as a
+core a small filament of carbon. This flashed in an atmosphere
+containing a vapor of a compound of silicon, became coated with silicon.
+This filament was of high specific resistance and appeared to have
+promise. It has not been introduced commercially and doubtless it cannot
+compete with the latest tungsten lamps.
+
+Electric incandescent lamps are the present mainstay of electric
+illumination and, it might be stated, of progress in lighting. Wonderful
+achievements have been accomplished in other modes of lighting and the
+foregoing statement is not meant to depreciate those achievements.
+However, the incandescent filament lamp has many inherent advantages.
+The light-source is enclosed in an air-tight bulb which makes for a
+safe, convenient lamp. The filament is capable of subdivision, with the
+result that such lamps vary from the minutest spark of the smallest
+miniature lamp to the enormous output of the largest gas-filled tungsten
+lamp. The outputs of these are respectively a fraction of a lumen and
+twenty-five thousand lumens; that is, the luminous intensity varies from
+an equivalent of a small fraction of a standard candle to a single
+light-source emitting light equivalent to two thousand standard candles.
+
+Statistics are cold facts and are usually uninteresting in a volume of
+this character, but they tell a story in a concise manner. The
+development of the modern incandescent lamp has increased the intensity
+of light available with a great decrease in cost, and this progressive
+development is shown easily by tables. For example, since the advent of
+the tungsten lamp the average candle-power and luminous efficiency of
+all the lamps sold in this country has steadily increased, while the
+average wattages of the lamps have remained virtually stationary.
+
+
+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            51           10.56
+
+It will be noted that the luminous intensity of incandescent filament
+lamps has steadily increased since the carbon lamp was superseded, and
+that in a period of ten years of organized research behind the tungsten
+lamp the luminous efficiency (lumens per watt) has trebled. In other
+words, everything else remaining unchanged, the cost of light in ten
+years was reduced to one third. But the reduction in cost has been more
+than this, as will be shown later. During the same span of years the
+percentage of carbon filament lamps of the total filament lamps sold
+decreased from 100 per cent. in 1907 to 13 per cent. in 1917. At the
+same time the percentage of tungsten (Mazda) lamps increased from
+virtually zero in 1907 to about 87 per cent. in 1917. The tantalum lamp
+had no opportunity to become established, because the tungsten lamp
+followed its appearance very closely. In 1910 the sales of the former
+reached their highest mark, which was only 3.5 per cent. of all the
+lamps sold in the United States. From a lowly beginning the number of
+incandescent filament lamps sold for use in this country has grown
+rapidly, reaching nearly two hundred million in 1919.
+
+
+
+
+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.
+
+[Illustration: THE MOORE NITROGEN TUBE
+
+In lobby of Madison Square Garden]
+
+[Illustration: CARBON-DIOXIDE TUBE FOR ACCURATE COLOR-MATCHING]
+
+[Illustration: MODERN STREET LIGHTING
+
+Tunnels of light boring through the darkness provide safe channels for
+modern traffic]
+
+The open-arc lamp possessed the disadvantage of emitting a very unsteady
+light and of consuming the carbons so rapidly that daily trimming was
+often necessary. In 1893 the enclosed arc appeared and although it
+consumed as much electrical energy as the open-arc and emitted
+considerably less light, it possessed the great advantage of operating a
+week without requiring a renewal of carbons. By surrounding the arc
+by means of a glass globe, little oxygen could come in contact with the
+carbons and they were not consumed very rapidly. The light was fairly
+steady and these arcs operated satisfactorily on alternating current.
+The latter feature simplified the generating and distributing equipment
+of the central station.
+
+The magnetite or luminous arc-lamp next appeared and met with
+considerable success. It was more efficient than the preceding lamps but
+was handicapped by being solely a direct-current device. Those familiar
+with the generation and distribution of electricity will realize this
+disadvantage. However, its luminous intensity just below the horizontal
+was about 700 candles and its general distribution of light was fairly
+satisfactory. Later the flame-arcs began to appear and they were
+installed to some extent. The arc-lamp has served well in
+street-lighting from the year 1877, when the open-arc was introduced,
+until the present time, when the luminous-arc is the chief survivor of
+all the arc-lamps.
+
+The carbon incandescent filament lamp was used extensively until 1909,
+when the tungsten filament lamp began to replace it very rapidly.
+However, it was not until 1914, when the gas-filled tungsten lamp
+appeared, that this type of light-source could compete with arc-lamps on
+the basis of efficiency. The helical construction of the filament made
+it possible to confine the filament of a high-intensity tungsten lamp in
+a small space and for the first time a high degree of control of the
+light of street lamps was possible. Prismatic "refractors" were
+designed, somewhat on the principle of the lighthouse refractor, so
+that the light would be emitted largely just below the horizontal. This
+type of distribution builds up the illumination at distant points
+between successive street lamps, which is very desirable in
+street-lighting. The incandescent filament lamp possesses many
+advantages over other systems. It is efficient; capable of subdivision;
+operates on direct and alternating current; requires little attention;
+and is capable of most successful use with light-controlling apparatus.
+
+According to the reports of the Department of Commerce the number of
+electric arc-lamps for street-lighting supplied by public electric-light
+plants decreased from 348,643 in 1912 to 256,838 in 1917, while the
+number of electric incandescent filament lamps increased from 681,957 in
+1912 to 1,389,382 in 1917.
+
+Street-lighting is not only a reinforcement for the police but it
+decreases accidents and has come to be looked upon as an advertising
+medium. In the downtown districts the high-intensity "white-way"
+lighting is festive. The ornamental street lamps have possibilities in
+making the streets attractive and in illuminating the buildings.
+However, it is to be hoped that in the present age the streets of cities
+and towns will be cleared of the ragged equipment of the telephone and
+lighting companies. These may be placed in the alleys or underground,
+leaving the streets beautiful by day and glorified at night by the
+torches of advanced civilization.
+
+
+
+
+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 square root of Height of object in
+feet. For example, the top of a tower 100 feet high is visible to an eye
+at sea-level a distance of 8/7 square root of 100 = 80/7 = 11.43
+miles. Now if the eye is 49 feet above sea-level, a similar computation
+will show how far away it may be seen by the original eye at sea-level.
+This is 8/7 square root of 49 = 8 miles. Hence an eye 49 feet above
+sea-level will be able to see the top of the 100-foot tower at a
+distance of 11.43 + 8 or 19.43 nautical miles. Under these conditions an
+imaginary line drawn from the top of the tower to the eye will be just
+tangent to the spherical surface of the sea at a distance of 8 miles
+from the eye and 11.43 miles from the tower.
+
+The luminous intensity of a light-source or of the beam of light is
+directly responsible for the range. The luminous intensity of the early
+beacon-fires and oil-lamps was equivalent to a few candles. The
+improvements in light-sources and also in reflecting and refracting
+optical systems have steadily increased the candle-power of the beams,
+until to-day the beams from gas-lamps have intensities as high as
+several hundred thousand candle-power. The beams sent forth by modern
+lighthouses equipped with electric lamps and enormous light-gathering
+devices are rated in millions of candle-power. In fact, Navesink Light
+at the entrance of New York Bay is rated as high as 60,000,000
+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.
+
+[Illustration: A. A COMPLETED LIGHTHOUSE LENS]
+
+[Illustration: B. TORRO POINT LIGHTHOUSE, PANAMA CANAL]
+
+[Illustration: AMERICAN SEARCH-LIGHT POSITION ON WESTERN FRONT IN 1919]
+
+[Illustration: AMERICAN STANDARD FIELD SEARCH-LIGHT AND POWER UNIT]
+
+Doubtless, the reader has noted that reliability, simplicity, and low
+cost of operation are the primary considerations for light-sources used
+as aids to navigation. This accounts for the continued use of oil and
+gas. From an optical standpoint the electric arc-lamps and
+concentrated-filament lamps are usually superior to the earlier sources
+of light, but the complexity of a plant for generating electricity is
+usually a disadvantage in isolated places. The larger light-ships are
+now using electricity generated by apparatus installed in the vessels.
+There seems to be a tendency toward the use of more buoys and fewer
+lighthouses, but the beam-intensities of the latter are increasing.
+
+In the hundred years since the Boston Light was built the same great
+changes wrought by the development of artificial light in other
+activities of civilization have appeared in the beacons of the mariner.
+The development of these aids to navigation has been wonderful, but it
+must go on and on. The surface of the earth comprises 51,886,000 square
+statute miles of land and 145,054,000 square miles of water. Three
+fourths of the earth's surface is water and the oceans will always be
+highways of world commerce. All the dangers cannot be overcome, but
+human ingenuity is capable of great achievements. Wreckage will appear
+along the shore-lines despite the lights, but the harvest of the shoals
+has been much reduced since the time described by Robert Louis
+Stevenson, when the coast people in the Orkneys looked upon wrecks as a
+source of gain. He states:
+
+     It had become proverbial with some of the inhabitants to
+     observe that "if wrecks were to happen, they might as well be
+     sent to the poor island of Sanday as anywhere else." On this
+     and the neighboring island, the inhabitants have certainly had
+     their share of wrecked goods. On complaining to one of the
+     pilots of the badness of his boat's sails, he replied with some
+     degree of pleasantry, "Had it been His [God's] will that you
+     come na here wi these lights, we might a' had better sails to
+     our boats and more o' other things."
+
+     In the leasing of farms, a location with a greater probability
+     of shipwreck on the shore brought a much higher rent.
+
+
+
+
+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 manoeuvers of the enemy; rockets brought aid to
+beleaguered vessels and troops; pistol lights fired by the aërial
+observer directed artillery fire; and many other devices of artificial
+light were in the fray. Many improvements were made in search-lights and
+in signaling devices and the elements of the festive fireworks of past
+ages were improved and developed for the needs of modern warfare.
+
+Night after night along the battle front flares were sent up to reveal
+patrols and any other enemy activity. On the slightest suspicion great
+swarms of these brilliant lights would burst forth as though flocks of
+huge fireflies had been disturbed. They were even used as light
+barrages, for movements could be executed in comparative safety when a
+large number of these lights lay before the enemy's trenches sputtering
+their brilliant light. The airman dropped flares to illuminate his
+target or his landing field. The torches of past parades aided the
+soldier in his night operations and rockets sent skyward radiated their
+messages to headquarters in the rear. The star-shell had the same
+missions as other flares, but it was projected by a charge of powder
+from a gun. These and many modifications represent the useful
+applications of what formerly were mere "fireworks." Those which are
+primarily signaling devices are discussed in another chapter, but the
+others will be described sufficiently to indicate the place which
+artificial light played in certain phases of warfare.
+
+The illuminating compounds used in these devices are not particularly
+new, consisting essentially of a combustible powder and chemical salts
+which make the flame luminous and give it color when desired. Among the
+ingredients are barium nitrate, potassium perchlorate, powdered
+aluminum, powdered magnesium, potassium nitrate, and sulphur. One of the
+simplest mixtures used by the English is,
+
+     Barium nitrate          37 per cent.
+     Powdered magnesium      34 per cent.
+     Potassium nitrate       29 per cent.
+
+The magnesium is coated with hot wax or paraffin, which not only acts as
+a binder for the mixture when it is pressed into its container but also
+serves to prevent oxidation of the magnesium when the shells are stored.
+The barium and potassium nitrates supply the oxygen to the magnesium,
+which burns with a brilliant white flame. The potassium nitrate takes
+fire more readily than the barium nitrate, but it is more expensive than
+the latter.
+
+Owing to the cost of magnesium, powdered aluminum has been used to some
+extent as a substitute. Aluminum does not have the illuminating value of
+magnesium and it is more difficult to ignite, but it is a good
+substitute in case of necessity. An English mixture containing these
+elements is,
+
+     Barium nitrate       58 per cent.
+     Magnesium            29 per cent.
+     Aluminum             13 per cent.
+
+Mixtures which are slow to ignite must be supplemented by a primary
+mixture which is readily ignited. For obtaining colored lights it is
+only necessary to add chemicals which will give the desired color. The
+mixtures can be proportioned by means of purely theoretical
+considerations; that is, just enough oxygen can be present to burn the
+fuel completely. However, usually more oxygen is supplied than called
+for by theory.
+
+The illuminating shell is perhaps the most useful of these devices to
+the soldier. It has been constructed with and without parachutes, the
+former providing an intense light for a brief period because it falls
+rapidly. These shells of the larger calibers are equipped with
+time-fuses and are generally rather elaborate in construction. The shell
+is of steel, and has a time-fuse at the tip. This fuse ignites a
+charge of black powder in the nose of the shell and this explosion
+ejects the star-shell out of the rear of the steel casing. At the same
+time the black powder ignites the priming mixture next to it, which in
+turn ignites the slow-burning illuminating compound. The star-shell has
+a large parachute of strong material folded in the rear of the casing
+and the cardboard tube containing the illuminating mixture is attached
+to it. The time of burning varies, but is ordinarily less than a minute.
+Certain structural details must be such as to endure the stresses of a
+high muzzle velocity. Furthermore, a velocity of perhaps 1000 feet per
+second still obtains when the star-shell with its parachute is ejected
+at the desired point in the air.
+
+The non-parachute illuminating shell is designed to give an intense
+light for a brief interval and is especially applicable to defense
+against air raids. Such a light aims to reveal the aircraft in order
+that the gunners may fire at it effectively. These shells are fitted
+with time-fuses which fire the charge of black powder at the desired
+interval after the discharge of the shell from the gun. The contents of
+the shell are thereby ejected and ignited. The container for the
+illuminating material is so designed that there is rapid combustion and
+consequently a brilliant light for about ten seconds. The enemy airman
+in this short time is unable to obtain any valuable knowledge pertaining
+to the earth below and furthermore he is likely to be temporarily
+blinded by the brilliant light if it is near him.
+
+The rifle-light which resembles an ordinary rocket, is fired from a
+rifle and is designed for short-range use. It consists of a steel
+cylindrical shell a few inches long fastened to a steel rod. A parachute
+is attached to the cardboard container in which the illuminating mixture
+is packed and the whole is stowed away in the steel shell. Shore
+delay-fuses are used for starting the usual cycle of events after the
+rifle-light has been fired from the gun. The steel rod is injected into
+the barrel of a rifle and a blank cartridge is used for ejecting this
+rocket-like apparatus. Owing to inertia the firing-pin in the shell
+operates and the short delay-fuse is thus fired automatically an instant
+after the trigger of the rifle is pulled.
+
+Illuminating "bombs" of the same general principles are used by airmen
+in search of a landing for himself or for a destructive bomb; in
+signaling to a gunner, and in many other ways. They are simple in
+construction because they need not withstand the stresses of being fired
+from a gun; they are merely dropped from the aircraft. The mechanism of
+ignition and the cycle of events which follow are similar to those of
+other illuminating shells.
+
+The value of such artificial-lighting devices depends both upon luminous
+intensity and time of burning. Although long-burning is not generally
+required in warfare, it is obvious that more than a momentary light is
+usually needed. In general, high candle-power and long-burning are
+opposed to each other, so that the most intense lights of this character
+usually are of short duration. Typical performances of two flares of the
+same composition are as follows:
+
+                                    Flare No. 1  Flare No. 2
+     Average candle-power            270,000       95,000
+     Seconds of burning                10            35
+     Candle-seconds                 2,700,000     3,325,000
+     Cubic inches of compound           6             7
+     Candle-seconds per cubic inch   450,000       475,000
+     Candle-hours per cubic inch       125           132
+
+The illuminating compound was the same in these two flares, which
+differed only in the time allowed for burning. Of course, the
+measurements of the luminous intensity of such flares is difficult
+because of the fluctuations, but within the errors of the measurements
+it is seen that the illuminating power of the compound is about the same
+regardless of the time of burning. The light-source in the case of
+burning powders is really a flame, and inasmuch as the burning end hangs
+downward, more light is emitted in the lower hemisphere than in the
+upper. The candle-power of the largest flares equals the combined
+luminous intensities of 200 street arc-lamps or of 10,000 ordinary
+40-watt tungsten lamps such as are used in residence lighting.
+
+It is interesting to note the candle-hours obtained per cubic inch of
+compound and to find that the cost of this light is less than that of
+candles at the present time and only five or ten times greater than that
+of modern electric lighting.
+
+Illuminating shells in use during the recent war were designed for
+muzzle velocities as high as 2700 feet per second and were gaged to
+ignite at any distance from a quarter of a mile to several miles. The
+maximum range of illuminating shells fired from rifles was about 200
+yards; for trench mortars about one mile; and from field and naval guns
+about four miles.
+
+The search-light has long been a valuable aid in warfare and during the
+recent conflict considerable attention was given to its development and
+application. It is used chiefly for detecting and illuminating distant
+targets, but this covers a wide range of conditions and requirements. In
+order that a search-light may be effective at a great distance, as much
+as possible of the light emitted by a source is directed into a beam of
+light of as nearly parallel rays as can be obtained. Reflectors are
+usually employed in military search-lights, and in order that the beam
+may be as nearly parallel (minimum divergence) as possible, the light
+must be emitted by the smallest source compatible with high intensity.
+This source is placed at the proper point in respect to a large
+parabolic reflecter which renders the rays parallel or nearly so.
+
+Ever since its advent the electric arc has been employed in large
+search-lights, with which the army and the navy were supplied; however,
+the greatest improvements have been made under the stress of war. The
+science of aëronautics advanced so rapidly during the recent war that
+the necessity for powerful search-lights was greatly augmented and as
+the conflict progressed the enemy airmen came to look upon the newly
+developed ones with considerable concern. The rapidly moving aircraft
+and its high altitude brought new factors into the design of these
+lights. It now became necessary to have the most intense beam and to be
+able to sweep the heavens with it by means of delicate controlling
+apparatus, for the targets were sometimes minute specks moving at high
+speed at altitudes as high as five miles. Furthermore, owing to the
+shifting battle areas, mobile apparatus was necessary.
+
+The control of light by means of reflectors has been studied for
+centuries, but until the advent of the electric arc the light-sources
+were of such large areas that effective control was impossible. Optical
+devices generally are considered in connection with "point sources," but
+inasmuch as no light can be obtained from a point, a source of small
+dimensions and of high brightness is the most effective compromise.
+Parabolic mirrors were in use in the eighteenth century and their
+properties were known long before the first search-light worthy of the
+name was made in 1825 by Drummond, who used as a source of light a piece
+of lime heated to incandescence in a blast flame. He finally developed
+the "lime-light" by directing an oxyhydrogen flame upon a piece of lime
+and this device was adapted to search-lights and to indoor projection.
+It is said that the first search-light to be used in warfare was a
+Drummond lime-light which played a part in the attack on Fort Wagner at
+Charleston in 1863.
+
+In 1848 the first electric arc lamp used for general lighting was
+installed in Paris. It was supplied with current by a large voltaic
+cell, but the success of the electric arc was obliged to await the
+development of a more satisfactory source of electricity. A score of
+years was destined to elapse, after the public was amazed by the first
+demonstration, before a suitable electric dynamo was invented. With the
+advent of the dynamo, the electric arc was rapidly developed and thus
+there became available a concentrated light-source of high intensity
+and great brilliancy. Gradually the size was increased, until at the
+present time mirrors as large as seven feet in diameter and electric
+currents as great as several hundred amperes are employed. The beam
+intensities of the most powerful search-lights are now as great as
+several hundred million candles.
+
+The most notable advance in the design of arc search-lights was achieved
+in recent years by Beck, who developed an intensive flame carbon-arc.
+His chief object was to send a much greater current through the arc than
+had been done previously without increasing the size of the carbons and
+the unsteadiness of the arc. In the ordinary arc excessive current
+causes the carbons to disintegrate rapidly unless they are of large
+diameter. Beck directed a stream of alcohol vapor at the arc and they
+were kept from oxidizing. He thus achieved a high current-density and
+much greater beam intensities. He also used cored carbons containing
+certain metallic salts which added to the luminous intensity, and by
+rotation of the positive carbon so that the crater was kept in a
+constant position, greater steadiness and uniformity were obtained.
+Tests show that, in addition to its higher luminous efficiency, an arc
+of this character directs a greater percentage of the light into the
+effective angle of the mirror. The small source results in a beam of
+small divergence; in other words, the beam differs from a cylinder by
+only one or two degrees. If the beam consisted entirely of parallel rays
+and if there were no loss of light in the atmosphere by scattering or by
+absorption, the beam intensity would be the same throughout its entire
+length. However, both divergence and atmospheric losses tend to reduce
+the intensity of the beam as the distance from the search-light
+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:
+
+              Hours       Equivalent of          Candle-hours
+     Year   per night    light in candles    per night     per year
+     1800       3               5               15            5,500
+     1850       3               8               24            8,700
+     1860       3              11               33           12,000
+     1870       3              22               66           24,000
+     1880       3.5            36              126           46,000
+     1890       4              50              200           73,000
+     1900       5             154              770          280,000
+
+It is seen from the foregoing that in a century the candle-equivalent
+obtainable for the same cost to the householder increased at least
+thirty times, while the hours during which this light is used have
+nearly doubled. In other words, in the nineteenth century the
+candle-hours obtainable for $20.00 per year increased about fifty
+times. Stated in another manner, the cost of light at the end of the
+century was about one fiftieth that of candle light at the beginning of
+the century. One authority in computing the expense of lighting to the
+householder in a large city of this country has stated that
+
+     coincident with an increase of 1700 per cent. in the amount of
+     night lighting of an American family, in average circumstances,
+     using gas for light, there has come a reduction in the cost of
+     the year's lighting of 34 per cent. or approximately $7.50 per
+     year; and that the cost of lighting per unit of light--the
+     candle-hour--is now but 2.8 per cent. of what it was in the
+     first half of the nineteenth century. No other necessity of
+     household use has been so cheapened and improved during the
+     last century.
+
+In general, the light-user has taken advantage of the decrease by
+increasing the amount of light used and the period during which it is
+used. In this manner the greatly diminished cost of light has been a
+marked sociological and economic influence.
+
+After Murdock made his first installation of gas-lighting in an
+industrial plant early in the nineteenth century, he published a
+comparison of the expense of operation with that of candle-lighting. He
+arrived at the costs of light equivalent to 1000 candle-hours as
+follows:
+
+                                                 1000 candle-hours
+     Gas-lighting at a rate of two hours per day     $1.95
+          "        " "  "   "  three "    "   "       1.40
+     Candle-lighting                                  6.50
+
+It is seen that the longer hours of burning reduce the cost of
+gas-lighting by reducing the percentage of overhead charges. There are
+no such factors in lighting by candles because the whole "installation"
+is consumed. This is an early example of which an authentic record is
+available. At the present time a certain amount of light obtained for
+$1.00 with efficient tungsten filament lamps, costs $2.00 if obtained
+from kerosene flames and about $50.00 if obtained by burning candles.
+
+In order to obtain the cost of an equivalent amount of light throughout
+the past century a great many factors must be considered. Obviously, the
+results obtained by various persons will differ owing to the unavoidable
+factor of judgment; however, the following list of approximate values
+will at least indicate the trend of the price of light throughout the
+century or more of rapid developments in light-production. A fair
+average of the retail values of fuels and of electrical energy and an
+average luminous efficiency of the light-sources involved have been used
+in making the computations. The figures apply particularly to this
+country.
+
+TABLE SHOWING THE APPROXIMATE TOTAL COST OF 1000 CANDLE-HOURS FOR
+VARIOUS PERIODS
+
+                                               Per 1000
+                                             candle-hours
+     1800 to 1850, sperm-oil                     $2.40
+                   tallow candle                  5.00
+     1850 to 1865, kerosene                       1.65
+                   tallow candle                  6.85
+     1865 to 1875, kerosene                        .75
+                   tallow candle                  6.25
+                   gas, open-flame                 .90
+     1875 to 1885, kerosene                        .25
+                   gas, open-flame                 .60
+     1885 to 1895, kerosene                        .15
+                   gas, open-flame                 .40
+     1895 to 1915, gas mantle                      .07
+                   carbon filament                 .38
+                   metallized filament             .28
+                   tungsten filament (vacuum)      .12
+                   tungsten filament (gas-filled)  .07
+
+In these days the cost of living has claimed considerable attention and
+it is interesting to compare that of lighting. In the following table
+the price of food and of electric lighting are compared for twenty years
+preceding the recent war. The great disturbance due to the war is
+thereby eliminated from consideration, but it should be noted that since
+1914 the price of food has greatly increased but that of electric
+lighting has not changed materially. The cost of each commodity is taken
+as one hundred units for the year 1894 but, of course, the actual cost
+of living for the householder is perhaps a hundred times greater than
+the cost of electric lighting.
+
+     Year         Food    Electric lighting
+     1894         100            100
+     1896          80             92
+     1898          92             90
+     1900         100             85
+     1902         113             77
+     1904         110             77
+     1906         115             57
+     1908         128             30
+     1910         138             28
+     1912         144             23
+     1914         145             17
+
+One feature of electric lighting which puzzles the consumer and which
+gives the politicians an opportunity for crying "discrimination" and
+"injustice" at the public-service company is the great variation in
+rates. There is no discrimination or injustice when the householder, for
+example, must pay more for his lighting than a factory pays. The rates
+are not only affected by "demand" but by the period in which the demand
+comes. Residence lighting is chiefly confined to certain hours from 5 to
+9 P. M. and there is a great "peak" of demand at this time. The
+central-stations must have equipment available for this short-time
+demand and much of the capacity of the equipment is unused during the
+remainder of the day. The factory which uses electricity throughout the
+day or night or both is helping to keep the central-station operating
+efficiently. The equipment necessary to supply electricity to the
+factory is operating long hours. Not only is this overhead charge much
+less for factories and many other consumers than for the householder,
+but the expense of accounting, of reading meters, etc., is about the
+same for all classes of consumers. Therefore, this is an appreciable
+item on the bill of the small consumer.
+
+Doubtless, the public does not realize that the enormous decrease in the
+cost of lighting during the past century is due largely to the fact that
+the lighting industry has grown large. Increased production is
+responsible for some of this decrease and science for much of it. The
+latter, having been called to the aid of the manufacturers, who are
+better able by virtue of their magnitude to spend time and resources
+upon scientific developments, has responded with many improvements which
+have increased the efficiency of light-production. Some figures of the
+Census Bureau may be of interest. These are given for 1914 in order that
+the abnormal conditions due to the recent war may be avoided. The
+figures pertaining to the manufacture of gas for sale which do not
+include private plants are as follows for the year 1914 for this
+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.
+
+[Illustration: SIGNAL-LIGHT FOR AIRPLANE]
+
+[Illustration: TRENCH LIGHT-SIGNALING OUTFIT]
+
+[Illustration: AVIATION FIELD LIGHT-SIGNAL PROJECTOR]
+
+[Illustration: SIGNAL SEARCH-LIGHT FOR AIRPLANE]
+
+[Illustration: UNSAFE, UNPRODUCTIVE LIGHTING WORTHY OF THE DARK AGES]
+
+[Illustration: THE SAME FACTORY MADE SAFE, CHEERFUL, AND MORE PRODUCTIVE
+BY MODERN LIGHTING]
+
+There is another aspect of the subject which deals particularly with the
+safety of the light-source or method of lighting. As each innovation
+in lighting appeared during the past century there immediately arose the
+question of safety. The fire-hazard of open flames received attention in
+early days, and when gas-lighting appeared it was condemned as a poison
+and an explosive. Mineral-oil lamps introduced the danger of explosions
+of the vapors produced by evaporation. When electric lighting appeared
+it was investigated thoroughly. The result of all this has been an
+effort to make lamps and methods safe. Insurance companies have the
+relative safety of these systems established to their satisfaction and
+to-day little fire-hazard is attached to the present modes of general
+lighting if proper precautions have been taken.
+
+When electric lighting was first introduced the public looked upon
+electricity as dangerous and naturally many questions pertaining to
+hazards arose. The distribution of electricity has been so highly
+perfected that little is heard of the hazards which were so magnified in
+the early years. Data gathered between 1884 and 1889 showed that about
+13,000 fires took place in a certain district. Of these, 42 were
+attributed to electric wires; 22 times as many to breakage and explosion
+of kerosene lamps; and ten times as many through carelessness with
+matches. These figures cannot be taken at their face value because of
+the absence of data showing the relative amount of electric and kerosene
+lighting; nevertheless they are interesting because they represent the
+early period.
+
+There are industries where unusual care must be exercised in regard to
+the lighting. In certain chemical industries no lamps are used excepting
+the incandescent lamp and this is enclosed in an air-tight glass globe.
+Even a public-service gas company cautions its employees and patrons
+thus: "_Do not look for a gas-leak with a naked light! Use electric
+light._" The coal-mine offers an interesting example of the precautions
+necessary because the same type of problems are found in it as in
+industries in general, with the additional difficulties attending the
+presence or possible presence of explosive gas. The surroundings in a
+coal-mine reflect a small percentage of the light, so that much light is
+wasted unless the walls are whitewashed. This is a practical method for
+increasing safety in coal-mines. However, the most dangerous feature is
+the light-source itself. According to the Bureau of Mines during the
+years 1916 and 1917 about 60 per cent. of the fatalities due to gas and
+coal-dust explosions were directly traceable to the use of defective
+safety lamps and to open flames.
+
+In the early days of coal-mining it was found that the flame of a candle
+occasionally caused explosions in the mines. It was also found that
+sparks of flint and steel would not readily ignite the gas or coal-dust
+and this primitive device was used as a light-source. Of course,
+statistics are unavailable concerning the casualties in coal-mines
+throughout the past centuries, but with the accidents not uncommon in
+this scientific age, with its elaborate organizations striving to stamp
+out such casualties, there is good reason to believe that previous to a
+century or two ago the risks of coal-mining must have been great. Open
+flames have been widely used in this industry, but there has always been
+the risk of the presence or the appearance of gas or explosive dust.
+
+The early open-flame lamps not only were sources of danger but their
+feeble varying intensity caused serious damage to the eyesight of
+miners. This factor is always present in inadequate and improper
+lighting, but its influence is noticeable in coal-mining in the nervous
+disease affecting the eyes which is known as nystagmus. The symptoms of
+the disease are inability to see at night and the dazzling effect of
+ordinary lamps. Finally objects appear to the sufferer to dance about
+and his vision is generally very much disturbed.
+
+The oil-lamps used in coal-mining have a luminous intensity equivalent
+to about one to four candles, but owing to the atmospheric conditions in
+the mines a flame does not burn as brightly as in the fresh air. The
+possibility of explosion due to the open flame was eliminated by
+surrounding it with a metal gauze. Davy was the inventor of this device
+and his safety lamp introduced about a hundred years ago has been a boon
+to the coal-miner. Various improvements have been devised, but Davy's
+lamp contained the essentials of a safety device. The flame is
+surrounded by a cylinder of metal gauze which by forming a much cooler
+boundary prevents the mine-gas from becoming heated locally by the lamp
+flame to a sufficient temperature to ignite and consequently to explode.
+This device not only keeps the flame from igniting the gas but it also
+serves as an indicator of the amount of gas present, by the variation in
+the size and appearance of the tip of the flame. However, the gauze
+reduces the luminous output, and as it accumulates soot and dust the
+light is greatly diminished. One of these lamps is about as luminous as
+a candle, initially, but its intensity is often reduced by accumulations
+upon the gauze to only one fifth of the initial value.
+
+The acetylene lamp is the best open-flame light-source available to the
+miner, for several reasons. It is of a higher candle-power than the
+others and as it is a burning gas, there is not the danger of flying
+sparks as in the case of burning wicks. The greater intensity of
+illumination affords a greater safety to the miner by enabling him to
+detect loose rock which may be ready to fall upon him. However, this
+lamp may be a source of danger, owing to the fact that it will burn more
+brilliantly in a vitiated atmosphere than other flame-lamps. Another
+disadvantage is the possibility of calcium carbide accidentally spilt
+coming in contact with water and thereby causing the generation of
+acetylene gas. If this is produced in the mine in sufficient quantities
+it is a danger which may not be suspected. If ignited it will explode
+and may also cause severe burns.
+
+The electric lamp, being an enclosed light-source capable of being
+subdivided and fed by a small portable battery, early gave promise of
+solving the problem of a safe mine-lamp of adequate candle-power. Much
+ingenuity has been applied to the development of a portable electric
+safety mine-lamp, and several such lamps are now approved by the Bureau
+of Mines. Two general types are being manufactured, the cap outfit and
+the hand outfit. They consist essentially of a lamp in a reflector whose
+aperture is closed with a sheet or a lens of clear glass. The battery
+may be of the "dry" or "storage" type and in the case of the cap outfit
+the battery is carried on the back. The specifications for these lamps
+demand that a luminous intensity averaging at least 0.4 candle be
+maintained throughout twelve consecutive hours of operation. At no time
+during this period shall the output of light fall below 1.25 lumens for
+a cap-lamp and below 3 lumens for a hand-lamp. Inasmuch as these are
+equipped with reflectors, the specifications insist that a circle of
+light at least seven feet in diameter shall be cast on a wall twenty
+inches away. It appears that a portable lamp is an economic necessity in
+the coal-mines, on account of the expense, inconvenience, and possible
+dangers introduced by distribution systems such as are used in most
+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.
+
+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.
+
+[Illustration: LOCOMOTIVE ELECTRIC HEADLIGHT]
+
+[Illustration: SEARCH-LIGHT ON A FIRE-BOAT]
+
+[Illustration: BUILDING SHIPS UNDER ARTIFICIAL LIGHT AT HOG ISLAND
+SHIPYARD]
+
+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.
+
+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.
+
+Many other instances could be cited in which artificial light is very
+closely associated with the cost of living. Overseas shipment of fruit
+from the Canadian Northwest is responsible for a decided innovation in
+fruit-picking. In searching for a cause of rotting during shipment it
+was finally concluded that the temperature at the time of picking was
+the controlling factor. As a consequence, daytime was considered
+undesirable for picking and an electric company supplied electric
+lighting for the orchards in order that the picking might be done during
+the cool of night. This change is said to have remedied the situation.
+Cases of threshing and other agricultural operations being carried on at
+night are becoming more numerous. These are just the beginnings of
+artificial light in a new field or in a new relation to civilization.
+Its economic value has been demonstrated in the ordinary fields of
+lighting and these new applications are merely the initial skirmishes
+which precede the conquest of new territory. The modern illuminants have
+been developed so recently that the new possibilities have not yet been
+established. However, artificial light is already a factor on the side
+of the people in the struggle against the increasing cost of living, and
+its future in this direction is still more promising.
+
+
+
+
+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.
+
+[Illustration: In a moving-picture studio
+
+In a portrait studio
+
+ARTIFICIAL LIGHT IN PHOTOGRAPHY]
+
+[Illustration: 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.
+
+[Illustration: In art work
+
+In a haberdashery
+
+JUDGING COLOR UNDER ARTIFICIAL DAYLIGHT]
+
+[Illustration: In an underground tunnel
+
+In an art gallery
+
+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.
+
+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.
+
+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.
+
+[Illustration: FIREWORKS AND ILLUMINATED BATTLE-FLEET AT HUDSON-FULTON
+CELEBRATION]
+
+[Illustration: 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.
+
+[Illustration: 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]
+
+[Illustration: NIAGARA FALLS FLOODED WITH LIGHT]
+
+After the close of the recent war artificial light played a prominent
+part throughout the country in the joyful festivals. A jeweled arch
+erected in New York in honor of the returning soldiers rivaled some of
+the spectacles of the Panama-Pacific Exposition. The arch hung like a
+gigantic curtain of jewels between two obelisks, which rose to a height
+of eighty feet and were surmounted by jeweled forms in the shape of
+sunbursts. Approximately thirty thousand jewels glittered in the beams
+of batteries of arc-projectors. Many of the signs and devices which
+played a part in the "Welcome Home" movement were of striking nature and
+of a character to indicate permanency. The equipment of a large building
+consisted of more than five thousand 10-watt lamps, the entire building
+being outlined with stars consisting of eleven lamps each. The "Brighten
+Up" campaign spread throughout the country. The lighting and
+installation of signs and special patriotic displays, the flooding of
+streets and shop-windows with light without stint, produced an inspiring
+and uplifting effect which did much to restore cheerfulness and
+optimism. A glowing example was set in Washington, where the
+flood-lighting of the Capitol, discontinued shortly after our entrance
+into the war, was resumed.
+
+In Chicago a "Victory Way" was established, with street-lighting posts
+on both sides of the street equipped with red, white, and blue globes
+surmounted by a golden goddess of Victory. One hundred and seventy-five
+projectors were installed along the way on the roofs and in the windows
+of office buildings. A brilliant, scintillating "Altar of Victory" was
+erected at the center of the Way. It was composed of two enormous
+candelabra erected one on each side of a platform ninety feet high.
+These were studded with jewels and supported a curtain of jewels
+suspended from the altar. In the center of the curtain was a huge
+jeweled eagle bearing the Allied flags. This was illuminated by
+arc-projectors which delivered 200,000,000 beam candle-power. In
+addition to these there were many smaller projectors. In the top of each
+candelabra six large red-and-orange lamps were installed in reflectors.
+These illuminated live steam which issued from the top. Surmounting the
+whole was a huge luminous fan formed by beams from large arc
+search-lights. These are only a few of the many lighting effects which
+welcomed the returning soldiers, but they illustrate how much modern
+civilization depends upon artificial light for expressing its feelings
+and emotions. Throughout all these festivals light silently symbolized
+happiness, freedom, and advancement.
+
+Projectors were used on a large scale in several cases before the advent
+of the concentrated filament lamp. W. D'A. Ryan, the leader in
+spectacular lighting, lighted the Niagara Falls in 1907 with batteries
+of arc-projectors aggregating 1,115,000,000-beam candle-power. In 1908
+he used thirty arc-projectors to flood the Singer Tower in New York with
+light and projected light to the flag on top by means of a search-light
+thirty inches in diameter. Many flags waved throughout the war in the
+beams of search-lights, symbolizing a patriotism fully aroused. The
+search-light beam as it bores through the atmosphere at night is usually
+faintly bright, owing to the small amount of fog, dust, and smoke in the
+air. By providing more "substance" in the atmosphere, the beams are made
+to appear brighter. Following this reasoning, Ryan developed his
+scintillator consisting of a battery of search-light beams projected
+upward through clouds of steam which provided an artificial fog. This
+was first displayed at the Hudson-Fulton celebration with a battery of
+arc search-lights totaling 1,000,000,000-candle-power.
+
+All these effects despite their magnitude were dwarfed by those at the
+Panama-Pacific Exposition, and inasmuch as this up to the present time
+represents the crowning achievement in spectacular lighting, some of the
+details worked out by Ryan may be of interest. In general, the lighting
+effects departed from the bizarre outline lighting in which glaring
+light-sources studded the structures. The radiant grandeur and beauty
+of flood-lighting from concealed light-sources was the key-note of the
+lighting. In this manner wonderful effects were obtained, which not only
+appealed to the eye and to the artistic sensibility but which were free
+from glare. By means of flood-lighting and relief-lighting from
+concealed light-sources the third dimension or depth was obtained and
+the architectural details and colorings were preserved. A great many
+different kinds of devices and lamps were used to make the night effects
+superior in grandeur to those of daytime. The Zone or amusement section
+was lighted with bare lamps in the older manner and the glaring bizarre
+effects contrasted the spectacular lighting of the past with the
+illumination of the future.
+
+In another section the visitor was greeted with a gorgeous display of
+carnival spirit. Beautifully colored heraldic shields on which were
+written the early history of the Pacific coast were illuminated by
+groups of luminous arc-lamps on standards varying from twenty-five to
+fifty-five feet in height. The Tower of Jewels with more than a hundred
+thousand dangling gems was flood-lighted, and the myriads of minute
+reflected images of light-sources glittering against the dark sky
+produced an effect surpassing the dreams of imagination. Shadows and
+high-lights of striking contrasts or of elusive colors greeted the
+visitor on every hand. Individual isolated effects of light were to be
+found here and there. Fire hissed from the mouths of serpents and cast
+the spell of mobile light over the composite Spanish-Gothic-Oriental
+setting. A colored beam of a search-light played here and there.
+Mysterious vapors rising from caldrons were in reality illuminated
+steam. Symbolic fountain groups did not escape the magic touch of the
+lighting wizard.
+
+In the Court of the Universe great areas were illuminated by two
+fountains rising about a hundred feet above the sunken gardens. One of
+these symbolized the setting sun, the other the rising sun. The shaft
+and ball at the crest of each fountain were glazed with heavy opal glass
+imitating travertine marble and in these were installed incandescent
+lamps of a total candle-power of 500,000. The balustrade seventy feet
+above the sunken gardens was surmounted by nearly two hundred
+incandescent filament search-lights. Light was everywhere, either
+varying in color into a harmonious scene or changing in light and shadow
+to mold the architecture and sculpture. The enormous glass dome of the
+Palace of Horticulture was converted into an astronomical sphere by
+projecting images upon it in such a manner that spots of light revolved;
+rings and comets which appeared at the horizon passed on their way
+through the heavens, changing in color and disappearing again at the
+horizon. All these effects and many more were mirrored in the waters of
+the lagoons and the whole was a Wonderland indeed.
+
+The scintillator consisted of 48 arc search-lights three feet in
+diameter totaling 2,600,000,000 beam candle-power. The lighting units
+were equipped with colored screens and the beams which radiated upward
+were supplied with an artificial fog by means of steam generated by a
+modern express locomotive. The latter was so arranged that the wheels
+could be driven at a speed of sixty miles per hour under brake, thereby
+emitting great volumes of steam and smoke, which when illuminated with
+various colors produced a magnificent spectacle. Over three hundred
+scintillator effects were worked out and this feature of fireless
+fireworks was widely varied. The aurora borealis and other effects
+created by this battery of search-lights extended for many miles. The
+many effects regularly available were augmented on special occasions and
+it is safe to state that this apparatus built upon a huge scale provided
+a flexibility of fireless fireworks never attained even with small-scale
+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.
+
+Those who have not viewed stage-lighting from behind the scenes would
+often be surprised at the crudity of the equipment, and especially at
+the superficial intellects which are responsible for some of the
+realistic effects obtained. But these are the result usually of
+experiment, not of directed knowledge. Furthermore, little thought is
+given to the emotional value of light, shade, and color. The flood of
+light and the spot of light are varied with gaudy color-effects, but how
+seldom is it possible to distinguish a deep relation between the
+lighting and the dramatic incidents!
+
+[Illustration: Soldiers' and Sailors' Monument
+
+Jeweled portal welcoming returned soldiers
+
+ARTIFICIAL LIGHT HONORING THOSE WHO FELL AND THOSE WHO RETURNED]
+
+[Illustration]
+
+[Illustration: 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 enjoys all the blessings of modern lighting, which is
+sufficient proof that cost is an insignificant item.
+
+In order to simplify the discussion of lighting the home the terminology
+of electric-lighting will be used. The principles expounded apply as
+well to gas as to electricity, and owing to the ingenuity of the
+gas-lighting experts, the possibilities of gas-lighting are extensive
+despite its handicaps. There are some places in the home, such as the
+kitchen and basement, where lighting is purely utilitarian in the narrow
+sense, but in most of the rooms the esthetic or, more broadly, the
+psychological aspects of lighting should dominate. Pure utility is
+always a by-product of artistic lighting and furthermore, the lighting
+effects will be without glare when they satisfy all the demands of
+esthetics.
+
+In dealing with lighting in the home the householder should concentrate
+his attention upon lighting effects. Unfortunately, he is not taught to
+do so, for everywhere he turns for help he finds the discussion directed
+toward fixtures and lamps instead of toward lighting effects. However,
+these are merely links in the chain from the meter to the eye. Lamps are
+of interest from the standpoint of quantity and quality of light, and
+fixtures are of importance chiefly as distributers of light. These
+details are merely means to an end and the end is the lighting effect.
+Of course, the fixtures are more important as objects than the wires
+because they are visible and should harmonize with the general
+decorative and architectural scheme.
+
+The home is the theater of life full of various moods and occasions;
+hence the lighting of a home should be flexible. A degree of variety
+should be possible. Controls, wiring, outlets, and fixtures should
+conspire to provide this variety. At the present time the average
+householder does not give much attention to lighting until he purchases
+fixtures. It is probable that he thought of it when he laid out or
+approved the wiring, but usually he does not consider it seriously until
+he visits the fixture-dealer to purchase fixtures. And then
+unfortunately the fixture-dealer does not light his home; he does not
+sell the householder lighting-effects designed to meet the requirements
+of the particular home; he sells merely fixtures.
+
+Unfortunately there are few fixtures available which have definite aims
+in lighting as demanded by the home. Of the great variety of fixtures
+available there are many artistic objects, but it is obvious that little
+attention is given to their design from the standpoint of lighting.
+That the fixture-dealer usually thinks of fixtures as objects and gives
+little or no thought to lighting effects is apparent from his
+conversation and from his display. He exhibits fixtures usually en masse
+and seldom attempts to illustrate the lighting effects produced in the
+room.
+
+The foregoing criticisms are presented to emphasize the fact that
+throughout the field of lighting the great possibilities which have been
+opened by modern light-sources are not fully appreciated. The point at
+which to begin to design the lighting for a home is the wiring.
+Unfortunately this is too often done by a contractor who has given no
+special thought to the possibilities of lighting and to the requirements
+in wiring and switches necessary in order to realize them. At this point
+the householder should attempt to form an opinion as to the relative
+values. Is artificial lighting important enough to warrant an
+expenditure of two per cent. of the total investment in the home and its
+furnishings? The answer will depend upon the extent to which artificial
+light is appreciated. It appears that four or five per cent. is not too
+much if it is admitted that the artificial lighting system ranks next to
+the heating plant in importance and that these two are the most
+important features of an interior of a residence. A switch or a
+baseboard outlet costs an insignificant sum but either may pay for
+itself many times in the course of a few years through its utility or
+convenience.
+
+It appears best to take up this subject room by room because the
+requirements vary considerably, but in order to be specific in the
+discussions, a middle-class home will be chosen. The more important
+rooms will be treated first and various simple details will be touched
+upon because, after all, the proper lighting of a home is realized by
+attention to small details.
+
+The living-room is the scene of many functions. It serves at times for
+the quiet gathering of the family, each member devoted to reading. At
+another time it may contain a happy company engaged at cards or in
+conversation. The lighting requirements vary from a spot or two of light
+to a flood of light. Excepting in the small living-rooms there does not
+appear to be a single good reason for a ceiling fixture. It is nearly
+always in the field of vision when occupants are engaged in
+conversation, and for reading purposes the portable lamp of satisfactory
+design has no rival. Wall brackets cannot supply general lighting
+without being too bright for comfort. If they are heavily shaded they
+may still emit plenty of light upward, but the adjacent spots on the
+walls or ceiling will generally be too bright. Wall brackets may be
+beautiful ornaments and decorative spots of light and have a right to
+exist as such, but they cannot be safely depended upon for adequate
+general lighting on those occasions which demand such lighting.
+
+As a general principle, it is well to visualize the furniture in the
+room when looking at the architect's drawings and it is advantageous
+even to cut out pieces of paper representing the furniture in scale. By
+placing these on the drawings the furnished room is readily visualized
+and the locations of baseboard outlets become evident. It appears that
+the best method of lighting a living-room is by means of decorative
+portable lamps. Such lamps are really lighting-furniture, for they aid
+in decorating and in furnishing the room at all times. A number of these
+lamps in the living-room insures great flexibility in the lighting, and
+the light may be kept localized if desired so that the room is restful.
+A room whose ceiling and walls are brilliantly illuminated is not so
+comfortable for long periods as one in which these areas are dimly
+lighted. Furthermore, the latter is more conducive to reading and to
+other efforts at concentration. The furniture may be readily shifted as
+desired and the portable lamps may be rearranged.
+
+Such lighting serves all the purposes of the living-room excepting those
+requiring a flood of light, but it is easy to conceal elaborate lighting
+mechanisms underneath the shades of portable lamps. Several types of
+portable lamps are available which supply an indirect component as well
+as direct light. The former illuminates the ceiling with a flood of
+light without any discomforting glare. Such a lighting-unit is one of
+the most satisfactory for the home, for two distinct effects and a
+combination of these introduce a desirable element of variety into the
+lighting. Not less than four and preferably six baseboard outlets should
+be provided in a living-room of moderate size. One outlet on the mantel
+is also to be desired for connecting decorative candlesticks, and
+brackets above the fireplace are of ornamental value. Although the
+absence of ceiling fixtures improves the appearance of the room, wiring
+may be provided for ceiling outlets in new houses as a matter of
+insurance against the possible needs of the future. When ceiling
+fixtures are not used, switches may be provided for the mantel brackets
+or certain baseboard outlets in order that light may be had upon
+entering the room.
+
+The merits of a portable lamp may be ascertained before purchasing by
+actual demonstration. Some of them are not satisfactory for
+reading-lamps, owing to the shape of the shade or to the position of the
+lamps. The utility of a table lamp may be determined by placing it upon
+a table and noting the spread of light while seated in a chair beside
+it. A floor lamp may also be tested very easily. A miniature floor lamp
+about four feet in height with an appropriate shade provides an
+excellent lamp for reading purposes because it may be placed by the side
+of a chair or moved about independent of other furniture. A tall floor
+lamp often serves for lighting the piano, but small piano lamps may be
+found which are decorative as well as serviceable in illuminating the
+music without glare.
+
+The dining-room presents an entirely different problem for the setting
+is very definite. The dining-table is the most important area in the
+room and it should be the most brilliantly illuminated area in the room.
+A demonstration of this point is thoroughly convincing. The decorator
+who designs wall brackets for the dining-room is interested in beautiful
+objects of art and not in a proper lighting effect. The fixture-dealer,
+having fixtures to sell and not recognizing that he could fill a crying
+need as a lighting specialist, is as likely to sell a semi-indirect or
+an indirect lighting fixture as he is to provide a properly balanced
+lighting effect with the table brightly illuminated. The indirect and
+semi-indirect units illuminate the ceiling predominantly with the
+result that this bright area distracts attention from the table. A
+brightly illuminated table holds the attention of the diners. Light
+attracts and a semi-darkness over the remainder of the room crowds in
+with a result that is far more satisfactory than that of a dining-room
+flooded with light.
+
+The old-fashioned dome which hung over the dining-table has served well,
+for it illuminated the table and left the remainder of the room dimly
+lighted. But its wide aperture made it necessary to suspend it rather
+low in order that the lamps within should not be visible. It is an
+obtrusive fixture and despite its excellent lighting effect, it went out
+of style. But satisfactory lighting principles never become antiquated,
+and as taste in fixtures changes the principles may be retained in new
+fixtures. Modern domes are available which are excellent for the
+dining-room if the lamps are well concealed. The so-called showers are
+satisfactory if the shades are dense and of such shape as to conceal the
+lamps from the eyes. Various modifications readily suggest themselves to
+the alert fixture-designer. Even the housewife can do much with silk
+shades when the principle of lighting the dining-table is understood.
+The so-called candelabra have been sold extensively for dining-rooms and
+they are fairly satisfactory if equipped with shades which reflect much
+of the light downward. Semi-indirect and indirect fixtures have many
+applications in lighting, but they do not provide the proper effect for
+a dining-room.
+
+It is easy to make a special fixture which will send a component of
+light downward to the table and will permit a small amount of diffused
+light to the ceiling and walls. If a daylight lamp is used for the
+direct component, the table will appear very beautiful. Under this light
+the linen and china are white, flowers and decorations on the china
+appear in their full colors, the silver is attractive, and the various
+color-harmonies such as butter, paprika, and baked potato are enticing.
+This is an excellent place for a daylight lamp if diffused light
+illuminating the remainder of the room and the faces of the diners is of
+a warm tone obtained by warm yellow lamps or by filtering these
+components of the light through orange shades. The ceiling fixture
+should be provided with two circuits and switches. In some cases it is
+easy to provide a dangling plug for connecting such electric equipment
+as a toaster, percolator, or candlesticks. Two candlesticks are
+effective on the buffet, but usually the smallest normal-voltage lamps
+available give too much light. Miniature lamps may be used with a small
+transformer, or two regular lamps may be connected in series. At least
+two baseboard outlets are convenient.
+
+The foregoing deals with the more or less essential lighting of a
+dining-room, but there are various practicable additional lighting
+effects which add much charm to certain occasions. Colored light of low
+intensity obtained from a cove or from "flower-boxes" fastened upon the
+wall is very pleasing. If a cove is provided around the room, two
+circuits containing orange and blue lamps respectively will supply two
+colors widely differing in effect. By mixing the two a beautiful rose
+tint may be obtained. This equipment has been installed with much
+satisfaction. A simpler method of obtaining a similar effect is to use
+imitation flower-boxes plugged into wall outlets. Artificial foliage
+adds to the charm of these boxes. The colored light is merely to add
+another effect on special occasions and its intensity should never be
+high. In the dining-room such unusual effects are not out of place and
+they need not be garish.
+
+The sun-room partakes of the characteristics of the living-room to some
+extent, but, it being smaller, a semi-indirect fixture may be
+satisfactory for general illumination. However, a portable lamp which
+supplies an indirect component of light besides the direct light serves
+admirably for reading as well as for flooding the room with light when
+necessary. Two or three baseboard outlets are desirable for attaching
+decorative or even purely utilitarian lamps. The sun-room is an
+excellent place for utilizing "flower-box" fixtures decorated with
+artificial foliage. In fact, a central fixture may assume the appearance
+of a "hanging basket" of foliage. The library and den offer no problems
+differing from those already discussed in the living-room. A careful
+consideration of the disposition of the furniture will reveal the best
+positions for the outlets. In a small library wall brackets may serve as
+decorative spots of light and if the shades are pendent they may serve
+as lamps for reading purposes. In both these rooms an excellent
+reading-lamp is desired, but it may be decorative as well. Wall outlets
+may be desired for decorative portable lamps upon the bookcases.
+
+The sleeping-room, which commonly is also a dressing-room, often
+exhibits the errors of a lack of foresight in lighting. In most rooms of
+this character there is one best arrangement of furniture and if this
+is determined it is easy to ascertain where the windows and outlets
+should be located. The windows may usually be arranged for twin beds as
+well as for a single one with obvious advantages of flexibility in
+arrangement. With the position of the bureau determined it is easy to
+locate outlets for two wall brackets, one on each side, about sixty-six
+inches above the floor and about five feet apart. When the brackets are
+equipped with dense upright shades, the figure before the mirror is well
+illuminated without glare and sufficient light reaches the ceiling to
+illuminate the whole room.
+
+A baseboard outlet should be available for small portable lamps which
+may be used upon the bureau or for electric heating devices. The same is
+true for the dressing-table; indeed, two small decorative lamps on the
+table serve better than high wall brackets owing to the fact that the
+user is seated. A baseboard outlet near the head of the bed or between
+the beds is convenient for a reading-lamp and for other purposes. An
+outlet in the center of the ceiling controlled by a convenient switch
+may be installed on building, as insurance against future needs or
+desires. But a single lighting-unit in the center of the ceiling does
+not serve adequately the needs at the bureau and dressing-table. In
+fact, two wall brackets properly located with respect to the bureau
+afford a lighting much superior for all purposes in the bedroom to that
+produced by a ceiling fixture.
+
+In the bath-room the principal problem is to illuminate the person,
+especially the face, before the mirror. Many mistakes are made at this
+point, despite the simplicity of the solution. In order to see the
+image of an object in a mirror, the object must be illuminated. It is
+best to do this in a straightforward manner by means of a small
+lighting-unit on each side of the mirror at a height of five feet. Both
+sides of the face will be well illuminated and the light-sources are low
+enough to eliminate objectionable shadows. The units may be merely
+pull-chain sockets containing frosted or opal lamps. A center bracket or
+a single unit suspended from the ceiling is not as satisfactory as the
+two brackets. These afford enough light for the entire bath-room. A
+baseboard or wall outlet is convenient for connecting a heater,
+curling-iron, and other electrically heated devices.
+
+The sewing-room, which in the middle-class home is usually a small room,
+is sometimes used as a bedroom. A ceiling fixture will supply adequate
+general lighting, but a baseboard outlet should be available for a short
+floor lamp or a table lamp for sewing purposes. An intense local light
+is necessary for this occupation, which severely taxes the eyes. A
+so-called daylight lamp serves very well in this case.
+
+[Illustration: OBTAINING TWO DIFFERENT MOODS IN A ROOM BY A PORTABLE
+LAMP WHICH SUPPLIES DIRECT AND INDIRECT COMPONENTS OF LIGHT]
+
+[Illustration: THE LIGHTS OF NEW YORK CITY
+
+Towering shafts of light defy the darkness and thousands of lighted
+windows symbolize man's successful struggle against nature]
+
+In the kitchen the wall brackets are easily located after the positions
+of the range, work-table, sink, etc., are determined. A bracket for each
+is advisable unless they are so located that one will serve two
+purposes. It is customary to have a combination fixture for gas and
+electricity. This is often suspended from the center of the ceiling, but
+inasmuch as the gas-light cannot be close to the ceiling, the fixture
+extends so far downward as to become a nuisance. Furthermore, a
+light-source hung low from the center of the ceiling is in such a
+position that the worker in the kitchen usually works in his shadow. If
+a ceiling outlet is used it should be an electrical socket at the
+ceiling. The combination fixture is best placed on the wall as a
+bracket. The so-called daylight lamps are valuable in the kitchen.
+
+In the basement a generous supply of ceiling outlets adds much to the
+satisfaction of a basement. One in each locker, one before the furnace,
+and a large daylight lamp above but to one side of the laundry trays are
+worth many times their cost. Furthermore, a wall socket for the electric
+iron and washing-machine is a convenience very much appreciated.
+
+In the stairways convenient three-way switches for each of the ceiling
+fixtures represents the best practice. A baseboard outlet in the upper
+hall affords a connection for a decorative lamp and pays for itself many
+times as a place to attach the vacuum-cleaner from which all the rooms
+on that floor may be served. In vestibules and on porches ceiling
+fixtures controlled by means of convenient switches are satisfactory.
+The entrance hall may be made to express hospitality by means of
+lighting which should be adequate and artistic.
+
+An adequate supply of outlets and wall switches is not costly and they
+pay generous dividends. With a scanty supply of these, the possibilities
+of lighting are very much curtailed. There is nothing intricate about
+locating switches and outlets, so the householder may do this himself,
+or he may view critically the plans as submitted. The chief difficulties
+are to throw aside his indifference and to readjust his ideas and
+values. It may be confidently stated that the possibilities of lighting
+far outrank most of the features which contribute to the cost of a house
+and of its furnishings.
+
+After considering the requirements and decorative schemes of the various
+rooms the householder should be competent to judge the appropriateness
+of the lighting effects obtained from fixtures which the dealer
+displays, but he should insist upon a demonstration. If the dealer is
+not equipped with a room for this purpose, he should be asked to
+demonstrate in the rooms to be lighted. If the fixture-dealer does not
+realize that he should be selling lighting effects, the householder
+should make him understand that lighting effects are of primary
+importance and the fixtures themselves are of secondary interest in most
+cases. The unused outlets that have been installed for possible future
+needs may be sealed in plastering if the positions are marked so that
+they may be found when desired.
+
+An advantage of portable lamps is that they may be taken away on moving.
+In fact, when lighting is eventually considered a powerful decorative
+medium, as it should be, it is probable that fixtures will be personal
+property attached to ceiling, wall, and floor outlets by means of plugs.
+
+A variety of incandescent lamps are available. For the home, opal,
+frosted, or bowl-frosted lamps are usually more satisfactory than clear
+lamps. Bare filaments should not be visible, for they not only cause
+discomfort and eye-strain but they spoil what might otherwise be an
+artistic effect. Lamps with diffusing bulbs do much toward eliminating
+harsh shadows cast by the edges of the shades, by the chains of the
+fixtures, etc. These lamps are available in many shapes and sizes and
+the householder should make a record of voltage, wattage, and shape of
+the lamps which he finds satisfactory in the various fixtures. The Mazda
+daylight lamp has several places in the home and the Mazda white-glass
+and other high-efficiency lamps supply many needs better than the vacuum
+lamps. In brackets and other purely decorative lighting-units small
+frosted lamps are usually the most satisfactory. There is a general
+desire for the warm yellowish light of the candle-flame, and this may be
+obtained by a tinted shade but usually more satisfactorily by means of a
+tinted lamp.
+
+The householder will find it interesting to become intimate with
+lighting, for it can serve him well. The housewife will often find much
+interest in making shades of textiles and of parchment. Charming
+glassware in appropriate tints and painted designs is available for all
+rooms. In the bedchamber and the nursery some of these painted designs
+are exceedingly effective. Fixtures should shield the lamps from the
+eyes, and the diffusing media whether glass or textile should be dense
+enough to prevent glare. No fixture can be beautiful and no lighting
+effect can be artistic if glare is present. If the architect and the
+householder will realize that light is a medium comparable with the
+decorator's media, better lighting will result. Light has the great
+advantage of being mobile and with adequate outlets and controls
+supplemented by fixtures from which different effects are available, the
+householder will find in lighting one of the most fruitful sources of
+interest and pleasure. It can do much toward expressing the taste of
+the householder or if neglected it can undo much of the effect of
+excellent decoration and furnishing. Artificial lighting, softly
+diffused and properly localized, is one of the most important factors in
+making a house a home.
+
+
+
+
+XXV
+
+LIGHTING--A FINE ART?
+
+
+In the preceding chapters the progress of light has been sketched from
+its obscure infancy to its vigorous youth of the present time. It has
+been seen that progress was slow until the beginning of the nineteenth
+century, after which it began to gain momentum until the present century
+has witnessed tremendous advances. Until the latter part of the
+nineteenth century artificial light was considered an expensive utility,
+but as modern lamps appeared which supplied adequate light at reasonable
+cost attention began to be centered upon utilization, and the lighting
+engineer was born. Gradually it is being realized that artificial light
+is no longer a luxury, that it may be used in great quantity, and that
+it may be directed, diffused, and altered in color as desired. Although
+the potentiality of light has been barely drawn upon, the present usages
+surpass the most extravagant dreams of civilized beings a half-century
+ago. Mere light of that time was changed into more light as gas-lighting
+developed, and more light has increased to adequate light of the present
+time through the work of scientists.
+
+It is apparent that a sudden enforced reversion to the primitive flames
+of fifty years ago would paralyze many activities. Much of interest and
+beauty would be blotted out of this brilliant, pulsating, productive
+age. It is startling to note that almost the entire progress in
+artificial lighting has taken place during the past hundred years and
+that most of it has been crowded into the latter part of this period. In
+fact, its development since it began in earnest has gone forward with
+ever-increasing momentum. On viewing the wonders of modern artificial
+lighting on every hand it is not difficult to muster the courage
+necessary to venture into its future.
+
+The lighting engineer has been a natural evolution of the present age,
+for the economic aspects of lighting have demanded attention. He is
+increasing the safety, efficiency, and happiness of mankind and
+civilization is beginning to feel his influence economically. However,
+with the advent of adequate, efficient, and controllable light, the
+potentiality of light as an artistic medium may be drawn upon and the
+lighting artist with a deep insight into the possibilities of artificial
+light now has his opportunity. But the artist who believes that a new
+art may be evolved to perfection in a few years is doomed to
+disappointment, for it is necessary only to view retrospectively such
+arts as painting and music to be convinced that understanding and
+appreciation develop slowly through centuries of experiment and contact.
+
+Will lighting ever become a fine art? Will it ever be able alone to
+arouse emotional man as do the fine arts? Are the powers of light
+sufficiently great to enthrall mankind without the aid of form, music,
+action, or spoken words? It is safer to answer "yes" than "no" to these
+questions. Painting has reached a high place as an art and this art is
+the expressiveness of secondary or reflected light reinforced by
+imitation forms, which by a combination of light and drawing comprise
+the "subjects." A painting is a momentary expression of light, a
+cross-section of something mobile, such as nature, thought, or action.
+Light has the essential qualifications of painting with the advantages
+of a greater range of brightness, of greater purity of colors, and the
+great potentiality of mobility. If lighting becomes a fine art it will
+doubtless be related to painting somewhat in the same manner that
+architecture is akin to sculpture. With the introduction of mobility it
+will borrow something from the arts of succession and especially from
+music.
+
+The art of lighting in its present infancy is leaning upon established
+arts, just as the infant learns to walk alone by first depending upon
+support. The use of color in painting developed slowly, being supported
+for centuries by the strength of drawing or subject. The landscapes of a
+century ago were dull, for color was employed hesitatingly and
+sparingly. The colors in the portraits of the past merely represented
+the gorgeous dress of bygone days. But the painter of the present shows
+that color is beginning to be used for itself and that the painter is no
+longer hesitant concerning its power to go hand in hand with drawing.
+Drafting and coloring are now in partnership, the former having given up
+guardianship when the latter reached maturity.
+
+Lighting is now an accompaniment of the drama, of the dance, of
+architecture, of decoration, and of music. It has been a background or a
+part of the "atmosphere" excepting occasionally when some one with
+imagination and daring has given it the leading rôle. Even in its
+infancy it has on occasions performed admirably almost without any aid.
+The bursting rocket, the marvelous effects at the Panama-Pacific
+Exposition, and some of the exhibitions on the theatrical stage are
+glimpses of the potentiality of light. To fall back upon the terminology
+of music, these may be glimmerings of light-symphonies.
+
+Harmony is simultaneity and a painting in this respect is a chord--a
+momentary expression fixed in material media. A melody of light requires
+succession just as the melody in music. The restless colors of the opal
+comprise a light melody like the songs of birds. The gorgeous splendor
+of the sunset compares in magnitude and in its various moods with the
+symphony orchestra and its powers. Throughout nature are to be found
+gentle chords, beautiful melodies and powerful symphonies of light and
+this music of light exhibits the complexity and structure analogous to
+music. There is no physical relation between music, poetry, and light,
+but it is easy to lean upon the established terminology for purposes of
+discussion. Those who would build color-music identical to sound music
+are making the mistake of starting with a physical foundation instead of
+basing the art of light-expression upon psychological effects of light.
+In other words, a relation between light and music can exist only in the
+psychological realm.
+
+These melodies and symphonies of light in nature are admittedly pleasing
+or impressive as the case may be, but are they as appealing as music,
+poetry, painting, or sculpture? The consensus of opinion of a large
+group of average persons might indicate a negative reply, but the
+combined opinion of this group is not so valuable as the opinion of a
+colorist or of an artist who has sensed the wonders of light. The
+unprejudiced opinion of artists is that light is a powerfully expressive
+and impressive medium. The psychologist will likely state that the
+emotive value of light or color is not comparable to the appeal of an
+excellent dinner or of many other commonplace things. But he has
+experimented only with single colors or with simple patterns and his
+subjects are selected more or less at random from the multitude. What
+would be his conclusion if he examined painters and others who have
+developed their sensibilities to a deep appreciation of light and color?
+It is certain that the painter who picks up a purple petal fallen from a
+rose and places it upon a green leaf is as thrilled by the powerful
+vibrant color-chord as the musician who hears an exquisite harmony of
+sounds.
+
+Music has been presented to civilized mankind in an organized manner for
+ages and the fundamental physical basis of modern music is a thousand
+years old. Would the primitive savage appreciate the modern symphony
+orchestra? Even the majority of civilized beings prefer the modern
+ragtime or jazz to the exquisite art of the symphony. An appreciation of
+the opera and the symphony is reached by educational methods extending
+over long periods. An appreciation of the expressiveness of light cannot
+be expected to be realized by any short-cut. Most persons to-day enjoy
+the melodramatic "movie" more than the drama and relatively few
+experience the deep appeal of the fine arts. Surely the symphony of
+light cannot be justly condemned because of a lack of appreciation and
+understanding of it, for it has not been introduced to the public.
+Furthermore, the expressiveness of music is still indefinite at best
+despite the many centuries of experimenting on the part of musicians.
+
+If poetry is to be believed, the symphonies of light as rendered by
+nature in the sunsets, in the aurora borealis, and in other sky-effects
+of great magnitude have deeply impressed the poet. If his descriptions
+are to be accepted at their face-value, the melodies of light rendered
+in the precious stone, in the ice-crystal, and in the iridescence of
+bird-plumage please his finer sensibilities. If he is sincere, mobile
+light is a seductive agency.
+
+The painter has contributed little of direct value in developing the
+music of light. He is concerned with an instantaneous expression. He
+waits for it patiently and, while waiting, learns to appreciate the
+fickleness of mood in nature, but when he fixes one of these moods he
+has contributed very little to the art of mobile light. Unfortunately
+the art schools teach the student little or nothing pertaining to color
+for color's sake. When the student is capable of drawing fairly well and
+is acquainted with a few stereotyped principles of color-harmony he is
+sent forth to follow in the footsteps of past masters. He may be seen at
+the art museum faithfully copying a famous painting or out in the fields
+stalking a tree with the hopes of an embryo Corot. The world moves and
+has only a position in the rank and file for imitators. Occasionally an
+artist goes to work with a vim and indulges in research, thereby
+demonstrating originality in two respects. Painting is just as much a
+field for research as light-production.
+
+Recently experiments are being made in the production of color-harmonies
+devoid of form. Surely there is a field for pure color-composition and
+this the field of the painter which leads toward the art of mobile
+light. Many of the formless paintings of the present day which pass
+under the banner of this _ism_ or that are merely experiments in the
+expressiveness of light. Being formless, they are devoid of subject in
+the ordinary sense and cannot be more or less than a fixed expression of
+light. Naturally they have received much criticism and have been
+ridiculed, but they can expect nothing else until they are understood.
+They cannot be understood until mankind learns their language and then
+they must be understandable. In other words, there are impostors
+gathered around the sincere research-artist because the former have
+neither the ability to paint for a living nor the inclination to forsake
+the comparative safety of the mystery of art for the practical world
+where their measure would be quickly taken. This army of camp-followers
+will not advance the art of mobile light, but the sincere seekers after
+the principles of light-expression who form the foundation of the
+various _isms_ may contribute much.
+
+The painter will always be available with his finer sensibility to
+appreciate and to aid in developing the art of mobile light, but his
+direct contribution appears most likely to come from the present chaos
+of experiments in pure color-composition, in the psychology of light,
+or, more broadly, in the expressiveness of light. The decorator and the
+designer of gowns and costumes do not arrogate to themselves the name
+"artist," but they are daily creating something which is leading toward
+a fuller appreciation of the expressiveness of light. If they do not
+contribute directly to the development of the art of mobile light, they
+are at least aiding in developing what may eventually be an appreciative
+public.
+
+The artist paints a "still-life," the decorator creates a color-harmony
+of abstract or conventional forms, and the costumer produces a
+color-composition in textiles. The decorator and costumer approach
+closer to pure color-composition than the artist in his still-life. The
+latter is a grouping of objects primarily for their color-notes. Why
+bother with a banana when a yellow-note is desired? Why utilize the
+abstract or conventional forms of the decorator? Why not follow this
+lead further to the less definite forms employed by the costumer? Why
+not eliminate form even more completely? This is an important point and
+an interesting lead, for to become rid of form has been one of the
+perplexing problems encountered by those who have dreamed of an art of
+mobile light.
+
+The painter who uses line and color imitatively has perhaps acquired
+skill in depicting objects and more or less appreciation of the
+beautiful. But if he is to be creative and to produce a higher art he
+must be able to use line and color without reference to objects. He thus
+may aid in the development of an abstract art which is the higher art
+and at the same time aid in educating the public to appreciate pure
+color-harmonies. From these momentary expressions of light and from the
+experience gained, the mobile colorist would receive material aid and
+his productions would be viewed by a more receptive audience or rather
+"optience" as it may be called. The development of taste for abstract
+art is needed in order that the art of mobile light may develop and,
+incidentally, an appreciation of the abstract in art is needed in all
+arts.
+
+Science has contributed much by way of clearing the decks. It has
+produced the light-sources and the apparatus for controlling light. It
+has analyzed the physical aspects of color-mixture and has accumulated
+extensive data pertaining to color-vision. It has pointed out pitfalls
+and during recent years has been delving further by investigating the
+psychology of light and color. The latter field is looked to for
+valuable information, but, after all, there is one way of making
+progress in the absence of data and that is to make attempts at the
+production of impressive effects of mobile light. Some of these have
+been made, but unfortunately they have been heralded as finished
+products.
+
+Perhaps the most general mistake made is in relating sounds and colors
+by stressing a mere analogy too far. Notwithstanding the vibratory
+nature of the propagation of sound and light, this is no reason for
+stressing a helpful analogy. After all it is the psychological effect
+that is of importance and it is absurd to attribute any connection
+between light-waves and sound-waves based upon a relation of physical
+quantities. No space will be given to such a relation because it is so
+absurdly superficial; however, the language of music will be borrowed
+with the understanding that no relation is assumed.
+
+A few facts pertaining to vision will indicate the trend of developments
+necessary in the presentation of mobile light. The visual process
+synthesizes colors and at this point departs widely from the auditory
+process. The sensation of white may be due to the synthesis of all the
+spectral colors in the proportions in which they exist in noon sunlight
+or it may be due to the synthesis of proper proportions of yellow and
+blue, of red, green, and blue, of purple and green, and a vast array of
+other combinations. A mixture of red and green lights may produce an
+exact match for a pure yellow. Thus it is seen that the mixture of
+lights will cause some difficulty. For example, the components of a
+musical chord may be picked out one by one by the trained ear, but if
+two or more colored lights are mixed they are merged completely and the
+resultant color is generally quite different from any of the components.
+In music of light, the components of color-chords must be kept
+separated, for if they are intermingled like those of musical chords
+they are indistinguishable. Therefore, the elements of harmony in mobile
+light must be introduced by giving the components different spatial
+positions.
+
+The visual process is more sluggish than the auditory process; that is,
+lights must succeed each other less rapidly than musical notes if they
+are to be distinguished separately. The ear can follow the most rapid
+execution of musical passages, but there is a tendency for colors to
+blend if they follow one another rapidly. This critical frequency or
+rate at which successive colors blend decreases with the brightness of
+the components. If red and green are alternated at a rate exceeding the
+critical frequency, a sensation of yellow will result; that is, neither
+component will be distinguishable and a steady yellow or a yellow of
+flickering brightness will be seen. The hues blend at a lower frequency
+than the brightness components of colors; hence there may be a blend of
+color which still flickers in brightness. Many weird results may be
+obtained by varying the rate of succession of colors. If this rate is so
+low that the colors do not tend to merge, they are much enriched by
+successive contrast. It is known that juxtaposed colors generally enrich
+one another and this phenomenon is known as simultaneous contrast.
+Successive contrast causes a similar effect of heightened color.
+
+An effect analogous to dynamic contrast in music may be obtained with
+mobile light by varying the intensity of the light or possibly the area.
+Melody may be simply obtained by mere succession of lights. Tone-quality
+has an analogy in the variation of the purity of color. For example, a
+given spectral hue may be converted into a large family of tints by the
+addition of various amounts of white light. Rhythm is as easily applied
+to light as to music, to poetry, to pattern, or to the dance, but in
+mobile lights its limitations already have been suggested. However, it
+is bound to play an important part in the art of mobile light because
+rhythmic experiences are much more agreeable than those which are
+non-rhythmic. Rhythm abounds everywhere and nothing so stirs mankind
+from the lowliest savage to the highly cultivated being as rhythmic
+sequences.
+
+Many psychological effects of light have been recorded from experiment
+and observation and affective values of light have been established in
+various other byways. It is possible that the degree of pleasure
+experienced by most persons on viewing a color-harmony or the delightful
+color-melody of a sunlit opal may be less than that experienced on
+listening to the rendition of music. However, if this were true it would
+offer no discouragement, because absolute values play a small part in
+life. Two events when directly compared apparently may differ enormously
+in their ability to arouse emotions, but the human organism is so
+adaptive that each in its proper environment may powerfully affect the
+emotions. For example, those who have sported in aërial antics in the
+heights of cloudland or have stormed the enemy's trench are still
+capable of enjoying a sunset or the call of a bird to its mate at dusk.
+The wonderful adaptability of the inner being is the salvation of art as
+well as of life.
+
+In the rendition of mobile light it is fair to give the medium every
+advantage. Sometimes this means to eliminate competitors and sometimes
+it means to remove handicaps. On the stage light has had competitors
+which are better understood. For example, in the drama words and action
+are easily understood, and regardless of the effectiveness of light it
+would not receive much credit for the emotive value of the production.
+In the wonderful harmony of music, dance, and light in certain recent
+exhibitions, the dance and music overpowered the effects of lights
+because they speak familiar languages.
+
+[Illustration: A community Christmas tree
+
+A community song-festival
+
+ARTIFICIAL LIGHT IN COMMUNITY AFFAIRS]
+
+[Illustration: PANAMA-PACIFIC EXPOSITION
+
+Artificial light not only reveals the beauty of decoration and
+architecture but enthralls mankind with its own unlimited powers]
+
+A number of attempts have been made to utilize light as an accompaniment
+of music and some of them on a small scale have been sincere and
+creditable, but a much-heralded exhibition on a large scale a few
+years ago was not the product of deep thought and sincere effort. For
+example, colored lights thrown upon a screen having an area of perhaps
+twenty square feet were expected to compete with a symphony orchestra in
+Carnegie Hall. The music reached the most distant auditor in sufficient
+volume, but the lighting effect dwindled to insignificance. Without
+entering into certain details which condemned the exhibition in advance,
+the method of rendition of the light-accompaniment revealed a lack of
+appreciation of the problems involved on the part of those responsible.
+
+Incidentally, it has been shown that the composer of this particular
+musical selection with its light accompaniment was psychologically
+abnormal; that is, he was affected with colored audition. It is not yet
+established to what extent normal persons are similarly affected by
+light and color. Certainly there is no similarity among the abnormal and
+none between the abnormal and normal.
+
+If light is to be used as an accompaniment to music, it must be given an
+opportunity to supply "atmosphere." This it cannot do if confined to an
+insignificant spot; it must be given extensity. Furthermore, by the use
+of diaphanous hangings, form will be minimized and the evanescent
+effects surely can be charming. But finally the lighting effects must
+fill the field of vision just as the music "fills the field of audition"
+in order to be effective. There are fundamental objections to the use of
+mobile light as an accompaniment to music and therefore the future of
+the art of mobile light must not be allowed to rest upon its success
+with music. If it progresses through its relation with music, so much
+is gained; if not, the relation may be broken for music is quite capable
+of standing alone.
+
+There is a tendency on the part of some revolutionary stage artists to
+give to lighting an emotional part in the play, or, in other words, to
+utilize lighting in obtaining the proper mood for the action of the
+play. Color and purely pictorial effect are the dominant notes of some
+of them. All of these modern stage-artists are abandoning the
+intricately realistic setting, and, as a consequence, light is enjoying
+a greater opportunity. In the more common and shallow theatrical
+production, lighting and color effects have many times saved the day,
+and, although these effects are not of the deeper emotional type, they
+may add a spectacular beauty which brings applause where the singing is
+mediocre and the comedy isn't comedy. The potentiality of lighting
+effects for the stage has been barely drawn upon, but as the
+expressiveness of light is more and more utilized on the stage, the art
+of mobile light will be advanced just so much more. Light, color, and
+darkness have many emotional suggestions which are easily understood and
+utilized, but the blending of mobile light with the action is difficult
+because its language is only faintly understood.
+
+It is futile to attempt to describe a future composition of mobile
+light. Certainly there is an extensive variety of possibilities. A
+sunset may be compressed into minutes or an opalescent sky may be a
+motif. Varying intensities of a single hue or of allied hues may serve
+as a gentle melody. Realistic effects may be introduced. The
+expressiveness of individual colors may be taken as a basis for
+constructing the various motifs. These may be woven into melody in which
+rhythm both in time and in intensity may be introduced. Action may be
+easily suggested and the number of different colors, in a broad sense,
+which are visible is comparable to the audible tones. Shading is as
+easily accomplished as in music and the development of this art need not
+be inhibited by a lack of mechanical devices and light-sources. The
+tools will be forthcoming if the conscientious artist requests them.
+
+Whatever the future of the art of mobile light may be, it is certain
+that the utilization of the expressiveness of light has barely begun. It
+may be that light-music must pass through the "ragtime" stage of
+fireworks and musical-revue color-effects. If so, it is gratifying to
+know that it is on its way. Certainly it has already served on a higher
+level in some of the artistic lighting effects in which mobility has
+featured to some extent.
+
+If the art does not develop rapidly it will be merely following the
+course of other arts. A vast amount of experimenting will be necessary
+and artists and public alike must learn. But if it ever does develop to
+the level of a fine art its only rival will be music, because the latter
+is the only other abstract art. Material civilization has progressed far
+and artificial light has been a powerful influence. May it not be true
+that artificial light will be responsible for the development of
+spiritual civilization to its highest level? If mobile light becomes a
+fine art, it will be man's most abstract achievement in art and it may
+be incomparably finer and more ethereal than music. If this is realized,
+artificial light in every sense may well deserve to be known as the
+torch of civilization.
+
+
+
+
+READING REFERENCES
+
+
+No attempt will be made to give a pretentious bibliography of the
+literature pertaining to the various aspects of artificial lighting, for
+there are many articles widely scattered through many journals. _The
+Transactions of the Illuminating Engineering Society_ afford the most
+fruitful source of further information; the _Illuminating Engineer_
+(London), contains much of interest; and _Zeitschrift für
+Beleuchtungswesen_ deals with lighting in Germany. H. R. D'Allemagne has
+compiled an elaborate "Historie du Luminaire" which is profusely
+illustrated, and L. von Benesch in his "Beleuchtungswesen" has presented
+many elaborate charts. In both these volumes lighting devices and
+fixtures from the early primitive ones to those of the nineteenth
+century are illustrated. A few of the latest books on lighting, in the
+English language, are "The Art of Illumination," by Bell; "Modern
+Illuminants and Illuminating Engineering," by Gaster and Dow;
+"Radiation, Light and Illumination," by Steinmetz; "The Lighting Art,"
+by Luckiesh; "Illuminating Engineering Practice," consisting of a course
+of lectures presented by various experts under the joint auspices of the
+University of Pennsylvania and the Illuminating Engineering Society;
+"Lectures on Illuminating Engineering," comprising a series of lectures
+presented under the joint auspices of Johns Hopkins University and the
+Illuminating Engineering Society; and "The Range of Electric Searchlight
+Projectors," by Rey; "The Electric Arc," by Mrs. Ayrton; "Electric Arc
+Lamps," by Zeidler and Lustgarten, and "The Electric Arc," by Child
+treat the scientific and technical aspects of the arc. G. B. Barham has
+furnished a book on "The Development of the Incandescent Electric Lamp."
+"Color and Its Applications," and "Light and Shade and Their
+Applications," are two books by Luckiesh which deal with lighting from
+unique points of view. "The Language of Color," by Luckiesh, aims to
+present what is definitely known regarding the expressiveness and
+impressiveness of color. W. P. Gerhard has supplied a volume on "The
+American Practice of Gaspiping and Gas Lighting in Buildings," and Leeds
+and Butterfield one on "Acetylene." A recent book in French by V.
+Trudelle treats "Lumière Electrique et ses différentes Applications au
+Théatre." Many books treat of photometry, power-plants, etc., but these
+are omitted because they deal with phases of light which have not been
+discussed in the present volume. "Light Energy," by Cleaves, is a large
+volume devoted to light-therapy, germicidal action of radiant energy,
+etc. References to individual articles will often be found in the
+various indexes of publications.
+
+
+THE END
+
+
+
+
+INDEX
+
+
+Aaron, 43
+
+Accidents: 8;
+  street-lighting in relation to, 225 _et seq._;
+  percentage (table) of, due to improper lighting, 231
+
+Acetylene: 62;
+  light-yield of, 106, 107, 170, 187, 191
+
+Actinic rays: effect of, upon human organism, 275
+
+Africa, public lighting in ancient, 31
+
+Agni, god of fire, 40
+
+Air-pump, 130
+
+Air-raids, 225
+
+Alaska, 18, 29
+
+Alchemy, 20
+
+Aleutians, 18
+
+Alexandria, 43, 163
+
+Allylene, 106
+
+Aluminum, 108, 179, 180
+
+Amiens, Treaty of, 69
+
+Amylene, 106
+
+Aniline dyes, 106
+
+Animal: distinction between, and human being, 3; 15;
+  production of light, 24 _et seq._;
+  sources of light, 30, 31;
+  oils, 51
+
+Antimony, 294
+
+Antioch, 153
+
+Arago, 114, 196
+
+Archbishop of Canterbury, 49
+
+Archimedes, 19
+
+Arc: lamps, 69, 89;
+  electric, 111 _et seq._;
+  distinction between spark and, 112;
+  Davy's notes on electric, 113;
+  formation of, 115, 116;
+  Staite and enclosed, 117, 118;
+  principle of enclosed, 118, 119;
+  types of, 120;
+  flame-, 121, 122;
+  luminous, 122;
+  electric, 127;
+  luminous efficiency of electric (table), 124; 160 _et seq._;
+  -lamp in lighthouses, 168 _et seq._;
+  magnetite-, 187; 261
+
+Ardois system of signaling, 199
+
+Argand, Ami: 52;
+  inaugurates new era in artificial lighting, 53, 54; 63, 70, 76, 77, 78,
+    97, 167, 196
+
+Argon, 137
+
+Aristophanes, "The Clouds," 19
+
+Art Museums, 9, 13, 322, 323
+
+Asbestos, 170
+
+Asia: public lighting in ancient, 31, 39
+
+Automobiles, 238
+
+
+Babylon, 39
+
+Bacteria: effect of artificial light upon, 272 _et seq._; 281, 282
+
+Bailey, Prof. L. H., 250
+
+Baltimore, 98
+
+Bamboo: carbon filaments, 169
+
+Bartholdi, 302, 303
+
+Beacons. _See_ Lighthouses.
+
+Beck, 186
+
+Beecher, 72
+
+Beeswax, 35, 51
+
+Benzene, 106
+
+Bible, cited on importance of artificial light, 42-44
+
+"Bluebird, The," Maeterlinck, 9
+
+Blue-prints, 261
+
+Bollman, 98
+
+Bolton, von, 132, 133
+
+Bombs, illuminating, 182 _et seq._
+
+Boston Light, 164, 165, 166, 177
+
+Bowditch, production of regenerative lamp by, 78, 79
+
+Boy Scouts, 17
+
+Bremer, 120
+
+Bristol University, 252
+
+Brush, 68, 159
+
+Building, 8
+
+Bunsen, 81, 85, 89, 148, 149
+
+Bureau of Mines: cited on open flames, 234; 236
+
+Burning-glasses, 19, 20.
+  _See also_ Lenses.
+
+Butylene, 106
+
+Byzantium, 34
+
+
+Cæsar, 163
+
+Canada, 254
+
+Candle-hour, defined, 215
+
+Candles: progress and, 7; 25, 28, 29, 30, 33;
+  religious uses of, 34, 35;
+  as a modern light-source, 36, 37;
+  ceremonial uses of, 38 _et seq._; 44, 48, 57, 82, 97, 222, 299, 304
+
+Calcium, 107, 108
+
+Carbolic acid, 106
+
+Carbon: 53, 80, 81;
+  physical characteristics of, 80, 81; 90, 104, 105, 128, 129, 144, 170
+
+Carbon filament: 127 _et seq._;
+  preparation of, 129, 130, 131;
+  luminous efficiency of, 131, 132;
+  lamps, 161;
+  lamps in greenhouses, 250 _et seq._
+
+Carbons, formation of, 115, 116
+
+Carbureted hydrogen, 75
+
+Carcel, invention of clockwork lamp by, 54, 55
+
+Cat-gut, 130
+
+Ceria, 85, 101
+
+Charleston, S. C., 185
+
+Charcoal: 113;
+  uses of, for electrodes, 115
+
+Chartered Gas Light and Coke Co., London, 74
+
+Chemistry: artificial light and, 256-268
+
+Chicago, 62, 304, 305
+
+Chimneys, 54, 60, 62
+
+China, 19, 31, 32
+
+Chlorate of potash, 22
+
+Christ, 33, 46, 47
+
+Christians, "children of light," 42
+
+Christmas trees, 43, 304
+
+Chromium, 294
+
+Church of England, 49
+
+Cities: economy of artificial lighting in congested, 13
+
+Civilization: effect of artificial light upon, 4 _et seq._;
+  fire and, 15
+
+Clark, Parker and, 139
+
+Clayton, Dr.: invention of portable gas-light by, 64;
+  quoted, 64, 65;
+  experiments of, with coal-gas, 67
+
+Claude, 147
+
+Cleaves, Dr., quoted, 276, 277
+
+Clegg, Samuel: 74;
+  gas-lighting accomplishments of, 75, 76
+
+Cleveland, 159
+
+"Clouds, The," Aristophanes, 19
+
+Coal: 32;
+  as a light-source, 55;
+  supply, 223; 228
+
+Coal-gas: 63 _et seq._;
+  public lighting by, developed, 70 _et seq._;
+  analytical production of, 103, 104;
+  yield of, retort (table), 105;
+  analysis of, 106
+
+Coal-mines, 234 _et seq._
+
+Cobalt, 294
+
+Coke, 68, 105
+
+Cologne, 157, 158
+
+Colomb, Philip, 197
+
+Color: 9;
+  relation of artificial light to, 284 _et seq._
+
+Colza, 31, 52, 167
+
+Combustion, 82 _et seq._
+
+Commerce, 8, 97
+
+Constantine, 42
+
+Copper, 262, 295
+
+Cornwall, 63
+
+Cotton: 101;
+  carbon filaments, 129, 130
+
+Cromartie, 78
+
+Crookes, 90, 146
+
+Crosley, Samuel, improvement of gas-meter by, 76
+
+Crusies, 32
+
+
+Daguerre, 258
+
+Dancing, 346
+
+Davy, Sir Humphrey: 33, 68, 73;
+  first use by, of charcoal for sparking points, 112;
+  notes of, on electric arc, 113; 114
+
+Daylight, artificial, 12: 284 _et seq._;
+  application of, 287
+
+Daylighting, 12-14
+
+Dollond, 195
+
+Doty, 61, 167
+
+Drake, Col. E. L., discovery of oil in Pennsylvania by, 56
+
+Drummond, Thomas: 171, 185, 196;
+  quoted on signaling, 197
+
+Dudgeon, Miss, 251, 252
+
+Dyes, 256, 265
+
+
+East Indies, 29
+
+Eddystone Light, 166, 167
+
+Edison: and problem of electric incandescent filament lamps, 128 _et seq._;
+    129;
+  quoted on birth of incandescent lamp, 130
+
+Edward I, 274
+
+Edward VI, 49
+
+Efficiency, effect of artificial light upon, 14
+
+Eggs: relation of artificial light to production of, 247, 248
+
+Egypt: 31;
+  sacredness of light in ancient, 39; 153, 195
+
+Electric filament: 81, 127 _et seq._:
+  approximate value of, lamps (table), 138
+
+Electric pile: construction of, 111; 127
+
+Electricity: 13, 22;
+  as a light-source, 57;
+  for home-lighting, 62, 84; 87, 89;
+  ignition of gas by, 102;
+  lighting by, 109 _et seq._
+
+Electromagnetic waves, 68, 86, 87
+
+Electromagnets, 114, 116
+
+Electrodes, 113, 114, 115 _et seq._;
+  life of, 122
+
+Elizabeth, Queen, 274
+
+England: 32;
+  petroleum discovered in, 56;
+  gas-lighting in, 63 _et seq._; 166, 251, 274
+
+Erbia, 85
+
+Esquimaux: 18;
+  use of artificial light by, 31
+
+Ethylene, 106
+
+
+Factories: 13;
+  artificial light in, 239 _et seq._
+
+Faraday, 113
+
+Filaments, carbon, 129 _et seq._
+
+Finsen: 273, 274, 275;
+  on stimulating action of artificial light, 277; 279, 280
+
+Fire: importance of, to man, 5 _et seq._;
+  man's dependence upon, 15;
+  mythical origin of, 16;
+  making, 17 _et seq._;
+  production of, in the stone age, 18;
+  in early civilization, 19;
+  ancient worship of, 29, 299
+
+Fireflies: 24, 81, 96, 148, 149, 150
+
+"First Men in the Moon, The," H. G. Wells, cited, 148
+
+Fish: artificial light as bait for, 249
+
+Flame-arcs, 120, 121, 122, 187
+
+Flames: 86, 88, 89;
+  open, 233, 234 _et seq._
+
+Flint, 33
+
+Fool's gold, 18
+
+Fort Wagner, 185
+
+France: lamps in, 55;
+  early gas-light in, 72
+
+Franchot, invention of moderator lamps by, 55
+
+Frankland, 77
+
+Franklin, Benjamin: 165;
+  quoted, 210-212; 213
+
+Fresnel, 167, 196
+
+Friction, 16, 17
+
+
+Gas: 13, 22;
+  discovery of coal, 32, 33;
+  early uses of, as light-source, 63 _et seq._;
+  installment of, pipes in England, 63, 64;
+  Shirley's report on Natural, 66, 67;
+  first public display of, lighting, 69;
+  cost of, lighting, 71;
+  first attempt at industrial, lighting, 72;
+  first English, company, 74;
+  first, explosion, 75;
+  house, lighting, 76, 77; 80, 82;
+  spectrum of, 90;
+  modern, lighting industry, 97 _et seq._;
+  origin of lighting by, 98;
+  first, works in America, 98;
+  growth of, consumption in United States, 99;
+  electrical ignition applied to, lighting, 102;
+  pressure, 102, 103;
+  water, 105;
+  carbons in, 106;
+  production of Pintsch, 109, 110;
+  salts applied to, flames, 120; 157;
+  Census Bureau figures on cost of, plants, 221, 222; 224, 341
+
+Gas-burners: 63, 64, 77;
+  candle-power of pioneer (table), 79;
+  improvements in, 84
+
+Gas-mantle: 61, 81;
+  influence of, 99;
+  characteristics of, 100 _et seq._; 187
+
+Gas-meter, Clegg's, 76
+
+Gasolene: lamps, 55; 57
+
+Gassiot, 114
+
+Gauss, 196
+
+Geissler, 146
+
+General Electric Company, 132, 135, 136
+
+Germany: development of lamps in, 56;
+  early gas-lighting in, 72
+
+Glass, 195, 290 _et seq._
+
+Glowers, 139
+
+Glow-worms, 24
+
+Glycerides, 52
+
+Gold, 293
+
+Gout, 275
+
+Gramme dynamo, 117
+
+Grass: 18;
+  carbon filaments, 129
+
+Greece: 39;
+  sacred lamps in ancient, 41; 42
+
+Greenhouses, carbon-filament lamps in, 250 _et seq._
+
+
+Hall of Fame, 134
+
+Happiness, effect of artificial light upon, 14
+Hayden and Steinmetz, 253
+
+Health, artificial light in relation to, 269-283
+
+Helium, 89
+
+Hemig, 155
+
+Hemp, 21
+
+Henry, William, 75
+
+Herodotus, 56
+
+Hertz, 68
+
+Hertzian waves, 271
+
+Hewitt, Cooper, produces mercury-arcs, 124, 125
+
+Home: artificial light in relation to, 6;
+  lighting, 325 _et seq._
+
+Hindu: light in, ceremonials, 40
+
+Hudson-Fulton Celebration, 306
+
+Huygens, 195
+
+Hydrocarbons, 82
+
+Hydrogen, 81
+
+
+Illiteracy, artificial light and, 9
+
+Invention, 7, 97
+
+Iowa, 238
+
+Iridium, 129
+
+Iron, 18, 262, 294
+
+Iron pyrites, 18
+
+Italy, 249
+
+
+Jablochkov: electric candle of, 117
+
+Jamaica, 19
+
+Jandus, 118, 122
+
+Japan: 19;
+  use of oil in, 30; 281
+
+Jerusalem, 43
+
+Jews: artificial light among, 40
+
+_Journal_, Paris, quoted, 210-212
+
+
+Kerosene: 57;
+  weight of, lumens, 60; 62, 187, 233
+
+Kitson, platinum-gauze mantle applied by, 61
+
+
+Laboratories: achievements of, 137
+
+Lamps: 16, 25;
+  Roman, 30; 31;
+  invention of safety, 33;
+  ancient funereal, 39;
+  sacred, of antiquity, 41;
+  ceremonial, 44;
+  scientific development of oil, 51 _et seq._;
+  Holliday, 55;
+  Carcel, 54, 55;
+  Franchot's moderator, 55;
+  gasolene, 55;
+  development of, in Germany, 56;
+  air pressure, 61;
+  supremacy of oil, ends, 62;
+  Bowditch's, 77, 78; 80, 97;
+  mercury-arc, 126;
+  electric incandescent filament, 127 _et seq._;
+  gem, 132;
+  tungsten, 133 _et seq._;
+  luminous efficiency (table) of incandescent filament, 141; 299;
+  in home, 328-333
+
+Lange, 167
+
+Lard-oil, 51
+
+Lavoisier, 195
+
+Lead, 262, 294
+
+Le Bon, 72
+
+"Legend of Montrose, The," Scott, cited on primitive lighting, 27
+
+Leigh, Edmund, quoted, 226
+
+Lenses, 20, 171 _et seq._
+
+Libanius, quoted, 153, 154
+
+Liberty, Statue of, 301, 302, 303
+
+Libraries, 9
+
+Light: relation of artificial, to progress, 3 _et seq._;
+  as a civilizing agency, 3-14;
+  primitive man and artificial, 4;
+  Milton, quoted on importance of, 5;
+  artificial, and science, 7;
+  artificial, and industrial development, 8;
+  Maeterlinck's tribute to, 9;
+  Lincoln's debt to artificial, 9;
+  symbolism of, 9, 10;
+  therapy, 10;
+  in war, 11;
+  adaptations of, 12; 13;
+  mythical origin of artificial, 16;
+  earliest source of, 16;
+  production of, in stone age, 18;
+  matches as source of, 21;
+  animals as, sources, 24, 25;
+  primitive sources of, 24-37;
+  evolution of artificial, sources, 24-37;
+  development, 28 _et seq._;
+  early outdoor use of artificial, 28;
+  Roman uses of artificial, 30;
+  beginning of scientific, 33, 34;
+  candles as modern, source, 36, 37;
+  symbolism and religious uses of, 38 _et seq._;
+  Bible cited on artificial, 42-44;
+  in relation to worship, 43, 45, 46;
+  Argand's contribution to, 53, 54;
+  coal as, source, 55;
+  early uses of gas as, source, 63 _et seq._;
+  as a public utility, 70;
+  first installation of industrial gas, 72;
+  science of, production, 80 _et seq._;
+  causes of, radiation, 80, 81; 83;
+  lime, 84; electric, 89 _et seq._;
+  principle of, production, 90, 91;
+  sources, 93;
+  various gas-burners', supply, 95;
+  relative efficiency of, sources, 95, 96;
+  in the home, 97;
+  influence of, upon science, invention, and commerce, 97 _et seq._;
+  yield of acetylene, 106, 107;
+  electric, 109;
+  influence of gas upon development of artificial, 110;
+  development of artificial, 111 _et seq._;
+  efforts to improve color of mercury-arc, 125;
+  electric-incandescent-filament, 127 _et seq._;
+  effect of tungsten, upon, 133 _et seq._;
+  of the future, 143-152;
+  in warfare, 178-193;
+  signaling, 194-207;
+  cost of, 208-224;
+  and safety, 225 _et seq._;
+  improper use of, 229, 230;
+  comparison of daylight and artificial, 240;
+  reducing action of, 258;
+  bactericidal action of, 272 _et seq._;
+  modifying, 284 _et seq._;
+  spectacular uses of, 298-309;
+  expressiveness of, 310-324;
+  utility of modern, 325-340;
+  evolution of the art of applying, 341-356;
+  mobile, 347, 348, 349, 350;
+  psychological effect of, 351 _et seq._;
+  as an accompaniment to music, 352-354
+
+Light-buoys, 10, 169
+
+Lighthouses: 10, 163-177;
+  optical apparatus of, 172 _et seq._
+
+Light-ships, 10, 169
+
+Lighting-systems: comparison of, 12-14
+
+Lime, 84, 107, 108, 294
+
+Lincoln, Abraham, 9
+
+Linen, 18
+
+Link-buoys, 28
+
+Lithopone, 265, 266
+
+Liverpool, 167
+
+Living: comparison of, standards, 238 _et seq._
+
+London, 152, 154, 155, 156, 157, 202
+
+London Gas Light and Coke Company, 74
+
+Lucigen, 61
+
+Lumen-hour: defined, 215
+
+Lumens: 60, 94, 215
+
+Lutheran Church, 49
+
+Lyceum Theatre, London, 73
+
+
+Maeterlinck, Maurice, 9
+
+Magazines, 8
+
+Magdsick, H. H., 303
+
+Magnesia: 84;
+  Nernst's application of, 138
+
+Magnesium, 179, 180
+
+Magnetite arc, 187
+
+Man: distinction between, and animal, 3;
+  artificial light and early, 4;
+  light-sources of primitive, 25
+
+Manganese, 262, 268, 294
+
+Mangin, 188
+
+Mann, 129
+
+Mantles, 95
+
+Manufacturing, 8
+
+Marconi, 68
+
+Marks, 118
+
+Matches: as light-sources, 21; 22, 82
+
+Maxwell, 68
+
+Mazda lamps, 289, 339
+
+Mecca, 40
+
+Mediterranean Sea, 163
+
+Mercury-arc: Way's, 124; 125, 126;
+  quartz, 125, 126;
+  attempts to improve color of, light, 125
+
+Middle Ages, 46, 47, 474
+
+Milton, quoted, 5
+
+Mirror, 19
+
+Mohammedans, 40
+
+Moore, Dr. McFarlan, 146, 147
+
+Morality, effect of light upon, 9
+
+Morse code: application of, to light-signaling, 198, 199
+
+Moses, 195
+
+Moving-pictures, 9, 260, 261
+
+Munich, 72
+
+Murdock, William: installment of gas-pipes by, 63; 68, 69, 70;
+  quoted on industrial use of artificial, 71; 72, 73, 74, 76, 78, 217, 309
+
+Museums: 13;
+  utilization of artificial light by, 322, 323
+
+Music: light as an accompaniment to, 352-354
+
+Mythology, 16
+
+
+Nantes, 85
+
+Napoleon, 111
+
+Napthalene, 106
+
+National Heat and Light Co., 72, 74
+
+Natural gas, 99
+
+Navesink Light, 206
+
+Nernst, 138, 139
+
+Newspapers, 8
+
+Newton, Sir Isaac: 7;
+  quoted on discovery of visible spectrum, 87; 88
+
+New York, 98, 165, 166, 206, 302, 304
+
+Niagara Falls, 108, 306
+
+Nickel, 262
+
+Nielson, 77
+
+Niepce, 258
+
+Niter, 21
+
+Nitrogen, 137
+
+Norfolk, 169
+
+
+Obesity, 275
+
+Offices, 13
+
+Oil: as a light-source, 29 _et seq._;
+  development of, lamps, 51 _et seq._; 155;
+  in lighthouse, 165 _et seq._; 222, 224, 299
+
+O'Leary, Mrs., and her lamp, 62
+
+Olive-oil, 51, 52, 167
+
+Orkney Islands, 29, 177
+
+Osmium, 133
+
+Oxygen: relative consumption of, by oil-lamps, 58, 59; 262
+
+Ozone, 262
+
+
+Painting, 342, 343, 347, 348, 349
+
+Pall Mall, 74
+
+Panama-Pacific Exposition: 304;
+  artificial lighting of, 306, 307, 308, 309
+
+Paper: 18;
+  carbon filaments, 129, 130
+
+Paraffin, 35, 57
+
+Parker and Clark, 139
+
+Paris: experimental gas-lighting in, 83, 84;
+  Volta in, 111; 154, 185, 210, 212, 213
+
+Peckham, John, 195
+
+Pennsylvania: discovery of oil in, 56
+
+Periodic Law, 145
+
+Petroleum: 35, 51, 55;
+  discovery of, 56;
+  constitution of crude, 57; 58, 214
+
+Pharos, 163
+
+Philadelphia, 98, 99, 157
+
+Phillips and Lee, 70, 72
+
+"Philosophical Transactions of the Royal Society of London," 33;
+  quoted on industrial lighting, 63;
+  Shirley's report on natural gas in, 66, 67;
+  quoted, 87
+
+Phoenicians, 34, 39
+
+Phosphorus, 21
+
+Photo-micrography, 12
+
+Photography: 126;
+  early experiments in, 258;
+  development of, 259; 291, 292
+
+Picric acid, 106
+
+Pigments, 265
+
+Pintsch: production of, gas, 109, 110, 170
+
+Pitch, 106
+
+Plant-growth: artificial light and, 11, 249 _et seq._
+
+Platinum, 85, 128, 129, 262
+
+Plumbago, 113, 130
+
+Plymouth, 166
+
+Poetry, 346
+
+Police, 162
+
+Potash, chlorate of, 22
+
+Priestley, Professor, quoted, 252
+
+Printing, 8
+
+Progress: influence of fire upon, 15 _et seq._
+
+Prometheus, 16, 41
+
+Propylene, 106
+
+Ptolemy II, 163
+
+
+Quartz: 18, 19;
+  mercury-arcs, 125;
+  uses of, 126;
+  in skin diseases, 278, 279
+
+
+Radiators, energy, 88 _et seq._
+
+Radium, 150
+
+Railway Signal Association, 205
+
+Railways: light-signaling applied to, 205
+
+Ramie fiber, 101
+
+Rane, 250, 251
+
+Rare-earth oxides: 85;
+  properties of, 88, 99
+
+Recreation, 9
+
+Redruth, 63
+
+Reformation: ceremonial uses of light during the, 48, 49
+
+Rheumatism, 275
+
+Robins, Benjamin, 201
+
+Rome, 30, 32, 34, 39, 41, 42, 44
+
+Röntgen, 270, 280.
+  _See also_ X-ray.
+
+Royal Society of London: 33, 63, 66, 67, 70, 73;
+  and first gas explosion, 75, 111, 112
+
+Rumford, 167
+
+Rushlights, 28, 33
+
+Russia, 281
+
+Ryan, W. D'A., 306
+
+
+Safety: artificial light in relation to, 14, 225 _et seq._
+
+Salts: chemical, 88, 89;
+  metallic, 120;
+  silver, 257, 258
+
+Sandy Hook Light, 165, 166
+
+San Francisco, 304, 306-309
+
+Savages, 3, 15, 17
+
+Sawyer, 129
+
+Scheele, K. W., 133;
+  quoted, 257, 258
+
+Schools, 9
+
+Science: light and, 6, 7; 97;
+  systematized, 268
+
+Scotland: 26, 31, 32, 48;
+  oil industry in, 56
+
+Scott, Sir Walter, cited, 27, 98
+
+Sculpture: artificial light in relation to, 184
+
+Search-lights, 11, 169
+
+Section of Plant Protection, 225, 226
+
+Selenium, 267, 293
+
+Semaphore, 199
+
+Shells: illuminating, 179 _et seq._
+
+Shirley, Thomas: quoted on natural gas, 66, 67
+
+Siemens, 78
+
+Signaling, 194-207
+
+Silicon: filament, 140
+
+Silk: artificial, 101;
+  carbon-filaments, 129
+
+Simpson, R. E., 227, 231
+
+Silver, 258, 293
+
+Skin diseases: treatment of, 278, 279, 280
+
+Skylights, 13
+
+Sleep, 8
+
+Smallpox, 274, 275
+
+Smeaton, 166
+
+Soho, 69, 72
+
+South Africa, 129
+
+Sparks: 33, 125
+
+Spectrum: visible, 86;
+  Newton quoted on, 87;
+  of elements, 89;
+  of gases, 90; 120, 121;
+  mercury, 124-126
+
+Sperm, 31, 51, 52, 167
+
+Spermaceti, 35, 51
+
+Splinter-holders, 27, 28
+
+Stage: and artificial light, 319 _et seq._; 343
+
+Staite, 117, 118
+
+Stearine, 35, 52
+
+Stearn, 129
+
+Steel, 18, 33
+
+Steinmetz, Hayden and, 253
+
+Sterilization: quartz-mercury-arc and, 280, 281, 282
+
+Stevenson, Robert Louis, quoted, 177
+
+Stores, 13
+
+St. Paul, 43
+
+St. Paul's Cathedral, 300
+
+Street-lighting: development of, 152-162
+
+Sugar, 22
+
+Sulphide of iron, 18
+
+Sulphur, 18, 21, 179, 180, 294
+
+Sulphuric acid, 21, 22
+
+Sun, 8, 16, 19, 20
+
+Swan, 129
+
+Syracuse, 19
+
+Syria, 153
+
+
+Tallow, 34, 35, 51, 52
+
+Tantalum: 132;
+  filament lamps, 133
+
+Tar, 68, 106
+
+Telegraphy, 195
+
+Telephony, 194
+
+Textiles, 256
+
+Thames, 169
+
+Theaters, 9, 319 _et seq._
+
+Thoria, 85
+
+Tin, 262
+
+Tinder-boxes, 18, 19, 22
+
+Travelers Insurance Company, 227
+
+Trees, 26
+
+Troy, 42
+
+Tuberculosis, 273
+
+Tungsten lamp, 161 _et seq._, 187, 261, 290, 303
+
+Typhus, 273
+
+
+Ultra-violet rays: 126, 150;
+  in photographic electricity, 267, 268; 270, 272, 294
+
+United States: petroleum in, 57;
+  gas-consumption in, 99; 164, 165, 166
+
+United States Geological Survey, cited on sale of gas, 222
+
+United States Military Intelligence, 225, 226
+
+
+Vacuum tubes, 81, 286
+
+Venetians, 195
+
+Ventilation, 13
+
+Verne, Jules, 143
+
+Vestal Virgins, 42
+
+Volcanoes, 166
+
+Volta, 111, 112, 127
+
+Voltaic pile: construction of, 111, 127
+
+Von Bolton. _See_ Bolton.
+
+
+War: and artificial light, 11, 178-193
+
+Washington, 305
+
+Water: sterilization of, by artificial light, 280 _et seq._
+
+Watson, Dr. Richard, 67, 68
+
+Watt, 94
+
+Waves: electro-magnetic, 68, 86, 125 _et seq._
+
+Wax, 34, 46, 51
+
+Way: mercury-arc produced by, 124
+
+Wells, 61
+
+Wells, H. G., cited, 148
+
+Welsbach, Auer von: 61;
+  invention of mantle by, 99, 100, 133
+
+Wenham, 78
+
+West Indies, 25
+
+Whale-oil, 31
+
+Wicks, 35, 36, 53, 54, 58, 59
+
+Winsor, 72, 73.
+  _See also_ Winzler.
+
+Winzler. _See_ Winsor.
+
+_Wolfram._ _See_ Tungsten.
+
+Wood, 26, 27, 28
+
+Woolworth Building, 302, 303
+
+Wounds: treatment of, by artificial light, 10
+
+
+X-ray: production of, tubes during War, 131; 137, 150, 270, 280
+
+
+Young, James: discovers petroleum, 56
+
+Yttria, 85
+
+
+_Zeitung_, Cologne: 157;
+   extract from, on street-lighting, 158
+
+Zinc, 125, 130, 267
+
+Zirconia, 84, 85
+
+
+
+
+Transcriber's List of Corrections
+
+
+LOCATION
+         ORIGINAL
+                  CORRECTED
+
+Chapter II
+         and similiar material
+                  and similar material
+
+Chapter XIII
+         as a constant level
+                  at a constant level
+
+Chapter XIV
+         the carbons to distintegrate
+                  the carbons to disintegrate
+
+Chapter XV
+         John Pechham
+                  John Peckham
+         coated with an allow
+                  coated with an alloy
+         with various billiant
+                  with various brilliant
+         key in depressed
+                  key is depressed
+
+Chapter XVI
+         has nearly doubled
+                  have nearly doubled
+
+Chapter XVII
+         this own indifference
+                  their own indifference
+
+Chapter XXIII
+         Nature's lighting varied
+                  Nature's lighting varies
+
+Chapter XXIV
+         so-called cadelabra
+                  so-called candelabra
+         possibilties
+                  possibilities
+
+READING REFERENCES
+         ...Applications an Théatre."
+                  ...Applications au Théatre."
+
+INDEX
+         Photo-micography
+                  Photo-micrography
+         Siemans
+                  Siemens
+
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Artificial Light, by M. Luckiesh
+
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+<pre>
+
+The Project Gutenberg EBook of Artificial Light, by M. Luckiesh
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Artificial Light
+       Its Influence upon Civilization
+
+Author: M. Luckiesh
+
+Release Date: January 29, 2006 [EBook #17625]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ARTIFICIAL LIGHT ***
+
+
+
+
+Produced by K.D. Thornton, Karina Aleksandrova and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+
+<div class="notes">
+<p>Transcriber's Notes:</p>
+<ol>
+  <li>Inconsistent hyphenation of words preserved.</li>
+  <li>Several misprints corrected. Hover over underlined
+  <ins class="correction" title="like this">word</ins> in
+  the text to see the corrections made. A full list of
+  corrections can be found at <a href="#corrections">the end</a> of the text.</li>
+  <li>On <a href="#Page_19">page 19</a>, Aristophanes's period
+  is noted as (488-385 <abbr>B.&nbsp;C.</abbr>); Aristophanes was born
+  circa 448 <abbr>B.&nbsp;C.</abbr></li>
+</ol>
+</div>
+
+<hr />
+<hr />
+
+<div class="center">
+<a id="image1" name="image1"></a>
+<img src="images/image1.png" alt="LIGHT AND LIBERTY" title="LIGHT AND LIBERTY" height="500" width="344" />
+<p class="caption">LIGHT AND LIBERTY</p>
+</div>
+
+
+<div class="titlepage">
+<h4>The Century Books of Useful Science</h4>
+
+<hr />
+
+<h1><span class="smcap">Artificial Light</span></h1>
+
+<h3>ITS INFLUENCE UPON CIVILIZATION</h3>
+
+<div style="height: 2em;"><br /></div>
+
+<h3>BY</h3>
+<h2>M. LUCKIESH</h2>
+
+<h4>DIRECTOR OF APPLIED SCIENCE. NELA RESEARCH LABORATORY,
+NATIONAL LAMP WORKS OF GENERAL ELECTRIC COMPANY<br />
+
+Author of "Color and Its Applications," "Light and Shade
+and Their Applications," "The Lighting Art,"
+"The Language of Color," etc.</h4>
+
+<div style="height: 2em;"><br /></div>
+
+<h4><em>ILLUSTRATED WITH
+PHOTOGRAPHS</em></h4>
+
+<div class="center"><img src="images/mark.png" alt="printer's mark" height="100" width="100" /></div>
+
+<h4>NEW YORK<br />
+THE CENTURY CO.<br />
+1920</h4>
+</div>
+
+<hr />
+
+<p class="center">Copyright, 1920, by<br />
+<span class="smcap">The Century Co.</span>
+</p>
+
+<hr style="width: 65%;" />
+
+<p class="dedication">DEDICATED<br />
+<br />
+TO THOSE WHO HAVE ENCOURAGED<br />
+ORGANIZED SCIENTIFIC RESEARCH FOR<br />
+THE ADVANCEMENT OF CIVILIZATION
+</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_ix" id="Page_ix"></a>PREFACE</h2>
+
+
+<p>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 <em>mere</em> light was available,
+but as the century progressed, the light-sources through the application
+of science became more powerful and efficient. Gradually <em>mere</em> light
+grew to <em>more</em> light and in the dawn of the twentieth century <em>adequate</em>
+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.</p>
+
+<p>The aim has been to show that artificial light has become intricately
+interwoven with human activities and <a class="pagenum" name="Page_x" id="Page_x"></a>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.</p>
+
+<p>
+<span style="margin-left: 2.5em;"><span class="smcap">M. Luckiesh.</span></span><br />
+</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_xi" id="Page_xi"></a>ACKNOWLEDGMENTS</h2>
+
+
+<p>It is a pleasant duty to acknowledge the co&ouml;peration 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.&nbsp;S. Army, for Plate
+13; to Lynn Works of G.&nbsp;E. Co. for Plates 14, 16; to Edison Lamp Works of
+G.&nbsp;E. Co. for Plates 17, 24; to Cooper Hewitt Co. for Plate 18a; to
+R.&nbsp;U.&nbsp;V. Co. for Plate 19; to New York Edison Co. for Plates 22, 26, 30;
+to W.&nbsp;D'A. Ryan and the Schenectady Works of G.&nbsp;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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_xii" id="Page_xii"></a>CONTENTS</h2>
+
+
+<div class="center">
+<table class="toc" cellpadding="5" summary="Table of Contents">
+<thead>
+<tr><th>CHAPTER</th><th>&nbsp;</th><th>PAGE</th></tr>
+</thead>
+<tbody>
+<tr><td align="right">I</td><td>Light and Progress</td>        <td align="right"><a href="#Page_3">3</a></td></tr>
+
+<tr><td align="right">II</td> <td>The Art of Making Fire</td>        <td align="right"><a href="#Page_15">15</a></td></tr>
+
+<tr><td align="right">III</td> <td>Primitive Light-Sources</td>        <td align="right"><a href="#Page_24">24</a></td></tr>
+
+<tr><td align="right">IV</td> <td>The Ceremonial Use of Light</td>         <td align="right"><a href="#Page_38">38</a></td></tr>
+
+<tr><td align="right">V</td> <td>Oil-Lamps of the Nineteenth Century</td>          <td align="right"><a href="#Page_51">51</a></td></tr>
+
+<tr><td align="right">VI</td> <td>Early Gas-Lighting</td>        <td align="right"><a href="#Page_63">63</a></td></tr>
+
+<tr><td align="right">VII</td> <td>The Science of Light-Production</td>          <td align="right"><a href="#Page_80">80</a></td></tr>
+
+<tr><td align="right">VIII</td> <td>Modern Gas-Lighting</td>         <td align="right"><a href="#Page_97">97</a></td></tr>
+
+<tr><td align="right">IX</td> <td>The Electric Arcs</td>         <td align="right"><a href="#Page_111">111</a></td></tr>
+
+<tr><td align="right">X</td> <td>The Electric Incandescent Filament Lamps</td>        <td align="right"><a href="#Page_127">127</a></td></tr>
+
+<tr><td align="right">XI</td> <td>The Light of the Future</td>         <td align="right"><a href="#Page_143">143</a></td></tr>
+
+<tr><td align="right">XII</td> <td>Lighting the Streets</td>         <td align="right"><a href="#Page_152">152</a></td></tr>
+
+<tr><td align="right">XIII</td> <td>Lighthouses</td>        <td align="right"><a href="#Page_163">163</a></td></tr>
+
+<tr><td align="right">XIV</td> <td>Artificial Light in Warfare</td>        <td align="right"><a href="#Page_178">178</a></td></tr>
+
+<tr><td align="right">XV</td> <td>Signaling</td>        <td align="right"><a href="#Page_194">194</a></td></tr>
+
+<tr><td align="right">XVI</td> <td>The Cost of Light</td>       <td align="right"><a href="#Page_208">208</a></td></tr>
+
+<tr><td align="right">XVII</td> <td>Light and Safety</td>        <td align="right"><a href="#Page_225">225</a></td></tr>
+
+<tr><td align="right">XVIII</td> <td>The Cost of Living</td>        <td align="right"><a href="#Page_238">238</a></td></tr>
+
+<tr><td align="right">XIX</td> <td>Artificial Light and Chemistry</td>          <td align="right"><a href="#Page_256">256</a></td></tr>
+
+<tr><td align="right">XX</td> <td>Light and Health</td>         <td align="right"><a href="#Page_269">269</a></td></tr>
+
+<tr><td align="right">XXI</td> <td>Modifying Artificial Light</td>        <td align="right"><a href="#Page_284">284</a></td></tr>
+
+<tr><td align="right">XXII</td> <td>Spectacular Lighting</td>         <td align="right"><a href="#Page_298">298</a></td></tr>
+
+<tr><td align="right">XXIII</td> <td>The Expressiveness of Light</td>        <td align="right"><a href="#Page_310">310</a></td></tr>
+
+<tr><td align="right">XXIV</td> <td>Lighting the Home</td>         <td align="right"><a href="#Page_325">325</a></td></tr>
+
+<tr><td align="right">XXV</td> <td>Lighting&mdash;A Fine Art?</td>      <td align="right"><a href="#Page_341">341</a></td></tr>
+
+<tr><td>&nbsp;</td><td>Reading References</td>        <td align="right"><a href="#Page_357">357</a></td></tr>
+
+<tr><td>&nbsp;</td><td>Index</td>       <td align="right"><a href="#Page_359">359</a></td></tr>
+</tbody>
+</table>
+</div>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_xiii" id="Page_xiii"></a>LIST OF ILLUSTRATIONS</h2>
+
+
+<div class="center">
+<table class="il" cellpadding="5" summary="List of Illustrations">
+<tr><td><a href="#image1">Light and Liberty</a></td>        <td align="right"><em>Frontispiece</em></td></tr>
+<tr><td>&nbsp;</td><th align="right">FACING PAGE</th></tr>
+<tr><td><a href="#image2">Primitive fire-baskets</a></td>         <td align="right"><a href="#Page_16">16</a></td></tr>
+
+<tr><td><a href="#image3">Crude splinter-holders</a></td>        <td align="right"><a href="#Page_16">16</a></td></tr>
+
+<tr><td><a href="#image4">Early open-flame oil and grease lamps</a></td>        <td align="right"><a href="#Page_17">17</a></td></tr>
+
+<tr><td><a href="#image5">A typical metal multiple-wick open-flame oil-lamp</a></td>          <td align="right"><a href="#Page_32">32</a></td></tr>
+
+<tr><td><a href="#image6">A group of oil-lamps of two centuries ago</a></td>         <td align="right"><a href="#Page_33">33</a></td></tr>
+
+<tr><td><a href="#image7">Lamps of a century or two ago</a></td>        <td align="right"><a href="#Page_56">56</a></td></tr>
+
+<tr><td><a href="#image8">Elaborate fixtures of the age of candles</a></td>        <td align="right"><a href="#Page_57">57</a></td></tr>
+
+<tr><td><a href="#image9">Flame arc</a></td>        <td align="right"><a href="#Page_128">128</a></td></tr>
+
+<tr><td><a href="#image10">Direct current arc</a></td>        <td align="right"><a href="#Page_128">128</a></td></tr>
+
+<tr><td><a href="#image11">On the testing-racks of the manufacturer of incandescent
+filament lamps</a></td>         <td align="right"><a href="#Page_129">129</a></td></tr>
+
+<tr><td><a href="#image13">Carbon-dioxide tube for accurate color-matching</a></td>        <td align="right"><a href="#Page_160">160</a></td></tr>
+
+<tr><td><a href="#image12">The Moore nitrogen tube</a></td>        <td align="right"><a href="#Page_160">160</a></td></tr>
+
+<tr><td><a href="#image14">Modern street lighting</a></td>         <td align="right"><a href="#Page_161">161</a></td></tr>
+
+<tr><td><a href="#image14">A completed lighthouse lens</a></td>        <td align="right"><a href="#Page_176">176</a></td></tr>
+
+<tr><td><a href="#image15">Torro Point Lighthouse, Panama Canal</a></td>        <td align="right"><a href="#Page_176">176</a></td></tr>
+
+<tr><td><a href="#image16">American search-light position on Western Front in 1919</a></td>         <td align="right"><a href="#Page_177">177</a></td></tr>
+
+<tr><td><a href="#image17">American standard field search-light and power unit</a></td>        <td align="right"><a href="#Page_177">177</a></td></tr>
+
+<tr><td><a href="#image18">Signal-light for airplane</a></td>        <td align="right"><a href="#Page_232">232</a></td></tr>
+
+<tr><td><a href="#image19">Trench light-signaling outfit</a></td>         <td align="right"><a href="#Page_232">232</a></td></tr>
+
+<tr><td><a href="#image20">Aviation field light-signal projector</a></td>        <td align="right"><a href="#Page_232">232</a></td></tr>
+
+<tr><td><a href="#image21">Signal search-light for airplane</a></td>         <td align="right"><a href="#Page_232">232</a></td></tr>
+
+<tr><td><a href="#image22">Unsafe, unproductive lighting worthy of the dark ages</a></td>          <td align="right"><a href="#Page_233">233</a></td></tr>
+
+<tr><td><a href="#image23">The same factory made safe, cheerful, and more productive
+by modern lighting</a></td>         <td align="right"><a href="#Page_233">233</a></td></tr>
+
+<tr><td><a href="#image24">Locomotive electric headlight</a></td>        <td align="right"><a href="#Page_240">240</a></td></tr>
+
+<tr><td><a href="#image25">Search-light on a fire-boat</a></td>        <td align="right"><a href="#Page_240">240</a></td></tr>
+
+<tr><td><a class="pagenum" name="Page_xiv" id="Page_xiv"></a><a href="#image26">Building ships under artificial light at Hog Island Shipyard</a></td>         <td align="right"><a href="#Page_241">241</a></td></tr>
+
+<tr><td><a href="#image27">Artificial light in photography</a></td>         <td align="right"><a href="#Page_256">256</a></td></tr>
+
+<tr><td><a href="#image29">Sterilizing water with radiant energy from quartz mercury-arcs</a></td>         <td align="right"><a href="#Page_257">257</a></td></tr>
+
+<tr><td><a href="#image31">Judging color under artificial daylight</a></td>          <td align="right"><a href="#Page_272">272</a></td></tr>
+
+<tr><td><a href="#image33">Artificial daylight</a></td>          <td align="right"><a href="#Page_273">273</a></td></tr>
+
+<tr><td><a href="#image35">Fireworks and illuminated battle-fleet at Hudson-Fulton
+Celebration</a></td>          <td align="right"><a href="#Page_288">288</a></td></tr>
+
+<tr><td><a href="#image38">Fireworks exhibition on May Day at Panama-Pacific Exposition</a></td>         <td align="right"><a href="#Page_289">289</a></td></tr>
+
+<tr><td><a href="#image39">The new flood lighting contrasted with the old outline
+lighting</a></td>         <td align="right"><a href="#Page_304">304</a></td></tr>
+
+<tr><td><a href="#image41">Niagara Falls flooded with light</a></td>          <td align="right"><a href="#Page_305">305</a></td></tr>
+
+<tr><td><a href="#image42">Artificial light honoring those who fell and those who
+returned</a></td>          <td align="right"><a href="#Page_320">320</a></td></tr>
+
+<tr><td><a href="#image44">The expressiveness of light in churches</a></td>          <td align="right"><a href="#Page_321">321</a></td></tr>
+
+<tr><td><a href="#image46">Obtaining two different moods in a room by a portable
+lamp which supplies direct and indirect components
+of light</a></td>          <td align="right"><a href="#Page_336">336</a></td></tr>
+
+<tr><td><a href="#image48">The lights of New York City</a></td>          <td align="right"><a href="#Page_337">337</a></td></tr>
+
+<tr><td><a href="#image49">Artificial light in community affairs</a></td>          <td align="right"><a href="#Page_352">352</a></td></tr>
+
+<tr><td><a href="#image51">Panama-Pacific Exposition</a></td>          <td align="right"><a href="#Page_353">353</a></td></tr>
+</table>
+</div>
+
+
+<hr style="width: 65%;" />
+<h1><a name="Page_1" id="Page_1"></a><a class="pagenum" name="Page_2" id="Page_2"></a>ARTIFICIAL LIGHT</h1>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_3" id="Page_3"></a>I</h2>
+
+<h2>LIGHT AND PROGRESS</h2>
+
+
+<p>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.</p>
+
+<p>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.<a class="pagenum" name="Page_4" id="Page_4"></a> 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
+<em>light</em>. 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.</p>
+
+<p>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 <a class="pagenum" name="Page_5" id="Page_5"></a>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,</p>
+
+<div class="poem"><div class="stanza">
+<p>O first created beam and thou great Word</p>
+<p>"Let there be light," and light was over all,</p>
+<p>Why am I thus bereaved thy prime decree?</p>
+</div></div>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_6" id="Page_6"></a>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.</p>
+
+<p>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 pro<a class="pagenum" name="Page_7" id="Page_7"></a>gresses. 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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_8" id="Page_8"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 con<a class="pagenum" name="Page_9" id="Page_9"></a>venient 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.</p>
+
+<p>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.</p>
+
+<p>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 <em>Light</em> the faithful companion of mankind. The
+Palace of Night, into which <em>Light</em> 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.</p>
+
+<p>By combining the symbolism of light, color, and darkness with the
+instincts which have been inherited <a class="pagenum" name="Page_10" id="Page_10"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_11" id="Page_11"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_12" id="Page_12"></a>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.</p>
+
+<p>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_13" id="Page_13"></a>gas or electricity. And there is window-breakage to be considered.</p>
+
+<p>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.</p>
+
+<p>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&mdash;the reliance
+upon artificial light alone&mdash;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.</p>
+
+<p>Naturally, with the tremendous development of artificial light during
+the present age, a new profession has <a class="pagenum" name="Page_14" id="Page_14"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_15" id="Page_15"></a>II</h2>
+
+<h2>THE ART OF MAKING FIRE</h2>
+
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_16" id="Page_16"></a>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.</p>
+
+<div class="floatl">
+<a id="image2" name="image2"></a>
+<img src="images/image2.png" alt="PRIMITIVE FIRE-BASKETS" title="PRIMITIVE FIRE-BASKETS" width="300" height="192" />
+<p class="caption">PRIMITIVE FIRE-BASKETS</p>
+</div>
+
+<div class="floatr">
+<a id="image3" name="image3"></a>
+<img src="images/image3.png" alt="CRUDE SPLINTER-HOLDERS" title="CRUDE SPLINTER-HOLDERS" width="300" height="232" />
+<p class="caption">CRUDE SPLINTER-HOLDERS</p>
+</div>
+
+<p>According to a certain myth, Prometheus stole fire from heaven and
+brought this blessing to earth. Throughout the mythologies of various
+races, fire and, as a consequence, light have been associated with
+divinity. They have been subjects of worship perhaps more generally than
+anything else, and these early impressions have survived in the
+ceremonial uses of light and fire even to the present time. The origin
+of fire as represented in any of the myths of the superstitious beings
+of early ages is as suitable as any other, inasmuch as definite
+knowledge is unavailable. Active volcanoes, spontaneous combustion,
+friction, accidental focusing of the sun's image, and other means may
+have introduced primitive beings to fire. A study of savage tribes of
+the present age combined with a survey of past history of mythology, of
+material relics, and of the absence of lamps or other lighting utensils
+leads to the conclusion that the earliest source of light was the wood
+fire.</p>
+
+<div class="center">
+<a id="image4" name="image4"></a>
+<img class="framed" src="images/image4.png" alt="EARLY OPEN-FLAME OIL AND GREASE LAMPS" title="EARLY OPEN-FLAME OIL AND GREASE LAMPS" width="700" height="337" />
+<p class="caption">EARLY OPEN-FLAME OIL AND GREASE LAMPS</p>
+</div>
+
+<p><a class="pagenum" name="Page_17" id="Page_17"></a>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 co&ouml;rdinated 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.</p>
+
+<p>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.<a class="pagenum" name="Page_18" id="Page_18"></a> 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.</p>
+
+<p>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 <ins class="correction" title="Transcriber's Note:
+Original reads &quot;similiar&quot;">similar</ins> 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.</p>
+
+<p>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
+<a class="pagenum" name="Page_19" id="Page_19"></a>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.</p>
+
+<p>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 <abbr>B.&nbsp;C.</abbr>), 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.</p>
+
+<p>The energy in sunlight varies enormously, even on clear days, because
+the water-vapor in the atmosphere <a class="pagenum" name="Page_20" id="Page_20"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_21" id="Page_21"></a>inconvenient methods of making fire were replaced by
+steadily improving scientific devices.</p>
+
+<p>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.</p>
+
+<p>Phosphorus has long played a dominant r&ocirc;le 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.</p>
+
+<p>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 <a class="pagenum" name="Page_22" id="Page_22"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Although many of these methods and devices have <a class="pagenum" name="Page_23" id="Page_23"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_24" id="Page_24"></a>III</h2>
+
+<h2>PRIMITIVE LIGHT-SOURCES</h2>
+
+
+<p>Many are familiar with the light of the firefly or of its larv&aelig;, 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?"</p>
+
+<p>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 <a class="pagenum" name="Page_25" id="Page_25"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_26" id="Page_26"></a>keeps on the
+lookout for live trees saturated with highly inflammable ingredients.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_27" id="Page_27"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_28" id="Page_28"></a>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.</p>
+
+<p>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 devel<a class="pagenum" name="Page_29" id="Page_29"></a>oping 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.</p>
+
+<p>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!</p>
+
+<p>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
+ar<a class="pagenum" name="Page_30" id="Page_30"></a>tificial 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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_31" id="Page_31"></a>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.</p>
+
+<p>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.</p>
+
+<div class="floatr">
+<a name="image5" id="image5"></a>
+<img src="images/image5.png" alt="A TYPICAL METAL MULTIPLE-WICK OPEN-FLAME OIL-LAMP" title="A TYPICAL METAL MULTIPLE-WICK OPEN-FLAME OIL-LAMP" height="400" width="257" />
+<p class="caption">A TYPICAL METAL MULTIPLE-WICK OPEN-FLAME OIL-LAMP</p>
+</div>
+
+<p>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 <a class="pagenum" name="Page_32" id="Page_32"></a>pan
+beneath the oil-receptacle, to catch drippings from the wick or oil
+which might run over during the filling. The Chinese lamps were
+sometimes made of bamboo, but the Scottish lamps were made of metal. A
+flat metal lamp, called a crusie, was one of the chief products of
+blacksmiths and was common in Scotland until the middle of the
+nineteenth century. This type of lamp was used by many nations and has
+been found in the catacombs of Rome. The crusie was usually suspended by
+an iron hook and the flow of oil to the wick could be regulated by
+tilting. The wick in the Scottish lamps consisted of the pith of rushes,
+cloth, or twisted threads. These early oil-lamps were almost always
+shallow vessels into which a short wick was dipped, and it was not until
+the latter part of the eighteenth century that other forms came into
+general use. The change in form was due chiefly to the introduction of
+scientific knowledge when mineral oil was introduced. As early as 1781
+the burning of naptha obtained by distilling coal at low temperatures
+was first discussed, but no general applications were made until a later
+period. This was the beginning of many marked improvements in oil-lamps,
+and was in reality the birth of the modern science of light-production.</p>
+
+<div class="center">
+<a name="image6" id="image6"></a>
+<img src="images/image6.png" alt="A GROUP OF OIL-LAMPS OF TWO CENTURIES AGO" title="A GROUP OF OIL-LAMPS OF TWO CENTURIES AGO" height="408" width="500" />
+<p class="caption">A GROUP OF OIL-LAMPS OF TWO CENTURIES AGO</p>
+</div>
+
+<p>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 <a class="pagenum" name="Page_33" id="Page_33"></a>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_34" id="Page_34"></a>age of
+artificial lighting, the candle stood pre&euml;minent 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 Ph&oelig;nicians. It is known that the
+Romans used them, especially the wax-candles, in religious ceremonies.
+The Ph&oelig;nicians introduced them into Byzantium, but they disappeared
+under the Turkish rule and did not come into use again until the twelfth
+century.</p>
+
+<p>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.</p>
+
+<p>With the rise of the Christian church, candles came to be used in
+religious ceremonies and many of the <a class="pagenum" name="Page_35" id="Page_35"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_36" id="Page_36"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_37" id="Page_37"></a>ceremonies, as a
+decorative element at banquets, and in the outposts of civilization.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_38" id="Page_38"></a>IV</h2>
+
+<h2>THE CEREMONIAL USE OF LIGHT</h2>
+
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_39" id="Page_39"></a>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.</p>
+
+<p>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 Ph&oelig;nicians and Romans apparently continued
+the custom, but no traces of it have been found in Greece and Egypt.</p>
+
+<p><a class="pagenum" name="Page_40" id="Page_40"></a>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 r&ocirc;les. 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.</p>
+
+<p>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 simi<a class="pagenum" name="Page_41" id="Page_41"></a>lar. 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.</p>
+
+<p>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 sanc<a class="pagenum" name="Page_42" id="Page_42"></a>tuaries
+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.</p>
+
+<p>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.</p>
+
+<p>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<a class="pagenum" name="Page_43" id="Page_43"></a> 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.</p>
+
+<p>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.</p>
+
+<p>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<a class="pagenum" name="Page_44" id="Page_44"></a> 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.</p>
+
+<p>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?"</p>
+
+<p>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 <a class="pagenum" name="Page_45" id="Page_45"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 class="pagenum" name="Page_46" id="Page_46"></a> 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.</p>
+
+<p>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, ...<a class="pagenum" name="Page_47" id="Page_47"></a> 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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_48" id="Page_48"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_49" id="Page_49"></a>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.</p>
+
+<p>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.</p>
+
+<p>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. Al<a class="pagenum" name="Page_50" id="Page_50"></a>though 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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_51" id="Page_51"></a>V</h2>
+
+<h2>OIL-LAMPS OF THE NINETEENTH CENTURY</h2>
+
+
+<p>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 pro<a class="pagenum" name="Page_52" id="Page_52"></a>duced 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.</p>
+
+<p>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 prod<a class="pagenum" name="Page_53" id="Page_53"></a>ucts 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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_54" id="Page_54"></a>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.</p>
+
+<p>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.</p>
+
+<p>The Carcel lamp, which appeared in 1800, consisted <a class="pagenum" name="Page_55" id="Page_55"></a>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.</p>
+
+<p>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.</p>
+
+<p>Although petroleum products were not used to any appreciable extent for
+illuminating-purposes until after the middle of the nineteenth century,
+mineral oil is <a class="pagenum" name="Page_56" id="Page_56"></a>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.&nbsp;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.</p>
+
+<div class="center">
+<a name="image7" id="image7"></a>
+<img src="images/image7.png" alt="LAMPS OF A CENTURY OR TWO AGO" title="LAMPS OF A CENTURY OR TWO AGO" width="500" height="374" />
+<p class="caption">LAMPS OF A CENTURY OR TWO AGO</p>
+</div>
+
+<p>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,
+<a class="pagenum" name="Page_57" id="Page_57"></a>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.</p>
+
+<div class="floatl">
+<a name="image8" id="image8"></a>
+<img src="images/image8.png" alt="ELABORATE FIXTURES OF THE AGE OF CANDLES" title="ELABORATE FIXTURES OF THE AGE OF CANDLES" width="305" height="500" />
+<p class="caption">ELABORATE FIXTURES OF THE AGE OF CANDLES</p>
+</div>
+
+<p>Crude petroleum possesses a very repugnant odor; it varies in color from
+yellow to black; and its specific gravity ranges from about 0.80 to
+1.00, but commonly is between 0.80 and 0.90. Its chemical constitution
+is chiefly of carbon and hydrogen, in the approximate ratio of about six
+to one respectively. It is a mixture of paraffin hydrocarbons having the
+general formula of C<sub>n</sub>H<sub>2n+2</sub> and the individual members of this
+series vary from CH<sub>4</sub> (methane) to C<sub>15</sub>H<sub>32</sub> (pentadecane),
+although the solid hydrocarbons are still more complex. Petroleum is
+found in many countries and the United States is particularly blessed
+with great stores of it.</p>
+
+<p>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 <a class="pagenum" name="Page_58" id="Page_58"></a>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.</p>
+
+<p>In oil-lamps at the present time mineral oils are used which possess
+flashing-points above 75&deg;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&deg;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 <a class="pagenum" name="Page_59" id="Page_59"></a>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.</p>
+
+<p>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.</p>
+
+<p>To supply the necessary amount of oxygen (air) to <a class="pagenum" name="Page_60" id="Page_60"></a>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_61" id="Page_61"></a>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.</p>
+
+<p>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&mdash;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.</p>
+
+<p><a class="pagenum" name="Page_62" id="Page_62"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_63" id="Page_63"></a>VI</h2>
+
+<h2>EARLY GAS-LIGHTING</h2>
+
+
+<p>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:</p>
+
+<blockquote><p>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....</p></blockquote>
+
+<p>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 <a class="pagenum" name="Page_64" id="Page_64"></a>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:</p>
+
+<blockquote><p>I got some coal, and distilled it in a retort in an open fire.
+At first there came over only phlegm, afterwards a black <em>oil</em>,
+and then likewise, a <em>spirit</em> 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 <em>caught
+fire</em> at the <em>flame</em> of the <em>candle</em>, and continued burning
+with violence as it <em>issued out</em> in a <em>stream</em>, which I blew
+out, and lighted again alternately several times.</p></blockquote>
+
+<p>He then turned his attention to saving some of the <a class="pagenum" name="Page_65" id="Page_65"></a>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."</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>The literature of an ancient nation is often referred to as revealing
+the civilization of the period. Surely <a class="pagenum" name="Page_66" id="Page_66"></a>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:</p>
+
+<blockquote><p>About the latter End of <em>Feb.</em> 1659, returning from a Journey
+to my House in Wigan, I was entertained with the Relation of an
+odd Spring situated in one Mr. <em>Hawkley's</em> Ground (if I mistake
+not) about a Mile from the Town, in that Road which leads to
+<em>Warrington</em> and <em>Chester</em>: The People of this Town did
+confidently affirm, That the Water of this Spring did burn like
+Oil.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_67" id="Page_67"></a>Fire, tho' by putting my
+Hand into it, I could not perceive it so much as warm.</p>
+
+<p>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 <em>Wigan</em>, <em>Ashton</em>, 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.</p>
+
+<p>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.</p></blockquote>
+
+<p>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 <a class="pagenum" name="Page_68" id="Page_68"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_69" id="Page_69"></a>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</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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."</p>
+
+<p>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 <a class="pagenum" name="Page_70" id="Page_70"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_71" id="Page_71"></a>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.</p>
+
+<p>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p><a class="pagenum" name="Page_72" id="Page_72"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_73" id="Page_73"></a>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.</p>
+
+<p>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."</p>
+
+<p><a class="pagenum" name="Page_74" id="Page_74"></a>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.</p>
+
+<p>The conditions imposed upon this company as presented in an early
+treatise on gas-lighting (by Accum in 1818) were as follows:</p>
+
+<blockquote><p>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
+&pound;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.</p></blockquote>
+
+<p>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
+in<a class="pagenum" name="Page_75" id="Page_75"></a>troduced. 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."</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_76" id="Page_76"></a>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.</p>
+
+<p>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.<a class="pagenum" name="Page_77" id="Page_77"></a> It was not until the latter half of the nineteenth
+century that it was generally used in residences.</p>
+
+<p>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.</p>
+
+<p>In 1854 Bowditch brought out a regenerative lamp <a class="pagenum" name="Page_78" id="Page_78"></a>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.</p>
+
+<p>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.</p>
+
+<p>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:</p>
+
+<div class="center">
+<table cellpadding="5" summary="candle-power">
+<thead>
+<tr><td><a class="pagenum" name="Page_79" id="Page_79"></a>&nbsp;</td><th>Candle-power<br />
+per cubic foot of<br />
+gas per hour</th></tr>
+</thead>
+<tbody>
+<tr><td>Fish-tail flames, depending upon size</td>      <td align="right">0.6 to 2.5</td></tr>
+<tr><td>Argand, depending upon improvements</td>        <td align="right">2.9 to 3.5</td></tr>
+<tr><td>Regenerative</td>                               <td align="right">7 to 10</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_80" id="Page_80"></a>VII</h2>
+
+<h2>THE SCIENCE OF LIGHT-PRODUCTION</h2>
+
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_81" id="Page_81"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_82" id="Page_82"></a>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.</p>
+
+<p>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&mdash;the uniting of carbon
+with oxygen&mdash;will continue. An ordinary flat gas-flame of the
+"bats-wing" type may vary in temperature in its central portion from
+300&deg;F. at the bot<a class="pagenum" name="Page_83" id="Page_83"></a>tom to about 3000&deg;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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_84" id="Page_84"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_85" id="Page_85"></a>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.</p>
+
+<p>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.</p>
+
+<p>The latter point will become clearer if the reader will refresh his
+memory regarding the nature of light.<a class="pagenum" name="Page_86" id="Page_86"></a> 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.</p>
+
+<p>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 <a class="pagenum" name="Page_87" id="Page_87"></a>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.</p>
+
+<p>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>Even Newton could not have had the faintest idea of <a class="pagenum" name="Page_88" id="Page_88"></a>the great
+developments which were to be based upon the spectrum.</p>
+
+<p>Now to return to the peculiar property of rare-earth oxides&mdash;namely,
+their unusual brilliance when heated in a flame&mdash;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.</p>
+
+<p>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 <a class="pagenum" name="Page_89" id="Page_89"></a>line) will be
+seen. This forms the basis of spectrum analysis as applied in chemistry.</p>
+
+<p>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.</p>
+
+<p>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.<a class="pagenum" name="Page_90" id="Page_90"></a> 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.</p>
+
+<p>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.</p>
+
+<p>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&deg;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 <a class="pagenum" name="Page_91" id="Page_91"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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 in<a class="pagenum" name="Page_92" id="Page_92"></a>tensity 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.</p>
+
+<p>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_93" id="Page_93"></a>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)<a class="pagenum" name="Page_94" id="Page_94"></a> red
+rays and absorbs the other rays in the illuminant. In other words, color
+is due to selective absorption reflection, or transmission.</p>
+
+<p>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.</p>
+
+<p>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&mdash;that is, by a
+normal radiator at a temperature of 10,000&deg;F., which is impracticable at
+present&mdash;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.<a class="pagenum" name="Page_95" id="Page_95"></a></p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<div class="center">
+<table cellpadding="5" summary="progress of light production">
+<thead>
+<tr><td>&nbsp;</td><th>Efficiency<br />in per cent.</th></tr>
+</thead>
+<tbody>
+<tr><td>Sperm-candle</td><td align="right">0.02</td></tr>
+<tr><td>Open gas-flame</td><td align="right">.04</td></tr>
+<tr><td>Incandescent gas-mantle</td><td align="right">.19</td></tr>
+<tr><td>Carbon filament lamp</td><td align="right">.05</td></tr>
+<tr><td>Vacuum Mazda lamp</td><td align="right">1.3</td></tr>
+<tr><td>Gas-filled Mazda lamp</td><td align="right">2 to 3</td></tr>
+<tr><td><a class="pagenum" name="Page_96" id="Page_96"></a>Arc-lamps</td><td align="right">2 to 7</td></tr>
+<tr><td>White light radiated by "black-body"</td><td align="right">16</td></tr>
+<tr><td>Most efficient white light</td><td align="right">40</td></tr>
+<tr><td>Firefly</td><td align="right">95</td></tr>
+<tr><td>Most efficient light (yellow-green)</td><td align="right">100</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_97" id="Page_97"></a>VIII</h2>
+
+<h2>MODERN GAS-LIGHTING</h2>
+
+
+<p>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?</p>
+
+<p><a class="pagenum" name="Page_98" id="Page_98"></a>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.</p>
+
+<p>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 &eacute;lite. 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<a class="pagenum" name="Page_99" id="Page_99"></a> 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&mdash;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.</p>
+
+<p>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.</p>
+
+<p>This gave him the idea of producing a mantle for <a class="pagenum" name="Page_100" id="Page_100"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_101" id="Page_101"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>The inverted mantle introduced greater possibilities <a class="pagenum" name="Page_102" id="Page_102"></a>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.</p>
+
+<p>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.</p>
+
+<p>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-pres<a class="pagenum" name="Page_103" id="Page_103"></a>sure 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.</p>
+
+<p>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.</p>
+
+<p>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&deg;F. through heating by an
+outside fire, the coal begins to fuse and hydrocarbon vapors begin to
+<a class="pagenum" name="Page_104" id="Page_104"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_105" id="Page_105"></a>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.</p>
+
+<p>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.</p>
+
+<p>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,</p>
+
+<div class="center">
+<table cellpadding="5" summary="gas yielded">
+<tr><td>10,000 cubic feet of gas</td><td align="right">17</td><td>per</td><td>cent.</td></tr>
+<tr><td>coke</td><td align="right">70</td><td align="center">"</td><td align="center">"</td></tr>
+<tr><td>tar</td><td align="right">5</td><td align="center">"</td><td align="center">"</td></tr>
+<tr><td>ammoniacal liquid</td><td align="right">8</td><td align="center">"</td><td align="center">"</td></tr>
+</table>
+</div>
+
+<p>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 <a class="pagenum" name="Page_106" id="Page_106"></a>the tar many products are derived such as aniline
+dyes, benzene, carbolic acid, picric acid, napthalene, pitch,
+anthracene, and saccharin.</p>
+
+<p>A typical analysis of the gas distilled from coal is very approximately
+as follows,</p>
+
+<div class="center">
+<table cellpadding="5" summary="gas distilled">
+<tr><td>Hydrocarbons</td><td align="right">40</td><td>per</td><td>cent.</td></tr>
+<tr><td>Hydrogen</td><td align="right">50</td><td align="center">"</td><td align="center">"</td></tr>
+<tr><td>Carbon monoxide</td><td align="right">4</td><td align="center">"</td><td align="center">"</td></tr>
+<tr><td>Nitrogen</td><td align="right">4</td><td align="center">"</td><td align="center">"</td></tr>
+<tr><td>Carbon dioxide</td><td align="right">1</td><td align="center">"</td><td align="center">"</td></tr>
+<tr><td>Various other gases</td><td align="right">1</td><td align="center">"</td><td align="center">"</td></tr>
+</table>
+</div>
+
+<p>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,</p>
+
+<div class="center">
+<table cellpadding="5" summary="constituents of illuminating gas">
+<tr><td>ethylene</td><td>C<sub>2</sub>H<sub>4</sub></td><td>crotonylene</td><td>C<sub>4</sub>H<sub>6</sub></td></tr>
+<tr><td>propylene</td><td>C<sub>3</sub>H<sub>6</sub></td><td>benzene</td><td>C<sub>6</sub>H<sub>6</sub></td></tr>
+<tr><td>butylene</td><td>C<sub>4</sub>H<sub>8</sub></td><td>toluene</td><td>C<sub>7</sub>H<sub>8</sub></td></tr>
+<tr><td>amylene</td><td>C<sub>5</sub>H<sub>10</sub></td><td> xylene</td><td>C<sub>8</sub>H<sub>10</sub></td></tr>
+<tr><td>acetylene</td><td>C<sub>2</sub>H<sub>2</sub></td><td>methane</td><td>C H<sub>4</sub></td></tr>
+<tr><td>allylene</td><td>C<sub>3</sub>H<sub>4</sub></td><td>ethane</td><td>C<sub>2</sub>H<sub>6</sub></td></tr>
+</table>
+</div>
+
+<p>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
+vol<a class="pagenum" name="Page_107" id="Page_107"></a>ume, 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.</p>
+
+<p>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.</p>
+
+<p>The reaction which takes place when water and calcium carbide are
+brought together is a double decomposition and is represented by,</p>
+
+<blockquote><p>CaC<sub>2</sub> + H<sub>2</sub>O = C<sub>2</sub>H<sub>2</sub> + CaO</p></blockquote>
+
+<p>It will be seen that the products are acetylene gas and calcium oxide or
+lime. The lime, being hydroscopic <a class="pagenum" name="Page_108" id="Page_108"></a>and being in the presence of water or
+water-vapor in the acetylene generator, really becomes calcium hydroxide
+Ca(OH)<sub>2</sub>, 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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_109" id="Page_109"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_110" id="Page_110"></a>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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_111" id="Page_111"></a>IX</h2>
+
+<h2>THE ELECTRIC ARCS</h2>
+
+
+<p>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&mdash;among them a call to Paris by Bonaparte to exhibit his
+electrical experiments, and to receive a medal struck in his honor.</p>
+
+<p>While Volta was being showered with honors, various scientific men with
+great enthusiasm were entering new <a class="pagenum" name="Page_112" id="Page_112"></a>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.</p>
+
+<p>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."</p>
+
+<p>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 <a class="pagenum" name="Page_113" id="Page_113"></a>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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:</p>
+
+<blockquote><p>...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.</p></blockquote>
+
+<p>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 <a class="pagenum" name="Page_114" id="Page_114"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_115" id="Page_115"></a>was melted for such a distance that it bent downward, but
+the negative remained quite straight.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_116" id="Page_116"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_117" id="Page_117"></a>is in the
+neighborhood of 6000&deg; to 7000&deg;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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_118" id="Page_118"></a>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.</p>
+
+<p>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-<a class="pagenum" name="Page_119" id="Page_119"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_120" id="Page_120"></a>reaches zero
+value and the arc is virtually extinguished. Therefore, there is a
+maximum brightness midway between the reversals.</p>
+
+<p>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.</p>
+
+<p>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."</p>
+
+<p>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 <a class="pagenum" name="Page_121" id="Page_121"></a>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.</p>
+
+<p>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.<a class="pagenum" name="Page_122" id="Page_122"></a> 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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_123" id="Page_123"></a>as the magnetite-arc, has a
+luminous efficiency of about 20 lumens per watt with a clear glass
+globe.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<div class="center">
+<table cellpadding="5" summary="lumens per watt">
+<thead>
+<tr><td><a class="pagenum" name="Page_124" id="Page_124"></a>&nbsp;</td><th align="right">Lumens per watt</th></tr>
+</thead>
+<tbody>
+<tr><td>Open carbon arc</td><td align="right">4 to 8</td></tr>
+<tr><td>Enclosed carbon arc</td><td align="right">7</td></tr>
+<tr><td>Enclosed flame-arc (yellow or white)</td><td align="right">15 to 25</td></tr>
+<tr><td>Luminous arc</td><td align="right">10 to 25</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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.</p>
+
+<p>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 con<a class="pagenum" name="Page_125" id="Page_125"></a>nects 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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_126" id="Page_126"></a>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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_127" id="Page_127"></a>X</h2>
+
+<h2>THE ELECTRIC INCANDESCENT FILAMENT LAMPS</h2>
+
+
+<p>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_128" id="Page_128"></a>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.</p>
+
+<div class="floatl">
+<a name="image9" id="image9"></a>
+<img src="images/image9.png" alt="DIRECT CURRENT ARC" title="DIRECT CURRENT ARC" height="400" width="265" />
+<p class="caption">DIRECT CURRENT ARC<br />
+Most of the light being emitted by the positive (upper) electrode</p>
+</div>
+
+<div class="floatr">
+<a name="image10" id="image10"></a>
+<img src="images/image10.png" alt="FLAME ARC" title="FLAME ARC" height="400" width="284" />
+<p class="caption">FLAME ARC<br />
+Most of the light being emitted by the flame</p>
+</div>
+
+<p>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&deg;F.) limited
+the success of the lamps. Carbon with its extremely high melting-point
+had long attracted attention and in 1879 Edison produced a carbon
+filament by carbonizing a strip of paper. He sealed this in a vessel of
+glass from which the air was exhausted and the electric current was led
+to the filament through platinum wires sealed in the glass. Platinum was
+used because its expansion and contraction is about the same as glass.
+Incidentally, many improvements were made in incandescent lamps and
+thirty years passed before a material was found to replace the platinum
+leading-in wires. The cost of platinum steadily increased and finally in
+the present century a substitute was made by the use of two metals whose
+combined expansion was the same as that of platinum or glass. In 1879
+and 1880 Edison had succeeded in overcoming the many <a class="pagenum" name="Page_129" id="Page_129"></a>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.</p>
+
+<div class="center">
+<a name="image11" id="image11"></a>
+<img src="images/image11.png" alt="ON THE TESTING-RACKS OF THE MANUFACTURER OF INCANDESCENT FILAMENT LAMPS" title="ON THE TESTING-RACKS OF THE MANUFACTURER OF INCANDESCENT FILAMENT LAMPS" height="388" width="500" />
+<p class="caption">ON THE TESTING-RACKS OF THE MANUFACTURER OF INCANDESCENT
+FILAMENT LAMPS<br />
+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
+</p>
+</div>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Of these early days, Edison said:</p>
+
+<blockquote><p>It occurred to me that perhaps a filament of carbon could be<a class="pagenum" name="Page_130" id="Page_130"></a>
+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.</p></blockquote>
+
+<p>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 <a class="pagenum" name="Page_131" id="Page_131"></a>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.</p>
+
+<p>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.</p>
+
+<p>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&deg;F.), but the carbon filament as operated in practice has a lower
+efficiency than any <a class="pagenum" name="Page_132" id="Page_132"></a>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.</p>
+
+<p>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&deg;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
+tan<a class="pagenum" name="Page_133" id="Page_133"></a>talum 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.</p>
+
+<p>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.</p>
+
+<p>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&mdash;which is known as "wolfram" in Germany, and to some extent
+in English-speaking countries&mdash;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<a class="pagenum" name="Page_134" id="Page_134"></a> 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&deg;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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_135" id="Page_135"></a>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.</p>
+
+<p>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.</p>
+
+<p>Much of this development work was done by the laboratories of the
+General Electric Company and they were destined to contribute another
+great improve<a class="pagenum" name="Page_136" id="Page_136"></a>ment. 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.</p>
+
+<p>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 <em>light</em> but a less efficient
+<em>lamp</em>. 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 fila<a class="pagenum" name="Page_137" id="Page_137"></a>ment 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.</p>
+
+<p>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 <a class="pagenum" name="Page_138" id="Page_138"></a>of the incandescent lamp would alter the
+attitude of many persons toward science and toward the large industrial
+companies.</p>
+
+<p>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.</p>
+
+<p class="center"><span class="smcap">Approximate Values</span></p>
+
+<div class="center">
+<table cellpadding="5" summary="lumens per watt">
+<thead>
+<tr><th>Date</th><th>Filament</th><th>Temperature</th><th>Lumens per watt</th></tr>
+</thead>
+<tbody>
+<tr><td>1880</td><td>Carbon</td><td align="center">3300&deg;F.</td><td align="center">3.0</td></tr>
+<tr><td>1906</td><td>Carbon (graphitized)</td><td align="center">3400</td><td align="center">4.5</td></tr>
+<tr><td>1905</td><td>Tantalum</td><td align="center">3550</td><td align="center">6.5</td></tr>
+<tr><td>1905</td><td>Osmium</td><td align="center">3600</td><td align="center">7.5</td></tr>
+<tr><td>1906</td><td>Tungsten (vacuum)</td><td align="center">3700</td><td align="center">8.0</td></tr>
+<tr><td>1914</td><td>Tungsten (gas-filled)</td><td align="center">up to 5300&deg;F.</td><td align="center">10 to 25</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_139" id="Page_139"></a>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.</p>
+
+<p>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 ap<a class="pagenum" name="Page_140" id="Page_140"></a>peared to have
+promise. It has not been introduced commercially and doubtless it cannot
+compete with the latest tungsten lamps.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+
+<p class="center"><span class="smcap"><a class="pagenum" name="Page_141" id="Page_141"></a>Average Candle-Power, Watts, and Efficiency of All the Lamps Sold in
+This Country</span></p>
+
+<div class="center">
+<table cellpadding="5" summary="candle-power">
+<thead>
+<tr><th>Year</th><th>Candle-power</th><th>Watts</th><th>Lumens<br/>per watt</th></tr>
+</thead>
+<tbody>
+<tr><td>1907</td><td align="center">18.0</td><td align="center">53</td><td align="right">3.33</td></tr>
+<tr><td>1908</td><td align="center">19.0</td><td align="center">53</td><td align="right">3.52</td></tr>
+<tr><td>1909</td><td align="center">21.0</td><td align="center">52</td><td align="right">3.96</td></tr>
+<tr><td>1910</td><td align="center">23.0</td><td align="center">51</td><td align="right">4.42</td></tr>
+<tr><td>1911</td><td align="center">25.0</td><td align="center">51</td><td align="right">4.82</td></tr>
+<tr><td>1912</td><td align="center">26.0</td><td align="center">49</td><td align="right">5.20</td></tr>
+<tr><td>1913</td><td align="center">29.4</td><td align="center">47</td><td align="right">6.13</td></tr>
+<tr><td>1914</td><td align="center">38.2</td><td align="center">48</td><td align="right">7.80</td></tr>
+<tr><td>1915</td><td align="center">42.2</td><td align="center">47</td><td align="right">8.74</td></tr>
+<tr><td>1916</td><td align="center">45.8</td><td align="center">49</td><td align="right">9.60</td></tr>
+<tr><td>1917</td><td align="center">48.7</td><td align="center">52</td><td align="right">10.56</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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 <a class="pagenum" name="Page_142" id="Page_142"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_143" id="Page_143"></a>XI</h2>
+
+<h2>THE LIGHT OF THE FUTURE</h2>
+
+
+<p>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 banish<a class="pagenum" name="Page_144" id="Page_144"></a>ing 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.</p>
+
+<p>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&deg;F. to
+11,000&deg;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&deg;F. and 7000&deg;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.</p>
+
+<p>Scientists are becoming more and more intimate with the structure of
+matter. They are learning secrets <a class="pagenum" name="Page_145" id="Page_145"></a>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.</p>
+
+<p>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_146" id="Page_146"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_147" id="Page_147"></a>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.</p>
+
+<p>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.</p>
+
+<p>There is another attractive method of producing light and it has not
+escaped the writer of fiction. H.&nbsp;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 <a class="pagenum" name="Page_148" id="Page_148"></a>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.</p>
+
+<p>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-<a class="pagenum" name="Page_149" id="Page_149"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_150" id="Page_150"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_151" id="Page_151"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_152" id="Page_152"></a>XII</h2>
+
+<h2>LIGHTING THE STREETS</h2>
+
+
+<p>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</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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 <a class="pagenum" name="Page_153" id="Page_153"></a>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.</p>
+
+<p>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.</p>
+
+<p>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p><a class="pagenum" name="Page_154" id="Page_154"></a>Although apparently labor was not on a strike, the soldiers caused
+disturbances, for in another passage he tells of riotous soldiers who</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_155" id="Page_155"></a>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,</p>
+
+<div class="poem"><div class="stanza">
+<p>A light here, maids, hang out your lights,</p>
+<p>And see your horns be clear and bright,</p>
+<p>That so your candle clear may shine,</p>
+<p>Continuing from six till nine;</p>
+<p>That honest men that walk along</p>
+<p>May see to pass safe without wrong.</p>
+</div></div>
+
+<p>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."</p>
+
+<p>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 <a class="pagenum" name="Page_156" id="Page_156"></a>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.</p>
+
+<p>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.</p>
+
+<p>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</p>
+
+<blockquote><p>that divers confederacies of great numbers of evil-disposed
+persons, armed with bludgeons, pistols, cutlasses, and other
+dangerous weapons, infest not only <a class="pagenum" name="Page_157" id="Page_157"></a>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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 <em>Zeitung</em> in 1816 <a class="pagenum" name="Page_158" id="Page_158"></a>indicate
+the character of the objections raised against street-lighting.</p>
+
+<ol>
+<li>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.</li>
+
+<li>From the judicial standpoint: Those people who
+     do not want light ought not to be compelled to pay
+     for its use.</li>
+
+<li>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.</li>
+
+<li>From the moral standpoint: The fear of darkness
+     will vanish and drunkenness and depravity increase.</li>
+
+<li>From the viewpoint of the police: The horses will
+     get frightened and the thieves emboldened.</li>
+
+<li>From the point of view of national economy: Great
+     sums of money will be exported to foreign countries.</li>
+
+<li>From the point of view of the common people: The
+     constant illumination of streets by night will rob
+     festive illuminations of their charm.</li>
+</ol>
+
+<p>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 <a class="pagenum" name="Page_159" id="Page_159"></a>hours of
+activity and commerce, industry, and knowledge grew apace.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_160" id="Page_160"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<div class="floatl">
+<a name="image12" id="image12"></a>
+<img src="images/image12.png" title="THE MOORE NITROGEN TUBE" alt="THE MOORE NITROGEN TUBE" width="349" height="500" />
+<p class="caption">THE MOORE NITROGEN TUBE<br />
+In lobby of Madison Square Garden</p>
+</div>
+
+<div class="floatr">
+<a name="image13" id="image13"></a>
+<img src="images/image13.png" title="CARBON-DIOXIDE TUBE FOR ACCURATE COLOR-MATCHING" alt="CARBON-DIOXIDE TUBE FOR ACCURATE COLOR-MATCHING" width="215" height="500" />
+<p class="caption">CARBON-DIOXIDE TUBE FOR <br />ACCURATE COLOR-MATCHING</p>
+</div>
+
+<p>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 with<a class="pagenum" name="Page_161" id="Page_161"></a>out 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.</p>
+
+<p>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.</p>
+
+<div class="center">
+<a name="image14" id="image14"></a>
+<img src="images/image14.png" alt="MODERN STREET LIGHTING" title="MODERN STREET LIGHTING" width="600" height="379" />
+<p class="caption">MODERN STREET LIGHTING<br />
+Tunnels of light boring through the darkness provide safe channels for
+modern traffic</p>
+</div>
+
+<p>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 <a class="pagenum" name="Page_162" id="Page_162"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_163" id="Page_163"></a>XIII</h2>
+
+<h2>LIGHTHOUSES</h2>
+
+
+<p>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.</p>
+
+<p>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. C&aelig;sar, who visited Alexandria two
+cen<a class="pagenum" name="Page_164" id="Page_164"></a>turies 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.</p>
+
+<p>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>This was the practical result of a petition of Boston merchants made
+three years before. The tower was <a class="pagenum" name="Page_165" id="Page_165"></a>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.</p>
+
+<p>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.</p>
+
+<p>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:</p>
+
+<blockquote><p>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 <a class="pagenum" name="Page_166" id="Page_166"></a>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.</p></blockquote>
+
+<p>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&mdash;a total of 5323.</p>
+
+<p>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 <a class="pagenum" name="Page_167" id="Page_167"></a>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.</p>
+
+<p>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.</p>
+
+<p>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&mdash;one in which oil is supplied to the burner under
+pressure and the other in which oil is maintained <ins class="correction" title="Transcriber's Note: Original reads &quot;as&quot;">at</ins> a constant level.
+In some of the smallest lamps the ordinary capillarity of the wick is
+depended on to supply oil to the flame.</p>
+
+<p><a class="pagenum" name="Page_168" id="Page_168"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_169" id="Page_169"></a>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.</p>
+
+<p>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.&nbsp;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.</p>
+
+<p>Untended lights were not developed until about 1880, <a class="pagenum" name="Page_170" id="Page_170"></a>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.</p>
+
+<p>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.</p>
+
+<p>The optical apparatus of navigation lights has undergone many
+improvements in the past century. The <a class="pagenum" name="Page_171" id="Page_171"></a>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.</p>
+
+<p>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.</p>
+
+<p>Lenses appear to have been introduced in the latter <a class="pagenum" name="Page_172" id="Page_172"></a>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_173" id="Page_173"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_174" id="Page_174"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_175" id="Page_175"></a>depends upon the height of the object. The relation is
+approximately expressed thus,&mdash;</p>
+
+<div class="floatr">
+<a name="image15" id="image15"></a>
+<img src="images/image15.png" alt="A. A COMPLETED LIGHTHOUSE LENS
+B. TORRO POINT LIGHTHOUSE, PANAMA CANAL" title="A. A COMPLETED LIGHTHOUSE LENS
+B. TORRO POINT LIGHTHOUSE, PANAMA CANAL" width="303" height="500" />
+<p class="caption">A. A COMPLETED LIGHTHOUSE LENS<br />
+B. TORRO POINT LIGHTHOUSE, PANAMA CANAL</p>
+</div>
+
+<p>Range in nautical miles = 8/7 &radic;<span style="border-top: solid 1px;">Height of object in
+feet</span>. For example, the top of a tower 100 feet high is visible to an eye
+at sea-level a distance of 8/7 &radic;<span style="border-top: solid 1px;">100</span> = 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 &radic;<span style="border-top: solid 1px;">49</span> = 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.</p>
+
+<p>The luminous intensity of a light-source or of the beam of light is
+directly responsible for the range. The luminous intensity of the early
+beacon-fires and oil-lamps was equivalent to a few candles. The
+improvements in light-sources and also in reflecting and refracting
+optical systems have steadily increased the candle-power of the beams,
+until to-day the beams from gas-lamps have intensities as high as
+several hundred thousand candle-power. The beams sent forth by modern
+lighthouses equipped with electric lamps and enormous light-gathering
+devices are rated in millions of candle-power. In fact, Navesink Light
+at the entrance of New York Bay is rated as high as 60,000,000
+candle-power.</p>
+
+<p><a class="pagenum" name="Page_176" id="Page_176"></a>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.</p>
+
+<p>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.</p>
+
+<div class="center">
+<a name="image16" id="image16"></a>
+<img src="images/image16.png" alt="AMERICAN SEARCH-LIGHT POSITION ON WESTERN FRONT IN 1919" title="AMERICAN SEARCH-LIGHT POSITION ON WESTERN FRONT IN 1919" width="500" height="242" />
+<p class="caption">AMERICAN SEARCH-LIGHT POSITION ON WESTERN FRONT IN 1919</p>
+</div>
+
+<p>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 <a class="pagenum" name="Page_177" id="Page_177"></a>of more buoys and fewer
+lighthouses, but the beam-intensities of the latter are increasing.</p>
+
+<div class="center">
+<a name="image17" id="image17"></a>
+<img src="images/image17.png" alt="AMERICAN STANDARD FIELD SEARCH-LIGHT AND POWER UNIT" title="AMERICAN STANDARD FIELD SEARCH-LIGHT AND POWER UNIT" width="500" height="347" />
+<p class="caption">AMERICAN STANDARD FIELD SEARCH-LIGHT AND POWER UNIT</p>
+</div>
+
+<p>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:</p>
+
+<blockquote><p>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."</p>
+
+<p>In the leasing of farms, a location with a greater probability
+of shipwreck on the shore brought a much higher rent.</p></blockquote>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_178" id="Page_178"></a>XIV</h2>
+
+<h2>ARTIFICIAL LIGHT IN WARFARE</h2>
+
+
+<p>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 a&euml;rial bomber; flares
+exposed the man&oelig;uvers of the enemy; rockets brought aid to
+beleaguered vessels and troops; pistol lights fired by the a&euml;rial
+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.</p>
+
+<p>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 bril<a class="pagenum" name="Page_179" id="Page_179"></a>liant 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.</p>
+
+<p>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,</p>
+
+<div class="center">
+<table cellpadding="5" summary="illuminating compounds">
+<tr><td>Barium nitrate</td><td>37 per cent.</td></tr>
+<tr><td>Powdered magnesium</td><td>34 per cent.</td></tr>
+<tr><td>Potassium nitrate</td><td>29 per cent.</td></tr>
+</table>
+</div>
+
+<p>The magnesium is coated with hot wax or paraffin, which not only acts as
+a binder for the mixture when <a class="pagenum" name="Page_180" id="Page_180"></a>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.</p>
+
+<p>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,</p>
+
+<div class="center">
+<table cellpadding="5" summary="element mixtures">
+<tr><td>Barium nitrate</td><td>58 per cent.</td></tr>
+<tr><td>Magnesium</td><td>29 per cent.</td></tr>
+<tr><td>Aluminum</td><td>13 per cent.</td></tr>
+</table>
+</div>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_181" id="Page_181"></a>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.</p>
+
+<p>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.</p>
+
+<p>The rifle-light which resembles an ordinary rocket, <a class="pagenum" name="Page_182" id="Page_182"></a>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.</p>
+
+<p>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.</p>
+
+<p>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:</p>
+
+<div class="center">
+<table cellpadding="5" summary="flare performance">
+<thead>
+<tr><td><a class="pagenum" name="Page_183" id="Page_183"></a>&nbsp;</td><th>Flare No. 1</th><th>Flare No. 2</th></tr>
+</thead>
+<tbody>
+<tr><td>Average candle-power</td><td align="center">270,000</td><td align="center">95,000</td></tr>
+<tr><td>Seconds of burning</td><td align="center">10</td><td align="center">35</td></tr>
+<tr><td>Candle-seconds</td><td align="center">2,700,000</td><td align="center">3,325,000</td></tr>
+<tr><td>Cubic inches of compound</td><td align="center">6</td><td align="center">7</td></tr>
+<tr><td>Candle-seconds per cubic inch</td><td align="center">450,000</td><td align="center">475,000</td></tr>
+<tr><td>Candle-hours per cubic inch</td><td align="center">125</td><td align="center">132</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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<a class="pagenum" name="Page_184" id="Page_184"></a> 200
+yards; for trench mortars about one mile; and from field and naval guns
+about four miles.</p>
+
+<p>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.</p>
+
+<p>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 a&euml;ronautics 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 some<a class="pagenum" name="Page_185" id="Page_185"></a>times minute specks moving at high
+speed at altitudes as high as five miles. Furthermore, owing to the
+shifting battle areas, mobile apparatus was necessary.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_186" id="Page_186"></a>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.</p>
+
+<p>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 <ins class="correction" title="Transcriber's Note: Original reads
+&quot;distintegrate&quot;">disintegrate</ins>
+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 <a class="pagenum" name="Page_187" id="Page_187"></a>to reduce the
+intensity of the beam as the distance from the search-light increases.</p>
+
+<p>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.</p>
+
+<p class="center"><span class="smcap">Brightness of Light-Sources in Candles per Square Inch</span></p>
+
+<div class="center">
+<table cellpadding="5" summary="brightness of light-source">
+<tr><td>Kerosene flame</td><td align="right">5 to</td><td align="right">10</td></tr>
+<tr><td>Acetylene</td><td align="right">30 to</td><td align="right">60</td></tr>
+<tr><td>Gas-mantle</td><td align="right">30 to</td><td align="right">500</td></tr>
+<tr><td>Tungsten filament (vacuum) lamp</td><td align="right">750 to</td><td align="right">1,200</td></tr>
+<tr><td>Tungsten filament (gas-filled) lamp</td><td align="right">3,500 to</td><td align="right">18,000</td></tr>
+<tr><td>Magnetite arc</td><td align="right">4,000 to</td><td align="right">6,000</td></tr>
+<tr><td>Carbon arc for search-lights</td><td align="right">80,000 to</td><td align="right">90,000</td></tr>
+<tr><td>Flame arc for search-lights</td><td align="right">250,000 to</td><td align="right">350,000</td></tr>
+<tr><td>Sun (computed mean)</td><td colspan="2" align="right">about 1,000,000</td></tr>
+</table>
+</div>
+
+<p>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 prac<a class="pagenum" name="Page_188" id="Page_188"></a>ticable. 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.</p>
+
+<p>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 <a class="pagenum" name="Page_189" id="Page_189"></a>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.</p>
+
+<p>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
+gen<a class="pagenum" name="Page_190" id="Page_190"></a>erator. 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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_191" id="Page_191"></a>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.</p>
+
+<p>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 a&euml;rial 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 a&euml;rial 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 <a class="pagenum" name="Page_192" id="Page_192"></a>beacon is revolved. Portable beacons employing gas were
+used during the war on some of the flying-fields near the battle front.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_193" id="Page_193"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_194" id="Page_194"></a>XV</h2>
+
+<h2>SIGNALING</h2>
+
+
+<p>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.</p>
+
+<p>The beginning of light-signaling is hidden in the obscurity of the past.
+Of course, the most primitive <a class="pagenum" name="Page_195" id="Page_195"></a>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 <ins class="correction" title="Transcriber's Note: Original reads
+&quot;Pechham&quot;.">Peckham</ins>, Archbishop of Canterbury in the thirteenth century,
+described mirrors of polished steel and of glass backed with lead.
+Mirrors of glass coated with an <ins class="correction" title="Transcriber's Note: Original reads
+&quot;allow&quot;.">alloy</ins> 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 <a class="pagenum" name="Page_196" id="Page_196"></a>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.</p>
+
+<p>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.</p>
+
+<p>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
+<ins class="correction" title="Transcriber's Note: Original reads &quot;billiant&quot;.">brilliant</ins> pyrotechnical
+preparations. However, flames <a class="pagenum" name="Page_197" id="Page_197"></a>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,</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_198" id="Page_198"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_199" id="Page_199"></a>or the
+curvature of the ocean's surface. By means of small search-lights it is
+easy to send signals ten miles.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_200" id="Page_200"></a>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 <ins class="correction" title="Transcriber's Note: Original reads &quot;in&quot;.">is</ins> 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.</p>
+
+<p>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.<a class="pagenum" name="Page_201" id="Page_201"></a> 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.</p>
+
+<p>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 <a class="pagenum" name="Page_202" id="Page_202"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_203" id="Page_203"></a>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_204" id="Page_204"></a>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 <a class="pagenum" name="Page_205" id="Page_205"></a>optical device having a
+fluorescent screen of barium-platino-cyanide. This device had a range of
+about four miles.</p>
+
+<p>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&mdash;red, green, and white&mdash;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.</p>
+
+<p><a class="pagenum" name="Page_206" id="Page_206"></a>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.</p>
+
+<p>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?</p>
+
+<p><a class="pagenum" name="Page_207" id="Page_207"></a>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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_208" id="Page_208"></a>XVI</h2>
+
+<h2>THE COST OF LIGHT</h2>
+
+
+<p>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.</p>
+
+<p>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 ar<a class="pagenum" name="Page_209" id="Page_209"></a>tistic 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.</p>
+
+<p>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
+ar<a class="pagenum" name="Page_210" id="Page_210"></a>rangement 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.</p>
+
+<p>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 <em>Journal</em> of Paris. The article, which appeared in the form of a
+letter, began thus:</p>
+
+<blockquote><p><span class="smcap">Messieurs</span>: You often entertain us with accounts of<a class="pagenum" name="Page_211" id="Page_211"></a>
+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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_212" id="Page_212"></a>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_213" id="Page_213"></a>window which had shutters. His closing paragraph was as follows:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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 <a class="pagenum" name="Page_214" id="Page_214"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_215" id="Page_215"></a>candle and a so-called safety match about one third as much.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_216" id="Page_216"></a>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:</p>
+
+<div class="center">
+<table cellpadding="5" summary="cost of light">
+<thead>
+<tr><th rowspan="2">Year</th><th rowspan="2">Hours per night</th><th rowspan="2">Equivalent of<br />light in candles</th><th colspan="2">Candle-hours</th></tr>
+<tr><th>per night</th><th>per year</th></tr>
+</thead>
+<tbody>
+<tr><td>1800</td><td align="center">3</td><td align="right">5</td><td align="right">15</td><td align="right">5,500</td></tr>
+<tr><td>1850</td><td align="center">3</td><td align="right">8</td><td align="right">24</td><td align="right">8,700</td></tr>
+<tr><td>1860</td><td align="center">3</td><td align="right">11</td><td align="right">33</td><td align="right">12,000</td></tr>
+<tr><td>1870</td><td align="center">3</td><td align="right">22</td><td align="right">66</td><td align="right">24,000</td></tr>
+<tr><td>1880</td><td align="center">3.5</td><td align="right">36</td><td align="right">126</td><td align="right">46,000</td></tr>
+<tr><td>1890</td><td align="center">4</td><td align="right">50</td><td align="right">200</td><td align="right">73,000</td></tr>
+<tr><td>1900</td><td align="center">5</td><td align="right">154</td><td align="right">770</td><td align="right">280,000</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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
+<ins class="correction" title="Transcriber's Note: Original reads &quot;has&quot;.">have</ins> nearly doubled. In other
+words, in the nineteenth century the candle-hours obtainable for $20.00
+per year increased <a class="pagenum" name="Page_217" id="Page_217"></a>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</p>
+
+<blockquote><p>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&mdash;the
+candle-hour&mdash;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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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:</p>
+
+<div class="center">
+<table cellpadding="5" summary="cost of light">
+<thead>
+<tr><td>&nbsp;</td><th>1000 candle-hours</th></tr>
+</thead>
+<tbody>
+<tr><td>Gas-lighting at a rate of two hours per day</td><td align="center">$1.95</td></tr>
+<tr><td>Gas-lighting at a rate of three hours per day</td><td align="center">1.40</td></tr>
+<tr><td>Candle-lighting</td><td align="center">6.50</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>It is seen that the longer hours of burning reduce the <a class="pagenum" name="Page_218" id="Page_218"></a>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.</p>
+
+<p>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.</p>
+
+<p class="center"><span class="smcap">Table Showing the Approximate Total Cost of 1000 Candle-Hours for
+Various Periods</span></p>
+
+<div class="center">
+<table cellpadding="5" class="top" summary="cost of light">
+<thead>
+<tr><td colspan="2">&nbsp;</td><th>Per 1000<br />candle-hours</th></tr>
+</thead>
+<tbody>
+<tr><td rowspan="2">1800 to 1850,</td><td>sperm-oil</td><td>$2.40</td></tr>
+<tr><td>tallow candle</td><td>5.00</td></tr>
+<tr><td rowspan="2">1850 to 1865,</td><td>kerosene</td><td>1.65</td></tr>
+<tr><td>tallow candle</td><td>6.85</td></tr>
+<tr><td rowspan="3">1865 to 1875,</td><td>kerosene</td><td>.75</td></tr>
+<tr><td>tallow candle</td><td>6.25</td></tr>
+<tr><td>gas, open-flame</td><td>.90</td></tr>
+<tr><td rowspan="2"><a class="pagenum" name="Page_219" id="Page_219"></a>1875 to 1885,</td><td>kerosene</td><td>.25</td></tr>
+<tr><td>gas, open-flame</td><td>.60</td></tr>
+<tr><td rowspan="2">1885 to 1895,</td><td>kerosene</td><td>.15</td></tr>
+<tr><td>gas, open-flame</td><td>.40</td></tr>
+<tr><td rowspan="5">1895 to 1915,</td><td>gas mantle</td><td>.07</td></tr>
+<tr><td>carbon filament</td><td>.38</td></tr>
+<tr><td>metallized filament</td><td>.28</td></tr>
+<tr><td>tungsten filament (vacuum)</td><td>.12</td></tr>
+<tr><td>tungsten filament (gas-filled)</td><td>.07</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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.</p>
+
+<div class="center">
+<table cellpadding="5" summary="comparative costs">
+<thead>
+<tr><th>Year</th><th>Food</th><th>Electric<br />lighting</th></tr>
+</thead>
+<tbody>
+<tr><td>1894</td><td align="right">100</td><td align="right">100</td></tr>
+<tr><td>1896</td><td align="right">80</td><td align="right">92</td></tr>
+<tr><td>1898</td><td align="right">92</td><td align="right">90</td></tr>
+<tr><td>1900</td><td align="right">100</td><td align="right">85</td></tr>
+<tr><td>1902</td><td align="right">113</td><td align="right">77</td></tr>
+<tr><td>1904</td><td align="right">110</td><td align="right">77</td></tr>
+<tr><td>1906</td><td align="right">115</td><td align="right">57</td></tr>
+<tr><td><a class="pagenum" name="Page_220" id="Page_220"></a>1908</td><td align="right">128</td><td align="right">30</td></tr>
+<tr><td>1910</td><td align="right">138</td><td align="right">28</td></tr>
+<tr><td>1912</td><td align="right">144</td><td align="right">23</td></tr>
+<tr><td>1914</td><td align="right">145</td><td align="right">17</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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 <abbr>P.&nbsp;M.</abbr> 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.</p>
+
+<p>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 in<a class="pagenum" name="Page_221" id="Page_221"></a>dustry 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:</p>
+
+<div class="center">
+<table cellpadding="5" summary="manufacture of gas">
+<tr><td>Number of establishments</td><td align="right">1,284</td></tr>
+<tr><td>Capital</td><td align="right">$1,252,421,584</td></tr>
+<tr><td>Value of products (gas, coke, tar, etc.)</td><td align="right">$220,237,790</td></tr>
+<tr><td>Cost of materials</td><td align="right">$76,779,288</td></tr>
+<tr><td>Value added by manufacture</td><td align="right">$143,458,502</td></tr>
+<tr><td>Value of gas</td><td align="right">$175,065,920</td></tr>
+<tr><td>Coal used (tons)</td><td align="right">6,116,672</td></tr>
+<tr><td>Coke used (tons)</td><td align="right">964,851</td></tr>
+<tr><td>Oil used (gallons)</td><td align="right">715,418,623</td></tr>
+<tr><td>Length of gas mains (miles)</td><td align="right">58,727</td></tr>
+<tr><td align="center">Manufactured products sold</td><td>&nbsp;</td></tr>
+<tr><td>Total gas (cubic feet)</td><td align="right">203,639,260,000</td></tr>
+<tr><td>Straight coal gas (cubic feet)</td><td align="right">10,509,946,000</td></tr>
+<tr><td>Carbureted water gas (cubic feet)</td><td align="right">90,017,725,000</td></tr>
+<tr><td>Mixed coal- and water-gas (cubic feet)</td><td align="right">86,281,339,000</td></tr>
+<tr><td>Oil gas (cubic feet)</td><td align="right">16,512,274,000</td></tr>
+<tr><td>Acetylene (cubic feet)</td><td align="right">136,564,000</td></tr>
+<tr><td>Other gas, chiefly gasolene (cubic feet)</td><td align="right">181,412,000</td></tr>
+<tr><td>Coke (bushels)</td><td align="right">114,091,753</td></tr>
+<tr><td><a class="pagenum" name="Page_222" id="Page_222"></a>Tar (gallons)</td><td align="right">125,938,607</td></tr>
+<tr><td>Ammonia liquors (gallons)</td><td align="right">50,737,762</td></tr>
+<tr><td>Ammonia, sulphate (pounds)</td><td align="right">6,216,618</td></tr>
+</table>
+</div>
+
+<p>Of course, only a small fraction of the total gas manufactured is used
+for lighting.</p>
+
+<p>According to the U.&nbsp;S. Geological Survey, the quantities of gas sold in
+this country in the year 1917 were as follows:</p>
+
+<div class="center">
+<table cellpadding="5" summary="gas sold">
+<tr><td>Coal-gas</td><td align="right">42,927,728,000</td><td>cubic feet</td></tr>
+<tr><td>Water-gas</td><td align="right">153,457,318,000</td><td align="center">" "</td></tr>
+<tr><td>Oil-gas</td><td align="right">14,739,508,000</td><td align="center">" "</td></tr>
+<tr><td>Byproduct gas</td><td align="right">131,026,575,000</td><td align="center">" "</td></tr>
+<tr><td>Natural gas</td><td align="right">795,110,376,000</td><td align="center">" "</td></tr>
+</table>
+</div>
+
+<p>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.</p>
+
+<p>Some figures pertaining to public electric light and power stations of
+the United States for the years 1907 and 1917 are as follows:</p>
+
+<div class="center">
+<table cellpadding="5" summary="power stations">
+<thead>
+<tr><td colspan="2"><a class="pagenum" name="Page_223" id="Page_223"></a>&nbsp;</td><th>1917</th><th>1907</th></tr>
+</thead>
+<tbody>
+<tr><td colspan="2">Number of establishments</td><td align="right">6,541</td><td align="right">4,714</td></tr>
+<tr><td class="indent">&nbsp;</td><td>Commercial</td><td align="right">4,224</td><td align="right">3,462</td></tr>
+<tr><td class="indent">&nbsp;</td><td>Municipal</td><td align="right">2,317</td><td align="right">1,562</td></tr>
+<tr><td colspan="2">Income</td><td align="right">$526,886,408</td><td align="right">$175,642,338</td></tr>
+<tr><td colspan="2">Total horse-power of plants</td><td align="right">12,857,998</td><td align="right">4,098,188</td></tr>
+<tr><td class="indent">&nbsp;</td><td>Steam engines</td><td align="right">8,389,389</td><td align="right">2,693,273</td></tr>
+<tr><td class="indent">&nbsp;</td><td>Internal combustion engines</td><td align="right"> 217,186</td><td align="right">55,828</td></tr>
+<tr><td class="indent">&nbsp;</td><td>Water-wheels</td><td align="right">4,251,423</td><td align="right">1,349,087</td></tr>
+<tr><td colspan="2">Kilowatt capacity of generators</td><td align="right">9,001,872</td><td align="right">2,709,225</td></tr>
+<tr><td colspan="2">Output in millions of kilowatt-hours</td><td align="right">25,438</td><td align="right">5,863</td></tr>
+<tr><td colspan="2">Motors served (horse-power)</td><td align="right">9,216,323</td><td align="right">1,649,026</td></tr>
+<tr><td colspan="2">Electric-arc street-lamps served</td><td align="right">256,838</td><td align="right">....</td></tr>
+<tr><td colspan="2">Electric-filament street-lamps served</td><td align="right"> 1,389,382</td><td align="right">....</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_224" id="Page_224"></a>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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_225" id="Page_225"></a>XVII</h2>
+
+<h2>LIGHT AND SAFETY</h2>
+
+
+<p>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.</p>
+
+<p>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.&nbsp;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 <a class="pagenum" name="Page_226" id="Page_226"></a>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_227" id="Page_227"></a>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.&nbsp;E. Simpson of the Travelers
+Insurance Company has stated that:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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.<a class="pagenum" name="Page_228" id="Page_228"></a> 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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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
+insignifi<a class="pagenum" name="Page_229" id="Page_229"></a>cant 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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_230" id="Page_230"></a>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 <ins class="correction" title="Transcriber's Note: Original
+reads &quot;this&quot;.">their</ins> own indifference or through the negligence of others.</p>
+
+<p><a class="pagenum" name="Page_231" id="Page_231"></a>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.</p>
+
+<p class="center"><span class="smcap">Seasonal Distribution of Industrial Accidents Due to Lighting
+Conditions and to Other Causes</span></p>
+
+<div class="center">
+<table cellpadding="5" summary="industrial accidents">
+<thead>
+<tr><td rowspan="2">&nbsp;</td><th colspan="2">Percentage due to</th></tr>
+<tr><th>Lighting conditions</th><th>Other causes</th></tr>
+</thead>
+<tbody>
+<tr><td>July</td><td align="center">4.8</td><td align="center">5.9</td></tr>
+<tr><td>August</td><td align="center">5.2</td><td align="center">6.2</td></tr>
+<tr><td>September</td><td align="center">6.1</td><td align="center">6.9</td></tr>
+<tr><td>October</td><td align="center">8.6</td><td align="center">8.5</td></tr>
+<tr><td>November</td><td align="center">10.9</td><td align="center">10.5</td></tr>
+<tr><td>December</td><td align="center">15.6</td><td align="center">12.2</td></tr>
+<tr><td>January</td><td align="center">16.1</td><td align="center">11.9</td></tr>
+<tr><td>February</td><td align="center">10.0</td><td align="center">10.5</td></tr>
+<tr><td>March</td><td align="center">7.6</td><td align="center">8.8</td></tr>
+<tr><td>April</td><td align="center">6.1</td><td align="center">6.9</td></tr>
+<tr><td>May</td><td align="center">5.2</td><td align="center">5.8</td></tr>
+<tr><td>June</td><td align="center">3.8</td><td align="center">5.9</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>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, De<a class="pagenum" name="Page_232" id="Page_232"></a>cember, 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 <abbr>P.&nbsp;M.</abbr> when
+artificial lighting is generally in use to help out the failing
+daylight. Only 7.3 per cent. occurred between 12 <abbr>M.</abbr> and 1
+<abbr>P.&nbsp;M.</abbr></p>
+
+<div style="width: 100%">
+
+<div style="width: 48%; float: left; margin-top: 1em; margin-bottom: 1em;">
+<a name="image18" id="image18"></a>
+<img src="images/image18.png" alt="SIGNAL-LIGHT FOR AIRPLANE" title="SIGNAL-LIGHT FOR AIRPLANE" width="126" height="200" />
+<p class="caption">SIGNAL-LIGHT FOR AIRPLANE</p>
+</div>
+
+<div style="width: 48%; float: right; margin-top: 1em; margin-bottom: 1em;">
+<a name="image19" id="image19"></a>
+<img src="images/image19.png" alt="TRENCH LIGHT-SIGNALING OUTFIT" title="TRENCH LIGHT-SIGNALING OUTFIT" width="242" height="200" />
+<p class="caption">TRENCH LIGHT-SIGNALING OUTFIT</p>
+</div>
+
+</div>
+
+<div style="width: 100%">
+
+<div style="width: 48%; float: left; margin-top: 1em; margin-bottom: 1em;">
+<a name="image20" id="image20"></a>
+<img src="images/image20.png" alt="AVIATION FIELD LIGHT-SIGNAL PROJECTOR" title="AVIATION FIELD LIGHT-SIGNAL PROJECTOR" width="149" height="300" />
+<p class="caption">AVIATION FIELD LIGHT-SIGNAL PROJECTOR</p>
+</div>
+
+<div style="width: 48%; float: right; margin-top: 1em; margin-bottom: 1em;">
+<a name="image21" id="image21"></a>
+<img src="images/image21.png" alt="SIGNAL SEARCH-LIGHT FOR AIRPLANE" title="SIGNAL SEARCH-LIGHT FOR AIRPLANE" width="217" height="300" />
+<p class="caption">SIGNAL SEARCH-LIGHT FOR AIRPLANE</p>
+</div>
+
+</div>
+
+<p>There is another aspect of the subject which deals particularly with the
+safety of the light-source or <a class="pagenum" name="Page_233" id="Page_233"></a>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.</p>
+
+<div class="center">
+<a name="image22" id="image22"></a>
+<img src="images/image22.png" alt="UNSAFE, UNPRODUCTIVE LIGHTING WORTHY OF THE DARK AGES" title="UNSAFE, UNPRODUCTIVE LIGHTING WORTHY OF THE DARK AGES" width="400" height="306" />
+<p class="caption">UNSAFE, UNPRODUCTIVE LIGHTING WORTHY OF THE DARK AGES</p>
+</div>
+
+<div class="center">
+<a name="image23" id="image23"></a>
+<img src="images/image23.png" alt="THE SAME FACTORY MADE SAFE, CHEERFUL, AND MORE PRODUCTIVE BY MODERN LIGHTING" title="THE SAME FACTORY MADE SAFE, CHEERFUL, AND MORE PRODUCTIVE BY MODERN LIGHTING" width="400" height="304" />
+<p class="caption">THE SAME FACTORY MADE SAFE, CHEERFUL, AND MORE PRODUCTIVE
+BY MODERN LIGHTING</p>
+</div>
+
+<p>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.</p>
+
+<p>There are industries where unusual care must be exercised in regard to
+the lighting. In certain chemical industries no lamps are used excepting
+the incandes<a class="pagenum" name="Page_234" id="Page_234"></a>cent lamp and this is enclosed in an air-tight glass globe.
+Even a public-service gas company cautions its employees and patrons
+thus: "<em>Do not look for a gas-leak with a naked light! Use electric
+light.</em>" 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.</p>
+
+<p>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
+<a class="pagenum" name="Page_235" id="Page_235"></a>the risk of the presence or the appearance of gas or explosive dust.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_236" id="Page_236"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_237" id="Page_237"></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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_238" id="Page_238"></a>XVIII</h2>
+
+<h2>THE COST OF LIVING</h2>
+
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_239" id="Page_239"></a>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.</p>
+
+<p>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.</p>
+
+<div class="center">
+<a name="image24" id="image24"></a>
+<img src="images/image24.png" alt="LOCOMOTIVE ELECTRIC HEADLIGHT" title="LOCOMOTIVE ELECTRIC HEADLIGHT" width="400" height="263" />
+<p class="caption">LOCOMOTIVE ELECTRIC HEADLIGHT</p>
+</div>
+
+<p><a class="pagenum" name="Page_240" id="Page_240"></a>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&mdash;and there is no excuse for
+improper artificial lighting&mdash;is superior to most interior daylighting
+conditions.</p>
+
+<div class="center">
+<a name="image25" id="image25"></a>
+<img src="images/image25.png" alt="SEARCH-LIGHT ON A FIRE-BOAT" title="SEARCH-LIGHT ON A FIRE-BOAT" width="400" height="287" />
+<p class="caption">SEARCH-LIGHT ON A FIRE-BOAT</p>
+</div>
+
+<p>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 <a class="pagenum" name="Page_241" id="Page_241"></a>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.</p>
+
+<div class="center">
+<a name="image26" id="image26"></a>
+<img src="images/image26.png" alt="BUILDING SHIPS UNDER ARTIFICIAL LIGHT AT HOG ISLAND SHIPYARD" title="BUILDING SHIPS UNDER ARTIFICIAL LIGHT AT HOG ISLAND SHIPYARD" width="600" height="376" />
+<p class="caption">BUILDING SHIPS UNDER ARTIFICIAL LIGHT AT HOG ISLAND SHIPYARD</p>
+</div>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_242" id="Page_242"></a>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.</p>
+
+<p>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
+contin<a class="pagenum" name="Page_243" id="Page_243"></a>uously idle in this country owing to inadequate and improper
+lighting.</p>
+
+<p>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.</p>
+
+<p>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 class="pagenum" name="Page_244" id="Page_244"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_245" id="Page_245"></a>well-designed lighting-system giving a high
+intensity of illumination.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Various other tests could be cited, but these would merely emphasize the
+same results. However, it may <a class="pagenum" name="Page_246" id="Page_246"></a>be stated that the factory
+superintendents involved are convinced that adequate and proper
+artificial lighting is a great factor in increasing production. Mr. W.&nbsp;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.</p>
+
+<p>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.</p>
+
+<p>Civilization has just passed the threshold of the age <a class="pagenum" name="Page_247" id="Page_247"></a>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.</p>
+
+<p>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.</p>
+
+<p>The hen, when permitted to follow her natural <a class="pagenum" name="Page_248" id="Page_248"></a>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.</p>
+
+<p>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 <abbr>P.&nbsp;M.</abbr> throughout the year.</p>
+
+<p>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 <abbr>P.&nbsp;M.</abbr>
+and the 16 candle-power lamps <a class="pagenum" name="Page_249" id="Page_249"></a>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 <abbr>P.&nbsp;M.</abbr> 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.</p>
+
+<p>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.</p>
+
+<p>Many experiments have been carried out in the forc<a class="pagenum" name="Page_250" id="Page_250"></a>ing 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.&nbsp;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.&nbsp;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:</p>
+
+<blockquote><p>The incandescent electric light has a marked effect upon
+greenhouse plants.</p>
+
+<p>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.</p>
+
+<p>Flowering plants blossomed earlier and continued to bloom
+longer under the light. <a class="pagenum" name="Page_251" id="Page_251"></a>The light influences some plants, such
+as spinach and endive, to quickly run to seed, which is
+objectionable in forcing these plants for sale.</p>
+
+<p>The stronger the candle-power the more marked the results,
+other conditions being the same.</p>
+
+<p>Most plants tended toward a taller growth under the light.</p>
+
+<p>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.</p>
+
+<p>There are many points about the incandescent electric light
+that appear to make it preferable to the arc light for
+greenhouse use.</p>
+
+<p>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_252" id="Page_252"></a>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:</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>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 green<a class="pagenum" name="Page_253" id="Page_253"></a>house 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.</p>
+
+<p>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 <a class="pagenum" name="Page_254" id="Page_254"></a>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.</p>
+
+<div style="width: 100%">
+
+
+<div style="width: 48%; float: left; margin-top: 1em; margin-bottom: 1em;">
+<a name="image27" id="image27"></a>
+<img src="images/image27.png" alt="In a moving-picture studio" title="In a moving-picture studio" width="235" height="400" />
+<p class="caption">In a moving-picture studio</p>
+</div>
+
+<div style="width: 48%; float: right; margin-top: 1em; margin-bottom: 1em;">
+<a name="image28" id="image28"></a>
+<img src="images/image28.png" alt="In a portrait studio" title="In a portrait studio" width="382" height="400" />
+<p class="caption">In a portrait studio</p>
+</div>
+
+<p class="caption">ARTIFICIAL LIGHT IN PHOTOGRAPHY</p>
+
+</div>
+
+<p>Many other instances could be cited in which artificial light is very
+closely associated with the cost of living. Overseas shipment of fruit
+from the Canadian Northwest is responsible for a decided innovation in
+fruit-picking. In searching for a cause of rotting during shipment it
+was finally concluded that the temperature at the time of picking was
+the controlling factor. As a consequence, daytime was considered
+undesirable for picking and an electric company supplied electric
+lighting for the orchards in order that the picking might be done during
+the cool of night. This change is said to have remedied the situation.
+Cases of threshing and other agricultural operations being carried on at
+night are becoming more numerous. These are just the beginnings of
+artificial light in a new field or in a new relation to civilization.
+Its economic value has been demonstrated in the ordinary fields of
+lighting and these new applications are merely the initial skirmishes
+which precede the conquest of new territory. The modern illuminants have
+been developed <a class="pagenum" name="Page_255" id="Page_255"></a>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.</p>
+
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_256" id="Page_256"></a>XIX</h2>
+
+<h2>ARTIFICIAL LIGHT AND CHEMISTRY</h2>
+
+
+<p>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
+<a class="pagenum" name="Page_257" id="Page_257"></a>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.</p>
+
+<div class="center">
+<a name="image29" id="image29"></a>
+<img src="images/image29.png" alt="Swimming pool" title="Swimming pool" width="400" height="275" />
+<p class="caption">Swimming pool</p>
+</div>
+
+<div class="center">
+<a name="image30" id="image30"></a>
+<img src="images/image30.png" alt="City waterworks" title="City waterworks" width="400" height="334" />
+<p class="caption">City waterworks</p>
+</div>
+
+<p class="caption">STERILIZING WATER WITH RADIANT ENERGY FROM QUARTZ MERCURY-ARCS</p>
+
+<p>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.&nbsp;W. Scheele in 1777
+on silver salts. An extract from his own account is as follows:</p>
+
+<blockquote><p>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 <em>silver by reduction</em>. 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 wa<a class="pagenum" name="Page_258" id="Page_258"></a>ter 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.</p></blockquote>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_259" id="Page_259"></a>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.</p>
+
+<p>Although two illuminants may be of the same luminous intensity, they may
+differ widely in actinic value.<a class="pagenum" name="Page_260" id="Page_260"></a> 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.</p>
+
+<p>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.</p>
+
+<p>The moving-picture studio is independent of daylight in indoor settings
+and there is a tendency toward <a class="pagenum" name="Page_261" id="Page_261"></a>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.</p>
+
+<p>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 reac<a class="pagenum" name="Page_262" id="Page_262"></a>tions. 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.</p>
+
+<p>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.</p>
+
+<p>There is a large number of reactions due to light in <a class="pagenum" name="Page_263" id="Page_263"></a>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 <a class="pagenum" name="Page_264" id="Page_264"></a>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_265" id="Page_265"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_266" id="Page_266"></a>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_267" id="Page_267"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_268" id="Page_268"></a>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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_269" id="Page_269"></a>XX</h2>
+
+<h2>LIGHT AND HEALTH</h2>
+
+
+<p>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 <a class="pagenum" name="Page_270" id="Page_270"></a>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.</p>
+
+<p>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:</p>
+
+<blockquote><p>R&ouml;ntgen or X-rays, which pass readily through many substances
+opaque to ordinary light-rays.</p>
+
+<p>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.</p>
+
+<p>Visible rays producing various sensations of color, such as
+violet, blue, green, yellow, orange, and red.</p>
+
+<p><a class="pagenum" name="Page_271" id="Page_271"></a>Infra-red or the invisible rays bordering on the red rays.</p>
+
+<p>An unknown, unmeasured, or unfilled region between the
+infra-red and the "electric" waves.</p>
+
+<p>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.</p></blockquote>
+
+<p>The R&ouml;ntgen rays were discovered by R&ouml;ntgen 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 <a class="pagenum" name="Page_272" id="Page_272"></a>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.</p>
+
+<div class="center">
+<a name="image31" id="image31"></a>
+<img src="images/image31.png" alt="In art work" title="In art work" width="400" height="288" />
+<p class="caption">In art work</p>
+</div>
+
+<div class="center">
+<a name="image32" id="image32"></a>
+<img src="images/image32.png" alt="In a haberdashery" title="In a haberdashery" width="400" height="325" />
+<p class="caption">In a haberdashery</p>
+</div>
+
+<p class="caption">JUDGING COLOR UNDER ARTIFICIAL DAYLIGHT</p>
+
+<p>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 <a class="pagenum" name="Page_273" id="Page_273"></a>rays. If the infra-red rays are not
+desired they can be readily eliminated by the use of a water-cell.</p>
+
+<div class="center">
+<a name="image33" id="image33"></a>
+<img src="images/image33.png" alt="In an underground tunnel" title="In an underground tunnel" width="400" height="370" />
+<p class="caption">In an underground tunnel</p>
+</div>
+
+<div class="center">
+<a name="image34" id="image34"></a>
+<img src="images/image34.png" alt="In an art gallery" title="In an art gallery" width="400" height="251" />
+<p class="caption">In an art gallery</p>
+</div>
+
+<p class="caption">ARTIFICIAL DAYLIGHT</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_274" id="Page_274"></a>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.</p>
+
+<p>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 an&aelig;sthetic powers and have been used in this r&ocirc;le for many
+minor operations.</p>
+
+<p>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 <a class="pagenum" name="Page_275" id="Page_275"></a>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_276" id="Page_276"></a>Any one who has been in touch with light-therapy in a scientific r&ocirc;le 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:</p>
+
+<blockquote><p>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 <a class="pagenum" name="Page_277" id="Page_277"></a>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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_278" id="Page_278"></a>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.</p>
+
+<p>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. R&ouml;ntgen rays and radium have also figured in
+recent years in the treatment of disease.</p>
+
+<p>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 Egyp<a class="pagenum" name="Page_279" id="Page_279"></a>tians 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.</p>
+
+<p>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,</p>
+
+<blockquote><p>treatment with the ultra-violet rays, especially in conjunction<a class="pagenum" name="Page_280" id="Page_280"></a>
+with the R&ouml;ntgen 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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_281" id="Page_281"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_282" id="Page_282"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_283" id="Page_283"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_284" id="Page_284"></a>XXI</h2>
+
+<h2>MODIFYING ARTIFICIAL LIGHT</h2>
+
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_285" id="Page_285"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_286" id="Page_286"></a>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.</p>
+
+<p>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_287" id="Page_287"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_288" id="Page_288"></a>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.</p>
+
+<div class="center">
+<a name="image35" id="image35"></a>
+<img src="images/image35.png" alt="" title="" width="400" height="260" />
+</div>
+
+<div class="center">
+<a name="image36" id="image36"></a>
+<img src="images/image36.png" alt="" title="" width="400" height="96" />
+</div>
+
+<div class="center">
+<a name="image37" id="image37"></a>
+<img src="images/image37.png" alt="" title="" width="400" height="242" />
+</div>
+
+<p class="caption">FIREWORKS AND ILLUMINATED BATTLE-FLEET AT HUDSON-FULTON CELEBRATION</p>
+
+<p>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.</p>
+
+<div class="center">
+<a name="image38" id="image38"></a>
+<img src="images/image38.png" alt="FIREWORKS EXHIBITION ON MAY DAY AT PANAMA-PACIFIC EXPOSITION" title="FIREWORKS EXHIBITION ON MAY DAY AT PANAMA-PACIFIC EXPOSITION" width="389" height="500" />
+<p class="caption">FIREWORKS EXHIBITION ON MAY DAY AT PANAMA-PACIFIC EXPOSITION</p>
+</div>
+
+<p>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 <a class="pagenum" name="Page_289" id="Page_289"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_290" id="Page_290"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_291" id="Page_291"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_292" id="Page_292"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_293" id="Page_293"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_294" id="Page_294"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>These are the principal coloring ingredients used in the manufacture of
+colored glass. The staining of <a class="pagenum" name="Page_295" id="Page_295"></a>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.</p>
+
+<p>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.</p>
+
+<p>The primary colors for this method of color-mixture are the same as
+those of the painter in mixing pigments&mdash;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,</p>
+
+<div class="center">
+<table cellpadding="5" summary="color mixing">
+<tr><td>Purple and yellow</td><td>= red</td></tr>
+<tr><td>Yellow and blue-green</td><td>= green</td></tr>
+<tr><td>Blue-green and purple</td><td>= blue</td></tr>
+</table>
+</div>
+
+<p><a class="pagenum" name="Page_296" id="Page_296"></a>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,</p>
+
+<div class="center">
+<table cellpadding="5" summary="color mixing">
+<tr><td>Red and blue</td><td>= purple</td></tr>
+<tr><td>Red and green</td><td>= yellow</td></tr>
+<tr><td>Green and blue</td><td>= blue-green</td></tr>
+</table>
+</div>
+
+<p>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 <a class="pagenum" name="Page_297" id="Page_297"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_298" id="Page_298"></a>XXII</h2>
+
+<h2>SPECTACULAR LIGHTING</h2>
+
+
+<p>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&mdash;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.</p>
+
+<p>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 pro<a class="pagenum" name="Page_299" id="Page_299"></a>cessions 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.</p>
+
+<p>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.</p>
+
+<p>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.<a class="pagenum" name="Page_300" id="Page_300"></a> 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.</p>
+
+<p>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.</p>
+
+<p>The next step was to conceal these lamps behind the cornices or other
+projections or in nooks constructed <a class="pagenum" name="Page_301" id="Page_301"></a>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.</p>
+
+<p>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<a class="pagenum" name="Page_302" id="Page_302"></a> 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.</p>
+
+<p>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 <a class="pagenum" name="Page_303" id="Page_303"></a>investment
+would not be wholly idle during the evening hours.</p>
+
+<p>Mr. H.&nbsp;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.</p>
+
+<p>Many prominent buildings and monuments have burst forth in a flood of
+light, and their beauty and <a class="pagenum" name="Page_304" id="Page_304"></a>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.</p>
+
+<div class="center">
+<a name="image39" id="image39"></a>
+<img src="images/image39.png" alt="The Capitol flooded with light" title="The Capitol flooded with light" width="400" height="251" />
+<p class="caption">The Capitol flooded with light</p>
+</div>
+
+<div class="center">
+<a name="image40" id="image40"></a>
+<img src="images/image40.png" alt="Luna Park, Coney Island, studded with 60,000 incandescent filament lamps" title="Luna Park, Coney Island, studded with 60,000 incandescent filament lamps" width="400" height="276" />
+<p class="caption">Luna Park, Coney Island, studded with 60,000 incandescent
+filament lamps</p>
+</div>
+
+<p class="caption">THE NEW FLOOD LIGHTING CONTRASTED WITH THE OLD OUTLINE LIGHTING</p>
+
+<p>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 <a class="pagenum" name="Page_305" id="Page_305"></a>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.</p>
+
+<div class="center">
+<a name="image41" id="image41"></a>
+<img src="images/image41.png" alt="NIAGARA FALLS FLOODED WITH LIGHT" title="NIAGARA FALLS FLOODED WITH LIGHT" width="600" height="377" />
+<p class="caption">NIAGARA FALLS FLOODED WITH LIGHT</p>
+</div>
+
+<p>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
+<a class="pagenum" name="Page_306" id="Page_306"></a>and emotions. Throughout all these festivals light silently symbolized
+happiness, freedom, and advancement.</p>
+
+<p>Projectors were used on a large scale in several cases before the advent
+of the concentrated filament lamp. W.&nbsp;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.</p>
+
+<p>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 <a class="pagenum" name="Page_307" id="Page_307"></a>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.</p>
+
+<p>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.<a class="pagenum" name="Page_308" id="Page_308"></a>
+Mysterious vapors rising from caldrons were in reality illuminated
+steam. Symbolic fountain groups did not escape the magic touch of the
+lighting wizard.</p>
+
+<p>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_309" id="Page_309"></a>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.</p>
+
+<p>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_310" id="Page_310"></a>XXIII</h2>
+
+<h2>THE EXPRESSIVENESS OF LIGHT</h2>
+
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_311" id="Page_311"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_312" id="Page_312"></a>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.</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_313" id="Page_313"></a>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.</p>
+
+<p>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
+<a class="pagenum" name="Page_314" id="Page_314"></a>it has been found that on a sunny day most persons experience a slight
+depression when a cloud obscures the sun. Nature's lighting
+<ins  class="correction" title="Transcriber's Note: Original reads &quot;varied&quot;.">varies</ins> 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.</p>
+
+<p>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 <a class="pagenum" name="Page_315" id="Page_315"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_316" id="Page_316"></a>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.</p>
+
+<p>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.</p>
+
+<p>Associations of this character became woven into mythology and thus
+became firmly established. Poets <a class="pagenum" name="Page_317" id="Page_317"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_318" id="Page_318"></a>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.</p>
+
+<p>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 <a class="pagenum" name="Page_319" id="Page_319"></a>who have not looked deeply enough into the subject through
+observation and experiment to see its complexity.</p>
+
+<p>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.</p>
+
+<p>The worthy efforts of stage artists in some of the <a class="pagenum" name="Page_320" id="Page_320"></a>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.</p>
+
+<div class="center">
+<a name="image42" id="image42"></a>
+<img src="images/image42.png" alt="Soldiers' and Sailors' Monument" title="Soldiers' and Sailors' Monument" width="400" height="329" />
+<p class="caption">Soldiers' and Sailors' Monument</p>
+</div>
+
+<div class="center">
+<a name="image43" id="image43"></a>
+<img src="images/image43.png" alt="Jeweled portal welcoming returned soldiers" title="Jeweled portal welcoming returned soldiers" width="400" height="317" />
+<p class="caption">Jeweled portal welcoming returned soldiers</p>
+</div>
+
+<p class="caption">ARTIFICIAL LIGHT HONORING THOSE WHO FELL AND THOSE WHO RETURNED</p>
+
+<p>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!</p>
+
+<div class="center">
+<a name="image44" id="image44"></a>
+<img src="images/image44.png" alt="" title="" width="400" height="289" />
+</div>
+
+<div class="center">
+<a name="image45" id="image45"></a>
+<img src="images/image45.png" alt="" title="" width="400" height="359" />
+</div>
+
+<p class="caption">THE EXPRESSIVENESS OF LIGHT IN CHURCHES</p>
+
+<p>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.</p>
+
+<p><a class="pagenum" name="Page_321" id="Page_321"></a>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.</p>
+
+<p>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 relat<a class="pagenum" name="Page_322" id="Page_322"></a>ing 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.</p>
+
+<p>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 <a class="pagenum" name="Page_323" id="Page_323"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 <a class="pagenum" name="Page_324" id="Page_324"></a>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.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_325" id="Page_325"></a>XXIV</h2>
+
+<h2>LIGHTING THE HOME</h2>
+
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.<a class="pagenum" name="Page_326" id="Page_326"></a> 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.</p>
+
+<p>The cost of light has been discussed in another chapter and it has been
+shown that it has decreased enormously in a century. It is now the most
+potential agency in the home when viewed from the standpoint of cost.
+The average householder pays less than twenty dollars per year for
+ever-ready light throughout his home. For about five cents per day the
+average family enjoys all the blessings of modern lighting, which is
+sufficient proof that cost is an insignificant item.</p>
+
+<p>In order to simplify the discussion of lighting the home the terminology
+of electric-lighting will be used. The principles expounded apply as
+well to gas as to electricity, and owing to the ingenuity of the
+gas-lighting experts, the possibilities of gas-lighting are extensive
+despite its handicaps. There are some places in the home, such as the
+kitchen and basement, where lighting is purely utilitarian in the narrow
+sense, but in most of the rooms the esthetic or, more broadly, the
+psychological aspects of lighting should dominate. Pure utility is
+always a by-product of artistic lighting and furthermore, the lighting
+effects will be without glare when they satisfy all the demands of
+esthetics.</p>
+
+<p><a class="pagenum" name="Page_327" id="Page_327"></a>In dealing with lighting in the home the householder should concentrate
+his attention upon lighting effects. Unfortunately, he is not taught to
+do so, for everywhere he turns for help he finds the discussion directed
+toward fixtures and lamps instead of toward lighting effects. However,
+these are merely links in the chain from the meter to the eye. Lamps are
+of interest from the standpoint of quantity and quality of light, and
+fixtures are of importance chiefly as distributers of light. These
+details are merely means to an end and the end is the lighting effect.
+Of course, the fixtures are more important as objects than the wires
+because they are visible and should harmonize with the general
+decorative and architectural scheme.</p>
+
+<p>The home is the theater of life full of various moods and occasions;
+hence the lighting of a home should be flexible. A degree of variety
+should be possible. Controls, wiring, outlets, and fixtures should
+conspire to provide this variety. At the present time the average
+householder does not give much attention to lighting until he purchases
+fixtures. It is probable that he thought of it when he laid out or
+approved the wiring, but usually he does not consider it seriously until
+he visits the fixture-dealer to purchase fixtures. And then
+unfortunately the fixture-dealer does not light his home; he does not
+sell the householder lighting-effects designed to meet the requirements
+of the particular home; he sells merely fixtures.</p>
+
+<p>Unfortunately there are few fixtures available which have definite aims
+in lighting as demanded by the home. Of the great variety of fixtures
+available there are many artistic objects, but it is obvious that little
+at<a class="pagenum" name="Page_328" id="Page_328"></a>tention is given to their design from the standpoint of lighting.
+That the fixture-dealer usually thinks of fixtures as objects and gives
+little or no thought to lighting effects is apparent from his
+conversation and from his display. He exhibits fixtures usually en masse
+and seldom attempts to illustrate the lighting effects produced in the
+room.</p>
+
+<p>The foregoing criticisms are presented to emphasize the fact that
+throughout the field of lighting the great possibilities which have been
+opened by modern light-sources are not fully appreciated. The point at
+which to begin to design the lighting for a home is the wiring.
+Unfortunately this is too often done by a contractor who has given no
+special thought to the possibilities of lighting and to the requirements
+in wiring and switches necessary in order to realize them. At this point
+the householder should attempt to form an opinion as to the relative
+values. Is artificial lighting important enough to warrant an
+expenditure of two per cent. of the total investment in the home and its
+furnishings? The answer will depend upon the extent to which artificial
+light is appreciated. It appears that four or five per cent. is not too
+much if it is admitted that the artificial lighting system ranks next to
+the heating plant in importance and that these two are the most
+important features of an interior of a residence. A switch or a
+baseboard outlet costs an insignificant sum but either may pay for
+itself many times in the course of a few years through its utility or
+convenience.</p>
+
+<p>It appears best to take up this subject room by room because the
+requirements vary considerably, but in order to be specific in the
+discussions, a middle-class <a class="pagenum" name="Page_329" id="Page_329"></a>home will be chosen. The more important
+rooms will be treated first and various simple details will be touched
+upon because, after all, the proper lighting of a home is realized by
+attention to small details.</p>
+
+<p>The living-room is the scene of many functions. It serves at times for
+the quiet gathering of the family, each member devoted to reading. At
+another time it may contain a happy company engaged at cards or in
+conversation. The lighting requirements vary from a spot or two of light
+to a flood of light. Excepting in the small living-rooms there does not
+appear to be a single good reason for a ceiling fixture. It is nearly
+always in the field of vision when occupants are engaged in
+conversation, and for reading purposes the portable lamp of satisfactory
+design has no rival. Wall brackets cannot supply general lighting
+without being too bright for comfort. If they are heavily shaded they
+may still emit plenty of light upward, but the adjacent spots on the
+walls or ceiling will generally be too bright. Wall brackets may be
+beautiful ornaments and decorative spots of light and have a right to
+exist as such, but they cannot be safely depended upon for adequate
+general lighting on those occasions which demand such lighting.</p>
+
+<p>As a general principle, it is well to visualize the furniture in the
+room when looking at the architect's drawings and it is advantageous
+even to cut out pieces of paper representing the furniture in scale. By
+placing these on the drawings the furnished room is readily visualized
+and the locations of baseboard outlets become evident. It appears that
+the best method of lighting a living-room is by means of decorative
+port<a class="pagenum" name="Page_330" id="Page_330"></a>able lamps. Such lamps are really lighting-furniture, for they aid
+in decorating and in furnishing the room at all times. A number of these
+lamps in the living-room insures great flexibility in the lighting, and
+the light may be kept localized if desired so that the room is restful.
+A room whose ceiling and walls are brilliantly illuminated is not so
+comfortable for long periods as one in which these areas are dimly
+lighted. Furthermore, the latter is more conducive to reading and to
+other efforts at concentration. The furniture may be readily shifted as
+desired and the portable lamps may be rearranged.</p>
+
+<p>Such lighting serves all the purposes of the living-room excepting those
+requiring a flood of light, but it is easy to conceal elaborate lighting
+mechanisms underneath the shades of portable lamps. Several types of
+portable lamps are available which supply an indirect component as well
+as direct light. The former illuminates the ceiling with a flood of
+light without any discomforting glare. Such a lighting-unit is one of
+the most satisfactory for the home, for two distinct effects and a
+combination of these introduce a desirable element of variety into the
+lighting. Not less than four and preferably six baseboard outlets should
+be provided in a living-room of moderate size. One outlet on the mantel
+is also to be desired for connecting decorative candlesticks, and
+brackets above the fireplace are of ornamental value. Although the
+absence of ceiling fixtures improves the appearance of the room, wiring
+may be provided for ceiling outlets in new houses as a matter of
+insurance against the possible needs of the future. When ceiling
+fixtures are not <a class="pagenum" name="Page_331" id="Page_331"></a>used, switches may be provided for the mantel brackets
+or certain baseboard outlets in order that light may be had upon
+entering the room.</p>
+
+<p>The merits of a portable lamp may be ascertained before purchasing by
+actual demonstration. Some of them are not satisfactory for
+reading-lamps, owing to the shape of the shade or to the position of the
+lamps. The utility of a table lamp may be determined by placing it upon
+a table and noting the spread of light while seated in a chair beside
+it. A floor lamp may also be tested very easily. A miniature floor lamp
+about four feet in height with an appropriate shade provides an
+excellent lamp for reading purposes because it may be placed by the side
+of a chair or moved about independent of other furniture. A tall floor
+lamp often serves for lighting the piano, but small piano lamps may be
+found which are decorative as well as serviceable in illuminating the
+music without glare.</p>
+
+<p>The dining-room presents an entirely different problem for the setting
+is very definite. The dining-table is the most important area in the
+room and it should be the most brilliantly illuminated area in the room.
+A demonstration of this point is thoroughly convincing. The decorator
+who designs wall brackets for the dining-room is interested in beautiful
+objects of art and not in a proper lighting effect. The fixture-dealer,
+having fixtures to sell and not recognizing that he could fill a crying
+need as a lighting specialist, is as likely to sell a semi-indirect or
+an indirect lighting fixture as he is to provide a properly balanced
+lighting effect with the table brightly illuminated. The indirect and
+semi-indirect units illuminate the ceiling predominantly with <a class="pagenum" name="Page_332" id="Page_332"></a>the
+result that this bright area distracts attention from the table. A
+brightly illuminated table holds the attention of the diners. Light
+attracts and a semi-darkness over the remainder of the room crowds in
+with a result that is far more satisfactory than that of a dining-room
+flooded with light.</p>
+
+<p>The old-fashioned dome which hung over the dining-table has served well,
+for it illuminated the table and left the remainder of the room dimly
+lighted. But its wide aperture made it necessary to suspend it rather
+low in order that the lamps within should not be visible. It is an
+obtrusive fixture and despite its excellent lighting effect, it went out
+of style. But satisfactory lighting principles never become antiquated,
+and as taste in fixtures changes the principles may be retained in new
+fixtures. Modern domes are available which are excellent for the
+dining-room if the lamps are well concealed. The so-called showers are
+satisfactory if the shades are dense and of such shape as to conceal the
+lamps from the eyes. Various modifications readily suggest themselves to
+the alert fixture-designer. Even the housewife can do much with silk
+shades when the principle of lighting the dining-table is understood.
+The so-called <ins class="correction" title="Transcriber's Note: Original reads &quot;cadelabra&quot;.">candelabra</ins>
+have been sold extensively for dining-rooms and they are fairly
+satisfactory if equipped with shades which reflect much of the light
+downward. Semi-indirect and indirect fixtures have many applications in
+lighting, but they do not provide the proper effect for a dining-room.</p>
+
+<p>It is easy to make a special fixture which will send a component of
+light downward to the table and will permit a small amount of diffused
+light to the ceiling and <a class="pagenum" name="Page_333" id="Page_333"></a>walls. If a daylight lamp is used for the
+direct component, the table will appear very beautiful. Under this light
+the linen and china are white, flowers and decorations on the china
+appear in their full colors, the silver is attractive, and the various
+color-harmonies such as butter, paprika, and baked potato are enticing.
+This is an excellent place for a daylight lamp if diffused light
+illuminating the remainder of the room and the faces of the diners is of
+a warm tone obtained by warm yellow lamps or by filtering these
+components of the light through orange shades. The ceiling fixture
+should be provided with two circuits and switches. In some cases it is
+easy to provide a dangling plug for connecting such electric equipment
+as a toaster, percolator, or candlesticks. Two candlesticks are
+effective on the buffet, but usually the smallest normal-voltage lamps
+available give too much light. Miniature lamps may be used with a small
+transformer, or two regular lamps may be connected in series. At least
+two baseboard outlets are convenient.</p>
+
+<p>The foregoing deals with the more or less essential lighting of a
+dining-room, but there are various practicable additional lighting
+effects which add much charm to certain occasions. Colored light of low
+intensity obtained from a cove or from "flower-boxes" fastened upon the
+wall is very pleasing. If a cove is provided around the room, two
+circuits containing orange and blue lamps respectively will supply two
+colors widely differing in effect. By mixing the two a beautiful rose
+tint may be obtained. This equipment has been installed with much
+satisfaction. A simpler method of obtaining a similar effect is to use
+imitation <a class="pagenum" name="Page_334" id="Page_334"></a>flower-boxes plugged into wall outlets. Artificial foliage
+adds to the charm of these boxes. The colored light is merely to add
+another effect on special occasions and its intensity should never be
+high. In the dining-room such unusual effects are not out of place and
+they need not be garish.</p>
+
+<p>The sun-room partakes of the characteristics of the living-room to some
+extent, but, it being smaller, a semi-indirect fixture may be
+satisfactory for general illumination. However, a portable lamp which
+supplies an indirect component of light besides the direct light serves
+admirably for reading as well as for flooding the room with light when
+necessary. Two or three baseboard outlets are desirable for attaching
+decorative or even purely utilitarian lamps. The sun-room is an
+excellent place for utilizing "flower-box" fixtures decorated with
+artificial foliage. In fact, a central fixture may assume the appearance
+of a "hanging basket" of foliage. The library and den offer no problems
+differing from those already discussed in the living-room. A careful
+consideration of the disposition of the furniture will reveal the best
+positions for the outlets. In a small library wall brackets may serve as
+decorative spots of light and if the shades are pendent they may serve
+as lamps for reading purposes. In both these rooms an excellent
+reading-lamp is desired, but it may be decorative as well. Wall outlets
+may be desired for decorative portable lamps upon the bookcases.</p>
+
+<p>The sleeping-room, which commonly is also a dressing-room, often
+exhibits the errors of a lack of foresight in lighting. In most rooms of
+this character <a class="pagenum" name="Page_335" id="Page_335"></a>there is one best arrangement of furniture and if this
+is determined it is easy to ascertain where the windows and outlets
+should be located. The windows may usually be arranged for twin beds as
+well as for a single one with obvious advantages of flexibility in
+arrangement. With the position of the bureau determined it is easy to
+locate outlets for two wall brackets, one on each side, about sixty-six
+inches above the floor and about five feet apart. When the brackets are
+equipped with dense upright shades, the figure before the mirror is well
+illuminated without glare and sufficient light reaches the ceiling to
+illuminate the whole room.</p>
+
+<p>A baseboard outlet should be available for small portable lamps which
+may be used upon the bureau or for electric heating devices. The same is
+true for the dressing-table; indeed, two small decorative lamps on the
+table serve better than high wall brackets owing to the fact that the
+user is seated. A baseboard outlet near the head of the bed or between
+the beds is convenient for a reading-lamp and for other purposes. An
+outlet in the center of the ceiling controlled by a convenient switch
+may be installed on building, as insurance against future needs or
+desires. But a single lighting-unit in the center of the ceiling does
+not serve adequately the needs at the bureau and dressing-table. In
+fact, two wall brackets properly located with respect to the bureau
+afford a lighting much superior for all purposes in the bedroom to that
+produced by a ceiling fixture.</p>
+
+<p>In the bath-room the principal problem is to illuminate the person,
+especially the face, before the mirror. Many mistakes are made at this
+point, despite the <a class="pagenum" name="Page_336" id="Page_336"></a>simplicity of the solution. In order to see the
+image of an object in a mirror, the object must be illuminated. It is
+best to do this in a straightforward manner by means of a small
+lighting-unit on each side of the mirror at a height of five feet. Both
+sides of the face will be well illuminated and the light-sources are low
+enough to eliminate objectionable shadows. The units may be merely
+pull-chain sockets containing frosted or opal lamps. A center bracket or
+a single unit suspended from the ceiling is not as satisfactory as the
+two brackets. These afford enough light for the entire bath-room. A
+baseboard or wall outlet is convenient for connecting a heater,
+curling-iron, and other electrically heated devices.</p>
+
+<div class="center">
+<a name="image46" id="image46"></a>
+<img src="images/image46.png" alt="" title="" width="400" height="314" />
+</div>
+
+<div class="center">
+<a name="image47" id="image47"></a>
+<img src="images/image47.png" alt="" title="" width="400" height="318" />
+</div>
+
+<p class="caption">OBTAINING TWO DIFFERENT MOODS IN A ROOM BY A PORTABLE
+LAMP WHICH SUPPLIES DIRECT AND INDIRECT COMPONENTS OF LIGHT</p>
+
+<p>The sewing-room, which in the middle-class home is usually a small room,
+is sometimes used as a bedroom. A ceiling fixture will supply adequate
+general lighting, but a baseboard outlet should be available for a short
+floor lamp or a table lamp for sewing purposes. An intense local light
+is necessary for this occupation, which severely taxes the eyes. A
+so-called daylight lamp serves very well in this case.</p>
+
+<div class="center">
+<a name="image48" id="image48"></a>
+<img src="images/image48.png" alt="THE LIGHTS OF NEW YORK CITY" title="THE LIGHTS OF NEW YORK CITY" width="600" height="414" />
+<p class="caption">THE LIGHTS OF NEW YORK CITY<br />
+
+Towering shafts of light defy the darkness and thousands of lighted
+windows symbolize man's successful struggle against nature</p>
+</div>
+
+<p>In the kitchen the wall brackets are easily located after the positions
+of the range, work-table, sink, etc., are determined. A bracket for each
+is advisable unless they are so located that one will serve two
+purposes. It is customary to have a combination fixture for gas and
+electricity. This is often suspended from the center of the ceiling, but
+inasmuch as the gas-light cannot be close to the ceiling, the fixture
+extends so far downward as to become a nuisance. Furthermore, a
+light-source hung low from the center of the <a class="pagenum" name="Page_337" id="Page_337"></a>ceiling is in such a
+position that the worker in the kitchen usually works in his shadow. If
+a ceiling outlet is used it should be an electrical socket at the
+ceiling. The combination fixture is best placed on the wall as a
+bracket. The so-called daylight lamps are valuable in the kitchen.</p>
+
+<p>In the basement a generous supply of ceiling outlets adds much to the
+satisfaction of a basement. One in each locker, one before the furnace,
+and a large daylight lamp above but to one side of the laundry trays are
+worth many times their cost. Furthermore, a wall socket for the electric
+iron and washing-machine is a convenience very much appreciated.</p>
+
+<p>In the stairways convenient three-way switches for each of the ceiling
+fixtures represents the best practice. A baseboard outlet in the upper
+hall affords a connection for a decorative lamp and pays for itself many
+times as a place to attach the vacuum-cleaner from which all the rooms
+on that floor may be served. In vestibules and on porches ceiling
+fixtures controlled by means of convenient switches are satisfactory.
+The entrance hall may be made to express hospitality by means of
+lighting which should be adequate and artistic.</p>
+
+<p>An adequate supply of outlets and wall switches is not costly and they
+pay generous dividends. With a scanty supply of these, the
+<ins class="correction" title="Transcriber's Note: Original reads &quot;possibilties&quot;.">possibilities</ins> of
+lighting are very much curtailed. There is nothing intricate about
+locating switches and outlets, so the householder may do this himself,
+or he may view critically the plans as submitted. The chief difficulties
+are to throw aside his indifference and to readjust his ideas and
+values. It <a class="pagenum" name="Page_338" id="Page_338"></a>may be confidently stated that the possibilities of lighting
+far outrank most of the features which contribute to the cost of a house
+and of its furnishings.</p>
+
+<p>After considering the requirements and decorative schemes of the various
+rooms the householder should be competent to judge the appropriateness
+of the lighting effects obtained from fixtures which the dealer
+displays, but he should insist upon a demonstration. If the dealer is
+not equipped with a room for this purpose, he should be asked to
+demonstrate in the rooms to be lighted. If the fixture-dealer does not
+realize that he should be selling lighting effects, the householder
+should make him understand that lighting effects are of primary
+importance and the fixtures themselves are of secondary interest in most
+cases. The unused outlets that have been installed for possible future
+needs may be sealed in plastering if the positions are marked so that
+they may be found when desired.</p>
+
+<p>An advantage of portable lamps is that they may be taken away on moving.
+In fact, when lighting is eventually considered a powerful decorative
+medium, as it should be, it is probable that fixtures will be personal
+property attached to ceiling, wall, and floor outlets by means of plugs.</p>
+
+<p>A variety of incandescent lamps are available. For the home, opal,
+frosted, or bowl-frosted lamps are usually more satisfactory than clear
+lamps. Bare filaments should not be visible, for they not only cause
+discomfort and eye-strain but they spoil what might otherwise be an
+artistic effect. Lamps with diffusing bulbs do much toward eliminating
+harsh shadows cast by the <a class="pagenum" name="Page_339" id="Page_339"></a>edges of the shades, by the chains of the
+fixtures, etc. These lamps are available in many shapes and sizes and
+the householder should make a record of voltage, wattage, and shape of
+the lamps which he finds satisfactory in the various fixtures. The Mazda
+daylight lamp has several places in the home and the Mazda white-glass
+and other high-efficiency lamps supply many needs better than the vacuum
+lamps. In brackets and other purely decorative lighting-units small
+frosted lamps are usually the most satisfactory. There is a general
+desire for the warm yellowish light of the candle-flame, and this may be
+obtained by a tinted shade but usually more satisfactorily by means of a
+tinted lamp.</p>
+
+<p>The householder will find it interesting to become intimate with
+lighting, for it can serve him well. The housewife will often find much
+interest in making shades of textiles and of parchment. Charming
+glassware in appropriate tints and painted designs is available for all
+rooms. In the bedchamber and the nursery some of these painted designs
+are exceedingly effective. Fixtures should shield the lamps from the
+eyes, and the diffusing media whether glass or textile should be dense
+enough to prevent glare. No fixture can be beautiful and no lighting
+effect can be artistic if glare is present. If the architect and the
+householder will realize that light is a medium comparable with the
+decorator's media, better lighting will result. Light has the great
+advantage of being mobile and with adequate outlets and controls
+supplemented by fixtures from which different effects are available, the
+householder will find in lighting one of the most fruitful sources of
+interest and <a class="pagenum" name="Page_340" id="Page_340"></a>pleasure. It can do much toward expressing the taste of
+the householder or if neglected it can undo much of the effect of
+excellent decoration and furnishing. Artificial lighting, softly
+diffused and properly localized, is one of the most important factors in
+making a house a home.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_341" id="Page_341"></a>XXV</h2>
+
+<h2>LIGHTING&mdash;A FINE ART?</h2>
+
+
+<p>In the preceding chapters the progress of light has been sketched from
+its obscure infancy to its vigorous youth of the present time. It has
+been seen that progress was slow until the beginning of the nineteenth
+century, after which it began to gain momentum until the present century
+has witnessed tremendous advances. Until the latter part of the
+nineteenth century artificial light was considered an expensive utility,
+but as modern lamps appeared which supplied adequate light at reasonable
+cost attention began to be centered upon utilization, and the lighting
+engineer was born. Gradually it is being realized that artificial light
+is no longer a luxury, that it may be used in great quantity, and that
+it may be directed, diffused, and altered in color as desired. Although
+the potentiality of light has been barely drawn upon, the present usages
+surpass the most extravagant dreams of civilized beings a half-century
+ago. Mere light of that time was changed into more light as gas-lighting
+developed, and more light has increased to adequate light of the present
+time through the work of scientists.</p>
+
+<p>It is apparent that a sudden enforced reversion to the primitive flames
+of fifty years ago would paralyze many activities. Much of interest and
+beauty would be blotted out of this brilliant, pulsating, productive
+age.<a class="pagenum" name="Page_342" id="Page_342"></a> It is startling to note that almost the entire progress in
+artificial lighting has taken place during the past hundred years and
+that most of it has been crowded into the latter part of this period. In
+fact, its development since it began in earnest has gone forward with
+ever-increasing momentum. On viewing the wonders of modern artificial
+lighting on every hand it is not difficult to muster the courage
+necessary to venture into its future.</p>
+
+<p>The lighting engineer has been a natural evolution of the present age,
+for the economic aspects of lighting have demanded attention. He is
+increasing the safety, efficiency, and happiness of mankind and
+civilization is beginning to feel his influence economically. However,
+with the advent of adequate, efficient, and controllable light, the
+potentiality of light as an artistic medium may be drawn upon and the
+lighting artist with a deep insight into the possibilities of artificial
+light now has his opportunity. But the artist who believes that a new
+art may be evolved to perfection in a few years is doomed to
+disappointment, for it is necessary only to view retrospectively such
+arts as painting and music to be convinced that understanding and
+appreciation develop slowly through centuries of experiment and contact.</p>
+
+<p>Will lighting ever become a fine art? Will it ever be able alone to
+arouse emotional man as do the fine arts? Are the powers of light
+sufficiently great to enthrall mankind without the aid of form, music,
+action, or spoken words? It is safer to answer "yes" than "no" to these
+questions. Painting has reached a high place as an art and this art is
+the expressiveness of <a class="pagenum" name="Page_343" id="Page_343"></a>secondary or reflected light reinforced by
+imitation forms, which by a combination of light and drawing comprise
+the "subjects." A painting is a momentary expression of light, a
+cross-section of something mobile, such as nature, thought, or action.
+Light has the essential qualifications of painting with the advantages
+of a greater range of brightness, of greater purity of colors, and the
+great potentiality of mobility. If lighting becomes a fine art it will
+doubtless be related to painting somewhat in the same manner that
+architecture is akin to sculpture. With the introduction of mobility it
+will borrow something from the arts of succession and especially from
+music.</p>
+
+<p>The art of lighting in its present infancy is leaning upon established
+arts, just as the infant learns to walk alone by first depending upon
+support. The use of color in painting developed slowly, being supported
+for centuries by the strength of drawing or subject. The landscapes of a
+century ago were dull, for color was employed hesitatingly and
+sparingly. The colors in the portraits of the past merely represented
+the gorgeous dress of bygone days. But the painter of the present shows
+that color is beginning to be used for itself and that the painter is no
+longer hesitant concerning its power to go hand in hand with drawing.
+Drafting and coloring are now in partnership, the former having given up
+guardianship when the latter reached maturity.</p>
+
+<p>Lighting is now an accompaniment of the drama, of the dance, of
+architecture, of decoration, and of music. It has been a background or a
+part of the "atmosphere" excepting occasionally when some one with
+<a class="pagenum" name="Page_344" id="Page_344"></a>imagination and daring has given it the leading r&ocirc;le. Even in its
+infancy it has on occasions performed admirably almost without any aid.
+The bursting rocket, the marvelous effects at the Panama-Pacific
+Exposition, and some of the exhibitions on the theatrical stage are
+glimpses of the potentiality of light. To fall back upon the terminology
+of music, these may be glimmerings of light-symphonies.</p>
+
+<p>Harmony is simultaneity and a painting in this respect is a chord&mdash;a
+momentary expression fixed in material media. A melody of light requires
+succession just as the melody in music. The restless colors of the opal
+comprise a light melody like the songs of birds. The gorgeous splendor
+of the sunset compares in magnitude and in its various moods with the
+symphony orchestra and its powers. Throughout nature are to be found
+gentle chords, beautiful melodies and powerful symphonies of light and
+this music of light exhibits the complexity and structure analogous to
+music. There is no physical relation between music, poetry, and light,
+but it is easy to lean upon the established terminology for purposes of
+discussion. Those who would build color-music identical to sound music
+are making the mistake of starting with a physical foundation instead of
+basing the art of light-expression upon psychological effects of light.
+In other words, a relation between light and music can exist only in the
+psychological realm.</p>
+
+<p>These melodies and symphonies of light in nature are admittedly pleasing
+or impressive as the case may be, but are they as appealing as music,
+poetry, painting, or sculpture? The consensus of opinion of a large
+<a class="pagenum" name="Page_345" id="Page_345"></a>group of average persons might indicate a negative reply, but the
+combined opinion of this group is not so valuable as the opinion of a
+colorist or of an artist who has sensed the wonders of light. The
+unprejudiced opinion of artists is that light is a powerfully expressive
+and impressive medium. The psychologist will likely state that the
+emotive value of light or color is not comparable to the appeal of an
+excellent dinner or of many other commonplace things. But he has
+experimented only with single colors or with simple patterns and his
+subjects are selected more or less at random from the multitude. What
+would be his conclusion if he examined painters and others who have
+developed their sensibilities to a deep appreciation of light and color?
+It is certain that the painter who picks up a purple petal fallen from a
+rose and places it upon a green leaf is as thrilled by the powerful
+vibrant color-chord as the musician who hears an exquisite harmony of
+sounds.</p>
+
+<p>Music has been presented to civilized mankind in an organized manner for
+ages and the fundamental physical basis of modern music is a thousand
+years old. Would the primitive savage appreciate the modern symphony
+orchestra? Even the majority of civilized beings prefer the modern
+ragtime or jazz to the exquisite art of the symphony. An appreciation of
+the opera and the symphony is reached by educational methods extending
+over long periods. An appreciation of the expressiveness of light cannot
+be expected to be realized by any short-cut. Most persons to-day enjoy
+the melodramatic "movie" more than the drama and relatively few
+experience the deep appeal of the <a class="pagenum" name="Page_346" id="Page_346"></a>fine arts. Surely the symphony of
+light cannot be justly condemned because of a lack of appreciation and
+understanding of it, for it has not been introduced to the public.
+Furthermore, the expressiveness of music is still indefinite at best
+despite the many centuries of experimenting on the part of musicians.</p>
+
+<p>If poetry is to be believed, the symphonies of light as rendered by
+nature in the sunsets, in the aurora borealis, and in other sky-effects
+of great magnitude have deeply impressed the poet. If his descriptions
+are to be accepted at their face-value, the melodies of light rendered
+in the precious stone, in the ice-crystal, and in the iridescence of
+bird-plumage please his finer sensibilities. If he is sincere, mobile
+light is a seductive agency.</p>
+
+<p>The painter has contributed little of direct value in developing the
+music of light. He is concerned with an instantaneous expression. He
+waits for it patiently and, while waiting, learns to appreciate the
+fickleness of mood in nature, but when he fixes one of these moods he
+has contributed very little to the art of mobile light. Unfortunately
+the art schools teach the student little or nothing pertaining to color
+for color's sake. When the student is capable of drawing fairly well and
+is acquainted with a few stereotyped principles of color-harmony he is
+sent forth to follow in the footsteps of past masters. He may be seen at
+the art museum faithfully copying a famous painting or out in the fields
+stalking a tree with the hopes of an embryo Corot. The world moves and
+has only a position in the rank and file for imitators. Occasionally an
+artist goes to work with a vim and indulges in research, thereby
+<a class="pagenum" name="Page_347" id="Page_347"></a>demonstrating originality in two respects. Painting is just as much a
+field for research as light-production.</p>
+
+<p>Recently experiments are being made in the production of color-harmonies
+devoid of form. Surely there is a field for pure color-composition and
+this the field of the painter which leads toward the art of mobile
+light. Many of the formless paintings of the present day which pass
+under the banner of this <em>ism</em> or that are merely experiments in the
+expressiveness of light. Being formless, they are devoid of subject in
+the ordinary sense and cannot be more or less than a fixed expression of
+light. Naturally they have received much criticism and have been
+ridiculed, but they can expect nothing else until they are understood.
+They cannot be understood until mankind learns their language and then
+they must be understandable. In other words, there are impostors
+gathered around the sincere research-artist because the former have
+neither the ability to paint for a living nor the inclination to forsake
+the comparative safety of the mystery of art for the practical world
+where their measure would be quickly taken. This army of camp-followers
+will not advance the art of mobile light, but the sincere seekers after
+the principles of light-expression who form the foundation of the
+various <em>isms</em> may contribute much.</p>
+
+<p>The painter will always be available with his finer sensibility to
+appreciate and to aid in developing the art of mobile light, but his
+direct contribution appears most likely to come from the present chaos
+of experiments in pure color-composition, in the psychology of light,
+or, more broadly, in the expressiveness of light. The decorator and the
+designer of gowns and cos<a class="pagenum" name="Page_348" id="Page_348"></a>tumes do not arrogate to themselves the name
+"artist," but they are daily creating something which is leading toward
+a fuller appreciation of the expressiveness of light. If they do not
+contribute directly to the development of the art of mobile light, they
+are at least aiding in developing what may eventually be an appreciative
+public.</p>
+
+<p>The artist paints a "still-life," the decorator creates a color-harmony
+of abstract or conventional forms, and the costumer produces a
+color-composition in textiles. The decorator and costumer approach
+closer to pure color-composition than the artist in his still-life. The
+latter is a grouping of objects primarily for their color-notes. Why
+bother with a banana when a yellow-note is desired? Why utilize the
+abstract or conventional forms of the decorator? Why not follow this
+lead further to the less definite forms employed by the costumer? Why
+not eliminate form even more completely? This is an important point and
+an interesting lead, for to become rid of form has been one of the
+perplexing problems encountered by those who have dreamed of an art of
+mobile light.</p>
+
+<p>The painter who uses line and color imitatively has perhaps acquired
+skill in depicting objects and more or less appreciation of the
+beautiful. But if he is to be creative and to produce a higher art he
+must be able to use line and color without reference to objects. He thus
+may aid in the development of an abstract art which is the higher art
+and at the same time aid in educating the public to appreciate pure
+color-harmonies. From these momentary expressions of light and from the
+experience gained, the mobile colorist <a class="pagenum" name="Page_349" id="Page_349"></a>would receive material aid and
+his productions would be viewed by a more receptive audience or rather
+"optience" as it may be called. The development of taste for abstract
+art is needed in order that the art of mobile light may develop and,
+incidentally, an appreciation of the abstract in art is needed in all
+arts.</p>
+
+<p>Science has contributed much by way of clearing the decks. It has
+produced the light-sources and the apparatus for controlling light. It
+has analyzed the physical aspects of color-mixture and has accumulated
+extensive data pertaining to color-vision. It has pointed out pitfalls
+and during recent years has been delving further by investigating the
+psychology of light and color. The latter field is looked to for
+valuable information, but, after all, there is one way of making
+progress in the absence of data and that is to make attempts at the
+production of impressive effects of mobile light. Some of these have
+been made, but unfortunately they have been heralded as finished
+products.</p>
+
+<p>Perhaps the most general mistake made is in relating sounds and colors
+by stressing a mere analogy too far. Notwithstanding the vibratory
+nature of the propagation of sound and light, this is no reason for
+stressing a helpful analogy. After all it is the psychological effect
+that is of importance and it is absurd to attribute any connection
+between light-waves and sound-waves based upon a relation of physical
+quantities. No space will be given to such a relation because it is so
+absurdly superficial; however, the language of music will be borrowed
+with the understanding that no relation is assumed.</p>
+
+<p><a class="pagenum" name="Page_350" id="Page_350"></a>A few facts pertaining to vision will indicate the trend of developments
+necessary in the presentation of mobile light. The visual process
+synthesizes colors and at this point departs widely from the auditory
+process. The sensation of white may be due to the synthesis of all the
+spectral colors in the proportions in which they exist in noon sunlight
+or it may be due to the synthesis of proper proportions of yellow and
+blue, of red, green, and blue, of purple and green, and a vast array of
+other combinations. A mixture of red and green lights may produce an
+exact match for a pure yellow. Thus it is seen that the mixture of
+lights will cause some difficulty. For example, the components of a
+musical chord may be picked out one by one by the trained ear, but if
+two or more colored lights are mixed they are merged completely and the
+resultant color is generally quite different from any of the components.
+In music of light, the components of color-chords must be kept
+separated, for if they are intermingled like those of musical chords
+they are indistinguishable. Therefore, the elements of harmony in mobile
+light must be introduced by giving the components different spatial
+positions.</p>
+
+<p>The visual process is more sluggish than the auditory process; that is,
+lights must succeed each other less rapidly than musical notes if they
+are to be distinguished separately. The ear can follow the most rapid
+execution of musical passages, but there is a tendency for colors to
+blend if they follow one another rapidly. This critical frequency or
+rate at which successive colors blend decreases with the brightness of
+the components. If red and green are alternated at a <a class="pagenum" name="Page_351" id="Page_351"></a>rate exceeding the
+critical frequency, a sensation of yellow will result; that is, neither
+component will be distinguishable and a steady yellow or a yellow of
+flickering brightness will be seen. The hues blend at a lower frequency
+than the brightness components of colors; hence there may be a blend of
+color which still flickers in brightness. Many weird results may be
+obtained by varying the rate of succession of colors. If this rate is so
+low that the colors do not tend to merge, they are much enriched by
+successive contrast. It is known that juxtaposed colors generally enrich
+one another and this phenomenon is known as simultaneous contrast.
+Successive contrast causes a similar effect of heightened color.</p>
+
+<p>An effect analogous to dynamic contrast in music may be obtained with
+mobile light by varying the intensity of the light or possibly the area.
+Melody may be simply obtained by mere succession of lights. Tone-quality
+has an analogy in the variation of the purity of color. For example, a
+given spectral hue may be converted into a large family of tints by the
+addition of various amounts of white light. Rhythm is as easily applied
+to light as to music, to poetry, to pattern, or to the dance, but in
+mobile lights its limitations already have been suggested. However, it
+is bound to play an important part in the art of mobile light because
+rhythmic experiences are much more agreeable than those which are
+non-rhythmic. Rhythm abounds everywhere and nothing so stirs mankind
+from the lowliest savage to the highly cultivated being as rhythmic
+sequences.</p>
+
+<p>Many psychological effects of light have been recorded from experiment
+and observation and affective <a class="pagenum" name="Page_352" id="Page_352"></a>values of light have been established in
+various other byways. It is possible that the degree of pleasure
+experienced by most persons on viewing a color-harmony or the delightful
+color-melody of a sunlit opal may be less than that experienced on
+listening to the rendition of music. However, if this were true it would
+offer no discouragement, because absolute values play a small part in
+life. Two events when directly compared apparently may differ enormously
+in their ability to arouse emotions, but the human organism is so
+adaptive that each in its proper environment may powerfully affect the
+emotions. For example, those who have sported in a&euml;rial antics in the
+heights of cloudland or have stormed the enemy's trench are still
+capable of enjoying a sunset or the call of a bird to its mate at dusk.
+The wonderful adaptability of the inner being is the salvation of art as
+well as of life.</p>
+
+<div class="center">
+<a name="image49" id="image49"></a>
+<img src="images/image49.png" alt="A community Christmas tree" title="A community Christmas tree" width="400" height="435" />
+<p class="caption">A community Christmas tree</p>
+</div>
+
+<div class="center">
+<a name="image50" id="image50"></a>
+<img src="images/image50.png" alt="A community song-festival" title="A community song-festival" width="400" height="212" />
+<p class="caption">A community song-festival</p>
+</div>
+
+<p class="caption">ARTIFICIAL LIGHT IN COMMUNITY AFFAIRS</p>
+
+<p>In the rendition of mobile light it is fair to give the medium every
+advantage. Sometimes this means to eliminate competitors and sometimes
+it means to remove handicaps. On the stage light has had competitors
+which are better understood. For example, in the drama words and action
+are easily understood, and regardless of the effectiveness of light it
+would not receive much credit for the emotive value of the production.
+In the wonderful harmony of music, dance, and light in certain recent
+exhibitions, the dance and music overpowered the effects of lights
+because they speak familiar languages.</p>
+
+<div class="center">
+<a name="image51" id="image51"></a>
+<img src="images/image51.png" alt="PANAMA-PACIFIC EXPOSITION" title="PANAMA-PACIFIC EXPOSITION" width="600" height="404" />
+<p class="caption">PANAMA-PACIFIC EXPOSITION<br />
+
+Artificial light not only reveals the beauty of decoration and
+architecture but enthralls mankind with its own unlimited powers</p>
+</div>
+
+<p>A number of attempts have been made to utilize light as an accompaniment
+of music and some of them on a small scale have been sincere and
+creditable, but a <a class="pagenum" name="Page_353" id="Page_353"></a>much-heralded exhibition on a large scale a few
+years ago was not the product of deep thought and sincere effort. For
+example, colored lights thrown upon a screen having an area of perhaps
+twenty square feet were expected to compete with a symphony orchestra in
+Carnegie Hall. The music reached the most distant auditor in sufficient
+volume, but the lighting effect dwindled to insignificance. Without
+entering into certain details which condemned the exhibition in advance,
+the method of rendition of the light-accompaniment revealed a lack of
+appreciation of the problems involved on the part of those responsible.</p>
+
+<p>Incidentally, it has been shown that the composer of this particular
+musical selection with its light accompaniment was psychologically
+abnormal; that is, he was affected with colored audition. It is not yet
+established to what extent normal persons are similarly affected by
+light and color. Certainly there is no similarity among the abnormal and
+none between the abnormal and normal.</p>
+
+<p>If light is to be used as an accompaniment to music, it must be given an
+opportunity to supply "atmosphere." This it cannot do if confined to an
+insignificant spot; it must be given extensity. Furthermore, by the use
+of diaphanous hangings, form will be minimized and the evanescent
+effects surely can be charming. But finally the lighting effects must
+fill the field of vision just as the music "fills the field of audition"
+in order to be effective. There are fundamental objections to the use of
+mobile light as an accompaniment to music and therefore the future of
+the art of mobile light must not be allowed to rest upon its success
+with <a class="pagenum" name="Page_354" id="Page_354"></a>music. If it progresses through its relation with music, so much
+is gained; if not, the relation may be broken for music is quite capable
+of standing alone.</p>
+
+<p>There is a tendency on the part of some revolutionary stage artists to
+give to lighting an emotional part in the play, or, in other words, to
+utilize lighting in obtaining the proper mood for the action of the
+play. Color and purely pictorial effect are the dominant notes of some
+of them. All of these modern stage-artists are abandoning the
+intricately realistic setting, and, as a consequence, light is enjoying
+a greater opportunity. In the more common and shallow theatrical
+production, lighting and color effects have many times saved the day,
+and, although these effects are not of the deeper emotional type, they
+may add a spectacular beauty which brings applause where the singing is
+mediocre and the comedy isn't comedy. The potentiality of lighting
+effects for the stage has been barely drawn upon, but as the
+expressiveness of light is more and more utilized on the stage, the art
+of mobile light will be advanced just so much more. Light, color, and
+darkness have many emotional suggestions which are easily understood and
+utilized, but the blending of mobile light with the action is difficult
+because its language is only faintly understood.</p>
+
+<p>It is futile to attempt to describe a future composition of mobile
+light. Certainly there is an extensive variety of possibilities. A
+sunset may be compressed into minutes or an opalescent sky may be a
+motif. Varying intensities of a single hue or of allied hues may serve
+as a gentle melody. Realistic effects may <a class="pagenum" name="Page_355" id="Page_355"></a>be introduced. The
+expressiveness of individual colors may be taken as a basis for
+constructing the various motifs. These may be woven into melody in which
+rhythm both in time and in intensity may be introduced. Action may be
+easily suggested and the number of different colors, in a broad sense,
+which are visible is comparable to the audible tones. Shading is as
+easily accomplished as in music and the development of this art need not
+be inhibited by a lack of mechanical devices and light-sources. The
+tools will be forthcoming if the conscientious artist requests them.</p>
+
+<p>Whatever the future of the art of mobile light may be, it is certain
+that the utilization of the expressiveness of light has barely begun. It
+may be that light-music must pass through the "ragtime" stage of
+fireworks and musical-revue color-effects. If so, it is gratifying to
+know that it is on its way. Certainly it has already served on a higher
+level in some of the artistic lighting effects in which mobility has
+featured to some extent.</p>
+
+<p>If the art does not develop rapidly it will be merely following the
+course of other arts. A vast amount of experimenting will be necessary
+and artists and public alike must learn. But if it ever does develop to
+the level of a fine art its only rival will be music, because the latter
+is the only other abstract art. Material civilization has progressed far
+and artificial light has been a powerful influence. May it not be true
+that artificial light will be responsible for the development of
+spiritual civilization to its highest level? If mobile <a class="pagenum" name="Page_356" id="Page_356"></a>light becomes a
+fine art, it will be man's most abstract achievement in art and it may
+be incomparably finer and more ethereal than music. If this is realized,
+artificial light in every sense may well deserve to be known as the
+torch of civilization.</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_357" id="Page_357"></a>READING REFERENCES</h2>
+
+
+<p>No attempt will be made to give a pretentious bibliography of the
+literature pertaining to the various aspects of artificial lighting, for
+there are many articles widely scattered through many journals. <em>The
+Transactions of the Illuminating Engineering Society</em> afford the most
+fruitful source of further information; the <em>Illuminating Engineer</em>
+(London), contains much of interest; and <em>Zeitschrift f&uuml;r
+Beleuchtungswesen</em> deals with lighting in Germany. H.&nbsp;R. D'Allemagne has
+compiled an elaborate "Historie du Luminaire" which is profusely
+illustrated, and L. von Benesch in his "Beleuchtungswesen" has presented
+many elaborate charts. In both these volumes lighting devices and
+fixtures from the early primitive ones to those of the nineteenth
+century are illustrated. A few of the latest books on lighting, in the
+English language, are "The Art of Illumination," by Bell; "Modern
+Illuminants and Illuminating Engineering," by Gaster and Dow;
+"Radiation, Light and Illumination," by Steinmetz; "The Lighting Art,"
+by Luckiesh; "Illuminating Engineering Practice," consisting of a course
+of lectures presented by various experts under the joint auspices of the
+University of Pennsylvania and the Illuminating Engineering Society;
+"Lectures on Illuminating Engineering," comprising a series of lectures
+presented under the joint auspices of Johns Hopkins University <a class="pagenum" name="Page_358" id="Page_358"></a>and the
+Illuminating Engineering Society; and "The Range of Electric Searchlight
+Projectors," by Rey; "The Electric Arc," by Mrs. Ayrton; "Electric Arc
+Lamps," by Zeidler and Lustgarten, and "The Electric Arc," by Child
+treat the scientific and technical aspects of the arc. G.&nbsp;B. Barham has
+furnished a book on "The Development of the Incandescent Electric Lamp."
+"Color and Its Applications," and "Light and Shade and Their
+Applications," are two books by Luckiesh which deal with lighting from
+unique points of view. "The Language of Color," by Luckiesh, aims to
+present what is definitely known regarding the expressiveness and
+impressiveness of color. W.&nbsp;P. Gerhard has supplied a volume on "The
+American Practice of Gaspiping and Gas Lighting in Buildings," and Leeds
+and Butterfield one on "Acetylene." A recent book in French by V.
+Trudelle treats "Lumi&egrave;re Electrique et ses diff&eacute;rentes Applications <ins class="correction" title="Transcriber's Note: Original reads &quot;an Th&eacute;atre&quot;.">au
+Th&eacute;atre</ins>." Many books
+treat of photometry, power-plants, etc., but these are omitted because
+they deal with phases of light which have not been discussed in the
+present volume. "Light Energy," by Cleaves, is a large volume devoted to
+light-therapy, germicidal action of radiant energy, etc. References to
+individual articles will often be found in the various indexes of
+publications.</p>
+
+
+<p class="center">THE END</p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a class="pagenum" name="Page_359" id="Page_359"></a>INDEX</h2>
+
+
+<div class="center">
+	<table style="width:75%; text-align: center;" border="1" summary="index">
+		<tr>
+			<td><a href="#IX_A">A</a></td>
+			<td><a href="#IX_B">B</a></td>
+			<td><a href="#IX_C">C</a></td>
+			<td><a href="#IX_D">D</a></td>
+			<td><a href="#IX_E">E</a></td>
+			<td><a href="#IX_F">F</a></td>
+			<td><a href="#IX_G">G</a></td>
+			<td><a href="#IX_H">H</a></td>
+			<td><a href="#IX_I">I</a></td>
+			<td><a href="#IX_J">J</a></td>
+			<td><a href="#IX_K">K</a></td>
+			<td><a href="#IX_L">L</a></td>
+			<td><a href="#IX_M">M</a></td>
+		</tr>
+		<tr>
+			<td><a href="#IX_N">N</a></td>
+			<td><a href="#IX_O">O</a></td>
+			<td><a href="#IX_P">P</a></td>
+			<td><a href="#IX_Q">Q</a></td>
+			<td><a href="#IX_R">R</a></td>
+			<td><a href="#IX_S">S</a></td>
+			<td><a href="#IX_T">T</a></td>
+			<td><a href="#IX_U">U</a></td>
+			<td><a href="#IX_V">V</a></td>
+			<td><a href="#IX_W">W</a></td>
+			<td><a href="#IX_X">X</a></td>
+			<td><a href="#IX_Y">Y</a></td>
+			<td><a href="#IX_Z">Z</a></td>
+
+		</tr>
+	</table>
+</div>
+
+<div class="index">
+<ul class="IX">
+<li><a name="IX_A" id="IX_A"></a>Aaron, <a href="#Page_43">43</a></li>
+
+<li>Accidents: <a href="#Page_8">8</a>;
+<ul class="IX">
+<li>street-lighting in relation to, <a href="#Page_225">225</a> <em>et seq.</em>;</li>
+<li>percentage (table) of, due to improper lighting, <a href="#Page_231">231</a></li></ul></li>
+
+<li>Acetylene: <a href="#Page_62">62</a>;
+<ul class="IX">
+<li>light-yield of, <a href="#Page_106">106</a>, <a href="#Page_107">107</a>, <a href="#Page_170">170</a>, <a href="#Page_187">187</a>, <a href="#Page_191">191</a></li></ul></li>
+
+<li>Actinic rays: effect of, upon human organism, <a href="#Page_275">275</a></li>
+
+<li>Africa, public lighting in ancient, <a href="#Page_31">31</a></li>
+
+<li>Agni, god of fire, <a href="#Page_40">40</a></li>
+
+<li>Air-pump, <a href="#Page_130">130</a></li>
+
+<li>Air-raids, <a href="#Page_225">225</a></li>
+
+<li>Alaska, <a href="#Page_18">18</a>, <a href="#Page_29">29</a></li>
+
+<li>Alchemy, <a href="#Page_20">20</a></li>
+
+<li>Aleutians, <a href="#Page_18">18</a></li>
+
+<li>Alexandria, <a href="#Page_43">43</a>, <a href="#Page_163">163</a></li>
+
+<li>Allylene, <a href="#Page_106">106</a></li>
+
+<li>Aluminum, <a href="#Page_108">108</a>, <a href="#Page_179">179</a>, <a href="#Page_180">180</a></li>
+
+<li>Amiens, Treaty of, <a href="#Page_69">69</a></li>
+
+<li>Amylene, <a href="#Page_106">106</a></li>
+
+<li>Aniline dyes, <a href="#Page_106">106</a></li>
+
+<li>Animal: distinction between, and human being, <a href="#Page_3">3</a>; <a href="#Page_15">15</a>;
+<ul class="IX">
+<li>production of light, <a href="#Page_24">24</a> <em>et seq.</em>;</li>
+<li>sources of light, <a href="#Page_30">30</a>, <a href="#Page_31">31</a>;</li>
+<li>oils, <a href="#Page_51">51</a></li></ul></li>
+
+<li>Antimony, <a href="#Page_294">294</a></li>
+
+<li>Antioch, <a href="#Page_153">153</a></li>
+
+<li>Arago, <a href="#Page_114">114</a>, <a href="#Page_196">196</a></li>
+
+<li>Archbishop of Canterbury, <a href="#Page_49">49</a></li>
+
+<li>Archimedes, <a href="#Page_19">19</a></li>
+
+<li>Arc: lamps, <a href="#Page_69">69</a>, <a href="#Page_89">89</a>;
+<ul class="IX">
+<li>electric, <a href="#Page_111">111</a> <em>et seq.</em>;</li>
+<li>distinction between spark and, <a href="#Page_112">112</a>;</li>
+<li>Davy's notes on electric, <a href="#Page_113">113</a>;</li>
+<li>formation of, <a href="#Page_115">115</a>, <a href="#Page_116">116</a>;</li>
+<li>Staite and enclosed, <a href="#Page_117">117</a>, <a href="#Page_118">118</a>;</li>
+<li>principle of enclosed, <a href="#Page_118">118</a>, <a href="#Page_119">119</a>;</li>
+<li>types of, <a href="#Page_120">120</a>;</li>
+<li>flame-, <a href="#Page_121">121</a>, <a href="#Page_122">122</a>;</li>
+<li>luminous, <a href="#Page_122">122</a>;</li>
+<li>electric, <a href="#Page_127">127</a>;</li>
+<li>luminous efficiency of electric (table), <a href="#Page_124">124</a>; <a href="#Page_160">160</a> <em>et seq.</em>;</li>
+<li>-lamp in lighthouses, <a href="#Page_168">168</a> <em>et seq.</em>;</li>
+<li>magnetite-, <a href="#Page_187">187</a>; <a href="#Page_261">261</a></li></ul></li>
+
+<li>Ardois system of signaling, <a href="#Page_199">199</a></li>
+
+<li>Argand, Ami: <a href="#Page_52">52</a>;
+<ul class="IX">
+<li>inaugurates new era in artificial lighting, <a href="#Page_53">53</a>, <a href="#Page_54">54</a>; <a href="#Page_63">63</a>, <a href="#Page_70">70</a>, <a href="#Page_76">76</a>, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_97">97</a>, <a href="#Page_167">167</a>, <a href="#Page_196">196</a></li></ul></li>
+
+<li>Argon, <a href="#Page_137">137</a></li>
+
+<li>Aristophanes, "The Clouds," <a href="#Page_19">19</a></li>
+
+<li>Art Museums, <a href="#Page_9">9</a>, <a href="#Page_13">13</a>, <a href="#Page_322">322</a>, <a href="#Page_323">323</a></li>
+
+<li>Asbestos, <a href="#Page_170">170</a></li>
+
+<li>Asia: public lighting in ancient, <a href="#Page_31">31</a>, <a href="#Page_39">39</a></li>
+
+<li>Automobiles, <a href="#Page_238">238</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_B" id="IX_B"></a>Babylon, <a href="#Page_39">39</a></li>
+
+<li>Bacteria: effect of artificial light upon, <a href="#Page_272">272</a> <em>et seq.</em>; <a href="#Page_281">281</a>, <a href="#Page_282">282</a></li>
+
+<li>Bailey, Prof. L.&nbsp;H., <a href="#Page_250">250</a></li>
+
+<li>Baltimore, <a href="#Page_98">98</a></li>
+
+<li>Bamboo: carbon filaments, <a href="#Page_169">169</a></li>
+
+<li>Bartholdi, <a href="#Page_302">302</a>, <a href="#Page_303">303</a></li>
+
+<li>Beacons. <em>See</em> Lighthouses.</li>
+
+<li>Beck, <a href="#Page_186">186</a></li>
+
+<li>Beecher, <a href="#Page_72">72</a></li>
+
+<li>Beeswax, <a href="#Page_35">35</a>, <a href="#Page_51">51</a></li>
+
+<li>Benzene, <a href="#Page_106">106</a></li>
+
+<li>Bible, cited on importance of artificial light, <a href="#Page_42">42</a>-<a href="#Page_44">44</a></li>
+
+<li>"Bluebird, The," Maeterlinck, <a href="#Page_9">9</a></li>
+
+<li>Blue-prints, <a href="#Page_261">261</a></li>
+
+<li>Bollman, <a href="#Page_98">98</a></li>
+
+<li>Bolton, von, <a href="#Page_132">132</a>, <a href="#Page_133">133</a></li>
+
+<li>Bombs, illuminating, <a href="#Page_182">182</a> <em>et seq.</em></li>
+
+<li>Boston Light, <a href="#Page_164">164</a>, <a href="#Page_165">165</a>, <a href="#Page_166">166</a>, <a href="#Page_177">177</a></li>
+
+<li>Bowditch, production of regenerative lamp by, <a href="#Page_78">78</a>, <a href="#Page_79">79</a></li>
+
+<li>Boy Scouts, <a href="#Page_17">17</a></li>
+
+<li>Bremer, <a href="#Page_120">120</a></li>
+
+<li>Bristol University, <a href="#Page_252">252</a></li>
+
+<li>Brush, <a href="#Page_68">68</a>, <a href="#Page_159">159</a></li>
+
+<li>Building, <a href="#Page_8">8</a></li>
+
+<li>Bunsen, <a href="#Page_81">81</a>, <a href="#Page_85">85</a>, <a href="#Page_89">89</a>, <a href="#Page_148">148</a>, <a href="#Page_149">149</a></li>
+
+<li>Bureau of Mines: cited on open flames, <a href="#Page_234">234</a>; <a href="#Page_236">236</a></li>
+
+<li>Burning-glasses, <a href="#Page_19">19</a>, <a href="#Page_20">20</a>.
+<ul class="IX">
+<li><em>See also</em> Lenses.</li></ul></li>
+
+<li>Butylene, <a href="#Page_106">106</a></li>
+
+<li><a class="pagenum" name="Page_360" id="Page_360"></a>Byzantium, <a href="#Page_34">34</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_C" id="IX_C"></a>C&aelig;sar, <a href="#Page_163">163</a></li>
+
+<li>Canada, <a href="#Page_254">254</a></li>
+
+<li>Candle-hour, defined, <a href="#Page_215">215</a></li>
+
+<li>Candles: progress and, <a href="#Page_7">7</a>; <a href="#Page_25">25</a>, <a href="#Page_28">28</a>, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>, <a href="#Page_33">33</a>;
+<ul class="IX">
+<li>religious uses of, <a href="#Page_34">34</a>, <a href="#Page_35">35</a>;</li>
+<li>as a modern light-source, <a href="#Page_36">36</a>, <a href="#Page_37">37</a>;</li>
+<li>ceremonial uses of, <a href="#Page_38">38</a> <em>et seq.</em>; <a href="#Page_44">44</a>, <a href="#Page_48">48</a>, <a href="#Page_57">57</a>, <a href="#Page_82">82</a>, <a href="#Page_97">97</a>, <a href="#Page_222">222</a>, <a href="#Page_299">299</a>, <a href="#Page_304">304</a></li></ul></li>
+
+<li>Calcium, <a href="#Page_107">107</a>, <a href="#Page_108">108</a></li>
+
+<li>Carbolic acid, <a href="#Page_106">106</a></li>
+
+<li>Carbon: <a href="#Page_53">53</a>, <a href="#Page_80">80</a>, <a href="#Page_81">81</a>;
+<ul class="IX">
+<li>physical characteristics of, <a href="#Page_80">80</a>, <a href="#Page_81">81</a>; <a href="#Page_90">90</a>, <a href="#Page_104">104</a>, <a href="#Page_105">105</a>, <a href="#Page_128">128</a>, <a href="#Page_129">129</a>, <a href="#Page_144">144</a>, <a href="#Page_170">170</a></li></ul></li>
+
+<li>Carbon filament: <a href="#Page_127">127</a> <em>et seq.</em>;
+<ul class="IX">
+<li>preparation of, <a href="#Page_129">129</a>, <a href="#Page_130">130</a>, <a href="#Page_131">131</a>;</li>
+<li>luminous efficiency of, <a href="#Page_131">131</a>, <a href="#Page_132">132</a>;</li>
+<li>lamps, <a href="#Page_161">161</a>;</li>
+<li>lamps in greenhouses, <a href="#Page_250">250</a> <em>et seq.</em></li></ul></li>
+
+<li>Carbons, formation of, <a href="#Page_115">115</a>, <a href="#Page_116">116</a></li>
+
+<li>Carbureted hydrogen, <a href="#Page_75">75</a></li>
+
+<li>Carcel, invention of clockwork lamp by, <a href="#Page_54">54</a>, <a href="#Page_55">55</a></li>
+
+<li>Cat-gut, <a href="#Page_130">130</a></li>
+
+<li>Ceria, <a href="#Page_85">85</a>, <a href="#Page_101">101</a></li>
+
+<li>Charleston, S.&nbsp;C., <a href="#Page_185">185</a></li>
+
+<li>Charcoal: <a href="#Page_113">113</a>;
+<ul class="IX">
+<li>uses of, for electrodes, <a href="#Page_115">115</a></li></ul></li>
+
+<li>Chartered Gas Light and Coke Co., London, <a href="#Page_74">74</a></li>
+
+<li>Chemistry: artificial light and, <a href="#Page_256">256</a>-<a href="#Page_268">268</a></li>
+
+<li>Chicago, <a href="#Page_62">62</a>, <a href="#Page_304">304</a>, <a href="#Page_305">305</a></li>
+
+<li>Chimneys, <a href="#Page_54">54</a>, <a href="#Page_60">60</a>, <a href="#Page_62">62</a></li>
+
+<li>China, <a href="#Page_19">19</a>, <a href="#Page_31">31</a>, <a href="#Page_32">32</a></li>
+
+<li>Chlorate of potash, <a href="#Page_22">22</a></li>
+
+<li>Christ, <a href="#Page_33">33</a>, <a href="#Page_46">46</a>, <a href="#Page_47">47</a></li>
+
+<li>Christians, "children of light," <a href="#Page_42">42</a></li>
+
+<li>Christmas trees, <a href="#Page_43">43</a>, <a href="#Page_304">304</a></li>
+
+<li>Chromium, <a href="#Page_294">294</a></li>
+
+<li>Church of England, <a href="#Page_49">49</a></li>
+
+<li>Cities: economy of artificial lighting in congested, <a href="#Page_13">13</a></li>
+
+<li>Civilization: effect of artificial light upon, <a href="#Page_4">4</a> <em>et seq.</em>;
+<ul class="IX">
+<li>fire and, <a href="#Page_15">15</a></li></ul></li>
+
+<li>Clark, Parker and, <a href="#Page_139">139</a></li>
+
+<li>Clayton, Dr.: invention of portable gas-light by, <a href="#Page_64">64</a>;
+<ul class="IX">
+<li>quoted, <a href="#Page_64">64</a>, <a href="#Page_65">65</a>;</li>
+<li>experiments of, with coal-gas, <a href="#Page_67">67</a></li></ul></li>
+
+<li>Claude, <a href="#Page_147">147</a></li>
+
+<li>Cleaves, Dr., quoted, <a href="#Page_276">276</a>, <a href="#Page_277">277</a></li>
+
+<li>Clegg, Samuel: <a href="#Page_74">74</a>;
+<ul class="IX">
+<li>gas-lighting accomplishments of, <a href="#Page_75">75</a>, <a href="#Page_76">76</a></li></ul></li>
+
+<li>Cleveland, <a href="#Page_159">159</a></li>
+
+<li>&quot;Clouds, The,&quot; Aristophanes, <a href="#Page_19">19</a></li>
+
+<li>Coal: <a href="#Page_32">32</a>;
+<ul class="IX">
+<li>as a light-source, <a href="#Page_55">55</a>;</li>
+<li>supply, <a href="#Page_223">223</a>; <a href="#Page_228">228</a></li></ul></li>
+
+<li>Coal-gas: <a href="#Page_63">63</a> <em>et seq.</em>;
+<ul class="IX">
+<li>public lighting by, developed, <a href="#Page_70">70</a> <em>et seq.</em>;</li>
+<li>analytical production of, <a href="#Page_103">103</a>, <a href="#Page_104">104</a>;</li>
+<li>yield of, retort (table), <a href="#Page_105">105</a>;</li>
+<li>analysis of, <a href="#Page_106">106</a></li></ul></li>
+
+<li>Coal-mines, <a href="#Page_234">234</a> <em>et seq.</em></li>
+
+<li>Cobalt, <a href="#Page_294">294</a></li>
+
+<li>Coke, <a href="#Page_68">68</a>, <a href="#Page_105">105</a></li>
+
+<li>Cologne, <a href="#Page_157">157</a>, <a href="#Page_158">158</a></li>
+
+<li>Colomb, Philip, <a href="#Page_197">197</a></li>
+
+<li>Color: <a href="#Page_9">9</a>;
+<ul class="IX">
+<li>relation of artificial light to, <a href="#Page_284">284</a> <em>et seq.</em></li></ul></li>
+
+<li>Colza, <a href="#Page_31">31</a>, <a href="#Page_52">52</a>, <a href="#Page_167">167</a></li>
+
+<li>Combustion, <a href="#Page_82">82</a> <em>et seq.</em></li>
+
+<li>Commerce, <a href="#Page_8">8</a>, <a href="#Page_97">97</a></li>
+
+<li>Constantine, <a href="#Page_42">42</a></li>
+
+<li>Copper, <a href="#Page_262">262</a>, <a href="#Page_295">295</a></li>
+
+<li>Cornwall, <a href="#Page_63">63</a></li>
+
+<li>Cotton: <a href="#Page_101">101</a>;
+<ul class="IX">
+<li>carbon filaments, <a href="#Page_129">129</a>, <a href="#Page_130">130</a></li></ul></li>
+
+<li>Cromartie, <a href="#Page_78">78</a></li>
+
+<li>Crookes, <a href="#Page_90">90</a>, <a href="#Page_146">146</a></li>
+
+<li>Crosley, Samuel, improvement of gas-meter by, <a href="#Page_76">76</a></li>
+
+<li>Crusies, <a href="#Page_32">32</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_D" id="IX_D"></a>Daguerre, <a href="#Page_258">258</a></li>
+
+<li>Dancing, <a href="#Page_346">346</a></li>
+
+<li>Davy, Sir Humphrey: <a href="#Page_33">33</a>, <a href="#Page_68">68</a>, <a href="#Page_73">73</a>;
+<ul class="IX">
+<li>first use by, of charcoal for sparking points, <a href="#Page_112">112</a>;</li>
+<li>notes of, on electric arc, <a href="#Page_113">113</a>; <a href="#Page_114">114</a></li></ul></li>
+
+<li>Daylight, artificial, <a href="#Page_12">12</a>: <a href="#Page_284">284</a> <em>et seq.</em>;
+<ul class="IX">
+<li>application of, <a href="#Page_287">287</a></li></ul></li>
+
+<li>Daylighting, <a href="#Page_12">12</a>-<a href="#Page_14">14</a></li>
+
+<li>Dollond, <a href="#Page_195">195</a></li>
+
+<li>Doty, <a href="#Page_61">61</a>, <a href="#Page_167">167</a></li>
+
+<li>Drake, Col. E.&nbsp;L., discovery of oil in Pennsylvania by, <a href="#Page_56">56</a></li>
+
+<li>Drummond, Thomas: <a href="#Page_171">171</a>, <a href="#Page_185">185</a>, <a href="#Page_196">196</a>;
+<ul class="IX">
+<li>quoted on signaling, <a href="#Page_197">197</a></li></ul></li>
+
+<li>Dudgeon, Miss, <a href="#Page_251">251</a>, <a href="#Page_252">252</a></li>
+
+<li>Dyes, <a href="#Page_256">256</a>, <a href="#Page_265">265</a></li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_E" id="IX_E"></a><a class="pagenum" name="Page_361" id="Page_361"></a>East Indies, <a href="#Page_29">29</a></li>
+
+<li>Eddystone Light, <a href="#Page_166">166</a>, <a href="#Page_167">167</a></li>
+
+<li>Edison: and problem of electric incandescent filament lamps, <a href="#Page_128">128</a> <em>et seq.</em>; <a href="#Page_129">129</a>;
+<ul class="IX">
+<li>quoted on birth of incandescent lamp, <a href="#Page_130">130</a></li></ul></li>
+
+<li>Edward I, <a href="#Page_274">274</a></li>
+
+<li>Edward VI, <a href="#Page_49">49</a></li>
+
+<li>Efficiency, effect of artificial light upon, <a href="#Page_14">14</a></li>
+
+<li>Eggs: relation of artificial light to production of, <a href="#Page_247">247</a>, <a href="#Page_248">248</a></li>
+
+<li>Egypt: <a href="#Page_31">31</a>;
+<ul class="IX">
+<li>sacredness of light in ancient, <a href="#Page_39">39</a>; <a href="#Page_153">153</a>, <a href="#Page_195">195</a></li></ul></li>
+
+<li>Electric filament: <a href="#Page_81">81</a>, <a href="#Page_127">127</a> <em>et seq.</em>:
+<ul class="IX">
+<li>approximate value of, lamps (table), <a href="#Page_138">138</a></li></ul></li>
+
+<li>Electric pile: construction of, <a href="#Page_111">111</a>; <a href="#Page_127">127</a></li>
+
+<li>Electricity: <a href="#Page_13">13</a>, <a href="#Page_22">22</a>;
+<ul class="IX">
+<li>as a light-source, <a href="#Page_57">57</a>;</li>
+<li>for home-lighting, <a href="#Page_62">62</a>, <a href="#Page_84">84</a>; <a href="#Page_87">87</a>, <a href="#Page_89">89</a>;</li>
+<li>ignition of gas by, <a href="#Page_102">102</a>;</li>
+<li>lighting by, <a href="#Page_109">109</a> <em>et seq.</em></li></ul></li>
+
+<li>Electromagnetic waves, <a href="#Page_68">68</a>, <a href="#Page_86">86</a>, <a href="#Page_87">87</a></li>
+
+<li>Electromagnets, <a href="#Page_114">114</a>, <a href="#Page_116">116</a></li>
+
+<li>Electrodes, <a href="#Page_113">113</a>, <a href="#Page_114">114</a>, <a href="#Page_115">115</a> <em>et seq.</em>;
+<ul class="IX">
+<li>life of, <a href="#Page_122">122</a></li></ul></li>
+
+<li>Elizabeth, Queen, <a href="#Page_274">274</a></li>
+
+<li>England: <a href="#Page_32">32</a>;
+<ul class="IX">
+<li>petroleum discovered in, <a href="#Page_56">56</a>;</li>
+<li>gas-lighting in, <a href="#Page_63">63</a> <em>et seq.</em>; <a href="#Page_166">166</a>, <a href="#Page_251">251</a>, <a href="#Page_274">274</a></li></ul></li>
+
+<li>Erbia, <a href="#Page_85">85</a></li>
+
+<li>Esquimaux: <a href="#Page_18">18</a>;
+<ul class="IX">
+<li>use of artificial light by, <a href="#Page_31">31</a></li></ul></li>
+
+<li>Ethylene, <a href="#Page_106">106</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_F" id="IX_F"></a>Factories: <a href="#Page_13">13</a>;
+<ul class="IX">
+<li>artificial light in, <a href="#Page_239">239</a> <em>et seq.</em></li></ul></li>
+
+<li>Faraday, <a href="#Page_113">113</a></li>
+
+<li>Filaments, carbon, <a href="#Page_129">129</a> <em>et seq.</em></li>
+
+<li>Finsen: <a href="#Page_273">273</a>, <a href="#Page_274">274</a>, <a href="#Page_275">275</a>;
+<ul class="IX">
+<li>on stimulating action of artificial light, <a href="#Page_277">277</a>; <a href="#Page_279">279</a>, <a href="#Page_280">280</a></li></ul></li>
+
+<li>Fire: importance of, to man, <a href="#Page_5">5</a> <em>et seq.</em>;
+<ul class="IX">
+<li>man's dependence upon, <a href="#Page_15">15</a>;</li>
+<li>mythical origin of, <a href="#Page_16">16</a>;</li>
+<li>making, <a href="#Page_17">17</a> <em>et seq.</em>;</li>
+<li>production of, in the stone age, <a href="#Page_18">18</a>;</li>
+<li>in early civilization, <a href="#Page_19">19</a>;</li>
+<li>ancient worship of, <a href="#Page_29">29</a>, <a href="#Page_299">299</a></li></ul></li>
+
+<li>Fireflies: <a href="#Page_24">24</a>, <a href="#Page_81">81</a>, <a href="#Page_96">96</a>, <a href="#Page_148">148</a>, <a href="#Page_149">149</a>, <a href="#Page_150">150</a></li>
+
+<li>"First Men in the Moon, The," H.&nbsp;G. Wells, cited, <a href="#Page_148">148</a></li>
+
+<li>Fish: artificial light as bait for, <a href="#Page_249">249</a></li>
+
+<li>Flame-arcs, <a href="#Page_120">120</a>, <a href="#Page_121">121</a>, <a href="#Page_122">122</a>, <a href="#Page_187">187</a></li>
+
+<li>Flames: <a href="#Page_86">86</a>, <a href="#Page_88">88</a>, <a href="#Page_89">89</a>;
+<ul class="IX">
+<li>open, <a href="#Page_233">233</a>, <a href="#Page_234">234</a> <em>et seq.</em></li></ul></li>
+
+<li>Flint, <a href="#Page_33">33</a></li>
+
+<li>Fool's gold, <a href="#Page_18">18</a></li>
+
+<li>Fort Wagner, <a href="#Page_185">185</a></li>
+
+<li>France: lamps in, <a href="#Page_55">55</a>;
+<ul class="IX">
+<li>early gas-light in, <a href="#Page_72">72</a></li></ul></li>
+
+<li>Franchot, invention of moderator lamps by, <a href="#Page_55">55</a></li>
+
+<li>Frankland, <a href="#Page_77">77</a></li>
+
+<li>Franklin, Benjamin: <a href="#Page_165">165</a>;
+<ul class="IX">
+<li>quoted, <a href="#Page_210">210</a>-<a href="#Page_212">212</a>; <a href="#Page_213">213</a></li></ul></li>
+
+<li>Fresnel, <a href="#Page_167">167</a>, <a href="#Page_196">196</a></li>
+
+<li>Friction, <a href="#Page_16">16</a>, <a href="#Page_17">17</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_G" id="IX_G"></a>Gas: <a href="#Page_13">13</a>, <a href="#Page_22">22</a>;
+<ul class="IX">
+<li>discovery of coal, <a href="#Page_32">32</a>, <a href="#Page_33">33</a>;</li>
+<li>early uses of, as light-source, <a href="#Page_63">63</a> <em>et seq.</em>;</li>
+<li>installment of, pipes in England, <a href="#Page_63">63</a>, <a href="#Page_64">64</a>;</li>
+<li>Shirley's report on Natural, <a href="#Page_66">66</a>, <a href="#Page_67">67</a>;</li>
+<li>first public display of, lighting, <a href="#Page_69">69</a>;</li>
+<li>cost of, lighting, <a href="#Page_71">71</a>;</li>
+<li>first attempt at industrial, lighting, <a href="#Page_72">72</a>;</li>
+<li>first English, company, <a href="#Page_74">74</a>;</li>
+<li>first, explosion, <a href="#Page_75">75</a>;</li>
+<li>house, lighting, <a href="#Page_76">76</a>, <a href="#Page_77">77</a>; <a href="#Page_80">80</a>, <a href="#Page_82">82</a>;</li>
+<li>spectrum of, <a href="#Page_90">90</a>;</li>
+<li>modern, lighting industry, <a href="#Page_97">97</a> <em>et seq.</em>;</li>
+<li>origin of lighting by, <a href="#Page_98">98</a>;</li>
+<li>first, works in America, <a href="#Page_98">98</a>;</li>
+<li>growth of, consumption in United States, <a href="#Page_99">99</a>;</li>
+<li>electrical ignition applied to, lighting, <a href="#Page_102">102</a>;</li>
+<li>pressure, <a href="#Page_102">102</a>, <a href="#Page_103">103</a>;</li>
+<li>water, <a href="#Page_105">105</a>;</li>
+<li>carbons in, <a href="#Page_106">106</a>;</li>
+<li>production of Pintsch, <a href="#Page_109">109</a>, <a href="#Page_110">110</a>;</li>
+<li>salts applied to, flames, <a href="#Page_120">120</a>; <a href="#Page_157">157</a>;</li>
+<li>Census Bureau figures on cost of, plants, <a href="#Page_221">221</a>, <a href="#Page_222">222</a>; <a href="#Page_224">224</a>, <a href="#Page_341">341</a></li></ul></li>
+
+<li>Gas-burners: <a href="#Page_63">63</a>, <a href="#Page_64">64</a>, <a href="#Page_77">77</a>;
+<ul class="IX">
+<li>candle-power of pioneer (table), <a href="#Page_79">79</a>;</li>
+<li>improvements in, <a href="#Page_84">84</a></li></ul></li>
+
+<li>Gas-mantle: <a href="#Page_61">61</a>, <a href="#Page_81">81</a>;
+<ul class="IX">
+<li>influence of, <a href="#Page_99">99</a>;</li>
+<li>characteristics of, <a href="#Page_100">100</a> <em>et seq.</em>; <a href="#Page_187">187</a></li></ul></li>
+
+<li>Gas-meter, Clegg's, <a href="#Page_76">76</a></li>
+
+<li>Gasolene: lamps, <a href="#Page_55">55</a>; <a href="#Page_57">57</a></li>
+
+<li>Gassiot, <a href="#Page_114">114</a></li>
+
+<li><a class="pagenum" name="Page_362" id="Page_362"></a>Gauss, <a href="#Page_196">196</a></li>
+
+<li>Geissler, <a href="#Page_146">146</a></li>
+
+<li>General Electric Company, <a href="#Page_132">132</a>, <a href="#Page_135">135</a>, <a href="#Page_136">136</a></li>
+
+<li>Germany: development of lamps in, <a href="#Page_56">56</a>;
+<ul class="IX">
+<li>early gas-lighting in, <a href="#Page_72">72</a></li></ul></li>
+
+<li>Glass, <a href="#Page_195">195</a>, <a href="#Page_290">290</a> <em>et seq.</em></li>
+
+<li>Glowers, <a href="#Page_139">139</a></li>
+
+<li>Glow-worms, <a href="#Page_24">24</a></li>
+
+<li>Glycerides, <a href="#Page_52">52</a></li>
+
+<li>Gold, <a href="#Page_293">293</a></li>
+
+<li>Gout, <a href="#Page_275">275</a></li>
+
+<li>Gramme dynamo, <a href="#Page_117">117</a></li>
+
+<li>Grass: <a href="#Page_18">18</a>;
+<ul class="IX">
+<li>carbon filaments, <a href="#Page_129">129</a></li></ul></li>
+
+<li>Greece: <a href="#Page_39">39</a>;
+<ul class="IX">
+<li>sacred lamps in ancient, <a href="#Page_41">41</a>; <a href="#Page_42">42</a></li></ul></li>
+
+<li>Greenhouses, carbon-filament lamps in, <a href="#Page_250">250</a> <em>et seq.</em></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_H" id="IX_H"></a>Hall of Fame, <a href="#Page_134">134</a></li>
+
+<li>Happiness, effect of artificial light upon, <a href="#Page_14">14</a></li>
+<li>Hayden and Steinmetz, <a href="#Page_253">253</a></li>
+
+<li>Health, artificial light in relation to, <a href="#Page_269">269</a>-<a href="#Page_283">283</a></li>
+
+<li>Helium, <a href="#Page_89">89</a></li>
+
+<li>Hemig, <a href="#Page_155">155</a></li>
+
+<li>Hemp, <a href="#Page_21">21</a></li>
+
+<li>Henry, William, <a href="#Page_75">75</a></li>
+
+<li>Herodotus, <a href="#Page_56">56</a></li>
+
+<li>Hertz, <a href="#Page_68">68</a></li>
+
+<li>Hertzian waves, <a href="#Page_271">271</a></li>
+
+<li>Hewitt, Cooper, produces mercury-arcs, <a href="#Page_124">124</a>, <a href="#Page_125">125</a></li>
+
+<li>Home: artificial light in relation to, <a href="#Page_6">6</a>;
+<ul class="IX">
+<li>lighting, <a href="#Page_325">325</a> <em>et seq.</em></li></ul></li>
+
+<li>Hindu: light in, ceremonials, <a href="#Page_40">40</a></li>
+
+<li>Hudson-Fulton Celebration, <a href="#Page_306">306</a></li>
+
+<li>Huygens, <a href="#Page_195">195</a></li>
+
+<li>Hydrocarbons, <a href="#Page_82">82</a></li>
+
+<li>Hydrogen, <a href="#Page_81">81</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_I" id="IX_I"></a>Illiteracy, artificial light and, <a href="#Page_9">9</a></li>
+
+<li>Invention, <a href="#Page_7">7</a>, <a href="#Page_97">97</a></li>
+
+<li>Iowa, <a href="#Page_238">238</a></li>
+
+<li>Iridium, <a href="#Page_129">129</a></li>
+
+<li>Iron, <a href="#Page_18">18</a>, <a href="#Page_262">262</a>, <a href="#Page_294">294</a></li>
+
+<li>Iron pyrites, <a href="#Page_18">18</a></li>
+
+<li>Italy, <a href="#Page_249">249</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_J" id="IX_J"></a>Jablochkov: electric candle of, <a href="#Page_117">117</a></li>
+
+<li>Jamaica, <a href="#Page_19">19</a></li>
+
+<li>Jandus, <a href="#Page_118">118</a>, <a href="#Page_122">122</a></li>
+
+<li>Japan: <a href="#Page_19">19</a>;
+<ul class="IX">
+<li>use of oil in, <a href="#Page_30">30</a>; <a href="#Page_281">281</a></li></ul></li>
+
+<li>Jerusalem, <a href="#Page_43">43</a></li>
+
+<li>Jews: artificial light among, <a href="#Page_40">40</a></li>
+
+<li><em>Journal</em>, Paris, quoted, <a href="#Page_210">210</a>-<a href="#Page_212">212</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_K" id="IX_K"></a>Kerosene: <a href="#Page_57">57</a>;
+<ul class="IX">
+<li>weight of, lumens, <a href="#Page_60">60</a>; <a href="#Page_62">62</a>, <a href="#Page_187">187</a>, <a href="#Page_233">233</a></li></ul></li>
+
+<li>Kitson, platinum-gauze mantle applied by, <a href="#Page_61">61</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_L" id="IX_L"></a>Laboratories: achievements of, <a href="#Page_137">137</a></li>
+
+<li>Lamps: <a href="#Page_16">16</a>, <a href="#Page_25">25</a>;
+<ul class="IX">
+<li>Roman, <a href="#Page_30">30</a>; <a href="#Page_31">31</a>;</li>
+<li>invention of safety, <a href="#Page_33">33</a>;</li>
+<li>ancient funereal, <a href="#Page_39">39</a>;</li>
+<li>sacred, of antiquity, <a href="#Page_41">41</a>;</li>
+<li>ceremonial, <a href="#Page_44">44</a>;</li>
+<li>scientific development of oil, <a href="#Page_51">51</a> <em>et seq.</em>;</li>
+<li>Holliday, <a href="#Page_55">55</a>;</li>
+<li>Carcel, <a href="#Page_54">54</a>, <a href="#Page_55">55</a>;</li>
+<li>Franchot's moderator, <a href="#Page_55">55</a>;</li>
+<li>gasolene, <a href="#Page_55">55</a>;</li>
+<li>development of, in Germany, <a href="#Page_56">56</a>;</li>
+<li>air pressure, <a href="#Page_61">61</a>;</li>
+<li>supremacy of oil, ends, <a href="#Page_62">62</a>;</li>
+<li>Bowditch's, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>; <a href="#Page_80">80</a>, <a href="#Page_97">97</a>;</li>
+<li>mercury-arc, <a href="#Page_126">126</a>;</li>
+<li>electric incandescent filament, <a href="#Page_127">127</a> <em>et seq.</em>;</li>
+<li>gem, <a href="#Page_132">132</a>;</li>
+<li>tungsten, <a href="#Page_133">133</a> <em>et seq.</em>;</li>
+<li>luminous efficiency (table) of incandescent filament, <a href="#Page_141">141</a>; <a href="#Page_299">299</a>;</li>
+<li>in home, <a href="#Page_328">328</a>-<a href="#Page_333">333</a></li></ul></li>
+
+<li>Lange, <a href="#Page_167">167</a></li>
+
+<li>Lard-oil, <a href="#Page_51">51</a></li>
+
+<li>Lavoisier, <a href="#Page_195">195</a></li>
+
+<li>Lead, <a href="#Page_262">262</a>, <a href="#Page_294">294</a></li>
+
+<li>Le Bon, <a href="#Page_72">72</a></li>
+
+<li>"Legend of Montrose, The," Scott, cited on primitive lighting, <a href="#Page_27">27</a></li>
+
+<li>Leigh, Edmund, quoted, <a href="#Page_226">226</a></li>
+
+<li>Lenses, <a href="#Page_20">20</a>, <a href="#Page_171">171</a> <em>et seq.</em></li>
+
+<li>Libanius, quoted, <a href="#Page_153">153</a>, <a href="#Page_154">154</a></li>
+
+<li>Liberty, Statue of, <a href="#Page_301">301</a>, <a href="#Page_302">302</a>, <a href="#Page_303">303</a></li>
+
+<li>Libraries, <a href="#Page_9">9</a></li>
+
+<li>Light: relation of artificial, to progress, <a href="#Page_3">3</a> <em>et seq.</em>;
+<ul class="IX">
+<li>as a civilizing agency, <a href="#Page_3">3</a>-<a href="#Page_14">14</a>;</li>
+<li>primitive man and artificial, <a href="#Page_4">4</a>;</li>
+<li>Milton, quoted on importance of, <a href="#Page_5">5</a>;</li>
+<li>artificial, and science, <a href="#Page_7">7</a>;</li>
+<li>artificial, and industrial development, <a href="#Page_8">8</a>;</li>
+<li>Maeterlinck's tribute to, <a href="#Page_9">9</a>;</li>
+<li>Lincoln's debt to artificial, <a href="#Page_9">9</a>;</li>
+<li>symbolism of, <a href="#Page_9">9</a>, <a href="#Page_10">10</a>;</li>
+<li>therapy, <a href="#Page_10">10</a>;</li>
+<li>in war, <a href="#Page_11">11</a>;</li>
+<li>adaptations of, <a href="#Page_12">12</a>; <a href="#Page_13">13</a>;</li>
+<li><a class="pagenum" name="Page_363" id="Page_363"></a>mythical origin of artificial, <a href="#Page_16">16</a>;</li>
+<li>earliest source of, <a href="#Page_16">16</a>;</li>
+<li>production of, in stone age, <a href="#Page_18">18</a>;</li>
+<li>matches as source of, <a href="#Page_21">21</a>;</li>
+<li>animals as, sources, <a href="#Page_24">24</a>, <a href="#Page_25">25</a>;</li>
+<li>primitive sources of, <a href="#Page_24">24</a>-<a href="#Page_37">37</a>;</li>
+<li>evolution of artificial, sources, <a href="#Page_24">24</a>-<a href="#Page_37">37</a>;</li>
+<li>development, <a href="#Page_28">28</a> <em>et seq.</em>;</li>
+<li>early outdoor use of artificial, <a href="#Page_28">28</a>;</li>
+<li>Roman uses of artificial, <a href="#Page_30">30</a>;</li>
+<li>beginning of scientific, <a href="#Page_33">33</a>, <a href="#Page_34">34</a>;</li>
+<li>candles as modern, source, <a href="#Page_36">36</a>, <a href="#Page_37">37</a>;</li>
+<li>symbolism and religious uses of, <a href="#Page_38">38</a> <em>et seq.</em>;</li>
+<li>Bible cited on artificial, <a href="#Page_42">42</a>-<a href="#Page_44">44</a>;</li>
+<li>in relation to worship, <a href="#Page_43">43</a>, <a href="#Page_45">45</a>, <a href="#Page_46">46</a>;</li>
+<li>Argand's contribution to, <a href="#Page_53">53</a>, <a href="#Page_54">54</a>;</li>
+<li>coal as, source, <a href="#Page_55">55</a>;</li>
+<li>early uses of gas as, source, <a href="#Page_63">63</a> <em>et seq.</em>;</li>
+<li>as a public utility, <a href="#Page_70">70</a>;</li>
+<li>first installation of industrial gas, <a href="#Page_72">72</a>;</li>
+<li>science of, production, <a href="#Page_80">80</a> <em>et seq.</em>;</li>
+<li>causes of, radiation, <a href="#Page_80">80</a>, <a href="#Page_81">81</a>; <a href="#Page_83">83</a>;</li>
+<li>lime, <a href="#Page_84">84</a>; electric, <a href="#Page_89">89</a> <em>et seq.</em>;</li>
+<li>principle of, production, <a href="#Page_90">90</a>, <a href="#Page_91">91</a>;</li>
+<li>sources, <a href="#Page_93">93</a>;</li>
+<li>various gas-burners', supply, <a href="#Page_95">95</a>;</li>
+<li>relative efficiency of, sources, <a href="#Page_95">95</a>, <a href="#Page_96">96</a>;</li>
+<li>in the home, <a href="#Page_97">97</a>;</li>
+<li>influence of, upon science, invention, and commerce, <a href="#Page_97">97</a> <em>et seq.</em>;</li>
+<li>yield of acetylene, <a href="#Page_106">106</a>, <a href="#Page_107">107</a>;</li>
+<li>electric, <a href="#Page_109">109</a>;</li>
+<li>influence of gas upon development of artificial, <a href="#Page_110">110</a>;</li>
+<li>development of artificial, <a href="#Page_111">111</a> <em>et seq.</em>;</li>
+<li>efforts to improve color of mercury-arc, <a href="#Page_125">125</a>;</li>
+<li>electric-incandescent-filament, <a href="#Page_127">127</a> <em>et seq.</em>;</li>
+<li>effect of tungsten, upon, <a href="#Page_133">133</a> <em>et seq.</em>;</li>
+<li>of the future, <a href="#Page_143">143</a>-<a href="#Page_152">152</a>;</li>
+<li>in warfare, <a href="#Page_178">178</a>-<a href="#Page_193">193</a>;</li>
+<li>signaling, <a href="#Page_194">194</a>-<a href="#Page_207">207</a>;</li>
+<li>cost of, <a href="#Page_208">208</a>-<a href="#Page_224">224</a>;</li>
+<li>and safety, <a href="#Page_225">225</a> <em>et seq.</em>;</li>
+<li>improper use of, <a href="#Page_229">229</a>, <a href="#Page_230">230</a>;</li>
+<li>comparison of daylight and artificial, <a href="#Page_240">240</a>;</li>
+<li>reducing action of, <a href="#Page_258">258</a>;</li>
+<li>bactericidal action of, <a href="#Page_272">272</a> <em>et seq.</em>;</li>
+<li>modifying, <a href="#Page_284">284</a> <em>et seq.</em>;</li>
+<li>spectacular uses of, <a href="#Page_298">298</a>-<a href="#Page_309">309</a>;</li>
+<li>expressiveness of, <a href="#Page_310">310</a>-<a href="#Page_324">324</a>;</li>
+<li>utility of modern, <a href="#Page_325">325</a>-<a href="#Page_340">340</a>;</li>
+<li>evolution of the art of applying, <a href="#Page_341">341</a>-<a href="#Page_356">356</a>;</li>
+<li>mobile, <a href="#Page_347">347</a>, <a href="#Page_348">348</a>, <a href="#Page_349">349</a>, <a href="#Page_350">350</a>;</li>
+<li>psychological effect of, <a href="#Page_351">351</a> <em>et seq.</em>;</li>
+<li>as an accompaniment to music, <a href="#Page_352">352</a>-<a href="#Page_354">354</a></li></ul></li>
+
+<li>Light-buoys, <a href="#Page_10">10</a>, <a href="#Page_169">169</a></li>
+
+<li>Lighthouses: <a href="#Page_10">10</a>, <a href="#Page_163">163</a>-<a href="#Page_177">177</a>;
+<ul class="IX">
+<li>optical apparatus of, <a href="#Page_172">172</a> <em>et seq.</em></li></ul></li>
+
+<li>Light-ships, <a href="#Page_10">10</a>, <a href="#Page_169">169</a></li>
+
+<li>Lighting-systems: comparison of, <a href="#Page_12">12</a>-<a href="#Page_14">14</a></li>
+
+<li>Lime, <a href="#Page_84">84</a>, <a href="#Page_107">107</a>, <a href="#Page_108">108</a>, <a href="#Page_294">294</a></li>
+
+<li>Lincoln, Abraham, <a href="#Page_9">9</a></li>
+
+<li>Linen, <a href="#Page_18">18</a></li>
+
+<li>Link-buoys, <a href="#Page_28">28</a></li>
+
+<li>Lithopone, <a href="#Page_265">265</a>, <a href="#Page_266">266</a></li>
+
+<li>Liverpool, <a href="#Page_167">167</a></li>
+
+<li>Living: comparison of, standards, <a href="#Page_238">238</a> <em>et seq.</em></li>
+
+<li>London, <a href="#Page_152">152</a>, <a href="#Page_154">154</a>, <a href="#Page_155">155</a>, <a href="#Page_156">156</a>, <a href="#Page_157">157</a>, <a href="#Page_202">202</a></li>
+
+<li>London Gas Light and Coke Company, <a href="#Page_74">74</a></li>
+
+<li>Lucigen, <a href="#Page_61">61</a></li>
+
+<li>Lumen-hour: defined, <a href="#Page_215">215</a></li>
+
+<li>Lumens: <a href="#Page_60">60</a>, <a href="#Page_94">94</a>, <a href="#Page_215">215</a></li>
+
+<li>Lutheran Church, <a href="#Page_49">49</a></li>
+
+<li>Lyceum Theatre, London, <a href="#Page_73">73</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_M" id="IX_M"></a>Maeterlinck, Maurice, <a href="#Page_9">9</a></li>
+
+<li>Magazines, <a href="#Page_8">8</a></li>
+
+<li>Magdsick, H.&nbsp;H., <a href="#Page_303">303</a></li>
+
+<li>Magnesia: <a href="#Page_84">84</a>;
+<ul class="IX">
+<li>Nernst's application of, <a href="#Page_138">138</a></li></ul></li>
+
+<li>Magnesium, <a href="#Page_179">179</a>, <a href="#Page_180">180</a></li>
+
+<li>Magnetite arc, <a href="#Page_187">187</a></li>
+
+<li>Man: distinction between, and animal, <a href="#Page_3">3</a>;
+<ul class="IX">
+<li>artificial light and early, <a href="#Page_4">4</a>;</li>
+<li>light-sources of primitive, <a href="#Page_25">25</a></li></ul></li>
+
+<li>Manganese, <a href="#Page_262">262</a>, <a href="#Page_268">268</a>, <a href="#Page_294">294</a></li>
+
+<li>Mangin, <a href="#Page_188">188</a></li>
+
+<li>Mann, <a href="#Page_129">129</a></li>
+
+<li>Mantles, <a href="#Page_95">95</a></li>
+
+<li>Manufacturing, <a href="#Page_8">8</a></li>
+
+<li>Marconi, <a href="#Page_68">68</a></li>
+
+<li>Marks, <a href="#Page_118">118</a></li>
+
+<li>Matches: as light-sources, <a href="#Page_21">21</a>; <a href="#Page_22">22</a>, <a href="#Page_82">82</a></li>
+
+<li>Maxwell, <a href="#Page_68">68</a></li>
+
+<li>Mazda lamps, <a href="#Page_289">289</a>, <a href="#Page_339">339</a></li>
+
+<li>Mecca, <a href="#Page_40">40</a></li>
+
+<li>Mediterranean Sea, <a href="#Page_163">163</a></li>
+
+<li>Mercury-arc: Way's, <a href="#Page_124">124</a>; <a href="#Page_125">125</a>, <a class="pagenum" name="Page_364" id="Page_364"></a><a href="#Page_126">126</a>;
+<ul class="IX">
+<li>quartz, <a href="#Page_125">125</a>, <a href="#Page_126">126</a>;</li>
+<li>attempts to improve color of, light, <a href="#Page_125">125</a></li></ul></li>
+
+<li>Middle Ages, <a href="#Page_46">46</a>, <a href="#Page_47">47</a>, <a href="#Page_274">274</a></li>
+
+<li>Milton, quoted, <a href="#Page_5">5</a></li>
+
+<li>Mirror, <a href="#Page_19">19</a></li>
+
+<li>Mohammedans, <a href="#Page_40">40</a></li>
+
+<li>Moore, Dr. McFarlan, <a href="#Page_146">146</a>, <a href="#Page_147">147</a></li>
+
+<li>Morality, effect of light upon, <a href="#Page_9">9</a></li>
+
+<li>Morse code: application of, to light-signaling, <a href="#Page_198">198</a>, <a href="#Page_199">199</a></li>
+
+<li>Moses, <a href="#Page_195">195</a></li>
+
+<li>Moving-pictures, <a href="#Page_9">9</a>, <a href="#Page_260">260</a>, <a href="#Page_261">261</a></li>
+
+<li>Munich, <a href="#Page_72">72</a></li>
+
+<li>Murdock, William: installment of gas-pipes by, <a href="#Page_63">63</a>; <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_70">70</a>;
+<ul class="IX">
+<li>quoted on industrial use of artificial, <a href="#Page_71">71</a>; <a href="#Page_72">72</a>, <a href="#Page_73">73</a>, <a href="#Page_74">74</a>, <a href="#Page_76">76</a>, <a href="#Page_78">78</a>, <a href="#Page_217">217</a>, <a href="#Page_309">309</a></li></ul></li>
+
+<li>Museums: <a href="#Page_13">13</a>;
+<ul class="IX">
+<li>utilization of artificial light by, <a href="#Page_322">322</a>, <a href="#Page_323">323</a></li></ul></li>
+
+<li>Music: light as an accompaniment to, <a href="#Page_352">352</a>-<a href="#Page_354">354</a></li>
+
+<li>Mythology, <a href="#Page_16">16</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_N" id="IX_N"></a>Nantes, <a href="#Page_85">85</a></li>
+
+<li>Napoleon, <a href="#Page_111">111</a></li>
+
+<li>Napthalene, <a href="#Page_106">106</a></li>
+
+<li>National Heat and Light Co., <a href="#Page_72">72</a>, <a href="#Page_74">74</a></li>
+
+<li>Natural gas, <a href="#Page_99">99</a></li>
+
+<li>Navesink Light, <a href="#Page_206">206</a></li>
+
+<li>Nernst, <a href="#Page_138">138</a>, <a href="#Page_139">139</a></li>
+
+<li>Newspapers, <a href="#Page_8">8</a></li>
+
+<li>Newton, Sir Isaac: <a href="#Page_7">7</a>;
+<ul class="IX">
+<li>quoted on discovery of visible spectrum, <a href="#Page_87">87</a>; <a href="#Page_88">88</a></li></ul></li>
+
+<li>New York, <a href="#Page_98">98</a>, <a href="#Page_165">165</a>, <a href="#Page_166">166</a>, <a href="#Page_206">206</a>, <a href="#Page_302">302</a>, <a href="#Page_304">304</a></li>
+
+<li>Niagara Falls, <a href="#Page_108">108</a>, <a href="#Page_306">306</a></li>
+
+<li>Nickel, <a href="#Page_262">262</a></li>
+
+<li>Nielson, <a href="#Page_77">77</a></li>
+
+<li>Niepce, <a href="#Page_258">258</a></li>
+
+<li>Niter, <a href="#Page_21">21</a></li>
+
+<li>Nitrogen, <a href="#Page_137">137</a></li>
+
+<li>Norfolk, <a href="#Page_169">169</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_O" id="IX_O"></a>Obesity, <a href="#Page_275">275</a></li>
+
+<li>Offices, <a href="#Page_13">13</a></li>
+
+<li>Oil: as a light-source, <a href="#Page_29">29</a> <em>et seq.</em>;
+<ul class="IX">
+<li>development of, lamps, <a href="#Page_51">51</a> <em>et seq.</em>; <a href="#Page_155">155</a>;</li>
+<li>in lighthouse, <a href="#Page_165">165</a> <em>et seq.</em>; <a href="#Page_222">222</a>, <a href="#Page_224">224</a>, <a href="#Page_299">299</a></li></ul></li>
+
+<li>O'Leary, Mrs., and her lamp, <a href="#Page_62">62</a></li>
+
+<li>Olive-oil, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>, <a href="#Page_167">167</a></li>
+
+<li>Orkney Islands, <a href="#Page_29">29</a>, <a href="#Page_177">177</a></li>
+
+<li>Osmium, <a href="#Page_133">133</a></li>
+
+<li>Oxygen: relative consumption of, by oil-lamps, <a href="#Page_58">58</a>, <a href="#Page_59">59</a>; <a href="#Page_262">262</a></li>
+
+<li>Ozone, <a href="#Page_262">262</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_P" id="IX_P"></a>Painting, <a href="#Page_342">342</a>, <a href="#Page_343">343</a>, <a href="#Page_347">347</a>, <a href="#Page_348">348</a>, <a href="#Page_349">349</a></li>
+
+<li>Pall Mall, <a href="#Page_74">74</a></li>
+
+<li>Panama-Pacific Exposition: <a href="#Page_304">304</a>;
+<ul class="IX">
+<li>artificial lighting of, <a href="#Page_306">306</a>, <a href="#Page_307">307</a>, <a href="#Page_308">308</a>, <a href="#Page_309">309</a></li></ul></li>
+
+<li>Paper: <a href="#Page_18">18</a>;
+<ul class="IX">
+<li>carbon filaments, <a href="#Page_129">129</a>, <a href="#Page_130">130</a></li></ul></li>
+
+<li>Paraffin, <a href="#Page_35">35</a>, <a href="#Page_57">57</a></li>
+
+<li>Parker and Clark, <a href="#Page_139">139</a></li>
+
+<li>Paris: experimental gas-lighting in, <a href="#Page_83">83</a>, <a href="#Page_84">84</a>;
+<ul class="IX">
+<li>Volta in, <a href="#Page_111">111</a>; <a href="#Page_154">154</a>, <a href="#Page_185">185</a>, <a href="#Page_210">210</a>, <a href="#Page_212">212</a>, <a href="#Page_213">213</a></li></ul></li>
+
+<li>Peckham, John, <a href="#Page_195">195</a></li>
+
+<li>Pennsylvania: discovery of oil in, <a href="#Page_56">56</a></li>
+
+<li>Periodic Law, <a href="#Page_145">145</a></li>
+
+<li>Petroleum: <a href="#Page_35">35</a>, <a href="#Page_51">51</a>, <a href="#Page_55">55</a>;
+<ul class="IX">
+<li>discovery of, <a href="#Page_56">56</a>;</li>
+<li>constitution of crude, <a href="#Page_57">57</a>; <a href="#Page_58">58</a>, <a href="#Page_214">214</a></li></ul></li>
+
+<li>Pharos, <a href="#Page_163">163</a></li>
+
+<li>Philadelphia, <a href="#Page_98">98</a>, <a href="#Page_99">99</a>, <a href="#Page_157">157</a></li>
+
+<li>Phillips and Lee, <a href="#Page_70">70</a>, <a href="#Page_72">72</a></li>
+
+<li>"Philosophical Transactions of the Royal Society of London," <a href="#Page_33">33</a>;
+<ul class="IX">
+<li>quoted on industrial lighting, <a href="#Page_63">63</a>;</li>
+<li>Shirley's report on natural gas in, <a href="#Page_66">66</a>, <a href="#Page_67">67</a>;</li>
+<li>quoted, <a href="#Page_87">87</a></li></ul></li>
+
+<li>Ph&oelig;nicians, <a href="#Page_34">34</a>, <a href="#Page_39">39</a></li>
+
+<li>Phosphorus, <a href="#Page_21">21</a></li>
+
+<li><ins class="correction" title="Transcriber's Note: Original reads &quot;Photo-micography&quot;.">Photo-micrography</ins>, <a href="#Page_12">12</a></li>
+
+<li>Photography: <a href="#Page_126">126</a>;
+<ul class="IX">
+<li>early experiments in, <a href="#Page_258">258</a>;</li>
+<li>development of, <a href="#Page_259">259</a>; <a href="#Page_291">291</a>, <a href="#Page_292">292</a></li></ul></li>
+
+<li>Picric acid, <a href="#Page_106">106</a></li>
+
+<li>Pigments, <a href="#Page_265">265</a></li>
+
+<li>Pintsch: production of, gas, <a href="#Page_109">109</a>, <a href="#Page_110">110</a>, <a href="#Page_170">170</a></li>
+
+<li>Pitch, <a href="#Page_106">106</a></li>
+
+<li>Plant-growth: artificial light and, <a href="#Page_11">11</a>, <a href="#Page_249">249</a> <em>et seq.</em></li>
+
+<li>Platinum, <a href="#Page_85">85</a>, <a href="#Page_128">128</a>, <a href="#Page_129">129</a>, <a href="#Page_262">262</a></li>
+
+<li>Plumbago, <a href="#Page_113">113</a>, <a href="#Page_130">130</a></li>
+
+<li>Plymouth, <a href="#Page_166">166</a></li>
+
+<li>Poetry, <a href="#Page_346">346</a></li>
+
+<li><a class="pagenum" name="Page_365" id="Page_365"></a>Police, <a href="#Page_162">162</a></li>
+
+<li>Potash, chlorate of, <a href="#Page_22">22</a></li>
+
+<li>Priestley, Professor, quoted, <a href="#Page_252">252</a></li>
+
+<li>Printing, <a href="#Page_8">8</a></li>
+
+<li>Progress: influence of fire upon, <a href="#Page_15">15</a> <em>et seq.</em></li>
+
+<li>Prometheus, <a href="#Page_16">16</a>, <a href="#Page_41">41</a></li>
+
+<li>Propylene, <a href="#Page_106">106</a></li>
+
+<li>Ptolemy II, <a href="#Page_163">163</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_Q" id="IX_Q"></a>Quartz: <a href="#Page_18">18</a>, <a href="#Page_19">19</a>;
+<ul class="IX">
+<li>mercury-arcs, <a href="#Page_125">125</a>;</li>
+<li>uses of, <a href="#Page_126">126</a>;</li>
+<li>in skin diseases, <a href="#Page_278">278</a>, <a href="#Page_279">279</a></li></ul></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_R" id="IX_R"></a>Radiators, energy, <a href="#Page_88">88</a> <em>et seq.</em></li>
+
+<li>Radium, <a href="#Page_150">150</a></li>
+
+<li>Railway Signal Association, <a href="#Page_205">205</a></li>
+
+<li>Railways: light-signaling applied to, <a href="#Page_205">205</a></li>
+
+<li>Ramie fiber, <a href="#Page_101">101</a></li>
+
+<li>Rane, <a href="#Page_250">250</a>, <a href="#Page_251">251</a></li>
+
+<li>Rare-earth oxides: <a href="#Page_85">85</a>;
+<ul class="IX">
+<li>properties of, <a href="#Page_88">88</a>, <a href="#Page_99">99</a></li></ul></li>
+
+<li>Recreation, <a href="#Page_9">9</a></li>
+
+<li>Redruth, <a href="#Page_63">63</a></li>
+
+<li>Reformation: ceremonial uses of light during the, <a href="#Page_48">48</a>, <a href="#Page_49">49</a></li>
+
+<li>Rheumatism, <a href="#Page_275">275</a></li>
+
+<li>Robins, Benjamin, <a href="#Page_201">201</a></li>
+
+<li>Rome, <a href="#Page_30">30</a>, <a href="#Page_32">32</a>, <a href="#Page_34">34</a>, <a href="#Page_39">39</a>, <a href="#Page_41">41</a>, <a href="#Page_42">42</a>, <a href="#Page_44">44</a></li>
+
+<li>R&ouml;ntgen, <a href="#Page_270">270</a>, <a href="#Page_280">280</a>.
+  <ul class="IX"><li><em>See also</em> X-ray.</li></ul></li>
+
+<li>Royal Society of London: <a href="#Page_33">33</a>, <a href="#Page_63">63</a>, <a href="#Page_66">66</a>, <a href="#Page_67">67</a>, <a href="#Page_70">70</a>, <a href="#Page_73">73</a>;
+<ul class="IX">
+<li>and first gas explosion, <a href="#Page_75">75</a>, <a href="#Page_111">111</a>, <a href="#Page_112">112</a></li></ul></li>
+
+<li>Rumford, <a href="#Page_167">167</a></li>
+
+<li>Rushlights, <a href="#Page_28">28</a>, <a href="#Page_33">33</a></li>
+
+<li>Russia, <a href="#Page_281">281</a></li>
+
+<li>Ryan, W.&nbsp;D'A., <a href="#Page_306">306</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_S" id="IX_S"></a>Safety: artificial light in relation to, <a href="#Page_14">14</a>, <a href="#Page_225">225</a> <em>et seq.</em></li>
+
+<li>Salts: chemical, <a href="#Page_88">88</a>, <a href="#Page_89">89</a>;
+<ul class="IX">
+<li>metallic, <a href="#Page_120">120</a>;</li>
+<li>silver, <a href="#Page_257">257</a>, <a href="#Page_258">258</a></li></ul></li>
+
+<li>Sandy Hook Light, <a href="#Page_165">165</a>, <a href="#Page_166">166</a></li>
+
+<li>San Francisco, <a href="#Page_304">304</a>, <a href="#Page_306">306</a>-<a href="#Page_309">309</a></li>
+
+<li>Savages, <a href="#Page_3">3</a>, <a href="#Page_15">15</a>, <a href="#Page_17">17</a></li>
+
+<li>Sawyer, <a href="#Page_129">129</a></li>
+
+<li>Scheele, K.&nbsp;W., <a href="#Page_133">133</a>;
+<ul class="IX">
+<li>quoted, <a href="#Page_257">257</a>, <a href="#Page_258">258</a></li></ul></li>
+
+<li>Schools, <a href="#Page_9">9</a></li>
+
+<li>Science: light and, <a href="#Page_6">6</a>, <a href="#Page_7">7</a>; <a href="#Page_97">97</a>;
+<ul class="IX">
+<li>systematized, <a href="#Page_268">268</a></li></ul></li>
+
+<li>Scotland: <a href="#Page_26">26</a>, <a href="#Page_31">31</a>, <a href="#Page_32">32</a>, <a href="#Page_48">48</a>;
+<ul class="IX">
+<li>oil industry in, <a href="#Page_56">56</a></li></ul></li>
+
+<li>Scott, Sir Walter, cited, <a href="#Page_27">27</a>, <a href="#Page_98">98</a></li>
+
+<li>Sculpture: artificial light in relation to, <a href="#Page_184">184</a></li>
+
+<li>Search-lights, <a href="#Page_11">11</a>, <a href="#Page_169">169</a></li>
+
+<li>Section of Plant Protection, <a href="#Page_225">225</a>, <a href="#Page_226">226</a></li>
+
+<li>Selenium, <a href="#Page_267">267</a>, <a href="#Page_293">293</a></li>
+
+<li>Semaphore, <a href="#Page_199">199</a></li>
+
+<li>Shells: illuminating, <a href="#Page_179">179</a> <em>et seq.</em></li>
+
+<li>Shirley, Thomas: quoted on natural gas, <a href="#Page_66">66</a>, <a href="#Page_67">67</a></li>
+
+<li><ins class="correction" title="Transcriber's Note: Original reads &quot;Siemans&quot;.">Siemens</ins>, <a href="#Page_78">78</a></li>
+
+<li>Signaling, <a href="#Page_194">194</a>-<a href="#Page_207">207</a></li>
+
+<li>Silicon: filament, <a href="#Page_140">140</a></li>
+
+<li>Silk: artificial, <a href="#Page_101">101</a>;
+<ul class="IX">
+<li>carbon-filaments, <a href="#Page_129">129</a></li></ul></li>
+
+<li>Simpson, R.&nbsp;E., <a href="#Page_227">227</a>, <a href="#Page_231">231</a></li>
+
+<li>Silver, <a href="#Page_258">258</a>, <a href="#Page_293">293</a></li>
+
+<li>Skin diseases: treatment of, <a href="#Page_278">278</a>, <a href="#Page_279">279</a>, <a href="#Page_280">280</a></li>
+
+<li>Skylights, <a href="#Page_13">13</a></li>
+
+<li>Sleep, <a href="#Page_8">8</a></li>
+
+<li>Smallpox, <a href="#Page_274">274</a>, <a href="#Page_275">275</a></li>
+
+<li>Smeaton, <a href="#Page_166">166</a></li>
+
+<li>Soho, <a href="#Page_69">69</a>, <a href="#Page_72">72</a></li>
+
+<li>South Africa, <a href="#Page_129">129</a></li>
+
+<li>Sparks: <a href="#Page_33">33</a>, <a href="#Page_125">125</a></li>
+
+<li>Spectrum: visible, <a href="#Page_86">86</a>;
+<ul class="IX">
+<li>Newton quoted on, <a href="#Page_87">87</a>;</li>
+<li>of elements, <a href="#Page_89">89</a>;</li>
+<li>of gases, <a href="#Page_90">90</a>; <a href="#Page_120">120</a>, <a href="#Page_121">121</a>;</li>
+<li>mercury, <a href="#Page_124">124</a>-<a href="#Page_126">126</a></li></ul></li>
+
+<li>Sperm, <a href="#Page_31">31</a>, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>, <a href="#Page_167">167</a></li>
+
+<li>Spermaceti, <a href="#Page_35">35</a>, <a href="#Page_51">51</a></li>
+
+<li>Splinter-holders, <a href="#Page_27">27</a>, <a href="#Page_28">28</a></li>
+
+<li>Stage: and artificial light, <a href="#Page_319">319</a> <em>et seq.</em>; <a href="#Page_343">343</a></li>
+
+<li>Staite, <a href="#Page_117">117</a>, <a href="#Page_118">118</a></li>
+
+<li>Stearine, <a href="#Page_35">35</a>, <a href="#Page_52">52</a></li>
+
+<li>Stearn, <a href="#Page_129">129</a></li>
+
+<li>Steel, <a href="#Page_18">18</a>, <a href="#Page_33">33</a></li>
+
+<li>Steinmetz, Hayden and, <a href="#Page_253">253</a></li>
+
+<li>Sterilization: quartz-mercury-arc and, <a href="#Page_280">280</a>, <a href="#Page_281">281</a>, <a href="#Page_282">282</a></li>
+
+<li>Stevenson, Robert Louis, quoted, <a href="#Page_177">177</a></li>
+
+<li>Stores, <a href="#Page_13">13</a></li>
+
+<li>St. Paul, <a href="#Page_43">43</a></li>
+
+<li>St. Paul's Cathedral, <a href="#Page_300">300</a></li>
+
+<li><a class="pagenum" name="Page_366" id="Page_366"></a>Street-lighting: development of, <a href="#Page_152">152</a>-<a href="#Page_162">162</a></li>
+
+<li>Sugar, <a href="#Page_22">22</a></li>
+
+<li>Sulphide of iron, <a href="#Page_18">18</a></li>
+
+<li>Sulphur, <a href="#Page_18">18</a>, <a href="#Page_21">21</a>, <a href="#Page_179">179</a>, <a href="#Page_180">180</a>, <a href="#Page_294">294</a></li>
+
+<li>Sulphuric acid, <a href="#Page_21">21</a>, <a href="#Page_22">22</a></li>
+
+<li>Sun, <a href="#Page_8">8</a>, <a href="#Page_16">16</a>, <a href="#Page_19">19</a>, <a href="#Page_20">20</a></li>
+
+<li>Swan, <a href="#Page_129">129</a></li>
+
+<li>Syracuse, <a href="#Page_19">19</a></li>
+
+<li>Syria, <a href="#Page_153">153</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_T" id="IX_T"></a>Tallow, <a href="#Page_34">34</a>, <a href="#Page_35">35</a>, <a href="#Page_51">51</a>, <a href="#Page_52">52</a></li>
+
+<li>Tantalum: <a href="#Page_132">132</a>;
+<ul class="IX">
+<li>filament lamps, <a href="#Page_133">133</a></li></ul></li>
+
+<li>Tar, <a href="#Page_68">68</a>, <a href="#Page_106">106</a></li>
+
+<li>Telegraphy, <a href="#Page_195">195</a></li>
+
+<li>Telephony, <a href="#Page_194">194</a></li>
+
+<li>Textiles, <a href="#Page_256">256</a></li>
+
+<li>Thames, <a href="#Page_169">169</a></li>
+
+<li>Theaters, <a href="#Page_9">9</a>, <a href="#Page_319">319</a> <em>et seq.</em></li>
+
+<li>Thoria, <a href="#Page_85">85</a></li>
+
+<li>Tin, <a href="#Page_262">262</a></li>
+
+<li>Tinder-boxes, <a href="#Page_18">18</a>, <a href="#Page_19">19</a>, <a href="#Page_22">22</a></li>
+
+<li>Travelers Insurance Company, <a href="#Page_227">227</a></li>
+
+<li>Trees, <a href="#Page_26">26</a></li>
+
+<li>Troy, <a href="#Page_42">42</a></li>
+
+<li>Tuberculosis, <a href="#Page_273">273</a></li>
+
+<li>Tungsten lamp, <a href="#Page_161">161</a> <em>et seq.</em>, <a href="#Page_187">187</a>, <a href="#Page_261">261</a>, <a href="#Page_290">290</a>, <a href="#Page_303">303</a></li>
+
+<li>Typhus, <a href="#Page_273">273</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_U" id="IX_U"></a>Ultra-violet rays: <a href="#Page_126">126</a>, <a href="#Page_150">150</a>;
+<ul class="IX">
+<li>in photographic electricity, <a href="#Page_267">267</a>, <a href="#Page_268">268</a>; <a href="#Page_270">270</a>, <a href="#Page_272">272</a>, <a href="#Page_294">294</a></li></ul></li>
+
+<li>United States: petroleum in, <a href="#Page_57">57</a>;
+<ul class="IX">
+<li>gas-consumption in, <a href="#Page_99">99</a>; <a href="#Page_164">164</a>, <a href="#Page_165">165</a>, <a href="#Page_166">166</a></li></ul></li>
+
+<li>United States Geological Survey, cited on sale of gas, <a href="#Page_222">222</a></li>
+
+<li>United States Military Intelligence, <a href="#Page_225">225</a>, <a href="#Page_226">226</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_V" id="IX_V"></a>Vacuum tubes, <a href="#Page_81">81</a>, <a href="#Page_286">286</a></li>
+
+<li>Venetians, <a href="#Page_195">195</a></li>
+
+<li>Ventilation, <a href="#Page_13">13</a></li>
+
+<li>Verne, Jules, <a href="#Page_143">143</a></li>
+
+<li>Vestal Virgins, <a href="#Page_42">42</a></li>
+
+<li>Volcanoes, <a href="#Page_166">166</a></li>
+
+<li>Volta, <a href="#Page_111">111</a>, <a href="#Page_112">112</a>, <a href="#Page_127">127</a></li>
+
+<li>Voltaic pile: construction of, <a href="#Page_111">111</a>, <a href="#Page_127">127</a></li>
+
+<li>Von Bolton. <em>See</em> Bolton.</li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_W" id="IX_W"></a>War: and artificial light, <a href="#Page_11">11</a>, <a href="#Page_178">178</a>-<a href="#Page_193">193</a></li>
+
+<li>Washington, <a href="#Page_305">305</a></li>
+
+<li>Water: sterilization of, by artificial light, <a href="#Page_280">280</a> <em>et seq.</em></li>
+
+<li>Watson, Dr. Richard, <a href="#Page_67">67</a>, <a href="#Page_68">68</a></li>
+
+<li>Watt, <a href="#Page_94">94</a></li>
+
+<li>Waves: electro-magnetic, <a href="#Page_68">68</a>, <a href="#Page_86">86</a>, <a href="#Page_125">125</a> <em>et seq.</em></li>
+
+<li>Wax, <a href="#Page_34">34</a>, <a href="#Page_46">46</a>, <a href="#Page_51">51</a></li>
+
+<li>Way: mercury-arc produced by, <a href="#Page_124">124</a></li>
+
+<li>Wells, <a href="#Page_61">61</a></li>
+
+<li>Wells, H.&nbsp;G., cited, <a href="#Page_148">148</a></li>
+
+<li>Welsbach, Auer von: <a href="#Page_61">61</a>;
+<ul class="IX">
+<li>invention of mantle by, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>, <a href="#Page_133">133</a></li></ul></li>
+
+<li>Wenham, <a href="#Page_78">78</a></li>
+
+<li>West Indies, <a href="#Page_25">25</a></li>
+
+<li>Whale-oil, <a href="#Page_31">31</a></li>
+
+<li>Wicks, <a href="#Page_35">35</a>, <a href="#Page_36">36</a>, <a href="#Page_53">53</a>, <a href="#Page_54">54</a>, <a href="#Page_58">58</a>, <a href="#Page_59">59</a></li>
+
+<li>Winsor, <a href="#Page_72">72</a>, <a href="#Page_73">73</a>.
+<ul class="IX">
+<li><em>See also</em> Winzler.</li></ul></li>
+
+
+<li>Winzler. <em>See</em> Winsor.</li>
+
+<li><em>Wolfram.</em> <em>See</em> Tungsten.</li>
+
+<li>Wood, <a href="#Page_26">26</a>, <a href="#Page_27">27</a>, <a href="#Page_28">28</a></li>
+
+<li>Woolworth Building, <a href="#Page_302">302</a>, <a href="#Page_303">303</a></li>
+
+<li>Wounds: treatment of, by artificial light, <a href="#Page_10">10</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_X" id="IX_X"></a>X-ray: production of, tubes during War, <a href="#Page_131">131</a>; <a href="#Page_137">137</a>, <a href="#Page_150">150</a>, <a href="#Page_270">270</a>, <a href="#Page_280">280</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_Y" id="IX_Y"></a>Young, James: discovers petroleum, <a href="#Page_56">56</a></li>
+
+<li>Yttria, <a href="#Page_85">85</a></li>
+</ul>
+
+
+<ul class="IX">
+<li><a name="IX_Z" id="IX_Z"></a><em>Zeitung</em>, Cologne: <a href="#Page_157">157</a>;
+<ul class="IX">
+<li>extract from, on street-lighting, <a href="#Page_158">158</a></li></ul></li>
+
+<li>Zinc, <a href="#Page_125">125</a>, <a href="#Page_130">130</a>, <a href="#Page_267">267</a></li>
+
+<li>Zirconia, <a href="#Page_84">84</a>, <a href="#Page_85">85</a></li></ul>
+</div>
+
+<hr />
+<hr />
+
+<p class="center"><a name="corrections" id="corrections"></a>Transcriber's List of Corrections</p>
+
+
+<div class="center">
+<table class="corr" cellspacing="0" cellpadding="5" border="1" summary="corrections">
+<tr><th colspan="2">Location</th><th rowspan="2">Original</th><th rowspan="2">Correction</th></tr>
+<tr><th>Chapter/Section</th><th>Page</th></tr>
+<tr>
+<td>Chapter II</td>
+<td><a href="#Page_18">18</a></td>
+<td>and similiar material</td>
+<td>and similar material</td>
+</tr>
+<tr>
+<td>Chapter XIII</td>
+<td><a href="#Page_167">167</a></td>
+<td>as a constant level</td>
+<td>at a constant level</td>
+</tr>
+<tr>
+<td>Chapter XIV</td>
+<td><a href="#Page_186">186</a></td>
+<td>the carbons to distintegrate</td>
+<td>the carbons to disintegrate</td>
+</tr>
+<tr>
+<td rowspan="4">Chapter XV</td>
+<td rowspan="2"><a href="#Page_195">195</a></td>
+<td>John Pechham</td>
+<td>John Peckham</td>
+</tr>
+<tr>
+<td>coated with an allow</td>
+<td>coated with an alloy</td>
+</tr>
+<tr>
+<td><a href="#Page_196">196</a></td>
+<td>with various billiant</td>
+<td>with various brilliant</td>
+</tr>
+<tr>
+<td><a href="#Page_200">200</a></td>
+<td>key in depressed</td>
+<td>key is depressed</td>
+</tr>
+<tr>
+<td>Chapter XVI</td>
+<td><a href="#Page_216">216</a></td>
+<td>has nearly doubled</td>
+<td>have nearly doubled</td>
+</tr>
+<tr>
+<td>Chapter XVII</td>
+<td><a href="#Page_230">230</a></td>
+<td>this own indifference</td>
+<td>their own indifference</td>
+</tr>
+<tr>
+<td>Chapter XXIII</td>
+<td><a href="#Page_314">314</a></td>
+<td>Nature's lighting varied</td>
+<td>Nature's lighting varies</td>
+</tr>
+<tr>
+<td rowspan="2">Chapter XXIV</td>
+<td><a href="#Page_332">332</a></td>
+<td>so-called cadelabra</td>
+<td>so-called candelabra</td>
+</tr>
+<tr>
+<td><a href="#Page_337">337</a></td>
+<td>possibilties</td>
+<td>possibilities</td>
+</tr>
+<tr>
+<td>READING REFERENCES</td>
+<td><a href="#Page_358">358</a></td>
+<td>...Applications an Th&eacute;atre."</td>
+<td>...Applications au Th&eacute;atre."</td>
+</tr>
+<tr>
+<td rowspan="2">INDEX</td>
+<td><a href="#Page_364">364</a></td>
+<td>Photo-micography</td>
+<td>Photo-micrography</td>
+</tr>
+<tr>
+<td><a href="#Page_365">365</a></td>
+<td>Siemans</td>
+<td>Siemens</td>
+</tr>
+</table>
+</div>
+
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Artificial Light, by M. Luckiesh
+
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+The Project Gutenberg EBook of Artificial Light, by M. Luckiesh
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: Artificial Light
+       Its Influence upon Civilization
+
+Author: M. Luckiesh
+
+Release Date: January 29, 2006 [EBook #17625]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ARTIFICIAL LIGHT ***
+
+
+
+
+Produced by K.D. Thornton, Karina Aleksandrova and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+Transcriber's Notes:
+
+1. Subscripts have been marked with an underscore character in front
+   with text surrounded in curly braces, for example: H_{2}O (formula
+   of water).
+
+2. Inconsistent hyphenation of words preserved.
+
+3. Several misprints fixed. A full list of corrections can be found at
+   the end of the text.
+
+
+
+[Illustration: 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 cooeperation 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 filament lamps                            129
+
+Carbon-dioxide tube for accurate color-matching        160
+
+The Moore nitrogen tube                                160
+
+Modern street lighting                                 161
+
+A completed lighthouse lens                            176
+
+Torro Point Lighthouse, Panama Canal                   176
+
+American search-light position on Western Front in
+1919                                                   177
+
+American standard field search-light and power unit    177
+
+Signal-light for airplane                              232
+
+Trench light-signaling outfit                          232
+
+Aviation field light-signal projector                  232
+
+Signal search-light for airplane                       232
+
+Unsafe, unproductive lighting worthy of the dark ages  233
+
+The same factory made safe, cheerful, and more
+productive by modern lighting                          233
+
+Locomotive electric headlight                          240
+
+Search-light on a fire-boat                            240
+
+Building ships under artificial light at Hog Island
+Shipyard                                               241
+
+Artificial light in photography                        256
+
+Sterilizing water with radiant energy from quartz
+mercury-arcs                                           257
+
+Judging color under artificial daylight                272
+
+Artificial daylight                                    273
+
+Fireworks and illuminated battle-fleet at
+Hudson-Fulton Celebration                              288
+
+Fireworks exhibition on May Day at Panama-Pacific
+Exposition                                             289
+
+The new flood lighting contrasted with the old
+outline lighting                                       304
+
+Niagara Falls flooded with light                       305
+
+Artificial light honoring those who fell and those
+who returned                                           320
+
+The expressiveness of light in churches                321
+
+Obtaining two different moods in a room by a portable
+lamp which supplies direct and indirect components
+of light                                               336
+
+The lights of New York City                            337
+
+Artificial light in community affairs                  352
+
+Panama-Pacific Exposition                              353
+
+
+
+
+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 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.
+
+[Illustration: PRIMITIVE FIRE-BASKETS]
+
+[Illustration: CRUDE SPLINTER-HOLDERS]
+
+[Illustration: 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 cooerdinated 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 role 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 larvae, the
+glow-worm, but few persons realize that a vast number of insects and
+lower organisms are endowed with the superhuman ability of producing
+light by physiological processes. Apparently the chief function of these
+lighting-plants within the living bodies is not to provide light in the
+sense that the human being uses it predominantly. That is, these
+wonderful light-sources seem to be utilized more for signaling, for
+luring prey, and for protection than for strictly illuminating-purposes.
+Much study has been given to the production of light by animals, because
+the secrets will be extremely valuable to mankind. As one floats over
+tide-water on a balmy evening after dark and watches the pulsating spots
+of phosphorescent light emitted by the lowly jellyfishes, his
+imaginative mood formulates the question, "Why are these lowly organisms
+endowed with such a wonderful ability?"
+
+Despite his highly developed mind and body and his boasted superiority,
+man must go forth and learn the secrets of light-production before he
+may emancipate himself from darkness. If man could emit light in
+relative proportion to his size as compared with the firefly, he would
+need no other torch in the coal-mine. How independent he would be in
+extreme darkness where his adapted eyes need only a feeble
+light-source! Primitive man, desiring a light-source and having no means
+of making fire, imprisoned the glowing insects in a perforated gourd or
+receptacle of clay, and thus invented the first lantern perhaps before
+he knew how to make fire. The fireflies of the West Indies emit a
+continuous glow of considerable luminous intensity and the natives have
+used these imprisoned insects as light-sources. Thus mankind has
+exhibited his superiority by adapting the facilities at hand to the
+growing requirements which his independent nature continuously
+nourished. His insistent demand for independence in turn has nourished
+his desire to learn nature's secrets and this desire has increased in
+intensity throughout the ages.
+
+The act of imprisoning a glowing insect was in itself no greater stride
+along the highway of progress than the act of picking a tasty fruit from
+its tree. However, the crude lantern perhaps directed his primitive mind
+to the possibilities of artificial light. The flaming fagot from the
+fire was the ancestor of the oil-lamp, the candle, the lantern, and the
+electric flash-light. It is a matter of conjecture how much time elapsed
+before his feeble intellect became aware that resinous wood afforded a
+better light-source than woods which were less inflammable.
+Nevertheless, pine knots and similar resinous pieces of wood eventually
+were favored as torches and their use has persisted until the present
+time. In some instances in ancient times resin was extracted from wood
+and burned in vessels. This was the forerunner of the grease-and the
+oil-lamp. In the woods to-day the craftsman of the wilds keeps on the
+lookout for live trees saturated with highly inflammable ingredients.
+
+Viewed from the present age, these smoking, flickering light-sources
+appear very crude; nevertheless they represent a wide gulf between their
+users and those primitive beings who were unacquainted with the art of
+making fire. Although the wood fire prevailed as a light-source
+throughout uncounted centuries, it was subjected to more or less
+improvement as civilization advanced. When the wood fire was brought
+indoors the day was extended and early man began to develop his crude
+arts. He thought and planned in the comfort and security of his cave or
+hut. By the firelight he devised implements and even decorated his stone
+surroundings with pictures which to-day reveal something of the thoughts
+and activities of mankind during a civilization which existed many
+thousand years ago.
+
+When it was too warm to have a roaring fire upon the hearth, man devised
+other means for obtaining light without undue warmth. He placed glowing
+embers upon ledges in the walls, upon stone slabs, or even upon
+suspended devices of non-inflammable material. Later he split long
+splinters of wood from pieces selected for their straightness of grain.
+These burning splinters emitting a smoking, feeble light were crude but
+they were refinements of considerable merit. A testimonial of their
+satisfactoriness is their use throughout many centuries. Until very
+recent times the burning splinter has been in use in Scotland and in
+other countries, and it is probable that at present in remote districts
+of highly civilized countries this crude device serves the meager needs
+of those whose requirements have been undisturbed by the progress of
+civilization. Scott, in "The Legend of Montrose," describes a table
+scene during a feast. Behind each seat a giant Highlander stood, holding
+a blazing torch of bog-pine. This was also the method of lighting in the
+Homeric age.
+
+Crude clay relics representing a human head, from the mouth of which the
+wood-splinters projected, appear to corroborate the report that the
+flaming splinter was sometimes held in the mouth in order that both
+hands of a workman would be free. Splinter-holders of many types have
+survived, but most of them are of the form of a crude pedestal with a
+notch or spring clip at its upper end. The splinter was held in this
+clip and burned for a time depending upon its length and the character
+of the wood. It was the business of certain individuals to prepare
+bundles of splinters, which in the later stages of civilization were
+sold at the market-place or from house to house. Those who have observed
+the frontiersman even among civilized races will be quite certain that
+the wood for splinters was selected and split with skill, and that the
+splinters were burned under conditions which would yield the most
+satisfactory light. It is a characteristic of those who live close to
+nature, and are thus limited in facilities, to acquire a surprising
+efficiency in their primitive activities.
+
+An obvious step in the use of burning wood as a light-source was to
+place such a fire on a shelf or in a cavity in the wall. Later when
+metal was available, gratings or baskets were suspended from the ceiling
+or from brackets and glowing embers or flaming chips were placed upon
+them. Some of these were equipped with crude chimneys to carry away the
+smoke, and perhaps to increase the draft. In more recent centuries the
+first attempt at lighting outdoor public places was by means of metal
+baskets in which flaming wood emitted light. It was the duty of the
+watchman to keep these baskets supplied with pine knots. In early
+centuries street-lighting was not attempted, and no serious efforts
+worthy of consideration as adequate lighting were made earlier than
+about a century ago. As a consequence the "link-boy" came into
+existence. With flaming torch he would escort pedestrians to their homes
+on dark nights. This practice was in vogue so recently that the
+"link-boy" is remembered by persons still living. In England the
+profession appears to have existed until about 1840.
+
+Somewhat akin to the wood-splinter, and a forerunner of the candle, was
+the rushlight. In burning wood man noticed that a resinous or fatty
+material increased the inflammability and added greatly to the amount of
+light emitted. It was a logical step to try to reproduce this condition
+by artificial means. As a consequence rushes were cut and soaked in
+water. They were then peeled, leaving lengths of pith partially
+supported by threads of the skin which were not stripped off. These
+sticks of pith were placed in the sun to bleach and to dry, and after
+they were thoroughly dry they were dipped in scalding grease, which was
+saved from cooking operations or was otherwise acquired for the purpose.
+A reed two or three feet long held in the splinter-holder would burn for
+about an hour. Thus it is seen that man was beginning to progress in the
+development of artificial light. In developing the rushlight he was
+laying the foundation for the invention of the candle. Pliny has
+mentioned the burning of reeds soaked in oil as a feature of funeral
+rites. Many crude forerunners of the candle were developed in various
+parts of the world by different races. For example, the Malays made a
+torch by wrapping resinous gum in palm leaves, thus devising a crude
+candle with the wick on the outside.
+
+Many primitive uses of vegetable and animal fats were forerunners of the
+oil-lamp. In the East Indies the candleberry, which contains oily seeds,
+has been burned for light by the natives. In many cases burning fish and
+birds have served as lamps. In the Orkney Islands the carcass of a
+stormy petrel with a wick in its mouth has been utilized as a
+light-source, and in Alaska a fish in a split stick has provided a crude
+torch for the natives. These primitive methods of obtaining artificial
+light have been employed for centuries and many are in use at the
+present time among uncivilized tribes and even by civilized beings in
+the remote outskirts of civilization. Surely progress is limited where a
+burning fish serves as a torch, or where, at best, the light-sources are
+feeble, smoking, flickering, and ill-smelling!
+
+Progress insisted upon a light-source which was free from the defects of
+the crude devices already described and the next developments were
+improvements to the extent at least that combustion was more thorough.
+The early oil-lamps and candles did not emit much smoke, but they were
+still feeble light-sources and not always without noticeable odors.
+Nevertheless, they marked a tremendous advance in the production of
+artificial light. Although they were not scientific developments in the
+modern sense, the early oil-lamp and the candle represented the great
+possibilities of utilizing knowledge rather than depending upon the raw
+products of nature in unmodified forms. The advent of these two
+light-sources in reality marked the beginning of the civilization which
+was destined to progress and survive.
+
+Although such primitive light-sources as the flaming splinter and the
+glowing ember have survived until the present age, lamps consisting of a
+wick dipped into a receptacle containing animal and vegetable oils have
+been in use among the more advanced peoples since prehistoric times.
+Oil-lamps are to be seen in the earliest Roman illustrations. During the
+height of ancient civilization along the eastern shores of the
+Mediterranean Sea, elaborate lighting was effected by means of the
+shallow grease-or oil-lamp. It is difficult to estimate the age in which
+this form of light-source originated, but some lamps in existence in
+collections at the present time appear to have been made as early as
+four or five thousand years before the Christian era. It is noteworthy
+that such lamps did not differ materially in essential details from
+those in use as late as a few centuries ago.
+
+At first the grease used was the crude fat from animals. Vegetable oils
+also were burned in the early lamps. The Japanese, for example,
+extracted oil from nuts. When the demands of civilization increased,
+extensive efforts were made to obtain the required fats and oils.
+Amphibious animals of the North and the huge mammals of the sea were
+slaughtered for their fat, and vegetable sources were cultivated.
+Later, sperm and colza were the most common oils used by the advanced
+races. The former is an animal oil obtained from the head cavities of
+the sperm-whale; the latter is a vegetable oil obtained from rape-seed.
+Mineral oil was introduced as an illuminant in 1853, and the modern lamp
+came into use.
+
+The grease-and oil-lamps in general were of such a form that they could
+be carried with ease and they had flat bottoms so that they would rest
+securely. The simplest forms had a single wick, but in others many wicks
+dipped into the same receptacle. The early ones were of stone, but
+later, lamps were modeled from clay or terra cotta and finally from
+metals. They were usually covered and the wick projected through a hole
+in the top near the edge. Large stone vases filled with a hundred pounds
+of liquid fat are known to have been used in early times. As a part of
+the setting in the celebration of festivals the ancient nations of Asia
+and Africa placed along the streets bronze vases filled with liquid fat.
+The Esquimaux to-day use this form of lamp, in which whale-oil and seal
+blubber is the fuel. Incidentally, these lamps also supply the only
+artificial heat for their huts and igloos. The heat from these feeble
+light-sources and from their bodies keeps these natives of the arctics
+warm within the icy walls of their abodes.
+
+Very beautiful oil-lamps of brass, bronze, and pewter evolved in such
+countries as Egypt. Many of these were designed for and used in
+religious ceremonies. The oil-lamps of China, Scotland, and other
+countries in later centuries were improved by the addition of a pan
+beneath the oil-receptacle, to catch drippings from the wick or oil
+which might run over during the filling. The Chinese lamps were
+sometimes made of bamboo, but the Scottish lamps were made of metal. A
+flat metal lamp, called a crusie, was one of the chief products of
+blacksmiths and was common in Scotland until the middle of the
+nineteenth century. This type of lamp was used by many nations and has
+been found in the catacombs of Rome. The crusie was usually suspended by
+an iron hook and the flow of oil to the wick could be regulated by
+tilting. The wick in the Scottish lamps consisted of the pith of rushes,
+cloth, or twisted threads. These early oil-lamps were almost always
+shallow vessels into which a short wick was dipped, and it was not until
+the latter part of the eighteenth century that other forms came into
+general use. The change in form was due chiefly to the introduction of
+scientific knowledge when mineral oil was introduced. As early as 1781
+the burning of naptha obtained by distilling coal at low temperatures
+was first discussed, but no general applications were made until a later
+period. This was the beginning of many marked improvements in oil-lamps,
+and was in reality the birth of the modern science of light-production.
+
+[Illustration: A TYPICAL METAL MULTIPLE-WICK OPEN-FLAME OIL-LAMP]
+
+[Illustration: 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 preeminent among early
+light-sources. It did not emit appreciable smoke or odor and it was
+conveniently portable and less fragile than the oil-lamp. Candles have
+been used throughout the Christian era and some authorities are inclined
+to attribute their origin to the Phoenicians. It is known that the
+Romans used them, especially the wax-candles, in religious ceremonies.
+The Phoenicians introduced them into Byzantium, but they disappeared
+under the Turkish rule and did not come into use again until the twelfth
+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 Phoenicians and Romans apparently continued
+the custom, but no traces of it have been found in Greece and Egypt.
+
+Fire and light have been closely associated in various religious creeds
+and their ceremonies. The Hindu festival in honor of the goddess of
+prosperity is attended by the burning of many lamps in the temples and
+homes. The Jewish synagogues have their eternal lamps and in their
+rituals fire and light have played prominent roles. 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.
+
+[Illustration: LAMPS OF A CENTURY OR TWO AGO]
+
+[Illustration: ELABORATE FIXTURES OF THE AGE OF CANDLES]
+
+The crude petroleum, of course, is not fit for illuminating purposes,
+but it contains components which are satisfactory. The various
+components are sorted out by fractional distillation and the oil for
+burning in lamps is selected according to its volatility, viscosity,
+stability, etc. It must not be so volatile as to have a dangerously
+low flashing-point, nor so stable as to hinder its burning well. In this
+fractional distillation a vast variety of products are now obtained.
+Gasolene is among the lighter products, with a density of about 0.65;
+kerosene has a density of about 0.80; the lubricating-oils from 0.85 to
+0.95; and there are many solids such as vaseline and paraffin which are
+widely used for many purposes. This process of refining oils is now the
+source of paraffin for making candles, in which it is usually mixed with
+substances like stearin in order to raise its melting-point.
+
+Crude petroleum possesses a very repugnant odor; it varies in color from
+yellow to black; and its specific gravity ranges from about 0.80 to
+1.00, but commonly is between 0.80 and 0.90. Its chemical constitution
+is chiefly of carbon and hydrogen, in the approximate ratio of about six
+to one respectively. It is a mixture of paraffin hydrocarbons having the
+general formula of C_{n}H_{2n+2} and the individual members of this
+series vary from CH_{4} (methane) to C_{15}H_{32} (pentadecane),
+although the solid hydrocarbons are still more complex. Petroleum is
+found in many countries and the United States is particularly blessed
+with great stores of it.
+
+The ordinary lamp consisting of a wick which draws up the mineral oil
+and feeds it to a flame is efficient and fairly free from danger. It
+requires care and may cause disaster if it is upset, but it has been
+blamed unjustly in many accidents. A disadvantage of the kerosene lamp
+over electric lighting, for example, is the relatively greater
+possibility of accidents through the carelessness of the user. This
+point is brought out in statistics of fire-insurance companies, which
+show that the fires caused by kerosene lamps are much more numerous than
+those from other methods of lighting. If in a modern lamp of proper
+construction a close-fitting wick is used and the lamp is extinguished
+by turning down and blowing across the chimney, there is little danger
+in its use excepting accidental breakage or overturning.
+
+In oil-lamps at the present time mineral oils are used which possess
+flashing-points above 75 deg.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 deg.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
+     L200,000, 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 deg.F. at the bottom to about 3000 deg.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 deg.F., it would appear white. All this time its
+luminous efficiency is increasing, because it is radiating not only an
+increasing percentage of visible radiant energy but an increasing amount
+of the most effective luminous energy. But even when it appears white, a
+large amount of the energy which it radiates is invisible infra-red and
+ultra-violet, which are ineffective in producing light, so at best the
+substance at this high temperature is inefficient as a light-producer.
+
+In this branch of the science of light-production substances are sought
+not only for their high melting-point, but for their ability to radiate
+selectively as much visible energy as possible and of the most luminous
+character. However, at best the present method of utilizing the
+temperature radiation of hot bodies has limitations.
+
+The luminous efficiencies of light-sources to-day are still very low,
+but great advances have been made in the past half-century. There must
+be some radical departures if the efficiency of light-production is to
+reach a much higher figure. A good deal has been said of the firefly and
+of phosphorescence. These light-sources appear to emit only visible
+energy and, therefore, are efficient as radiators of luminous radiant
+energy. But much remains to be unearthed concerning them before they
+will be generally applicable to lighting. If ultra-violet radiation is
+allowed to impinge upon a phosphorescent material, it will glow with a
+considerable brightness but will be cool to the touch. A substance of
+the same brightness by virtue of its temperature would be hot; hence
+phosphorescence is said to be "cold" light.
+
+An acquaintance with certain terms is necessary if the reader is to
+understand certain parts of the text. The early candle gradually became
+a standard, and uniform candles are still satisfactory standards where
+high accuracy is not required. Their luminous intensity and
+illuminating value became units just as the foot was arbitrarily adopted
+as a unit of length. The intensity of other light-sources was
+represented in terms of the number of candles or fraction of a candle
+which gave the same amount of light. But the luminous intensity of the
+candle was taken only in the horizontal direction. In the same manner
+the luminous intensities of light-sources until a short time ago were
+expressed in candles as measured in a certain direction. Incandescent
+lamps were rated in terms of mean horizontal candles, which would be
+satisfactory if the luminous intensity were the same in all directions,
+but it is not. Therefore, the candle-power in one direction does not
+give a measure of the total light-output.
+
+If a source of light has a luminous intensity of one candle in all
+directions, the illumination at a distance of one foot in any direction
+is said to be a foot-candle. This is the unit of illumination intensity.
+A lumen is the quantity of light which falls on one square foot if the
+intensity of illumination is one foot-candle. It is seen that the area
+of a sphere with a radius of one foot is 4 pi or 12.57 square feet;
+therefore, a light-source having a luminous intensity of one candle in
+all directions emits 12.57 lumens. This is the satisfactory unit, for it
+measures total quantity of light, and luminous efficiencies may be
+expressed in terms of lumens per watt, lumens per cubic foot of gas per
+hour, etc.
+
+Of course, the efficiencies of light-sources are usually of interest to
+the consumer if they are expressed in terms of cost. But from a
+practical point of view there are many elements which combine to make
+another important factor, namely, satisfactoriness. Therefore, the
+efficiency of artificial lighting from the standpoint of the consumer
+should be the ratio of satisfactoriness to cost. However, the scientist
+is interested chiefly in the efficiency of the light-source which may be
+expressed in lumens per watt, or the amount of light obtained from a
+given rate of consumption or of emission of energy. This method of
+rating light-sources penalizes those radiating considerable energy which
+does not produce the sensation of light or which at best is of
+wave-lengths that are inefficient in this respect. That radiant energy
+which is wholly of a wave-length of maximum visibility, or, in other
+words, excites the sensation of yellow-green, is the most efficient in
+producing luminous sensation. Of course, no illuminants are available
+which approach this theoretical ideal and it is not likely that this
+would be a practical ideal. Under monochromatic yellow-green light the
+magical drapery of color would disappear and the surroundings would be a
+monochrome of shades of this hue. Having no colors with which to
+contrast this color, the world would be colorless. This should be
+obvious when it is considered that an object which is red under an
+illuminant containing all colors such as sunlight would be black or dark
+gray under monochromatic yellow-green light. The red under present
+conditions is kept alive by contrast with other colors, because the
+latter live by virtue of the fact that most of our present illuminants
+contain their hues. It is assumed that the reader knows that a red
+object, for example, appears red because it reflects (or transmits) red
+rays and absorbs the other rays in the illuminant. In other words, color
+is due to selective absorption reflection, or transmission.
+
+Perhaps the ideal illuminant, which is most generally satisfactory for
+general activities, is a white light corresponding to noon sunlight. If
+this is chosen as the scientific ideal, the illuminants of the present
+time are much more "efficient" than if the most efficient light is the
+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 deg.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 elite. 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 deg.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    C_{2}H_{4}    crotonylene  C_{4}H_{6}
+     propylene   C_{3}H_{6}    benzene      C_{6}H_{6}
+     butylene    C_{4}H_{8}    toluene      C_{7}H_{8}
+     amylene     C_{5}H_{10}   xylene       C_{8}H_{10}
+     acetylene   C_{2}H_{2}    methane      C H_{4}
+     allylene    C_{3}H_{4}    ethane       C_{2}H_{6}
+
+A gas which has played a prominent part in lighting is acetylene,
+produced by the interaction of water and calcium carbide. No other gas
+easily produced upon a commercial scale yields as much light, volume for
+volume, as acetylene. It has the great advantage of being easily
+prepared from raw material whose yield of gas is considerably greater
+for a given amount than the raw materials which are used in making other
+illuminating gases. The simplicity of the manufacture of acetylene from
+calcium carbide and water gives to this gas a great advantage in some
+cases. It has served for individual lighting in houses and in other
+places where gas or electric service was unavailable. Where space is
+limited it also had an advantage and was adopted to some extent on
+automobiles, motor-boats, ships, lighthouses, and railway cars before
+electric lighting was developed for these purposes.
+
+The color of the acetylene flame is satisfactory and it is extremely
+brilliant compared with most flames. An interesting experiment is found
+in placing a spark-gap in the flame and sending a series of sparks
+across it. If the conditions are proper the flame will became very much
+brighter. When the gas issues from a proper jet under sufficient
+pressure, the flame is quite steady. Its luminous efficiency gives it an
+advantage over other open gas-flames in lighting rooms, because for the
+same amount of light it vitiates the air and exhausts the oxygen to a
+less degree than the others. Of course, in these respects the gas-mantle
+is superior.
+
+The reaction which takes place when water and calcium carbide are
+brought together is a double decomposition and is represented by,
+
+     CaC_{2} + H_{2}O = C_{2}H_{2} + CaO
+
+It will be seen that the products are acetylene gas and calcium oxide or
+lime. The lime, being hydroscopic and being in the presence of water or
+water-vapor in the acetylene generator, really becomes calcium hydroxide
+Ca(OH)_{2}, commonly called slaked lime. If there are impurities in the
+calcium carbide, it is sometimes necessary to purify the gas before it
+may be safely used for interior lighting.
+
+The burners and mantles used in acetylene lighting are essentially the
+same as those for other gas-lighting, excepting, of course, that they
+are especially adapted for it in minor details.
+
+The chief source of calcium carbide in this country is the electric
+furnace. Cheap electrical energy from hydro-electric developments, such
+as the Niagara plants, have done much to make the earth yield its
+elements. Aluminum is very prevalent in the soil of the earth's surface,
+because its oxide, alumina, is a chief constituent of ordinary clay. But
+the elements, aluminum and oxygen, cling tenaciously to each other and
+only the electric furnace with its excessively high temperatures has
+been able to separate them on a large commercial scale. Similarly,
+calcium is found in various compounds over the earth's surface.
+Limestone abounds widely, hence the oxide and carbonate of lime are
+wide-spread. But calcium clings tightly to the other elements of its
+compounds and it has taken the electric furnace to bring it to
+submission. The cheapness of calcium carbide is due to the development
+of cheap electric power. It is said that calcium carbide was discovered
+as a by-product of the electric furnace by accidentally throwing water
+upon the waste materials of a furnace process. The discovery of a
+commercial scale of manufacture of calcium carbide has been a boon to
+isolated lighting. Electric lighting has usurped its place on the
+automobile and is making inroads in country-home lighting. Doubtless,
+acetylene will continue to serve for many years, but its future does not
+appear as bright as it did many years ago.
+
+The Pintsch gas, used to some extent in railroad passenger-cars in this
+country, is an oil-gas produced by the destructive distillation of
+petroleum or other mineral oil in retorts heated externally. The product
+consists chiefly of methane and heavy hydrocarbons with a small amount
+of hydrogen. In the early days of railways, some trains were not run
+after dark and those which were operated were not always lighted. At
+first attempts were made at lighting railway cars with compressed
+coal-gas, but the disadvantage of this was the large tank required.
+Obviously, a gas of higher illuminating-value per volume was desired
+where limited storage space was available, and Pintsch turned his
+attention to oil-gas. Gas suffers in illuminating-value upon being
+compressed, but oil-gas suffers only about half the loss that coal-gas
+does. In about 1880 Pintsch developed a method of welding cylinders and
+buoys which satisfied lighthouse authorities and he was enabled to
+furnish these filled with compressed gas. Thus the buoy was its own
+gas-tank. He devised lanterns which would remain lighted regardless of
+wind and waves and thus gained a start with his compressed-gas systems.
+He compressed the gas to a pressure of about one hundred and fifty
+pounds per square inch and was obliged to devise a reducer which would
+deliver the gas to the burner at about one pound per square inch. This
+regulator served well throughout many years of exacting service. The
+system began to be adopted on ships and railroads in 1880 and for many
+years it has served well.
+
+Although gas-lighting has affected the activities of mankind
+considerably by intensifying commerce and industry and by advancing
+social progress, the illuminants which eventually took the lead have
+extended the possibilities and influences of artificial light. In the
+brief span of a century civilized man is almost totally independent of
+natural light in those fields over which he has control. What another
+century will bring can be predicted only from the accomplishments of the
+past. These indicate possibilities beyond the powers of imagination.
+
+
+
+
+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 deg. to 7000 deg.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                         3 to  7
+     Enclosed flame-arc (yellow or white)       15 to 25
+     Luminous arc                               10 to 25
+
+Another lamp differing widely in appearance from the preceding arcs may
+be described here because it is known as the mercury-arc. In this lamp
+mercury is confined in a transparent tube and an arc is started by
+making and breaking a mercury connection between the two electrodes. The
+arc may be maintained of a length of several feet. Perhaps the first
+mercury-arc was produced in 1860 by Way, who permitted a fine jet of
+mercury to fall from a reservoir into a vessel, the reservoir and
+receiver being connected to the poles of a battery. The electric current
+scattered the jet and between the drops arcs were formed. He exhibited
+this novel light-source on the mast of a yacht and it received great
+attention. Later, various investigators experimented on the production
+of a mercury-arc and the first successful ones were made in the form of
+an inverted U-tube with the ends filled with mercury and the remainder
+of the tube exhausted.
+
+Cooper Hewitt was a successful pioneer in the production of practicable
+mercury-arcs. He made them chiefly in the form of straight tubes of
+glass up to several feet in length, with enlarged ends to facilitate
+cooling. The tubes are inclined so that the mercury vapor which
+condenses will run back into the enlarged end, where a pool of mercury
+forms the negative electrode. The arc may be started by tilting the tube
+so that a mercury thread runs down the side and connects with the
+positive electrode of iron. The heat of the arc volatilizes the mercury
+so that an arc of considerable length is maintained. The tilting is done
+by electromagnets. Starting has also been accomplished by means of a
+heating coil and also by an electric spark. The lamps are stabilized by
+resistance and inductance coils.
+
+One of the defects of the light emitted by the incandescent vapor of
+mercury is its paucity of spectral colors. Its visible spectrum consists
+chiefly of violet, blue, green, and yellow rays. It emits virtually no
+red rays, and, therefore, red objects appear devoid of red. The human
+face appears ghastly under this light and it distorts colors in general.
+However, it possesses the advantages of high efficiency, of reasonably
+low brightness, of high actinic value, and of revealing detail clearly.
+Various attempts have been made to improve the color of the light by
+adding red rays. Reflectors of a fluorescent red dye have been used with
+some success, but such a method reduces the luminous efficiency of the
+lamp considerably. The dye fluoresces red under the illumination of
+ultra-violet, violet, and blue rays; that is, it has the property of
+converting radiation of these wave-lengths into radiant energy of longer
+wave-lengths. By the use of electric incandescent filament lamps in
+conjunction with mercury-arcs, a fairly satisfactory light is obtained.
+Many experiments have been made by adding other substances to the
+mercury, such as zinc, with the hope that the spectrum of the other
+substance would compensate the defects in the mercury spectrum. However
+no success has been reached in this direction.
+
+By the use of a quartz tube which can withstand a much higher
+temperature than glass, the current density can be greatly increased.
+Thus a small quartz tube of incandescent mercury vapor will emit as much
+light as a long glass tube. The quartz mercury-arc produces a light
+which is almost white, but the actual spectrum is very different from
+that of white sunlight. Although some red rays are emitted by the quartz
+arc, its spectrum is essentially the same as that of the glass-tube arc.
+Quartz transmits ultra-violet radiation, which is harmful to the eyes,
+and inasmuch as the mercury vapor emits such rays, a glass globe should
+be used to enclose the quartz tube when the lamp is used for ordinary
+lighting purposes.
+
+It is fortunate that such radically different kinds of light-sources are
+available, for in the complex activities of the present time all are in
+demand. The quartz mercury-arc finds many isolated uses, owing to its
+wealth of ultra-violet radiation. It is valuable as a source of
+ultra-violet for exciting phosphorescence, for examining the
+transmission of glasses for this radiation, for sterilizing water, for
+medical purposes, and for photography.
+
+
+
+
+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.
+
+[Illustration: DIRECT CURRENT ARC
+
+Most of the light being emitted by the positive (upper) electrode]
+
+[Illustration: FLAME ARC
+
+Most of the light being emitted by the flame]
+
+[Illustration: 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]
+
+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 deg.F.) limited
+the success of the lamps. Carbon with its extremely high melting-point
+had long attracted attention and in 1879 Edison produced a carbon
+filament by carbonizing a strip of paper. He sealed this in a vessel of
+glass from which the air was exhausted and the electric current was led
+to the filament through platinum wires sealed in the glass. Platinum was
+used because its expansion and contraction is about the same as glass.
+Incidentally, many improvements were made in incandescent lamps and
+thirty years passed before a material was found to replace the platinum
+leading-in wires. The cost of platinum steadily increased and finally in
+the present century a substitute was made by the use of two metals whose
+combined expansion was the same as that of platinum or glass. In 1879
+and 1880 Edison had succeeded in overcoming the many difficulties
+sufficiently to give to the world a practicable incandescent filament
+lamp. About this time Swan and Stearn in England had also produced a
+successful lamp.
+
+In Edison's early experiments with filaments he used platinum wire
+coated with carbon but without much success. He also made thin rods of a
+mixture of finely divided metals such as platinum and iridium mixed with
+such oxides as magnesia, zirconia, and lime. He even coiled platinum
+wire around a piece of one of these oxides, with the aim of obtaining
+light from the wire and from the heated oxide. However, these
+experiments served little purpose besides indicating that the filament
+was best if it consisted solely of carbon and that it should be
+contained in an evacuated vessel.
+
+One of the chief difficulties was to make the carbon filaments. Some of
+the pioneers, such as Sawyer and Mann, attempted to cut these from a
+piece of carbon. However, Edison and also Swan turned their attention to
+forming them by carbonizing a fiber of organic matter. Filaments cut
+from paper and threads of cotton and silk were carbonized for this
+purpose. Edison scoured the earth for better materials. He tried a
+fibrous grass from South America and various kinds of bamboo from other
+parts of the world. Thin filaments of split bamboo eventually proved the
+best material up to that time. He made many lamps containing filaments
+of this material, and even until 1910 bamboo was used to some extent in
+certain lamps.
+
+Of these early days, Edison said:
+
+     It occurred to me that perhaps a filament of carbon could be
+     made to stand in sealed glass vessels, or bulbs, which we were
+     using, exhausted to a high vacuum. Separate lamps were made in
+     this way independent of the air-pump, and, in October, 1879, we
+     made lamps of paper carbon, and with carbons of common sewing
+     thread, placed in a receiver or bulb made entirely of glass,
+     with the leading-in wires sealed in by fusion. The whole thing
+     was exhausted by the Sprengel pump to nearly one-millionth of
+     an atmosphere. The filaments of carbon, although naturally
+     quite fragile owing to their length and small mass, had a
+     smaller radiating surface and higher resistance than we had
+     dared hope. We had virtually reached the position and condition
+     where the carbons were stable. In other words, the incandescent
+     lamp as we still know it to-day [1904], in essentially all its
+     particulars unchanged, had been born.
+
+After Edison's later success with bamboo, Swan invented a process of
+squirting filaments of nitrocellulose into a coagulating liquid, after
+which they are carbonized. Very fine uniform filaments can be made by
+this process and although improvements have been made from time to time,
+this method has been employed ever since its invention. In these later
+years cotton is dissolved in a suitable solvent such as a solution of
+zinc chloride and this material is forced through a small diamond die.
+This thread when hardened appears similar to cat-gut. It is cut into
+proper lengths and bent upon a form. It is then immersed in plumbago and
+heated to a high temperature in order to destroy the organic matter. A
+carbon filament is the result. From this point to the finished lamp many
+operations are performed, but a discussion of these would lead far
+afield. The production of a high vacuum is one of the most important
+processes and manufacturers of incandescent lamps have mastered the art
+perhaps more thoroughly than any other manufacturers. At least, their
+experience in this field made it possible for them to produce quickly
+and on a large scale such devices as X-ray tubes during the recent war.
+
+During the early years of incandescent lamps, improvements were made
+from time to time which increased the life and the luminous efficiency
+of the carbon filaments, but it was not until 1906 that any radical
+improvement was achieved. In that year in this country a process was
+devised whereby the carbon filament was made more compact. In fact, from
+its appearance it received the name "metallized filament." These carbon
+filaments are prepared in the same manner as the earlier ones but are
+finally "treated" by heating in an atmosphere of hydrocarbons such as
+coal-gas. The filament is heated by electric current and the heat breaks
+down the hydrocarbons, with the result that carbon is deposited upon the
+filament. This "treated" filament has a coating of hard carbon and its
+electrical resistance is greater than that of the untreated filament.
+
+The luminous efficiency of a carbon filament is a function of its
+temperature and it increases very rapidly with increasing temperature.
+For this reason it is a constant aim to reach high filament
+temperatures. Of all the materials used in filaments up to the present
+time, carbon possesses the highest melting-point (perhaps as high as
+7000 deg.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 deg.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 deg.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
+
+                                                               Lumens per
+     Date    Filament                      Temperature            watt
+     1880    Carbon                          3300 deg.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 deg.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            51           10.56
+
+It will be noted that the luminous intensity of incandescent filament
+lamps has steadily increased since the carbon lamp was superseded, and
+that in a period of ten years of organized research behind the tungsten
+lamp the luminous efficiency (lumens per watt) has trebled. In other
+words, everything else remaining unchanged, the cost of light in ten
+years was reduced to one third. But the reduction in cost has been more
+than this, as will be shown later. During the same span of years the
+percentage of carbon filament lamps of the total filament lamps sold
+decreased from 100 per cent. in 1907 to 13 per cent. in 1917. At the
+same time the percentage of tungsten (Mazda) lamps increased from
+virtually zero in 1907 to about 87 per cent. in 1917. The tantalum lamp
+had no opportunity to become established, because the tungsten lamp
+followed its appearance very closely. In 1910 the sales of the former
+reached their highest mark, which was only 3.5 per cent. of all the
+lamps sold in the United States. From a lowly beginning the number of
+incandescent filament lamps sold for use in this country has grown
+rapidly, reaching nearly two hundred million in 1919.
+
+
+
+
+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 deg.F. to
+11,000 deg.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 deg.F. and 7000 deg.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.
+
+[Illustration: THE MOORE NITROGEN TUBE
+
+In lobby of Madison Square Garden]
+
+[Illustration: CARBON-DIOXIDE TUBE FOR ACCURATE COLOR-MATCHING]
+
+[Illustration: MODERN STREET LIGHTING
+
+Tunnels of light boring through the darkness provide safe channels for
+modern traffic]
+
+The open-arc lamp possessed the disadvantage of emitting a very unsteady
+light and of consuming the carbons so rapidly that daily trimming was
+often necessary. In 1893 the enclosed arc appeared and although it
+consumed as much electrical energy as the open-arc and emitted
+considerably less light, it possessed the great advantage of operating a
+week without requiring a renewal of carbons. By surrounding the arc
+by means of a glass globe, little oxygen could come in contact with the
+carbons and they were not consumed very rapidly. The light was fairly
+steady and these arcs operated satisfactorily on alternating current.
+The latter feature simplified the generating and distributing equipment
+of the central station.
+
+The magnetite or luminous arc-lamp next appeared and met with
+considerable success. It was more efficient than the preceding lamps but
+was handicapped by being solely a direct-current device. Those familiar
+with the generation and distribution of electricity will realize this
+disadvantage. However, its luminous intensity just below the horizontal
+was about 700 candles and its general distribution of light was fairly
+satisfactory. Later the flame-arcs began to appear and they were
+installed to some extent. The arc-lamp has served well in
+street-lighting from the year 1877, when the open-arc was introduced,
+until the present time, when the luminous-arc is the chief survivor of
+all the arc-lamps.
+
+The carbon incandescent filament lamp was used extensively until 1909,
+when the tungsten filament lamp began to replace it very rapidly.
+However, it was not until 1914, when the gas-filled tungsten lamp
+appeared, that this type of light-source could compete with arc-lamps on
+the basis of efficiency. The helical construction of the filament made
+it possible to confine the filament of a high-intensity tungsten lamp in
+a small space and for the first time a high degree of control of the
+light of street lamps was possible. Prismatic "refractors" were
+designed, somewhat on the principle of the lighthouse refractor, so
+that the light would be emitted largely just below the horizontal. This
+type of distribution builds up the illumination at distant points
+between successive street lamps, which is very desirable in
+street-lighting. The incandescent filament lamp possesses many
+advantages over other systems. It is efficient; capable of subdivision;
+operates on direct and alternating current; requires little attention;
+and is capable of most successful use with light-controlling apparatus.
+
+According to the reports of the Department of Commerce the number of
+electric arc-lamps for street-lighting supplied by public electric-light
+plants decreased from 348,643 in 1912 to 256,838 in 1917, while the
+number of electric incandescent filament lamps increased from 681,957 in
+1912 to 1,389,382 in 1917.
+
+Street-lighting is not only a reinforcement for the police but it
+decreases accidents and has come to be looked upon as an advertising
+medium. In the downtown districts the high-intensity "white-way"
+lighting is festive. The ornamental street lamps have possibilities in
+making the streets attractive and in illuminating the buildings.
+However, it is to be hoped that in the present age the streets of cities
+and towns will be cleared of the ragged equipment of the telephone and
+lighting companies. These may be placed in the alleys or underground,
+leaving the streets beautiful by day and glorified at night by the
+torches of advanced civilization.
+
+
+
+
+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. Caesar, 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 square root of Height of object in
+feet. For example, the top of a tower 100 feet high is visible to an eye
+at sea-level a distance of 8/7 square root of 100 = 80/7 = 11.43
+miles. Now if the eye is 49 feet above sea-level, a similar computation
+will show how far away it may be seen by the original eye at sea-level.
+This is 8/7 square root of 49 = 8 miles. Hence an eye 49 feet above
+sea-level will be able to see the top of the 100-foot tower at a
+distance of 11.43 + 8 or 19.43 nautical miles. Under these conditions an
+imaginary line drawn from the top of the tower to the eye will be just
+tangent to the spherical surface of the sea at a distance of 8 miles
+from the eye and 11.43 miles from the tower.
+
+The luminous intensity of a light-source or of the beam of light is
+directly responsible for the range. The luminous intensity of the early
+beacon-fires and oil-lamps was equivalent to a few candles. The
+improvements in light-sources and also in reflecting and refracting
+optical systems have steadily increased the candle-power of the beams,
+until to-day the beams from gas-lamps have intensities as high as
+several hundred thousand candle-power. The beams sent forth by modern
+lighthouses equipped with electric lamps and enormous light-gathering
+devices are rated in millions of candle-power. In fact, Navesink Light
+at the entrance of New York Bay is rated as high as 60,000,000
+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.
+
+[Illustration: A. A COMPLETED LIGHTHOUSE LENS]
+
+[Illustration: B. TORRO POINT LIGHTHOUSE, PANAMA CANAL]
+
+[Illustration: AMERICAN SEARCH-LIGHT POSITION ON WESTERN FRONT IN 1919]
+
+[Illustration: AMERICAN STANDARD FIELD SEARCH-LIGHT AND POWER UNIT]
+
+Doubtless, the reader has noted that reliability, simplicity, and low
+cost of operation are the primary considerations for light-sources used
+as aids to navigation. This accounts for the continued use of oil and
+gas. From an optical standpoint the electric arc-lamps and
+concentrated-filament lamps are usually superior to the earlier sources
+of light, but the complexity of a plant for generating electricity is
+usually a disadvantage in isolated places. The larger light-ships are
+now using electricity generated by apparatus installed in the vessels.
+There seems to be a tendency toward the use of more buoys and fewer
+lighthouses, but the beam-intensities of the latter are increasing.
+
+In the hundred years since the Boston Light was built the same great
+changes wrought by the development of artificial light in other
+activities of civilization have appeared in the beacons of the mariner.
+The development of these aids to navigation has been wonderful, but it
+must go on and on. The surface of the earth comprises 51,886,000 square
+statute miles of land and 145,054,000 square miles of water. Three
+fourths of the earth's surface is water and the oceans will always be
+highways of world commerce. All the dangers cannot be overcome, but
+human ingenuity is capable of great achievements. Wreckage will appear
+along the shore-lines despite the lights, but the harvest of the shoals
+has been much reduced since the time described by Robert Louis
+Stevenson, when the coast people in the Orkneys looked upon wrecks as a
+source of gain. He states:
+
+     It had become proverbial with some of the inhabitants to
+     observe that "if wrecks were to happen, they might as well be
+     sent to the poor island of Sanday as anywhere else." On this
+     and the neighboring island, the inhabitants have certainly had
+     their share of wrecked goods. On complaining to one of the
+     pilots of the badness of his boat's sails, he replied with some
+     degree of pleasantry, "Had it been His [God's] will that you
+     come na here wi these lights, we might a' had better sails to
+     our boats and more o' other things."
+
+     In the leasing of farms, a location with a greater probability
+     of shipwreck on the shore brought a much higher rent.
+
+
+
+
+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 aerial bomber; flares
+exposed the manoeuvers of the enemy; rockets brought aid to
+beleaguered vessels and troops; pistol lights fired by the aerial
+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 aeronautics 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 aerial 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 aerial 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:
+
+              Hours       Equivalent of          Candle-hours
+     Year   per night    light in candles    per night     per year
+     1800       3               5               15            5,500
+     1850       3               8               24            8,700
+     1860       3              11               33           12,000
+     1870       3              22               66           24,000
+     1880       3.5            36              126           46,000
+     1890       4              50              200           73,000
+     1900       5             154              770          280,000
+
+It is seen from the foregoing that in a century the candle-equivalent
+obtainable for the same cost to the householder increased at least
+thirty times, while the hours during which this light is used have
+nearly doubled. In other words, in the nineteenth century the
+candle-hours obtainable for $20.00 per year increased about fifty
+times. Stated in another manner, the cost of light at the end of the
+century was about one fiftieth that of candle light at the beginning of
+the century. One authority in computing the expense of lighting to the
+householder in a large city of this country has stated that
+
+     coincident with an increase of 1700 per cent. in the amount of
+     night lighting of an American family, in average circumstances,
+     using gas for light, there has come a reduction in the cost of
+     the year's lighting of 34 per cent. or approximately $7.50 per
+     year; and that the cost of lighting per unit of light--the
+     candle-hour--is now but 2.8 per cent. of what it was in the
+     first half of the nineteenth century. No other necessity of
+     household use has been so cheapened and improved during the
+     last century.
+
+In general, the light-user has taken advantage of the decrease by
+increasing the amount of light used and the period during which it is
+used. In this manner the greatly diminished cost of light has been a
+marked sociological and economic influence.
+
+After Murdock made his first installation of gas-lighting in an
+industrial plant early in the nineteenth century, he published a
+comparison of the expense of operation with that of candle-lighting. He
+arrived at the costs of light equivalent to 1000 candle-hours as
+follows:
+
+                                                 1000 candle-hours
+     Gas-lighting at a rate of two hours per day     $1.95
+          "        " "  "   "  three "    "   "       1.40
+     Candle-lighting                                  6.50
+
+It is seen that the longer hours of burning reduce the cost of
+gas-lighting by reducing the percentage of overhead charges. There are
+no such factors in lighting by candles because the whole "installation"
+is consumed. This is an early example of which an authentic record is
+available. At the present time a certain amount of light obtained for
+$1.00 with efficient tungsten filament lamps, costs $2.00 if obtained
+from kerosene flames and about $50.00 if obtained by burning candles.
+
+In order to obtain the cost of an equivalent amount of light throughout
+the past century a great many factors must be considered. Obviously, the
+results obtained by various persons will differ owing to the unavoidable
+factor of judgment; however, the following list of approximate values
+will at least indicate the trend of the price of light throughout the
+century or more of rapid developments in light-production. A fair
+average of the retail values of fuels and of electrical energy and an
+average luminous efficiency of the light-sources involved have been used
+in making the computations. The figures apply particularly to this
+country.
+
+TABLE SHOWING THE APPROXIMATE TOTAL COST OF 1000 CANDLE-HOURS FOR
+VARIOUS PERIODS
+
+                                               Per 1000
+                                             candle-hours
+     1800 to 1850, sperm-oil                     $2.40
+                   tallow candle                  5.00
+     1850 to 1865, kerosene                       1.65
+                   tallow candle                  6.85
+     1865 to 1875, kerosene                        .75
+                   tallow candle                  6.25
+                   gas, open-flame                 .90
+     1875 to 1885, kerosene                        .25
+                   gas, open-flame                 .60
+     1885 to 1895, kerosene                        .15
+                   gas, open-flame                 .40
+     1895 to 1915, gas mantle                      .07
+                   carbon filament                 .38
+                   metallized filament             .28
+                   tungsten filament (vacuum)      .12
+                   tungsten filament (gas-filled)  .07
+
+In these days the cost of living has claimed considerable attention and
+it is interesting to compare that of lighting. In the following table
+the price of food and of electric lighting are compared for twenty years
+preceding the recent war. The great disturbance due to the war is
+thereby eliminated from consideration, but it should be noted that since
+1914 the price of food has greatly increased but that of electric
+lighting has not changed materially. The cost of each commodity is taken
+as one hundred units for the year 1894 but, of course, the actual cost
+of living for the householder is perhaps a hundred times greater than
+the cost of electric lighting.
+
+     Year         Food    Electric lighting
+     1894         100            100
+     1896          80             92
+     1898          92             90
+     1900         100             85
+     1902         113             77
+     1904         110             77
+     1906         115             57
+     1908         128             30
+     1910         138             28
+     1912         144             23
+     1914         145             17
+
+One feature of electric lighting which puzzles the consumer and which
+gives the politicians an opportunity for crying "discrimination" and
+"injustice" at the public-service company is the great variation in
+rates. There is no discrimination or injustice when the householder, for
+example, must pay more for his lighting than a factory pays. The rates
+are not only affected by "demand" but by the period in which the demand
+comes. Residence lighting is chiefly confined to certain hours from 5 to
+9 P. M. and there is a great "peak" of demand at this time. The
+central-stations must have equipment available for this short-time
+demand and much of the capacity of the equipment is unused during the
+remainder of the day. The factory which uses electricity throughout the
+day or night or both is helping to keep the central-station operating
+efficiently. The equipment necessary to supply electricity to the
+factory is operating long hours. Not only is this overhead charge much
+less for factories and many other consumers than for the householder,
+but the expense of accounting, of reading meters, etc., is about the
+same for all classes of consumers. Therefore, this is an appreciable
+item on the bill of the small consumer.
+
+Doubtless, the public does not realize that the enormous decrease in the
+cost of lighting during the past century is due largely to the fact that
+the lighting industry has grown large. Increased production is
+responsible for some of this decrease and science for much of it. The
+latter, having been called to the aid of the manufacturers, who are
+better able by virtue of their magnitude to spend time and resources
+upon scientific developments, has responded with many improvements which
+have increased the efficiency of light-production. Some figures of the
+Census Bureau may be of interest. These are given for 1914 in order that
+the abnormal conditions due to the recent war may be avoided. The
+figures pertaining to the manufacture of gas for sale which do not
+include private plants are as follows for the year 1914 for this
+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.
+
+[Illustration: SIGNAL-LIGHT FOR AIRPLANE]
+
+[Illustration: TRENCH LIGHT-SIGNALING OUTFIT]
+
+[Illustration: AVIATION FIELD LIGHT-SIGNAL PROJECTOR]
+
+[Illustration: SIGNAL SEARCH-LIGHT FOR AIRPLANE]
+
+[Illustration: UNSAFE, UNPRODUCTIVE LIGHTING WORTHY OF THE DARK AGES]
+
+[Illustration: THE SAME FACTORY MADE SAFE, CHEERFUL, AND MORE PRODUCTIVE
+BY MODERN LIGHTING]
+
+There is another aspect of the subject which deals particularly with the
+safety of the light-source or method of lighting. As each innovation
+in lighting appeared during the past century there immediately arose the
+question of safety. The fire-hazard of open flames received attention in
+early days, and when gas-lighting appeared it was condemned as a poison
+and an explosive. Mineral-oil lamps introduced the danger of explosions
+of the vapors produced by evaporation. When electric lighting appeared
+it was investigated thoroughly. The result of all this has been an
+effort to make lamps and methods safe. Insurance companies have the
+relative safety of these systems established to their satisfaction and
+to-day little fire-hazard is attached to the present modes of general
+lighting if proper precautions have been taken.
+
+When electric lighting was first introduced the public looked upon
+electricity as dangerous and naturally many questions pertaining to
+hazards arose. The distribution of electricity has been so highly
+perfected that little is heard of the hazards which were so magnified in
+the early years. Data gathered between 1884 and 1889 showed that about
+13,000 fires took place in a certain district. Of these, 42 were
+attributed to electric wires; 22 times as many to breakage and explosion
+of kerosene lamps; and ten times as many through carelessness with
+matches. These figures cannot be taken at their face value because of
+the absence of data showing the relative amount of electric and kerosene
+lighting; nevertheless they are interesting because they represent the
+early period.
+
+There are industries where unusual care must be exercised in regard to
+the lighting. In certain chemical industries no lamps are used excepting
+the incandescent lamp and this is enclosed in an air-tight glass globe.
+Even a public-service gas company cautions its employees and patrons
+thus: "_Do not look for a gas-leak with a naked light! Use electric
+light._" The coal-mine offers an interesting example of the precautions
+necessary because the same type of problems are found in it as in
+industries in general, with the additional difficulties attending the
+presence or possible presence of explosive gas. The surroundings in a
+coal-mine reflect a small percentage of the light, so that much light is
+wasted unless the walls are whitewashed. This is a practical method for
+increasing safety in coal-mines. However, the most dangerous feature is
+the light-source itself. According to the Bureau of Mines during the
+years 1916 and 1917 about 60 per cent. of the fatalities due to gas and
+coal-dust explosions were directly traceable to the use of defective
+safety lamps and to open flames.
+
+In the early days of coal-mining it was found that the flame of a candle
+occasionally caused explosions in the mines. It was also found that
+sparks of flint and steel would not readily ignite the gas or coal-dust
+and this primitive device was used as a light-source. Of course,
+statistics are unavailable concerning the casualties in coal-mines
+throughout the past centuries, but with the accidents not uncommon in
+this scientific age, with its elaborate organizations striving to stamp
+out such casualties, there is good reason to believe that previous to a
+century or two ago the risks of coal-mining must have been great. Open
+flames have been widely used in this industry, but there has always been
+the risk of the presence or the appearance of gas or explosive dust.
+
+The early open-flame lamps not only were sources of danger but their
+feeble varying intensity caused serious damage to the eyesight of
+miners. This factor is always present in inadequate and improper
+lighting, but its influence is noticeable in coal-mining in the nervous
+disease affecting the eyes which is known as nystagmus. The symptoms of
+the disease are inability to see at night and the dazzling effect of
+ordinary lamps. Finally objects appear to the sufferer to dance about
+and his vision is generally very much disturbed.
+
+The oil-lamps used in coal-mining have a luminous intensity equivalent
+to about one to four candles, but owing to the atmospheric conditions in
+the mines a flame does not burn as brightly as in the fresh air. The
+possibility of explosion due to the open flame was eliminated by
+surrounding it with a metal gauze. Davy was the inventor of this device
+and his safety lamp introduced about a hundred years ago has been a boon
+to the coal-miner. Various improvements have been devised, but Davy's
+lamp contained the essentials of a safety device. The flame is
+surrounded by a cylinder of metal gauze which by forming a much cooler
+boundary prevents the mine-gas from becoming heated locally by the lamp
+flame to a sufficient temperature to ignite and consequently to explode.
+This device not only keeps the flame from igniting the gas but it also
+serves as an indicator of the amount of gas present, by the variation in
+the size and appearance of the tip of the flame. However, the gauze
+reduces the luminous output, and as it accumulates soot and dust the
+light is greatly diminished. One of these lamps is about as luminous as
+a candle, initially, but its intensity is often reduced by accumulations
+upon the gauze to only one fifth of the initial value.
+
+The acetylene lamp is the best open-flame light-source available to the
+miner, for several reasons. It is of a higher candle-power than the
+others and as it is a burning gas, there is not the danger of flying
+sparks as in the case of burning wicks. The greater intensity of
+illumination affords a greater safety to the miner by enabling him to
+detect loose rock which may be ready to fall upon him. However, this
+lamp may be a source of danger, owing to the fact that it will burn more
+brilliantly in a vitiated atmosphere than other flame-lamps. Another
+disadvantage is the possibility of calcium carbide accidentally spilt
+coming in contact with water and thereby causing the generation of
+acetylene gas. If this is produced in the mine in sufficient quantities
+it is a danger which may not be suspected. If ignited it will explode
+and may also cause severe burns.
+
+The electric lamp, being an enclosed light-source capable of being
+subdivided and fed by a small portable battery, early gave promise of
+solving the problem of a safe mine-lamp of adequate candle-power. Much
+ingenuity has been applied to the development of a portable electric
+safety mine-lamp, and several such lamps are now approved by the Bureau
+of Mines. Two general types are being manufactured, the cap outfit and
+the hand outfit. They consist essentially of a lamp in a reflector whose
+aperture is closed with a sheet or a lens of clear glass. The battery
+may be of the "dry" or "storage" type and in the case of the cap outfit
+the battery is carried on the back. The specifications for these lamps
+demand that a luminous intensity averaging at least 0.4 candle be
+maintained throughout twelve consecutive hours of operation. At no time
+during this period shall the output of light fall below 1.25 lumens for
+a cap-lamp and below 3 lumens for a hand-lamp. Inasmuch as these are
+equipped with reflectors, the specifications insist that a circle of
+light at least seven feet in diameter shall be cast on a wall twenty
+inches away. It appears that a portable lamp is an economic necessity in
+the coal-mines, on account of the expense, inconvenience, and possible
+dangers introduced by distribution systems such as are used in most
+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.
+
+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.
+
+[Illustration: LOCOMOTIVE ELECTRIC HEADLIGHT]
+
+[Illustration: SEARCH-LIGHT ON A FIRE-BOAT]
+
+[Illustration: BUILDING SHIPS UNDER ARTIFICIAL LIGHT AT HOG ISLAND
+SHIPYARD]
+
+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.
+
+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.
+
+Many other instances could be cited in which artificial light is very
+closely associated with the cost of living. Overseas shipment of fruit
+from the Canadian Northwest is responsible for a decided innovation in
+fruit-picking. In searching for a cause of rotting during shipment it
+was finally concluded that the temperature at the time of picking was
+the controlling factor. As a consequence, daytime was considered
+undesirable for picking and an electric company supplied electric
+lighting for the orchards in order that the picking might be done during
+the cool of night. This change is said to have remedied the situation.
+Cases of threshing and other agricultural operations being carried on at
+night are becoming more numerous. These are just the beginnings of
+artificial light in a new field or in a new relation to civilization.
+Its economic value has been demonstrated in the ordinary fields of
+lighting and these new applications are merely the initial skirmishes
+which precede the conquest of new territory. The modern illuminants have
+been developed so recently that the new possibilities have not yet been
+established. However, artificial light is already a factor on the side
+of the people in the struggle against the increasing cost of living, and
+its future in this direction is still more promising.
+
+
+
+
+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.
+
+[Illustration: In a moving-picture studio
+
+In a portrait studio
+
+ARTIFICIAL LIGHT IN PHOTOGRAPHY]
+
+[Illustration: 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:
+
+     Roentgen 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 Roentgen rays were discovered by Roentgen in 1896 and they have been
+studied and applied very widely ever since. Their great use has been in
+X-ray photography, but they are also being used in therapeutics. The
+extreme ultra-violet rays are not available in sunlight and are
+available only near a source rich in ultra-violet rays, such as the
+arc-lamps. They are absorbed by air, so that they are studied in a
+vacuum. These are the rays which convert oxygen into ozone because the
+former strongly absorbs them. The middle ultra-violet rays are not found
+in sunlight, because they are absorbed by the atmosphere. They are also
+absorbed by ordinary glass but are freely transmitted by quartz. The
+nearer ultra-violet rays are found in sunlight and in most artificial
+illuminants and are transmitted by ordinary glass. Next to this region
+is the visible spectrum with the various colors, from violet to red,
+induced by radiant energy of increasing wave-length. The infra-red rays
+are sometimes called heat-rays, but all radiant energy may be converted
+into heat. Various substances transmit and absorb these rays in general
+quite differently from the visible rays. Water is opaque to most of the
+infra-red rays. Next there is a region of wave-lengths or frequencies
+for which no radiant energy has been found. The so-called electric waves
+vary in wave-length over a great range and they include those employed
+in wireless telegraphy. All these radiations are of the same general
+character, consisting of electromagnetic energy, but differing in
+wave-length or frequency of vibration and also in their effects. In
+effect they may overlap in many cases and the whole is a chaos if the
+physical details of quantity and wave-length are not specified in
+experimental work.
+
+[Illustration: In art work
+
+In a haberdashery
+
+JUDGING COLOR UNDER ARTIFICIAL DAYLIGHT]
+
+[Illustration: In an underground tunnel
+
+In an art gallery
+
+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.
+
+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 anaesthetic powers and have been used in this role 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 role 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. Roentgen 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 Roentgen 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.
+
+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.
+
+[Illustration: FIREWORKS AND ILLUMINATED BATTLE-FLEET AT HUDSON-FULTON
+CELEBRATION]
+
+[Illustration: 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.
+
+[Illustration: 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]
+
+[Illustration: NIAGARA FALLS FLOODED WITH LIGHT]
+
+After the close of the recent war artificial light played a prominent
+part throughout the country in the joyful festivals. A jeweled arch
+erected in New York in honor of the returning soldiers rivaled some of
+the spectacles of the Panama-Pacific Exposition. The arch hung like a
+gigantic curtain of jewels between two obelisks, which rose to a height
+of eighty feet and were surmounted by jeweled forms in the shape of
+sunbursts. Approximately thirty thousand jewels glittered in the beams
+of batteries of arc-projectors. Many of the signs and devices which
+played a part in the "Welcome Home" movement were of striking nature and
+of a character to indicate permanency. The equipment of a large building
+consisted of more than five thousand 10-watt lamps, the entire building
+being outlined with stars consisting of eleven lamps each. The "Brighten
+Up" campaign spread throughout the country. The lighting and
+installation of signs and special patriotic displays, the flooding of
+streets and shop-windows with light without stint, produced an inspiring
+and uplifting effect which did much to restore cheerfulness and
+optimism. A glowing example was set in Washington, where the
+flood-lighting of the Capitol, discontinued shortly after our entrance
+into the war, was resumed.
+
+In Chicago a "Victory Way" was established, with street-lighting posts
+on both sides of the street equipped with red, white, and blue globes
+surmounted by a golden goddess of Victory. One hundred and seventy-five
+projectors were installed along the way on the roofs and in the windows
+of office buildings. A brilliant, scintillating "Altar of Victory" was
+erected at the center of the Way. It was composed of two enormous
+candelabra erected one on each side of a platform ninety feet high.
+These were studded with jewels and supported a curtain of jewels
+suspended from the altar. In the center of the curtain was a huge
+jeweled eagle bearing the Allied flags. This was illuminated by
+arc-projectors which delivered 200,000,000 beam candle-power. In
+addition to these there were many smaller projectors. In the top of each
+candelabra six large red-and-orange lamps were installed in reflectors.
+These illuminated live steam which issued from the top. Surmounting the
+whole was a huge luminous fan formed by beams from large arc
+search-lights. These are only a few of the many lighting effects which
+welcomed the returning soldiers, but they illustrate how much modern
+civilization depends upon artificial light for expressing its feelings
+and emotions. Throughout all these festivals light silently symbolized
+happiness, freedom, and advancement.
+
+Projectors were used on a large scale in several cases before the advent
+of the concentrated filament lamp. W. D'A. Ryan, the leader in
+spectacular lighting, lighted the Niagara Falls in 1907 with batteries
+of arc-projectors aggregating 1,115,000,000-beam candle-power. In 1908
+he used thirty arc-projectors to flood the Singer Tower in New York with
+light and projected light to the flag on top by means of a search-light
+thirty inches in diameter. Many flags waved throughout the war in the
+beams of search-lights, symbolizing a patriotism fully aroused. The
+search-light beam as it bores through the atmosphere at night is usually
+faintly bright, owing to the small amount of fog, dust, and smoke in the
+air. By providing more "substance" in the atmosphere, the beams are made
+to appear brighter. Following this reasoning, Ryan developed his
+scintillator consisting of a battery of search-light beams projected
+upward through clouds of steam which provided an artificial fog. This
+was first displayed at the Hudson-Fulton celebration with a battery of
+arc search-lights totaling 1,000,000,000-candle-power.
+
+All these effects despite their magnitude were dwarfed by those at the
+Panama-Pacific Exposition, and inasmuch as this up to the present time
+represents the crowning achievement in spectacular lighting, some of the
+details worked out by Ryan may be of interest. In general, the lighting
+effects departed from the bizarre outline lighting in which glaring
+light-sources studded the structures. The radiant grandeur and beauty
+of flood-lighting from concealed light-sources was the key-note of the
+lighting. In this manner wonderful effects were obtained, which not only
+appealed to the eye and to the artistic sensibility but which were free
+from glare. By means of flood-lighting and relief-lighting from
+concealed light-sources the third dimension or depth was obtained and
+the architectural details and colorings were preserved. A great many
+different kinds of devices and lamps were used to make the night effects
+superior in grandeur to those of daytime. The Zone or amusement section
+was lighted with bare lamps in the older manner and the glaring bizarre
+effects contrasted the spectacular lighting of the past with the
+illumination of the future.
+
+In another section the visitor was greeted with a gorgeous display of
+carnival spirit. Beautifully colored heraldic shields on which were
+written the early history of the Pacific coast were illuminated by
+groups of luminous arc-lamps on standards varying from twenty-five to
+fifty-five feet in height. The Tower of Jewels with more than a hundred
+thousand dangling gems was flood-lighted, and the myriads of minute
+reflected images of light-sources glittering against the dark sky
+produced an effect surpassing the dreams of imagination. Shadows and
+high-lights of striking contrasts or of elusive colors greeted the
+visitor on every hand. Individual isolated effects of light were to be
+found here and there. Fire hissed from the mouths of serpents and cast
+the spell of mobile light over the composite Spanish-Gothic-Oriental
+setting. A colored beam of a search-light played here and there.
+Mysterious vapors rising from caldrons were in reality illuminated
+steam. Symbolic fountain groups did not escape the magic touch of the
+lighting wizard.
+
+In the Court of the Universe great areas were illuminated by two
+fountains rising about a hundred feet above the sunken gardens. One of
+these symbolized the setting sun, the other the rising sun. The shaft
+and ball at the crest of each fountain were glazed with heavy opal glass
+imitating travertine marble and in these were installed incandescent
+lamps of a total candle-power of 500,000. The balustrade seventy feet
+above the sunken gardens was surmounted by nearly two hundred
+incandescent filament search-lights. Light was everywhere, either
+varying in color into a harmonious scene or changing in light and shadow
+to mold the architecture and sculpture. The enormous glass dome of the
+Palace of Horticulture was converted into an astronomical sphere by
+projecting images upon it in such a manner that spots of light revolved;
+rings and comets which appeared at the horizon passed on their way
+through the heavens, changing in color and disappearing again at the
+horizon. All these effects and many more were mirrored in the waters of
+the lagoons and the whole was a Wonderland indeed.
+
+The scintillator consisted of 48 arc search-lights three feet in
+diameter totaling 2,600,000,000 beam candle-power. The lighting units
+were equipped with colored screens and the beams which radiated upward
+were supplied with an artificial fog by means of steam generated by a
+modern express locomotive. The latter was so arranged that the wheels
+could be driven at a speed of sixty miles per hour under brake, thereby
+emitting great volumes of steam and smoke, which when illuminated with
+various colors produced a magnificent spectacle. Over three hundred
+scintillator effects were worked out and this feature of fireless
+fireworks was widely varied. The aurora borealis and other effects
+created by this battery of search-lights extended for many miles. The
+many effects regularly available were augmented on special occasions and
+it is safe to state that this apparatus built upon a huge scale provided
+a flexibility of fireless fireworks never attained even with small-scale
+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.
+
+Those who have not viewed stage-lighting from behind the scenes would
+often be surprised at the crudity of the equipment, and especially at
+the superficial intellects which are responsible for some of the
+realistic effects obtained. But these are the result usually of
+experiment, not of directed knowledge. Furthermore, little thought is
+given to the emotional value of light, shade, and color. The flood of
+light and the spot of light are varied with gaudy color-effects, but how
+seldom is it possible to distinguish a deep relation between the
+lighting and the dramatic incidents!
+
+[Illustration: Soldiers' and Sailors' Monument
+
+Jeweled portal welcoming returned soldiers
+
+ARTIFICIAL LIGHT HONORING THOSE WHO FELL AND THOSE WHO RETURNED]
+
+[Illustration]
+
+[Illustration: 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 enjoys all the blessings of modern lighting, which is
+sufficient proof that cost is an insignificant item.
+
+In order to simplify the discussion of lighting the home the terminology
+of electric-lighting will be used. The principles expounded apply as
+well to gas as to electricity, and owing to the ingenuity of the
+gas-lighting experts, the possibilities of gas-lighting are extensive
+despite its handicaps. There are some places in the home, such as the
+kitchen and basement, where lighting is purely utilitarian in the narrow
+sense, but in most of the rooms the esthetic or, more broadly, the
+psychological aspects of lighting should dominate. Pure utility is
+always a by-product of artistic lighting and furthermore, the lighting
+effects will be without glare when they satisfy all the demands of
+esthetics.
+
+In dealing with lighting in the home the householder should concentrate
+his attention upon lighting effects. Unfortunately, he is not taught to
+do so, for everywhere he turns for help he finds the discussion directed
+toward fixtures and lamps instead of toward lighting effects. However,
+these are merely links in the chain from the meter to the eye. Lamps are
+of interest from the standpoint of quantity and quality of light, and
+fixtures are of importance chiefly as distributers of light. These
+details are merely means to an end and the end is the lighting effect.
+Of course, the fixtures are more important as objects than the wires
+because they are visible and should harmonize with the general
+decorative and architectural scheme.
+
+The home is the theater of life full of various moods and occasions;
+hence the lighting of a home should be flexible. A degree of variety
+should be possible. Controls, wiring, outlets, and fixtures should
+conspire to provide this variety. At the present time the average
+householder does not give much attention to lighting until he purchases
+fixtures. It is probable that he thought of it when he laid out or
+approved the wiring, but usually he does not consider it seriously until
+he visits the fixture-dealer to purchase fixtures. And then
+unfortunately the fixture-dealer does not light his home; he does not
+sell the householder lighting-effects designed to meet the requirements
+of the particular home; he sells merely fixtures.
+
+Unfortunately there are few fixtures available which have definite aims
+in lighting as demanded by the home. Of the great variety of fixtures
+available there are many artistic objects, but it is obvious that little
+attention is given to their design from the standpoint of lighting.
+That the fixture-dealer usually thinks of fixtures as objects and gives
+little or no thought to lighting effects is apparent from his
+conversation and from his display. He exhibits fixtures usually en masse
+and seldom attempts to illustrate the lighting effects produced in the
+room.
+
+The foregoing criticisms are presented to emphasize the fact that
+throughout the field of lighting the great possibilities which have been
+opened by modern light-sources are not fully appreciated. The point at
+which to begin to design the lighting for a home is the wiring.
+Unfortunately this is too often done by a contractor who has given no
+special thought to the possibilities of lighting and to the requirements
+in wiring and switches necessary in order to realize them. At this point
+the householder should attempt to form an opinion as to the relative
+values. Is artificial lighting important enough to warrant an
+expenditure of two per cent. of the total investment in the home and its
+furnishings? The answer will depend upon the extent to which artificial
+light is appreciated. It appears that four or five per cent. is not too
+much if it is admitted that the artificial lighting system ranks next to
+the heating plant in importance and that these two are the most
+important features of an interior of a residence. A switch or a
+baseboard outlet costs an insignificant sum but either may pay for
+itself many times in the course of a few years through its utility or
+convenience.
+
+It appears best to take up this subject room by room because the
+requirements vary considerably, but in order to be specific in the
+discussions, a middle-class home will be chosen. The more important
+rooms will be treated first and various simple details will be touched
+upon because, after all, the proper lighting of a home is realized by
+attention to small details.
+
+The living-room is the scene of many functions. It serves at times for
+the quiet gathering of the family, each member devoted to reading. At
+another time it may contain a happy company engaged at cards or in
+conversation. The lighting requirements vary from a spot or two of light
+to a flood of light. Excepting in the small living-rooms there does not
+appear to be a single good reason for a ceiling fixture. It is nearly
+always in the field of vision when occupants are engaged in
+conversation, and for reading purposes the portable lamp of satisfactory
+design has no rival. Wall brackets cannot supply general lighting
+without being too bright for comfort. If they are heavily shaded they
+may still emit plenty of light upward, but the adjacent spots on the
+walls or ceiling will generally be too bright. Wall brackets may be
+beautiful ornaments and decorative spots of light and have a right to
+exist as such, but they cannot be safely depended upon for adequate
+general lighting on those occasions which demand such lighting.
+
+As a general principle, it is well to visualize the furniture in the
+room when looking at the architect's drawings and it is advantageous
+even to cut out pieces of paper representing the furniture in scale. By
+placing these on the drawings the furnished room is readily visualized
+and the locations of baseboard outlets become evident. It appears that
+the best method of lighting a living-room is by means of decorative
+portable lamps. Such lamps are really lighting-furniture, for they aid
+in decorating and in furnishing the room at all times. A number of these
+lamps in the living-room insures great flexibility in the lighting, and
+the light may be kept localized if desired so that the room is restful.
+A room whose ceiling and walls are brilliantly illuminated is not so
+comfortable for long periods as one in which these areas are dimly
+lighted. Furthermore, the latter is more conducive to reading and to
+other efforts at concentration. The furniture may be readily shifted as
+desired and the portable lamps may be rearranged.
+
+Such lighting serves all the purposes of the living-room excepting those
+requiring a flood of light, but it is easy to conceal elaborate lighting
+mechanisms underneath the shades of portable lamps. Several types of
+portable lamps are available which supply an indirect component as well
+as direct light. The former illuminates the ceiling with a flood of
+light without any discomforting glare. Such a lighting-unit is one of
+the most satisfactory for the home, for two distinct effects and a
+combination of these introduce a desirable element of variety into the
+lighting. Not less than four and preferably six baseboard outlets should
+be provided in a living-room of moderate size. One outlet on the mantel
+is also to be desired for connecting decorative candlesticks, and
+brackets above the fireplace are of ornamental value. Although the
+absence of ceiling fixtures improves the appearance of the room, wiring
+may be provided for ceiling outlets in new houses as a matter of
+insurance against the possible needs of the future. When ceiling
+fixtures are not used, switches may be provided for the mantel brackets
+or certain baseboard outlets in order that light may be had upon
+entering the room.
+
+The merits of a portable lamp may be ascertained before purchasing by
+actual demonstration. Some of them are not satisfactory for
+reading-lamps, owing to the shape of the shade or to the position of the
+lamps. The utility of a table lamp may be determined by placing it upon
+a table and noting the spread of light while seated in a chair beside
+it. A floor lamp may also be tested very easily. A miniature floor lamp
+about four feet in height with an appropriate shade provides an
+excellent lamp for reading purposes because it may be placed by the side
+of a chair or moved about independent of other furniture. A tall floor
+lamp often serves for lighting the piano, but small piano lamps may be
+found which are decorative as well as serviceable in illuminating the
+music without glare.
+
+The dining-room presents an entirely different problem for the setting
+is very definite. The dining-table is the most important area in the
+room and it should be the most brilliantly illuminated area in the room.
+A demonstration of this point is thoroughly convincing. The decorator
+who designs wall brackets for the dining-room is interested in beautiful
+objects of art and not in a proper lighting effect. The fixture-dealer,
+having fixtures to sell and not recognizing that he could fill a crying
+need as a lighting specialist, is as likely to sell a semi-indirect or
+an indirect lighting fixture as he is to provide a properly balanced
+lighting effect with the table brightly illuminated. The indirect and
+semi-indirect units illuminate the ceiling predominantly with the
+result that this bright area distracts attention from the table. A
+brightly illuminated table holds the attention of the diners. Light
+attracts and a semi-darkness over the remainder of the room crowds in
+with a result that is far more satisfactory than that of a dining-room
+flooded with light.
+
+The old-fashioned dome which hung over the dining-table has served well,
+for it illuminated the table and left the remainder of the room dimly
+lighted. But its wide aperture made it necessary to suspend it rather
+low in order that the lamps within should not be visible. It is an
+obtrusive fixture and despite its excellent lighting effect, it went out
+of style. But satisfactory lighting principles never become antiquated,
+and as taste in fixtures changes the principles may be retained in new
+fixtures. Modern domes are available which are excellent for the
+dining-room if the lamps are well concealed. The so-called showers are
+satisfactory if the shades are dense and of such shape as to conceal the
+lamps from the eyes. Various modifications readily suggest themselves to
+the alert fixture-designer. Even the housewife can do much with silk
+shades when the principle of lighting the dining-table is understood.
+The so-called candelabra have been sold extensively for dining-rooms and
+they are fairly satisfactory if equipped with shades which reflect much
+of the light downward. Semi-indirect and indirect fixtures have many
+applications in lighting, but they do not provide the proper effect for
+a dining-room.
+
+It is easy to make a special fixture which will send a component of
+light downward to the table and will permit a small amount of diffused
+light to the ceiling and walls. If a daylight lamp is used for the
+direct component, the table will appear very beautiful. Under this light
+the linen and china are white, flowers and decorations on the china
+appear in their full colors, the silver is attractive, and the various
+color-harmonies such as butter, paprika, and baked potato are enticing.
+This is an excellent place for a daylight lamp if diffused light
+illuminating the remainder of the room and the faces of the diners is of
+a warm tone obtained by warm yellow lamps or by filtering these
+components of the light through orange shades. The ceiling fixture
+should be provided with two circuits and switches. In some cases it is
+easy to provide a dangling plug for connecting such electric equipment
+as a toaster, percolator, or candlesticks. Two candlesticks are
+effective on the buffet, but usually the smallest normal-voltage lamps
+available give too much light. Miniature lamps may be used with a small
+transformer, or two regular lamps may be connected in series. At least
+two baseboard outlets are convenient.
+
+The foregoing deals with the more or less essential lighting of a
+dining-room, but there are various practicable additional lighting
+effects which add much charm to certain occasions. Colored light of low
+intensity obtained from a cove or from "flower-boxes" fastened upon the
+wall is very pleasing. If a cove is provided around the room, two
+circuits containing orange and blue lamps respectively will supply two
+colors widely differing in effect. By mixing the two a beautiful rose
+tint may be obtained. This equipment has been installed with much
+satisfaction. A simpler method of obtaining a similar effect is to use
+imitation flower-boxes plugged into wall outlets. Artificial foliage
+adds to the charm of these boxes. The colored light is merely to add
+another effect on special occasions and its intensity should never be
+high. In the dining-room such unusual effects are not out of place and
+they need not be garish.
+
+The sun-room partakes of the characteristics of the living-room to some
+extent, but, it being smaller, a semi-indirect fixture may be
+satisfactory for general illumination. However, a portable lamp which
+supplies an indirect component of light besides the direct light serves
+admirably for reading as well as for flooding the room with light when
+necessary. Two or three baseboard outlets are desirable for attaching
+decorative or even purely utilitarian lamps. The sun-room is an
+excellent place for utilizing "flower-box" fixtures decorated with
+artificial foliage. In fact, a central fixture may assume the appearance
+of a "hanging basket" of foliage. The library and den offer no problems
+differing from those already discussed in the living-room. A careful
+consideration of the disposition of the furniture will reveal the best
+positions for the outlets. In a small library wall brackets may serve as
+decorative spots of light and if the shades are pendent they may serve
+as lamps for reading purposes. In both these rooms an excellent
+reading-lamp is desired, but it may be decorative as well. Wall outlets
+may be desired for decorative portable lamps upon the bookcases.
+
+The sleeping-room, which commonly is also a dressing-room, often
+exhibits the errors of a lack of foresight in lighting. In most rooms of
+this character there is one best arrangement of furniture and if this
+is determined it is easy to ascertain where the windows and outlets
+should be located. The windows may usually be arranged for twin beds as
+well as for a single one with obvious advantages of flexibility in
+arrangement. With the position of the bureau determined it is easy to
+locate outlets for two wall brackets, one on each side, about sixty-six
+inches above the floor and about five feet apart. When the brackets are
+equipped with dense upright shades, the figure before the mirror is well
+illuminated without glare and sufficient light reaches the ceiling to
+illuminate the whole room.
+
+A baseboard outlet should be available for small portable lamps which
+may be used upon the bureau or for electric heating devices. The same is
+true for the dressing-table; indeed, two small decorative lamps on the
+table serve better than high wall brackets owing to the fact that the
+user is seated. A baseboard outlet near the head of the bed or between
+the beds is convenient for a reading-lamp and for other purposes. An
+outlet in the center of the ceiling controlled by a convenient switch
+may be installed on building, as insurance against future needs or
+desires. But a single lighting-unit in the center of the ceiling does
+not serve adequately the needs at the bureau and dressing-table. In
+fact, two wall brackets properly located with respect to the bureau
+afford a lighting much superior for all purposes in the bedroom to that
+produced by a ceiling fixture.
+
+In the bath-room the principal problem is to illuminate the person,
+especially the face, before the mirror. Many mistakes are made at this
+point, despite the simplicity of the solution. In order to see the
+image of an object in a mirror, the object must be illuminated. It is
+best to do this in a straightforward manner by means of a small
+lighting-unit on each side of the mirror at a height of five feet. Both
+sides of the face will be well illuminated and the light-sources are low
+enough to eliminate objectionable shadows. The units may be merely
+pull-chain sockets containing frosted or opal lamps. A center bracket or
+a single unit suspended from the ceiling is not as satisfactory as the
+two brackets. These afford enough light for the entire bath-room. A
+baseboard or wall outlet is convenient for connecting a heater,
+curling-iron, and other electrically heated devices.
+
+The sewing-room, which in the middle-class home is usually a small room,
+is sometimes used as a bedroom. A ceiling fixture will supply adequate
+general lighting, but a baseboard outlet should be available for a short
+floor lamp or a table lamp for sewing purposes. An intense local light
+is necessary for this occupation, which severely taxes the eyes. A
+so-called daylight lamp serves very well in this case.
+
+[Illustration: OBTAINING TWO DIFFERENT MOODS IN A ROOM BY A PORTABLE
+LAMP WHICH SUPPLIES DIRECT AND INDIRECT COMPONENTS OF LIGHT]
+
+[Illustration: THE LIGHTS OF NEW YORK CITY
+
+Towering shafts of light defy the darkness and thousands of lighted
+windows symbolize man's successful struggle against nature]
+
+In the kitchen the wall brackets are easily located after the positions
+of the range, work-table, sink, etc., are determined. A bracket for each
+is advisable unless they are so located that one will serve two
+purposes. It is customary to have a combination fixture for gas and
+electricity. This is often suspended from the center of the ceiling, but
+inasmuch as the gas-light cannot be close to the ceiling, the fixture
+extends so far downward as to become a nuisance. Furthermore, a
+light-source hung low from the center of the ceiling is in such a
+position that the worker in the kitchen usually works in his shadow. If
+a ceiling outlet is used it should be an electrical socket at the
+ceiling. The combination fixture is best placed on the wall as a
+bracket. The so-called daylight lamps are valuable in the kitchen.
+
+In the basement a generous supply of ceiling outlets adds much to the
+satisfaction of a basement. One in each locker, one before the furnace,
+and a large daylight lamp above but to one side of the laundry trays are
+worth many times their cost. Furthermore, a wall socket for the electric
+iron and washing-machine is a convenience very much appreciated.
+
+In the stairways convenient three-way switches for each of the ceiling
+fixtures represents the best practice. A baseboard outlet in the upper
+hall affords a connection for a decorative lamp and pays for itself many
+times as a place to attach the vacuum-cleaner from which all the rooms
+on that floor may be served. In vestibules and on porches ceiling
+fixtures controlled by means of convenient switches are satisfactory.
+The entrance hall may be made to express hospitality by means of
+lighting which should be adequate and artistic.
+
+An adequate supply of outlets and wall switches is not costly and they
+pay generous dividends. With a scanty supply of these, the possibilities
+of lighting are very much curtailed. There is nothing intricate about
+locating switches and outlets, so the householder may do this himself,
+or he may view critically the plans as submitted. The chief difficulties
+are to throw aside his indifference and to readjust his ideas and
+values. It may be confidently stated that the possibilities of lighting
+far outrank most of the features which contribute to the cost of a house
+and of its furnishings.
+
+After considering the requirements and decorative schemes of the various
+rooms the householder should be competent to judge the appropriateness
+of the lighting effects obtained from fixtures which the dealer
+displays, but he should insist upon a demonstration. If the dealer is
+not equipped with a room for this purpose, he should be asked to
+demonstrate in the rooms to be lighted. If the fixture-dealer does not
+realize that he should be selling lighting effects, the householder
+should make him understand that lighting effects are of primary
+importance and the fixtures themselves are of secondary interest in most
+cases. The unused outlets that have been installed for possible future
+needs may be sealed in plastering if the positions are marked so that
+they may be found when desired.
+
+An advantage of portable lamps is that they may be taken away on moving.
+In fact, when lighting is eventually considered a powerful decorative
+medium, as it should be, it is probable that fixtures will be personal
+property attached to ceiling, wall, and floor outlets by means of plugs.
+
+A variety of incandescent lamps are available. For the home, opal,
+frosted, or bowl-frosted lamps are usually more satisfactory than clear
+lamps. Bare filaments should not be visible, for they not only cause
+discomfort and eye-strain but they spoil what might otherwise be an
+artistic effect. Lamps with diffusing bulbs do much toward eliminating
+harsh shadows cast by the edges of the shades, by the chains of the
+fixtures, etc. These lamps are available in many shapes and sizes and
+the householder should make a record of voltage, wattage, and shape of
+the lamps which he finds satisfactory in the various fixtures. The Mazda
+daylight lamp has several places in the home and the Mazda white-glass
+and other high-efficiency lamps supply many needs better than the vacuum
+lamps. In brackets and other purely decorative lighting-units small
+frosted lamps are usually the most satisfactory. There is a general
+desire for the warm yellowish light of the candle-flame, and this may be
+obtained by a tinted shade but usually more satisfactorily by means of a
+tinted lamp.
+
+The householder will find it interesting to become intimate with
+lighting, for it can serve him well. The housewife will often find much
+interest in making shades of textiles and of parchment. Charming
+glassware in appropriate tints and painted designs is available for all
+rooms. In the bedchamber and the nursery some of these painted designs
+are exceedingly effective. Fixtures should shield the lamps from the
+eyes, and the diffusing media whether glass or textile should be dense
+enough to prevent glare. No fixture can be beautiful and no lighting
+effect can be artistic if glare is present. If the architect and the
+householder will realize that light is a medium comparable with the
+decorator's media, better lighting will result. Light has the great
+advantage of being mobile and with adequate outlets and controls
+supplemented by fixtures from which different effects are available, the
+householder will find in lighting one of the most fruitful sources of
+interest and pleasure. It can do much toward expressing the taste of
+the householder or if neglected it can undo much of the effect of
+excellent decoration and furnishing. Artificial lighting, softly
+diffused and properly localized, is one of the most important factors in
+making a house a home.
+
+
+
+
+XXV
+
+LIGHTING--A FINE ART?
+
+
+In the preceding chapters the progress of light has been sketched from
+its obscure infancy to its vigorous youth of the present time. It has
+been seen that progress was slow until the beginning of the nineteenth
+century, after which it began to gain momentum until the present century
+has witnessed tremendous advances. Until the latter part of the
+nineteenth century artificial light was considered an expensive utility,
+but as modern lamps appeared which supplied adequate light at reasonable
+cost attention began to be centered upon utilization, and the lighting
+engineer was born. Gradually it is being realized that artificial light
+is no longer a luxury, that it may be used in great quantity, and that
+it may be directed, diffused, and altered in color as desired. Although
+the potentiality of light has been barely drawn upon, the present usages
+surpass the most extravagant dreams of civilized beings a half-century
+ago. Mere light of that time was changed into more light as gas-lighting
+developed, and more light has increased to adequate light of the present
+time through the work of scientists.
+
+It is apparent that a sudden enforced reversion to the primitive flames
+of fifty years ago would paralyze many activities. Much of interest and
+beauty would be blotted out of this brilliant, pulsating, productive
+age. It is startling to note that almost the entire progress in
+artificial lighting has taken place during the past hundred years and
+that most of it has been crowded into the latter part of this period. In
+fact, its development since it began in earnest has gone forward with
+ever-increasing momentum. On viewing the wonders of modern artificial
+lighting on every hand it is not difficult to muster the courage
+necessary to venture into its future.
+
+The lighting engineer has been a natural evolution of the present age,
+for the economic aspects of lighting have demanded attention. He is
+increasing the safety, efficiency, and happiness of mankind and
+civilization is beginning to feel his influence economically. However,
+with the advent of adequate, efficient, and controllable light, the
+potentiality of light as an artistic medium may be drawn upon and the
+lighting artist with a deep insight into the possibilities of artificial
+light now has his opportunity. But the artist who believes that a new
+art may be evolved to perfection in a few years is doomed to
+disappointment, for it is necessary only to view retrospectively such
+arts as painting and music to be convinced that understanding and
+appreciation develop slowly through centuries of experiment and contact.
+
+Will lighting ever become a fine art? Will it ever be able alone to
+arouse emotional man as do the fine arts? Are the powers of light
+sufficiently great to enthrall mankind without the aid of form, music,
+action, or spoken words? It is safer to answer "yes" than "no" to these
+questions. Painting has reached a high place as an art and this art is
+the expressiveness of secondary or reflected light reinforced by
+imitation forms, which by a combination of light and drawing comprise
+the "subjects." A painting is a momentary expression of light, a
+cross-section of something mobile, such as nature, thought, or action.
+Light has the essential qualifications of painting with the advantages
+of a greater range of brightness, of greater purity of colors, and the
+great potentiality of mobility. If lighting becomes a fine art it will
+doubtless be related to painting somewhat in the same manner that
+architecture is akin to sculpture. With the introduction of mobility it
+will borrow something from the arts of succession and especially from
+music.
+
+The art of lighting in its present infancy is leaning upon established
+arts, just as the infant learns to walk alone by first depending upon
+support. The use of color in painting developed slowly, being supported
+for centuries by the strength of drawing or subject. The landscapes of a
+century ago were dull, for color was employed hesitatingly and
+sparingly. The colors in the portraits of the past merely represented
+the gorgeous dress of bygone days. But the painter of the present shows
+that color is beginning to be used for itself and that the painter is no
+longer hesitant concerning its power to go hand in hand with drawing.
+Drafting and coloring are now in partnership, the former having given up
+guardianship when the latter reached maturity.
+
+Lighting is now an accompaniment of the drama, of the dance, of
+architecture, of decoration, and of music. It has been a background or a
+part of the "atmosphere" excepting occasionally when some one with
+imagination and daring has given it the leading role. Even in its
+infancy it has on occasions performed admirably almost without any aid.
+The bursting rocket, the marvelous effects at the Panama-Pacific
+Exposition, and some of the exhibitions on the theatrical stage are
+glimpses of the potentiality of light. To fall back upon the terminology
+of music, these may be glimmerings of light-symphonies.
+
+Harmony is simultaneity and a painting in this respect is a chord--a
+momentary expression fixed in material media. A melody of light requires
+succession just as the melody in music. The restless colors of the opal
+comprise a light melody like the songs of birds. The gorgeous splendor
+of the sunset compares in magnitude and in its various moods with the
+symphony orchestra and its powers. Throughout nature are to be found
+gentle chords, beautiful melodies and powerful symphonies of light and
+this music of light exhibits the complexity and structure analogous to
+music. There is no physical relation between music, poetry, and light,
+but it is easy to lean upon the established terminology for purposes of
+discussion. Those who would build color-music identical to sound music
+are making the mistake of starting with a physical foundation instead of
+basing the art of light-expression upon psychological effects of light.
+In other words, a relation between light and music can exist only in the
+psychological realm.
+
+These melodies and symphonies of light in nature are admittedly pleasing
+or impressive as the case may be, but are they as appealing as music,
+poetry, painting, or sculpture? The consensus of opinion of a large
+group of average persons might indicate a negative reply, but the
+combined opinion of this group is not so valuable as the opinion of a
+colorist or of an artist who has sensed the wonders of light. The
+unprejudiced opinion of artists is that light is a powerfully expressive
+and impressive medium. The psychologist will likely state that the
+emotive value of light or color is not comparable to the appeal of an
+excellent dinner or of many other commonplace things. But he has
+experimented only with single colors or with simple patterns and his
+subjects are selected more or less at random from the multitude. What
+would be his conclusion if he examined painters and others who have
+developed their sensibilities to a deep appreciation of light and color?
+It is certain that the painter who picks up a purple petal fallen from a
+rose and places it upon a green leaf is as thrilled by the powerful
+vibrant color-chord as the musician who hears an exquisite harmony of
+sounds.
+
+Music has been presented to civilized mankind in an organized manner for
+ages and the fundamental physical basis of modern music is a thousand
+years old. Would the primitive savage appreciate the modern symphony
+orchestra? Even the majority of civilized beings prefer the modern
+ragtime or jazz to the exquisite art of the symphony. An appreciation of
+the opera and the symphony is reached by educational methods extending
+over long periods. An appreciation of the expressiveness of light cannot
+be expected to be realized by any short-cut. Most persons to-day enjoy
+the melodramatic "movie" more than the drama and relatively few
+experience the deep appeal of the fine arts. Surely the symphony of
+light cannot be justly condemned because of a lack of appreciation and
+understanding of it, for it has not been introduced to the public.
+Furthermore, the expressiveness of music is still indefinite at best
+despite the many centuries of experimenting on the part of musicians.
+
+If poetry is to be believed, the symphonies of light as rendered by
+nature in the sunsets, in the aurora borealis, and in other sky-effects
+of great magnitude have deeply impressed the poet. If his descriptions
+are to be accepted at their face-value, the melodies of light rendered
+in the precious stone, in the ice-crystal, and in the iridescence of
+bird-plumage please his finer sensibilities. If he is sincere, mobile
+light is a seductive agency.
+
+The painter has contributed little of direct value in developing the
+music of light. He is concerned with an instantaneous expression. He
+waits for it patiently and, while waiting, learns to appreciate the
+fickleness of mood in nature, but when he fixes one of these moods he
+has contributed very little to the art of mobile light. Unfortunately
+the art schools teach the student little or nothing pertaining to color
+for color's sake. When the student is capable of drawing fairly well and
+is acquainted with a few stereotyped principles of color-harmony he is
+sent forth to follow in the footsteps of past masters. He may be seen at
+the art museum faithfully copying a famous painting or out in the fields
+stalking a tree with the hopes of an embryo Corot. The world moves and
+has only a position in the rank and file for imitators. Occasionally an
+artist goes to work with a vim and indulges in research, thereby
+demonstrating originality in two respects. Painting is just as much a
+field for research as light-production.
+
+Recently experiments are being made in the production of color-harmonies
+devoid of form. Surely there is a field for pure color-composition and
+this the field of the painter which leads toward the art of mobile
+light. Many of the formless paintings of the present day which pass
+under the banner of this _ism_ or that are merely experiments in the
+expressiveness of light. Being formless, they are devoid of subject in
+the ordinary sense and cannot be more or less than a fixed expression of
+light. Naturally they have received much criticism and have been
+ridiculed, but they can expect nothing else until they are understood.
+They cannot be understood until mankind learns their language and then
+they must be understandable. In other words, there are impostors
+gathered around the sincere research-artist because the former have
+neither the ability to paint for a living nor the inclination to forsake
+the comparative safety of the mystery of art for the practical world
+where their measure would be quickly taken. This army of camp-followers
+will not advance the art of mobile light, but the sincere seekers after
+the principles of light-expression who form the foundation of the
+various _isms_ may contribute much.
+
+The painter will always be available with his finer sensibility to
+appreciate and to aid in developing the art of mobile light, but his
+direct contribution appears most likely to come from the present chaos
+of experiments in pure color-composition, in the psychology of light,
+or, more broadly, in the expressiveness of light. The decorator and the
+designer of gowns and costumes do not arrogate to themselves the name
+"artist," but they are daily creating something which is leading toward
+a fuller appreciation of the expressiveness of light. If they do not
+contribute directly to the development of the art of mobile light, they
+are at least aiding in developing what may eventually be an appreciative
+public.
+
+The artist paints a "still-life," the decorator creates a color-harmony
+of abstract or conventional forms, and the costumer produces a
+color-composition in textiles. The decorator and costumer approach
+closer to pure color-composition than the artist in his still-life. The
+latter is a grouping of objects primarily for their color-notes. Why
+bother with a banana when a yellow-note is desired? Why utilize the
+abstract or conventional forms of the decorator? Why not follow this
+lead further to the less definite forms employed by the costumer? Why
+not eliminate form even more completely? This is an important point and
+an interesting lead, for to become rid of form has been one of the
+perplexing problems encountered by those who have dreamed of an art of
+mobile light.
+
+The painter who uses line and color imitatively has perhaps acquired
+skill in depicting objects and more or less appreciation of the
+beautiful. But if he is to be creative and to produce a higher art he
+must be able to use line and color without reference to objects. He thus
+may aid in the development of an abstract art which is the higher art
+and at the same time aid in educating the public to appreciate pure
+color-harmonies. From these momentary expressions of light and from the
+experience gained, the mobile colorist would receive material aid and
+his productions would be viewed by a more receptive audience or rather
+"optience" as it may be called. The development of taste for abstract
+art is needed in order that the art of mobile light may develop and,
+incidentally, an appreciation of the abstract in art is needed in all
+arts.
+
+Science has contributed much by way of clearing the decks. It has
+produced the light-sources and the apparatus for controlling light. It
+has analyzed the physical aspects of color-mixture and has accumulated
+extensive data pertaining to color-vision. It has pointed out pitfalls
+and during recent years has been delving further by investigating the
+psychology of light and color. The latter field is looked to for
+valuable information, but, after all, there is one way of making
+progress in the absence of data and that is to make attempts at the
+production of impressive effects of mobile light. Some of these have
+been made, but unfortunately they have been heralded as finished
+products.
+
+Perhaps the most general mistake made is in relating sounds and colors
+by stressing a mere analogy too far. Notwithstanding the vibratory
+nature of the propagation of sound and light, this is no reason for
+stressing a helpful analogy. After all it is the psychological effect
+that is of importance and it is absurd to attribute any connection
+between light-waves and sound-waves based upon a relation of physical
+quantities. No space will be given to such a relation because it is so
+absurdly superficial; however, the language of music will be borrowed
+with the understanding that no relation is assumed.
+
+A few facts pertaining to vision will indicate the trend of developments
+necessary in the presentation of mobile light. The visual process
+synthesizes colors and at this point departs widely from the auditory
+process. The sensation of white may be due to the synthesis of all the
+spectral colors in the proportions in which they exist in noon sunlight
+or it may be due to the synthesis of proper proportions of yellow and
+blue, of red, green, and blue, of purple and green, and a vast array of
+other combinations. A mixture of red and green lights may produce an
+exact match for a pure yellow. Thus it is seen that the mixture of
+lights will cause some difficulty. For example, the components of a
+musical chord may be picked out one by one by the trained ear, but if
+two or more colored lights are mixed they are merged completely and the
+resultant color is generally quite different from any of the components.
+In music of light, the components of color-chords must be kept
+separated, for if they are intermingled like those of musical chords
+they are indistinguishable. Therefore, the elements of harmony in mobile
+light must be introduced by giving the components different spatial
+positions.
+
+The visual process is more sluggish than the auditory process; that is,
+lights must succeed each other less rapidly than musical notes if they
+are to be distinguished separately. The ear can follow the most rapid
+execution of musical passages, but there is a tendency for colors to
+blend if they follow one another rapidly. This critical frequency or
+rate at which successive colors blend decreases with the brightness of
+the components. If red and green are alternated at a rate exceeding the
+critical frequency, a sensation of yellow will result; that is, neither
+component will be distinguishable and a steady yellow or a yellow of
+flickering brightness will be seen. The hues blend at a lower frequency
+than the brightness components of colors; hence there may be a blend of
+color which still flickers in brightness. Many weird results may be
+obtained by varying the rate of succession of colors. If this rate is so
+low that the colors do not tend to merge, they are much enriched by
+successive contrast. It is known that juxtaposed colors generally enrich
+one another and this phenomenon is known as simultaneous contrast.
+Successive contrast causes a similar effect of heightened color.
+
+An effect analogous to dynamic contrast in music may be obtained with
+mobile light by varying the intensity of the light or possibly the area.
+Melody may be simply obtained by mere succession of lights. Tone-quality
+has an analogy in the variation of the purity of color. For example, a
+given spectral hue may be converted into a large family of tints by the
+addition of various amounts of white light. Rhythm is as easily applied
+to light as to music, to poetry, to pattern, or to the dance, but in
+mobile lights its limitations already have been suggested. However, it
+is bound to play an important part in the art of mobile light because
+rhythmic experiences are much more agreeable than those which are
+non-rhythmic. Rhythm abounds everywhere and nothing so stirs mankind
+from the lowliest savage to the highly cultivated being as rhythmic
+sequences.
+
+Many psychological effects of light have been recorded from experiment
+and observation and affective values of light have been established in
+various other byways. It is possible that the degree of pleasure
+experienced by most persons on viewing a color-harmony or the delightful
+color-melody of a sunlit opal may be less than that experienced on
+listening to the rendition of music. However, if this were true it would
+offer no discouragement, because absolute values play a small part in
+life. Two events when directly compared apparently may differ enormously
+in their ability to arouse emotions, but the human organism is so
+adaptive that each in its proper environment may powerfully affect the
+emotions. For example, those who have sported in aerial antics in the
+heights of cloudland or have stormed the enemy's trench are still
+capable of enjoying a sunset or the call of a bird to its mate at dusk.
+The wonderful adaptability of the inner being is the salvation of art as
+well as of life.
+
+In the rendition of mobile light it is fair to give the medium every
+advantage. Sometimes this means to eliminate competitors and sometimes
+it means to remove handicaps. On the stage light has had competitors
+which are better understood. For example, in the drama words and action
+are easily understood, and regardless of the effectiveness of light it
+would not receive much credit for the emotive value of the production.
+In the wonderful harmony of music, dance, and light in certain recent
+exhibitions, the dance and music overpowered the effects of lights
+because they speak familiar languages.
+
+[Illustration: A community Christmas tree
+
+A community song-festival
+
+ARTIFICIAL LIGHT IN COMMUNITY AFFAIRS]
+
+[Illustration: PANAMA-PACIFIC EXPOSITION
+
+Artificial light not only reveals the beauty of decoration and
+architecture but enthralls mankind with its own unlimited powers]
+
+A number of attempts have been made to utilize light as an accompaniment
+of music and some of them on a small scale have been sincere and
+creditable, but a much-heralded exhibition on a large scale a few
+years ago was not the product of deep thought and sincere effort. For
+example, colored lights thrown upon a screen having an area of perhaps
+twenty square feet were expected to compete with a symphony orchestra in
+Carnegie Hall. The music reached the most distant auditor in sufficient
+volume, but the lighting effect dwindled to insignificance. Without
+entering into certain details which condemned the exhibition in advance,
+the method of rendition of the light-accompaniment revealed a lack of
+appreciation of the problems involved on the part of those responsible.
+
+Incidentally, it has been shown that the composer of this particular
+musical selection with its light accompaniment was psychologically
+abnormal; that is, he was affected with colored audition. It is not yet
+established to what extent normal persons are similarly affected by
+light and color. Certainly there is no similarity among the abnormal and
+none between the abnormal and normal.
+
+If light is to be used as an accompaniment to music, it must be given an
+opportunity to supply "atmosphere." This it cannot do if confined to an
+insignificant spot; it must be given extensity. Furthermore, by the use
+of diaphanous hangings, form will be minimized and the evanescent
+effects surely can be charming. But finally the lighting effects must
+fill the field of vision just as the music "fills the field of audition"
+in order to be effective. There are fundamental objections to the use of
+mobile light as an accompaniment to music and therefore the future of
+the art of mobile light must not be allowed to rest upon its success
+with music. If it progresses through its relation with music, so much
+is gained; if not, the relation may be broken for music is quite capable
+of standing alone.
+
+There is a tendency on the part of some revolutionary stage artists to
+give to lighting an emotional part in the play, or, in other words, to
+utilize lighting in obtaining the proper mood for the action of the
+play. Color and purely pictorial effect are the dominant notes of some
+of them. All of these modern stage-artists are abandoning the
+intricately realistic setting, and, as a consequence, light is enjoying
+a greater opportunity. In the more common and shallow theatrical
+production, lighting and color effects have many times saved the day,
+and, although these effects are not of the deeper emotional type, they
+may add a spectacular beauty which brings applause where the singing is
+mediocre and the comedy isn't comedy. The potentiality of lighting
+effects for the stage has been barely drawn upon, but as the
+expressiveness of light is more and more utilized on the stage, the art
+of mobile light will be advanced just so much more. Light, color, and
+darkness have many emotional suggestions which are easily understood and
+utilized, but the blending of mobile light with the action is difficult
+because its language is only faintly understood.
+
+It is futile to attempt to describe a future composition of mobile
+light. Certainly there is an extensive variety of possibilities. A
+sunset may be compressed into minutes or an opalescent sky may be a
+motif. Varying intensities of a single hue or of allied hues may serve
+as a gentle melody. Realistic effects may be introduced. The
+expressiveness of individual colors may be taken as a basis for
+constructing the various motifs. These may be woven into melody in which
+rhythm both in time and in intensity may be introduced. Action may be
+easily suggested and the number of different colors, in a broad sense,
+which are visible is comparable to the audible tones. Shading is as
+easily accomplished as in music and the development of this art need not
+be inhibited by a lack of mechanical devices and light-sources. The
+tools will be forthcoming if the conscientious artist requests them.
+
+Whatever the future of the art of mobile light may be, it is certain
+that the utilization of the expressiveness of light has barely begun. It
+may be that light-music must pass through the "ragtime" stage of
+fireworks and musical-revue color-effects. If so, it is gratifying to
+know that it is on its way. Certainly it has already served on a higher
+level in some of the artistic lighting effects in which mobility has
+featured to some extent.
+
+If the art does not develop rapidly it will be merely following the
+course of other arts. A vast amount of experimenting will be necessary
+and artists and public alike must learn. But if it ever does develop to
+the level of a fine art its only rival will be music, because the latter
+is the only other abstract art. Material civilization has progressed far
+and artificial light has been a powerful influence. May it not be true
+that artificial light will be responsible for the development of
+spiritual civilization to its highest level? If mobile light becomes a
+fine art, it will be man's most abstract achievement in art and it may
+be incomparably finer and more ethereal than music. If this is realized,
+artificial light in every sense may well deserve to be known as the
+torch of civilization.
+
+
+
+
+READING REFERENCES
+
+
+No attempt will be made to give a pretentious bibliography of the
+literature pertaining to the various aspects of artificial lighting, for
+there are many articles widely scattered through many journals. _The
+Transactions of the Illuminating Engineering Society_ afford the most
+fruitful source of further information; the _Illuminating Engineer_
+(London), contains much of interest; and _Zeitschrift fuer
+Beleuchtungswesen_ deals with lighting in Germany. H. R. D'Allemagne has
+compiled an elaborate "Historie du Luminaire" which is profusely
+illustrated, and L. von Benesch in his "Beleuchtungswesen" has presented
+many elaborate charts. In both these volumes lighting devices and
+fixtures from the early primitive ones to those of the nineteenth
+century are illustrated. A few of the latest books on lighting, in the
+English language, are "The Art of Illumination," by Bell; "Modern
+Illuminants and Illuminating Engineering," by Gaster and Dow;
+"Radiation, Light and Illumination," by Steinmetz; "The Lighting Art,"
+by Luckiesh; "Illuminating Engineering Practice," consisting of a course
+of lectures presented by various experts under the joint auspices of the
+University of Pennsylvania and the Illuminating Engineering Society;
+"Lectures on Illuminating Engineering," comprising a series of lectures
+presented under the joint auspices of Johns Hopkins University and the
+Illuminating Engineering Society; and "The Range of Electric Searchlight
+Projectors," by Rey; "The Electric Arc," by Mrs. Ayrton; "Electric Arc
+Lamps," by Zeidler and Lustgarten, and "The Electric Arc," by Child
+treat the scientific and technical aspects of the arc. G. B. Barham has
+furnished a book on "The Development of the Incandescent Electric Lamp."
+"Color and Its Applications," and "Light and Shade and Their
+Applications," are two books by Luckiesh which deal with lighting from
+unique points of view. "The Language of Color," by Luckiesh, aims to
+present what is definitely known regarding the expressiveness and
+impressiveness of color. W. P. Gerhard has supplied a volume on "The
+American Practice of Gaspiping and Gas Lighting in Buildings," and Leeds
+and Butterfield one on "Acetylene." A recent book in French by V.
+Trudelle treats "Lumiere Electrique et ses differentes Applications au
+Theatre." Many books treat of photometry, power-plants, etc., but these
+are omitted because they deal with phases of light which have not been
+discussed in the present volume. "Light Energy," by Cleaves, is a large
+volume devoted to light-therapy, germicidal action of radiant energy,
+etc. References to individual articles will often be found in the
+various indexes of publications.
+
+
+THE END
+
+
+
+
+INDEX
+
+
+Aaron, 43
+
+Accidents: 8;
+  street-lighting in relation to, 225 _et seq._;
+  percentage (table) of, due to improper lighting, 231
+
+Acetylene: 62;
+  light-yield of, 106, 107, 170, 187, 191
+
+Actinic rays: effect of, upon human organism, 275
+
+Africa, public lighting in ancient, 31
+
+Agni, god of fire, 40
+
+Air-pump, 130
+
+Air-raids, 225
+
+Alaska, 18, 29
+
+Alchemy, 20
+
+Aleutians, 18
+
+Alexandria, 43, 163
+
+Allylene, 106
+
+Aluminum, 108, 179, 180
+
+Amiens, Treaty of, 69
+
+Amylene, 106
+
+Aniline dyes, 106
+
+Animal: distinction between, and human being, 3; 15;
+  production of light, 24 _et seq._;
+  sources of light, 30, 31;
+  oils, 51
+
+Antimony, 294
+
+Antioch, 153
+
+Arago, 114, 196
+
+Archbishop of Canterbury, 49
+
+Archimedes, 19
+
+Arc: lamps, 69, 89;
+  electric, 111 _et seq._;
+  distinction between spark and, 112;
+  Davy's notes on electric, 113;
+  formation of, 115, 116;
+  Staite and enclosed, 117, 118;
+  principle of enclosed, 118, 119;
+  types of, 120;
+  flame-, 121, 122;
+  luminous, 122;
+  electric, 127;
+  luminous efficiency of electric (table), 124; 160 _et seq._;
+  -lamp in lighthouses, 168 _et seq._;
+  magnetite-, 187; 261
+
+Ardois system of signaling, 199
+
+Argand, Ami: 52;
+  inaugurates new era in artificial lighting, 53, 54; 63, 70, 76, 77, 78,
+    97, 167, 196
+
+Argon, 137
+
+Aristophanes, "The Clouds," 19
+
+Art Museums, 9, 13, 322, 323
+
+Asbestos, 170
+
+Asia: public lighting in ancient, 31, 39
+
+Automobiles, 238
+
+
+Babylon, 39
+
+Bacteria: effect of artificial light upon, 272 _et seq._; 281, 282
+
+Bailey, Prof. L. H., 250
+
+Baltimore, 98
+
+Bamboo: carbon filaments, 169
+
+Bartholdi, 302, 303
+
+Beacons. _See_ Lighthouses.
+
+Beck, 186
+
+Beecher, 72
+
+Beeswax, 35, 51
+
+Benzene, 106
+
+Bible, cited on importance of artificial light, 42-44
+
+"Bluebird, The," Maeterlinck, 9
+
+Blue-prints, 261
+
+Bollman, 98
+
+Bolton, von, 132, 133
+
+Bombs, illuminating, 182 _et seq._
+
+Boston Light, 164, 165, 166, 177
+
+Bowditch, production of regenerative lamp by, 78, 79
+
+Boy Scouts, 17
+
+Bremer, 120
+
+Bristol University, 252
+
+Brush, 68, 159
+
+Building, 8
+
+Bunsen, 81, 85, 89, 148, 149
+
+Bureau of Mines: cited on open flames, 234; 236
+
+Burning-glasses, 19, 20.
+  _See also_ Lenses.
+
+Butylene, 106
+
+Byzantium, 34
+
+
+Caesar, 163
+
+Canada, 254
+
+Candle-hour, defined, 215
+
+Candles: progress and, 7; 25, 28, 29, 30, 33;
+  religious uses of, 34, 35;
+  as a modern light-source, 36, 37;
+  ceremonial uses of, 38 _et seq._; 44, 48, 57, 82, 97, 222, 299, 304
+
+Calcium, 107, 108
+
+Carbolic acid, 106
+
+Carbon: 53, 80, 81;
+  physical characteristics of, 80, 81; 90, 104, 105, 128, 129, 144, 170
+
+Carbon filament: 127 _et seq._;
+  preparation of, 129, 130, 131;
+  luminous efficiency of, 131, 132;
+  lamps, 161;
+  lamps in greenhouses, 250 _et seq._
+
+Carbons, formation of, 115, 116
+
+Carbureted hydrogen, 75
+
+Carcel, invention of clockwork lamp by, 54, 55
+
+Cat-gut, 130
+
+Ceria, 85, 101
+
+Charleston, S. C., 185
+
+Charcoal: 113;
+  uses of, for electrodes, 115
+
+Chartered Gas Light and Coke Co., London, 74
+
+Chemistry: artificial light and, 256-268
+
+Chicago, 62, 304, 305
+
+Chimneys, 54, 60, 62
+
+China, 19, 31, 32
+
+Chlorate of potash, 22
+
+Christ, 33, 46, 47
+
+Christians, "children of light," 42
+
+Christmas trees, 43, 304
+
+Chromium, 294
+
+Church of England, 49
+
+Cities: economy of artificial lighting in congested, 13
+
+Civilization: effect of artificial light upon, 4 _et seq._;
+  fire and, 15
+
+Clark, Parker and, 139
+
+Clayton, Dr.: invention of portable gas-light by, 64;
+  quoted, 64, 65;
+  experiments of, with coal-gas, 67
+
+Claude, 147
+
+Cleaves, Dr., quoted, 276, 277
+
+Clegg, Samuel: 74;
+  gas-lighting accomplishments of, 75, 76
+
+Cleveland, 159
+
+"Clouds, The," Aristophanes, 19
+
+Coal: 32;
+  as a light-source, 55;
+  supply, 223; 228
+
+Coal-gas: 63 _et seq._;
+  public lighting by, developed, 70 _et seq._;
+  analytical production of, 103, 104;
+  yield of, retort (table), 105;
+  analysis of, 106
+
+Coal-mines, 234 _et seq._
+
+Cobalt, 294
+
+Coke, 68, 105
+
+Cologne, 157, 158
+
+Colomb, Philip, 197
+
+Color: 9;
+  relation of artificial light to, 284 _et seq._
+
+Colza, 31, 52, 167
+
+Combustion, 82 _et seq._
+
+Commerce, 8, 97
+
+Constantine, 42
+
+Copper, 262, 295
+
+Cornwall, 63
+
+Cotton: 101;
+  carbon filaments, 129, 130
+
+Cromartie, 78
+
+Crookes, 90, 146
+
+Crosley, Samuel, improvement of gas-meter by, 76
+
+Crusies, 32
+
+
+Daguerre, 258
+
+Dancing, 346
+
+Davy, Sir Humphrey: 33, 68, 73;
+  first use by, of charcoal for sparking points, 112;
+  notes of, on electric arc, 113; 114
+
+Daylight, artificial, 12: 284 _et seq._;
+  application of, 287
+
+Daylighting, 12-14
+
+Dollond, 195
+
+Doty, 61, 167
+
+Drake, Col. E. L., discovery of oil in Pennsylvania by, 56
+
+Drummond, Thomas: 171, 185, 196;
+  quoted on signaling, 197
+
+Dudgeon, Miss, 251, 252
+
+Dyes, 256, 265
+
+
+East Indies, 29
+
+Eddystone Light, 166, 167
+
+Edison: and problem of electric incandescent filament lamps, 128 _et seq._;
+    129;
+  quoted on birth of incandescent lamp, 130
+
+Edward I, 274
+
+Edward VI, 49
+
+Efficiency, effect of artificial light upon, 14
+
+Eggs: relation of artificial light to production of, 247, 248
+
+Egypt: 31;
+  sacredness of light in ancient, 39; 153, 195
+
+Electric filament: 81, 127 _et seq._:
+  approximate value of, lamps (table), 138
+
+Electric pile: construction of, 111; 127
+
+Electricity: 13, 22;
+  as a light-source, 57;
+  for home-lighting, 62, 84; 87, 89;
+  ignition of gas by, 102;
+  lighting by, 109 _et seq._
+
+Electromagnetic waves, 68, 86, 87
+
+Electromagnets, 114, 116
+
+Electrodes, 113, 114, 115 _et seq._;
+  life of, 122
+
+Elizabeth, Queen, 274
+
+England: 32;
+  petroleum discovered in, 56;
+  gas-lighting in, 63 _et seq._; 166, 251, 274
+
+Erbia, 85
+
+Esquimaux: 18;
+  use of artificial light by, 31
+
+Ethylene, 106
+
+
+Factories: 13;
+  artificial light in, 239 _et seq._
+
+Faraday, 113
+
+Filaments, carbon, 129 _et seq._
+
+Finsen: 273, 274, 275;
+  on stimulating action of artificial light, 277; 279, 280
+
+Fire: importance of, to man, 5 _et seq._;
+  man's dependence upon, 15;
+  mythical origin of, 16;
+  making, 17 _et seq._;
+  production of, in the stone age, 18;
+  in early civilization, 19;
+  ancient worship of, 29, 299
+
+Fireflies: 24, 81, 96, 148, 149, 150
+
+"First Men in the Moon, The," H. G. Wells, cited, 148
+
+Fish: artificial light as bait for, 249
+
+Flame-arcs, 120, 121, 122, 187
+
+Flames: 86, 88, 89;
+  open, 233, 234 _et seq._
+
+Flint, 33
+
+Fool's gold, 18
+
+Fort Wagner, 185
+
+France: lamps in, 55;
+  early gas-light in, 72
+
+Franchot, invention of moderator lamps by, 55
+
+Frankland, 77
+
+Franklin, Benjamin: 165;
+  quoted, 210-212; 213
+
+Fresnel, 167, 196
+
+Friction, 16, 17
+
+
+Gas: 13, 22;
+  discovery of coal, 32, 33;
+  early uses of, as light-source, 63 _et seq._;
+  installment of, pipes in England, 63, 64;
+  Shirley's report on Natural, 66, 67;
+  first public display of, lighting, 69;
+  cost of, lighting, 71;
+  first attempt at industrial, lighting, 72;
+  first English, company, 74;
+  first, explosion, 75;
+  house, lighting, 76, 77; 80, 82;
+  spectrum of, 90;
+  modern, lighting industry, 97 _et seq._;
+  origin of lighting by, 98;
+  first, works in America, 98;
+  growth of, consumption in United States, 99;
+  electrical ignition applied to, lighting, 102;
+  pressure, 102, 103;
+  water, 105;
+  carbons in, 106;
+  production of Pintsch, 109, 110;
+  salts applied to, flames, 120; 157;
+  Census Bureau figures on cost of, plants, 221, 222; 224, 341
+
+Gas-burners: 63, 64, 77;
+  candle-power of pioneer (table), 79;
+  improvements in, 84
+
+Gas-mantle: 61, 81;
+  influence of, 99;
+  characteristics of, 100 _et seq._; 187
+
+Gas-meter, Clegg's, 76
+
+Gasolene: lamps, 55; 57
+
+Gassiot, 114
+
+Gauss, 196
+
+Geissler, 146
+
+General Electric Company, 132, 135, 136
+
+Germany: development of lamps in, 56;
+  early gas-lighting in, 72
+
+Glass, 195, 290 _et seq._
+
+Glowers, 139
+
+Glow-worms, 24
+
+Glycerides, 52
+
+Gold, 293
+
+Gout, 275
+
+Gramme dynamo, 117
+
+Grass: 18;
+  carbon filaments, 129
+
+Greece: 39;
+  sacred lamps in ancient, 41; 42
+
+Greenhouses, carbon-filament lamps in, 250 _et seq._
+
+
+Hall of Fame, 134
+
+Happiness, effect of artificial light upon, 14
+Hayden and Steinmetz, 253
+
+Health, artificial light in relation to, 269-283
+
+Helium, 89
+
+Hemig, 155
+
+Hemp, 21
+
+Henry, William, 75
+
+Herodotus, 56
+
+Hertz, 68
+
+Hertzian waves, 271
+
+Hewitt, Cooper, produces mercury-arcs, 124, 125
+
+Home: artificial light in relation to, 6;
+  lighting, 325 _et seq._
+
+Hindu: light in, ceremonials, 40
+
+Hudson-Fulton Celebration, 306
+
+Huygens, 195
+
+Hydrocarbons, 82
+
+Hydrogen, 81
+
+
+Illiteracy, artificial light and, 9
+
+Invention, 7, 97
+
+Iowa, 238
+
+Iridium, 129
+
+Iron, 18, 262, 294
+
+Iron pyrites, 18
+
+Italy, 249
+
+
+Jablochkov: electric candle of, 117
+
+Jamaica, 19
+
+Jandus, 118, 122
+
+Japan: 19;
+  use of oil in, 30; 281
+
+Jerusalem, 43
+
+Jews: artificial light among, 40
+
+_Journal_, Paris, quoted, 210-212
+
+
+Kerosene: 57;
+  weight of, lumens, 60; 62, 187, 233
+
+Kitson, platinum-gauze mantle applied by, 61
+
+
+Laboratories: achievements of, 137
+
+Lamps: 16, 25;
+  Roman, 30; 31;
+  invention of safety, 33;
+  ancient funereal, 39;
+  sacred, of antiquity, 41;
+  ceremonial, 44;
+  scientific development of oil, 51 _et seq._;
+  Holliday, 55;
+  Carcel, 54, 55;
+  Franchot's moderator, 55;
+  gasolene, 55;
+  development of, in Germany, 56;
+  air pressure, 61;
+  supremacy of oil, ends, 62;
+  Bowditch's, 77, 78; 80, 97;
+  mercury-arc, 126;
+  electric incandescent filament, 127 _et seq._;
+  gem, 132;
+  tungsten, 133 _et seq._;
+  luminous efficiency (table) of incandescent filament, 141; 299;
+  in home, 328-333
+
+Lange, 167
+
+Lard-oil, 51
+
+Lavoisier, 195
+
+Lead, 262, 294
+
+Le Bon, 72
+
+"Legend of Montrose, The," Scott, cited on primitive lighting, 27
+
+Leigh, Edmund, quoted, 226
+
+Lenses, 20, 171 _et seq._
+
+Libanius, quoted, 153, 154
+
+Liberty, Statue of, 301, 302, 303
+
+Libraries, 9
+
+Light: relation of artificial, to progress, 3 _et seq._;
+  as a civilizing agency, 3-14;
+  primitive man and artificial, 4;
+  Milton, quoted on importance of, 5;
+  artificial, and science, 7;
+  artificial, and industrial development, 8;
+  Maeterlinck's tribute to, 9;
+  Lincoln's debt to artificial, 9;
+  symbolism of, 9, 10;
+  therapy, 10;
+  in war, 11;
+  adaptations of, 12; 13;
+  mythical origin of artificial, 16;
+  earliest source of, 16;
+  production of, in stone age, 18;
+  matches as source of, 21;
+  animals as, sources, 24, 25;
+  primitive sources of, 24-37;
+  evolution of artificial, sources, 24-37;
+  development, 28 _et seq._;
+  early outdoor use of artificial, 28;
+  Roman uses of artificial, 30;
+  beginning of scientific, 33, 34;
+  candles as modern, source, 36, 37;
+  symbolism and religious uses of, 38 _et seq._;
+  Bible cited on artificial, 42-44;
+  in relation to worship, 43, 45, 46;
+  Argand's contribution to, 53, 54;
+  coal as, source, 55;
+  early uses of gas as, source, 63 _et seq._;
+  as a public utility, 70;
+  first installation of industrial gas, 72;
+  science of, production, 80 _et seq._;
+  causes of, radiation, 80, 81; 83;
+  lime, 84; electric, 89 _et seq._;
+  principle of, production, 90, 91;
+  sources, 93;
+  various gas-burners', supply, 95;
+  relative efficiency of, sources, 95, 96;
+  in the home, 97;
+  influence of, upon science, invention, and commerce, 97 _et seq._;
+  yield of acetylene, 106, 107;
+  electric, 109;
+  influence of gas upon development of artificial, 110;
+  development of artificial, 111 _et seq._;
+  efforts to improve color of mercury-arc, 125;
+  electric-incandescent-filament, 127 _et seq._;
+  effect of tungsten, upon, 133 _et seq._;
+  of the future, 143-152;
+  in warfare, 178-193;
+  signaling, 194-207;
+  cost of, 208-224;
+  and safety, 225 _et seq._;
+  improper use of, 229, 230;
+  comparison of daylight and artificial, 240;
+  reducing action of, 258;
+  bactericidal action of, 272 _et seq._;
+  modifying, 284 _et seq._;
+  spectacular uses of, 298-309;
+  expressiveness of, 310-324;
+  utility of modern, 325-340;
+  evolution of the art of applying, 341-356;
+  mobile, 347, 348, 349, 350;
+  psychological effect of, 351 _et seq._;
+  as an accompaniment to music, 352-354
+
+Light-buoys, 10, 169
+
+Lighthouses: 10, 163-177;
+  optical apparatus of, 172 _et seq._
+
+Light-ships, 10, 169
+
+Lighting-systems: comparison of, 12-14
+
+Lime, 84, 107, 108, 294
+
+Lincoln, Abraham, 9
+
+Linen, 18
+
+Link-buoys, 28
+
+Lithopone, 265, 266
+
+Liverpool, 167
+
+Living: comparison of, standards, 238 _et seq._
+
+London, 152, 154, 155, 156, 157, 202
+
+London Gas Light and Coke Company, 74
+
+Lucigen, 61
+
+Lumen-hour: defined, 215
+
+Lumens: 60, 94, 215
+
+Lutheran Church, 49
+
+Lyceum Theatre, London, 73
+
+
+Maeterlinck, Maurice, 9
+
+Magazines, 8
+
+Magdsick, H. H., 303
+
+Magnesia: 84;
+  Nernst's application of, 138
+
+Magnesium, 179, 180
+
+Magnetite arc, 187
+
+Man: distinction between, and animal, 3;
+  artificial light and early, 4;
+  light-sources of primitive, 25
+
+Manganese, 262, 268, 294
+
+Mangin, 188
+
+Mann, 129
+
+Mantles, 95
+
+Manufacturing, 8
+
+Marconi, 68
+
+Marks, 118
+
+Matches: as light-sources, 21; 22, 82
+
+Maxwell, 68
+
+Mazda lamps, 289, 339
+
+Mecca, 40
+
+Mediterranean Sea, 163
+
+Mercury-arc: Way's, 124; 125, 126;
+  quartz, 125, 126;
+  attempts to improve color of, light, 125
+
+Middle Ages, 46, 47, 474
+
+Milton, quoted, 5
+
+Mirror, 19
+
+Mohammedans, 40
+
+Moore, Dr. McFarlan, 146, 147
+
+Morality, effect of light upon, 9
+
+Morse code: application of, to light-signaling, 198, 199
+
+Moses, 195
+
+Moving-pictures, 9, 260, 261
+
+Munich, 72
+
+Murdock, William: installment of gas-pipes by, 63; 68, 69, 70;
+  quoted on industrial use of artificial, 71; 72, 73, 74, 76, 78, 217, 309
+
+Museums: 13;
+  utilization of artificial light by, 322, 323
+
+Music: light as an accompaniment to, 352-354
+
+Mythology, 16
+
+
+Nantes, 85
+
+Napoleon, 111
+
+Napthalene, 106
+
+National Heat and Light Co., 72, 74
+
+Natural gas, 99
+
+Navesink Light, 206
+
+Nernst, 138, 139
+
+Newspapers, 8
+
+Newton, Sir Isaac: 7;
+  quoted on discovery of visible spectrum, 87; 88
+
+New York, 98, 165, 166, 206, 302, 304
+
+Niagara Falls, 108, 306
+
+Nickel, 262
+
+Nielson, 77
+
+Niepce, 258
+
+Niter, 21
+
+Nitrogen, 137
+
+Norfolk, 169
+
+
+Obesity, 275
+
+Offices, 13
+
+Oil: as a light-source, 29 _et seq._;
+  development of, lamps, 51 _et seq._; 155;
+  in lighthouse, 165 _et seq._; 222, 224, 299
+
+O'Leary, Mrs., and her lamp, 62
+
+Olive-oil, 51, 52, 167
+
+Orkney Islands, 29, 177
+
+Osmium, 133
+
+Oxygen: relative consumption of, by oil-lamps, 58, 59; 262
+
+Ozone, 262
+
+
+Painting, 342, 343, 347, 348, 349
+
+Pall Mall, 74
+
+Panama-Pacific Exposition: 304;
+  artificial lighting of, 306, 307, 308, 309
+
+Paper: 18;
+  carbon filaments, 129, 130
+
+Paraffin, 35, 57
+
+Parker and Clark, 139
+
+Paris: experimental gas-lighting in, 83, 84;
+  Volta in, 111; 154, 185, 210, 212, 213
+
+Peckham, John, 195
+
+Pennsylvania: discovery of oil in, 56
+
+Periodic Law, 145
+
+Petroleum: 35, 51, 55;
+  discovery of, 56;
+  constitution of crude, 57; 58, 214
+
+Pharos, 163
+
+Philadelphia, 98, 99, 157
+
+Phillips and Lee, 70, 72
+
+"Philosophical Transactions of the Royal Society of London," 33;
+  quoted on industrial lighting, 63;
+  Shirley's report on natural gas in, 66, 67;
+  quoted, 87
+
+Phoenicians, 34, 39
+
+Phosphorus, 21
+
+Photo-micrography, 12
+
+Photography: 126;
+  early experiments in, 258;
+  development of, 259; 291, 292
+
+Picric acid, 106
+
+Pigments, 265
+
+Pintsch: production of, gas, 109, 110, 170
+
+Pitch, 106
+
+Plant-growth: artificial light and, 11, 249 _et seq._
+
+Platinum, 85, 128, 129, 262
+
+Plumbago, 113, 130
+
+Plymouth, 166
+
+Poetry, 346
+
+Police, 162
+
+Potash, chlorate of, 22
+
+Priestley, Professor, quoted, 252
+
+Printing, 8
+
+Progress: influence of fire upon, 15 _et seq._
+
+Prometheus, 16, 41
+
+Propylene, 106
+
+Ptolemy II, 163
+
+
+Quartz: 18, 19;
+  mercury-arcs, 125;
+  uses of, 126;
+  in skin diseases, 278, 279
+
+
+Radiators, energy, 88 _et seq._
+
+Radium, 150
+
+Railway Signal Association, 205
+
+Railways: light-signaling applied to, 205
+
+Ramie fiber, 101
+
+Rane, 250, 251
+
+Rare-earth oxides: 85;
+  properties of, 88, 99
+
+Recreation, 9
+
+Redruth, 63
+
+Reformation: ceremonial uses of light during the, 48, 49
+
+Rheumatism, 275
+
+Robins, Benjamin, 201
+
+Rome, 30, 32, 34, 39, 41, 42, 44
+
+Roentgen, 270, 280.
+  _See also_ X-ray.
+
+Royal Society of London: 33, 63, 66, 67, 70, 73;
+  and first gas explosion, 75, 111, 112
+
+Rumford, 167
+
+Rushlights, 28, 33
+
+Russia, 281
+
+Ryan, W. D'A., 306
+
+
+Safety: artificial light in relation to, 14, 225 _et seq._
+
+Salts: chemical, 88, 89;
+  metallic, 120;
+  silver, 257, 258
+
+Sandy Hook Light, 165, 166
+
+San Francisco, 304, 306-309
+
+Savages, 3, 15, 17
+
+Sawyer, 129
+
+Scheele, K. W., 133;
+  quoted, 257, 258
+
+Schools, 9
+
+Science: light and, 6, 7; 97;
+  systematized, 268
+
+Scotland: 26, 31, 32, 48;
+  oil industry in, 56
+
+Scott, Sir Walter, cited, 27, 98
+
+Sculpture: artificial light in relation to, 184
+
+Search-lights, 11, 169
+
+Section of Plant Protection, 225, 226
+
+Selenium, 267, 293
+
+Semaphore, 199
+
+Shells: illuminating, 179 _et seq._
+
+Shirley, Thomas: quoted on natural gas, 66, 67
+
+Siemens, 78
+
+Signaling, 194-207
+
+Silicon: filament, 140
+
+Silk: artificial, 101;
+  carbon-filaments, 129
+
+Simpson, R. E., 227, 231
+
+Silver, 258, 293
+
+Skin diseases: treatment of, 278, 279, 280
+
+Skylights, 13
+
+Sleep, 8
+
+Smallpox, 274, 275
+
+Smeaton, 166
+
+Soho, 69, 72
+
+South Africa, 129
+
+Sparks: 33, 125
+
+Spectrum: visible, 86;
+  Newton quoted on, 87;
+  of elements, 89;
+  of gases, 90; 120, 121;
+  mercury, 124-126
+
+Sperm, 31, 51, 52, 167
+
+Spermaceti, 35, 51
+
+Splinter-holders, 27, 28
+
+Stage: and artificial light, 319 _et seq._; 343
+
+Staite, 117, 118
+
+Stearine, 35, 52
+
+Stearn, 129
+
+Steel, 18, 33
+
+Steinmetz, Hayden and, 253
+
+Sterilization: quartz-mercury-arc and, 280, 281, 282
+
+Stevenson, Robert Louis, quoted, 177
+
+Stores, 13
+
+St. Paul, 43
+
+St. Paul's Cathedral, 300
+
+Street-lighting: development of, 152-162
+
+Sugar, 22
+
+Sulphide of iron, 18
+
+Sulphur, 18, 21, 179, 180, 294
+
+Sulphuric acid, 21, 22
+
+Sun, 8, 16, 19, 20
+
+Swan, 129
+
+Syracuse, 19
+
+Syria, 153
+
+
+Tallow, 34, 35, 51, 52
+
+Tantalum: 132;
+  filament lamps, 133
+
+Tar, 68, 106
+
+Telegraphy, 195
+
+Telephony, 194
+
+Textiles, 256
+
+Thames, 169
+
+Theaters, 9, 319 _et seq._
+
+Thoria, 85
+
+Tin, 262
+
+Tinder-boxes, 18, 19, 22
+
+Travelers Insurance Company, 227
+
+Trees, 26
+
+Troy, 42
+
+Tuberculosis, 273
+
+Tungsten lamp, 161 _et seq._, 187, 261, 290, 303
+
+Typhus, 273
+
+
+Ultra-violet rays: 126, 150;
+  in photographic electricity, 267, 268; 270, 272, 294
+
+United States: petroleum in, 57;
+  gas-consumption in, 99; 164, 165, 166
+
+United States Geological Survey, cited on sale of gas, 222
+
+United States Military Intelligence, 225, 226
+
+
+Vacuum tubes, 81, 286
+
+Venetians, 195
+
+Ventilation, 13
+
+Verne, Jules, 143
+
+Vestal Virgins, 42
+
+Volcanoes, 166
+
+Volta, 111, 112, 127
+
+Voltaic pile: construction of, 111, 127
+
+Von Bolton. _See_ Bolton.
+
+
+War: and artificial light, 11, 178-193
+
+Washington, 305
+
+Water: sterilization of, by artificial light, 280 _et seq._
+
+Watson, Dr. Richard, 67, 68
+
+Watt, 94
+
+Waves: electro-magnetic, 68, 86, 125 _et seq._
+
+Wax, 34, 46, 51
+
+Way: mercury-arc produced by, 124
+
+Wells, 61
+
+Wells, H. G., cited, 148
+
+Welsbach, Auer von: 61;
+  invention of mantle by, 99, 100, 133
+
+Wenham, 78
+
+West Indies, 25
+
+Whale-oil, 31
+
+Wicks, 35, 36, 53, 54, 58, 59
+
+Winsor, 72, 73.
+  _See also_ Winzler.
+
+Winzler. _See_ Winsor.
+
+_Wolfram._ _See_ Tungsten.
+
+Wood, 26, 27, 28
+
+Woolworth Building, 302, 303
+
+Wounds: treatment of, by artificial light, 10
+
+
+X-ray: production of, tubes during War, 131; 137, 150, 270, 280
+
+
+Young, James: discovers petroleum, 56
+
+Yttria, 85
+
+
+_Zeitung_, Cologne: 157;
+   extract from, on street-lighting, 158
+
+Zinc, 125, 130, 267
+
+Zirconia, 84, 85
+
+
+
+
+Transcriber's List of Corrections
+
+
+LOCATION
+         ORIGINAL
+                  CORRECTED
+
+Chapter II
+         and similiar material
+                  and similar material
+
+Chapter XIII
+         as a constant level
+                  at a constant level
+
+Chapter XIV
+         the carbons to distintegrate
+                  the carbons to disintegrate
+
+Chapter XV
+         John Pechham
+                  John Peckham
+         coated with an allow
+                  coated with an alloy
+         with various billiant
+                  with various brilliant
+         key in depressed
+                  key is depressed
+
+Chapter XVI
+         has nearly doubled
+                  have nearly doubled
+
+Chapter XVII
+         this own indifference
+                  their own indifference
+
+Chapter XXIII
+         Nature's lighting varied
+                  Nature's lighting varies
+
+Chapter XXIV
+         so-called cadelabra
+                  so-called candelabra
+         possibilties
+                  possibilities
+
+READING REFERENCES
+         ...Applications an Theatre."
+                  ...Applications au Theatre."
+
+INDEX
+         Photo-micography
+                  Photo-micrography
+         Siemans
+                  Siemens
+
+
+
+
+
+
+
+End of the Project Gutenberg EBook of Artificial Light, by M. Luckiesh
+
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