,transcriber's ,notes3 #a4 ,subscripts have been marked with an underscore character in front with text surrounded in curly braces1 for example3 ,h#b,o 7formula of water74 #b4 ,inconsistent hyphenation of words preserved4 #c4 ,several misprints fixed4 ,a full list of corrections can be found at the end of the text4 ,illustration3 ,,light ,,and ,,liberty ,the ,century ,books of ,useful ,science ,,artificial ,,light ,,its ,,influence ,,upon ,,civilization ,,by ,m4 ,,luckiesh ,,director ,,of ,,applied ,,science4 ,,nela ,,research ,,laboratory1 ,,national ,,lamp ,,works ,,of ,,general ,,electric ,,company ,author of ,color and ,its ,applications1 ,light and ,shade and ,their ,applications1 ,the ,lighting ,art1 ,the ,language of ,color1 etc4 ,,illustrated ,,with ,,photographs ,,new ,,york ,,the ,,century ,,co4 #aibj ,copyright1 #aibj1 by ,,the ,,century ,,co4 ,,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 reader1 in a manner as devoid as possible of intricate details4 ,the early chapters deal particularly with primitive artificial light and their contents are generally historical4 ,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 time4 ,until the middle of the nineteenth century mere light was available1 but as the century progressed1 the light-sources through the application of science became more powerful and efficient4 ,gradually mere light grew to more light and in the dawn of the twentieth century adequate light became available4 ,in a single century1 after the development of artificial light began in earnest1 the efficiency of light-production increased fifty-fold and the cost diminished correspondingly4 ,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 mankind4 ,on passing through the spectacular aspects of lighting we finally emerge into the esthetics of light and lighting4 ,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 civilization4 ,the subject is too extensive to be treated in detail in a single volume1 but an effort has been made to present a discussion fairly complete in scope4 ,it is hoped that the reader will gain a greater appreciation of artificial light as an economic factor1 as an artistic medium1 and as a mighty influence upon the safety1 efficiency1 health1 happiness1 and general progress of mankind4 ,m4 ,,luckiesh4 ,,acknowledgments ,it is a pleasant duty to acknowledge the coperation of various companies in obtaining the photographs which illustrate this book4 ,with the exception of ,plates #b and #g1 which are reproduced from the excellent works of ,benesch and ,allegemane respectively1 the illustrations of early lighting devices are taken from an historical collection in the possession of the ,national ,lamp ,works of the ,general ,electric ,co4 ,to this company the author is indebted for ,plates #a1 #c1 #d1 #e1 #f1 #i1 #aa1 #ae1 #ah;b1 #bj1 #ba1 #bi2 to ,dr4 ,mc,farlan ,moore for ,plate #aj2 to ,macbeth ,evans ,glass ,co4 for ,plate #ab2 to the ,corps of ,engineers1 ,u4 ,s4 ,army1 for ,plate #ac2 to ,lynn ,works of ,g4 ,e4 ,co4 for ,plates #ad1 #af2 to ,edison ,lamp ,works of ,g4 ,e4 ,co4 for ,plates #ag1 #bd2 to ,cooper ,hewitt ,co4 for ,plate #ah;a2 to ,r4 ,u4 ,v4 ,co4 for ,plate #ai2 to ,new ,york ,edison ,co4 for ,plates #bb1 #bf1 #cj2 to ,w4 ,d',a4 ,ryan and the ,schenectady ,works of ,g4 ,e4 ,co4 for ,plates #bc1 #be1 #ca2 to ,national ,x-,ray ,reflector ,co4 for ,plate #bh4 ,besides the companies and the individuals particularly involved in the foregoing1 the author is glad to acknowledge his appreciation of the assistance of others during the preparation of this volume4 ,,contents ,,chapter ,,page ,i ,,light ,,and ,,progress #c ,,ii ,,the ,,art ,,of ,,making ,,fire #ae ,,iii ,,primitive ,,light-,,sources #bd ,,iv ,,the ,,ceremonial ,,use ,,of ,,light #ch ,v ,,oil-,,lamps ,,of ,,the ,,nineteenth ,,century #ea ,,vi ,,early ,,gas-,,lighting #fc ,,vii ,,the ,,science ,,of ,,light-,,production #hj ,,viii ,,modern ,,gas-,,lighting #ig ,,ix ,,the ,,electric ,,arcs #aaa ,x ,,the ,,electric ,,incandescent ,,filament ,,lamps #abg ,,xi ,,the ,,light ,,of ,,the ,,future #adc ,,xii ,,lighting ,,the ,,streets #aeb ,,xiii ,,lighthouses #afc ,,xiv ,,artificial ,,light ,,in ,,warfare #agh ,,xv ,,signaling #aid ,,xvi ,,the ,,cost ,,of ,,light #bjh ,,xvii ,,light ,,and ,,safety #bbe ,,xviii ,,the ,,cost ,,of ,,living #bch ,,xix ,,artificial ,,light ,,and ,,chemistry #bef ,,xx ,,light ,,and ,,health #bfi ,,xxi ,,modifying ,,artificial ,,light #bhd ,,xxii ,,spectacular ,,lighting #bih ,,xxiii ,,the ,,expressiveness ,,of ,,light #caj ,,xxiv ,,lighting ,,the ,,home #cbe ,,xxv ,,lighting--,a ,,fine ,,art8 #cda ,,reading ,,references #ceg ,,index #cei ,,list ,,of ,,illustrations ,light and ,liberty ,frontispiece ,,facing ,,page ,primitive fire-baskets #af ,crude splinter-holders #af ,early open-flame oil and grease lamps #ag ,a typical metal multiple-wick open-flame oil-lamp #cb ,a group of oil-lamps of two centuries ago #cc ,lamps of a century or two ago #ef ,elaborate fixtures of the age of candles #eg ,flame arc #abh ,direct current arc #abh ,on the testing-racks of the manufacturer of incandescent filament lamps #abi ,carbon-dioxide tube for accurate color-matching #afj ,the ,moore nitrogen tube #afj ,modern street lighting #afa ,a completed lighthouse lens #agf ,torro ,point ,lighthouse1 ,panama ,canal #agf ,american search-light position on ,western ,front in #aiai #agg ,american standard field search-light and power unit #agg ,signal-light for airplane #bcb ,trench light-signaling outfit #bcb ,aviation field light-signal projector #bcb ,signal search-light for airplane #bcb ,unsafe1 unproductive lighting worthy of the dark ages #bcc ,the same factory made safe1 cheerful1 and more productive by modern lighting #bcc ,locomotive electric headlight #bdj ,search-light on a fire-boat #bdj ,building ships under artificial light at ,hog ,island ,shipyard #bda ,artificial light in photography #bef ,sterilizing water with radiant energy from quartz mercury-arcs #beg ,judging color under artificial daylight #bgb ,artificial daylight #bgc ,fireworks and illuminated battle-fleet at ,hudson-,fulton ,celebration #bhh ,fireworks exhibition on ,may ,day at ,panama-,pacific ,exposition #bhi ,the new flood lighting contrasted with the old outline lighting #cjd ,niagara ,falls flooded with light #cje ,artificial light honoring those who fell and those who returned #cbj ,the expressiveness of light in churches #cba ,obtaining two different moods in a room by a portable lamp which supplies direct and indirect components of light #ccf ,the lights of ,new ,york ,city #ccg ,artificial light in community affairs #ceb ,panama-,pacific ,exposition #cec ,,artificial ,,light ,i ,,light ,,and ,,progress ,the human race was born in slavery1 totally subservient to nature4 ,the earliest primitive beings feasted or starved according to nature's bounty and sweltered or shivered according to the weather4 ,when night fell they sought shelter with animal instinct1 for not only were activities almost completely curtailed by darkness but beyond its screen lurked many dangers4 ,it is interesting to philosophize upon a distinction between a human being and the animal just below him in the scale1 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 independence4 ,the effort to escape from the bondage of nature is not solely a human instinct2 animals burrow or build retreats through the instinct of self-preservation4 ,but this instinct in animals is soon satisfied1 whereas in human beings it has been leading ever onward toward complete emancipation4 ,the progress of civilization is a long chain of countless achievements each one of which has increased man's independence4 ,early man perhaps did not conceive the idea of fire and then set out to produce it4 ,his infant mind did not operate in this manner4 ,but when he accidentally struck a spark1 produced fire by friction1 or discovered it in some other manner1 he saw its possibility4 ,it is thrilling to picture primitive man at his first bonfire1 enjoying the warmth1 or at least interested in it4 ,but how wonderful it must have become as twilight's curtain was drawn across the heavens6 ,this controllable fire emitted light4 ,it is easy to imagine primitive man pondering over this phenomenon with his sluggish mind4 ,doubtless he cautiously picked up a flaming stick and timidly explored the crowding darkness4 ,perhaps he carried it into his cave and behold6 night had retreated from his abode6 ,no longer was it necessary for him to retire to his bed of leaves when daylight failed4 ,the fire not only banished the chill of night but was a power over darkness4 ,viewed from the standpoint of civilization1 its discovery was one of the greatest strides along the highway of human progress4 ,the activities of man were no longer bounded by sunrise and sunset4 ,the march of civilization had begun4 ,in the present age of abundant artificial light1 with its manifold light-sources and accessories which have made possible countless applications of light1 mankind does not realize the importance of this comfort4 ,its wonderful convenience and omnipresence have resulted in indifference toward it by mankind in general1 notwithstanding the fact that it is essential to man's most important and educative sense4 ,by extinguishing the light and pondering upon his helplessness in the resulting darkness1 man may gain an idea of its overwhelming importance4 ,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 light4 ,milton1 whose eyesight had failed1 laments1 ,o first created beam and thou great ,word ,let there be light1 and light was over all1 ,why am ,i thus bereaved thy prime decree8 ,perhaps only through a similar loss would one fully appreciate the tremendous importance of light to him1 but imagination should be capable of convincing him that it is one of the most essential and pleasure-giving phenomena known to mankind4 ,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 time4 ,written history fails long before the primitive races are reached1 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 wanes4 ,impelled by the restless spirit of progress1 this primitive being grasped the opportunity which fire afforded to extend his activities beyond the boundaries of daylight4 ,the crude art upon the walls of his cave was executed by the flame of a smoking fagot4 ,the fire on the ledge at the entrance to his abode became a symbol of home1 as the fire on the hearth has symbolized home and hospitality throughout succeeding ages4 ,the accompanying light and the protection from cold combined to establish the home circle4 ,the ties of mated animals expanded through these influences to the bonds of family4 ,thus light was woven early into family life and has been throughout the ages a moralizing and civilizing influence4 ,to-day the residence functions as a home mainly under artificial light1 for owing to the conditions of living and working1 the family group gathers chiefly after daylight has failed4 ,from the pine knot of primitive man to the wonderfully convenient light-sources of to-day there is a great interval1 consisting1 as appears retrospectively1 of small and simple steps long periods apart4 ,measured by present standards and achievements1 development was slow at first and modern man may be inclined to impatience as he views the history of light and human progress4 ,but the achievements of early centuries1 which appear so simple at the present time1 were really great accomplishments when considered in the light of the knowledge of those remote periods4 ,science as it exists to-day is founded upon proved facts4 ,the scientist1 equipped with a knowledge of physical and chemical laws1 is led by his imagination into the darkness of the unexplored unknown4 ,this knowledge illuminates the pathway so that hypotheses are intelligently formed4 ,these evolve into theories which are gradually altered to fit the accumulating facts1 for along the battle area of progress there are innumerable scouting-parties gaining secrets from nature4 ,these are supported by individuals and by groups1 who verify1 amplify1 and organize the facts1 and they in turn are followed by inventors who apply them4 ,liaison is maintained at all points1 but the attack varies from time to time4 ,it may be intense at certain places and other sectors may be quiet for a time4 ,there are occasional reverses1 but the whole line in general progresses4 ,each year witnesses the acquirement of new territory4 ,it is seen that through the centuries there is an ever-growing momentum as knowledge1 efficiency1 and organization increase the strength of this invading army of scientists and inventors4 ,the burning fagot rescued mankind from the shackles of darkness1 and the grease-lamp and tallow-candle have done their part4 ,progress was slow in those early centuries because the great minds of those ages philosophized without a basis of established facts3 scientific progress resulted more from an accumulation of accidental discoveries than by a directed attack of philosophy supported by the facts established by experiment4 ,it was not until comparatively recent times1 at most three centuries ago1 that the great intellects turned to systematically organized scientific research4 ,such men as ,newton laid the foundation for the tremendous strides of to-day4 ,the store of facts increased and as the attitude changed from philosophizing to investigating1 the organized knowledge grew apace4 ,all of this paved the way for the momentous successes of the present time4 ,the end is not in sight and perhaps never will be4 ,the unexplored region extends to infinity and1 judged by the past1 the momentum of discovery will continue to increase for ages to come1 unless the human race decays through the comfort and ease gained from utilizing the magic secrets which are constantly being wrested from nature4 ,among the achievements of science and invention1 the production and application of artificial light ranks high4 ,as an influence upon civilization1 no single achievement surpasses it4 ,without artificial light1 mankind would be comparatively inactive about one half its lifetime4 ,to-day it has been fairly well established that the human organism can flourish on eight hours' sleep in a period of twenty-four hours4 ,another eight hours spent in work should settle man's obligation to the world4 ,the remaining hours should be his own4 ,artificial light has made such a distribution of time possible4 ,the working-periods in many cases may be arranged in the interests of economy1 which often means continuous operations4 ,the sun need not be considered when these operations are confined to interiors or localized outdoors4 ,thus1 artificial light has been an important factor in the great industrial development of the present time4 ,man now burrows into the earth1 navigates under water1 travels upon the surface of land and sea1 and soars among the clouds piloted by light of his own making4 ,progress does not halt at sunset but continues twenty-four hours each day4 ,building1 printing1 manufacturing1 commerce1 and other activities are prosecuted continuously1 the working-shifts changing at certain periods regardless of the rising or setting sun4 ,adequate artificial lighting decreases spoilage1 increases production1 and is a powerful factor in the prevention of industrial accidents4 ,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 work4 ,the highly developed artificial lighting of the present time may account for much of the vast industry of publication4 ,books1 magazines1 and newspapers owe much to convenient and inexpensive artificial light1 for without it fewer hours would be available for recreation and advancement through reading4 ,schools1 libraries1 and art museums may be attended at night for the betterment of the human race4 ,the immortal ,lincoln1 it is said1 gained his early education largely by the light of the fireplace4 ,but all were not endowed with the persistence of ,lincoln1 so that illiteracy was more common in his day than in the present age of adequate illumination4 ,the theatrical stage not only depends for its effectiveness upon artificial light but owes its existence and development largely to this agency4 ,in the moving-picture theater1 pictures are projected upon the screen by means of it and even the production of the pictures is independent of daylight4 ,these and a vast number of recreational activities owe much1 and in some cases their existence1 to artificial light4 ,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 harm4 ,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 property4 ,maeterlinck in his poetical drama1 ,the ,bluebird1 appropriately has made ,light the faithful companion of mankind4 ,the ,palace of ,night1 into which ,light is not permitted to enter1 is the abode of many evils4 ,thus the poet has played upon the primitive instincts of the impressiveness of light and darkness4 ,by combining the symbolism of light1 color1 and darkness with the instincts which have been inherited by mankind from its superstitious ancestry of the age of mythology1 another field of application of artificial light is opened4 ,light has gradually assumed such attributes as truth1 knowledge1 progress1 enlightenment4 ,throughout the early ages light was more or less worshiped and thus artificial lights became woven in many religious ceremonies4 ,some of these have persisted to the present time4 ,the great pageants of peace celebrations and world's expositions appropriately feature artificial light4 ,in drawing upon the potentiality of the expressiveness and impressiveness of light and color1 artificial light is playing a major part4 ,doubtless the future generations will be entertained by gorgeous symphonies of light4 ,experiments are performed in this direction now and then1 and it is reasonable to expect that after many centuries of cultivation of the appreciation of light-symphonies1 these will take a place among the arts4 ,the elaborate and complicated music of the present time is appreciated by civilized nations only after many centuries of slow cultivation of taste and understanding4 ,light-therapy is to-day a distinct science and art4 ,the germicidal action of light-rays and of some of the invisible rays which ordinarily accompany the luminous rays is well proved4 ,wounds are treated effectively and water is sterilized by the ultraviolet radiant energy in modern artificial illuminants4 ,thousands of lighthouses1 light-ships1 and light-buoys are scattered along sea-coasts1 rivers1 and channels4 ,they guide the wheelman and warn the lookout of shoals and reefs4 ,some of these send forth flashes of light whose intensities are measured in millions of candle-power4 ,many are unattended for days and even months4 ,these powerful lights dominated by automatic mechanisms have replaced the wood-fires which were maintained a few centuries ago upon certain prominent points4 ,signal-lights now guide the railroad train through the night4 ,a burning flare dropped from the rear of a train keeps the following train at a safe distance4 ,huge search-lights penetrate the night air for many miles4 ,when these are equipped with shutters1 a code may be flashed from one ship to another or between the vessel and land4 ,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 horizon4 ,artificial light played its part in the recent war4 ,huge search-light equipments were devised for portability4 ,this mobile apparatus was utilized against enemy aircraft and in various other ways4 ,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 trigger4 ,raiding-parties are no longer concealed by the curtain of darkness1 for rockets and star-shells are used to illuminate large areas4 ,flares sent upward to drift slowly downward supported by parachutes saved and cost many lives during the recent war4 ,rockets are used by ships in distress and also by beleaguered troops4 ,experiments are being prosecuted to ascertain the possibilities of artificial light in the forcing of plant-growth1 and even chickens are made to work longer hours by its use4 ,artificial light is now modified in color or spectral character to meet many requirements4 ,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 daylight4 ,colored light is made of the correct quality which does not affect photographic plates of various sensibilities4 ,monochromatic light is utilized in photo-micrography for the best rendition of detail4 ,light-waves have been utilized as standards of length because they are invariable and fundamental4 ,numerous other interesting adaptations of artificial light are in daily use4 ,this is in reality the age of artificial light1 for mankind has not only become independent of daylight in certain respects1 but has improved upon natural light4 ,the controllability of artificial light makes it superior to natural light in many ways4 ,in fact1 uses have been made of artificial light which are impossible with natural light4 ,light-sources may be made of a vast variety of shapes1 and those may be transported wherever desired4 ,they may be equipped with reflectors and other optical devices to direct or to diffuse the light as required4 ,thus1 artificial light to-day has numerous advantages over light which has been furnished by the ,creator4 ,it is sometimes stated that it can never compete with daylight in cheapness1 inasmuch as the latter costs nothing4 ,but this is not true4 ,even in the residence1 daylight costs something1 because windows are more expensive than plain walls4 ,the expense of washing windows is an appreciable percentage of the cost of gas or electricity4 ,and there is window-breakage to be considered4 ,in the more elaborate buildings of the congested portions of cities1 daylight is satisfactory a lesser number of hours than in the outlying districts4 ,in some stores1 offices1 and factories artificial light is used throughout the day4 ,still1 the daylighting-equipment is installed and maintained4 ,furthermore1 when it is considered that much expensive area is given to light-courts and much valuable wall space to windows1 it is seen that the cost of daylight in congested cities is in reality considerable4 ,of course1 the daylighting-equipment has value in ventilating1 but ventilation may be taken care of in a very satisfactory manner as a separate problem4 ,the cost of skylights in museums and other large buildings is far greater than that of ordinary ceilings and walls1 and the extra allowance for heating is appreciable4 ,the expense of maintenance of some skylights is considerable4 ,thus it is seen that the cost and maintenance of daylighting-equipment1 the loss of valuable rental space and of wall area1 and the increased expense of heating are factors which challenge the statement that daylight costs nothing4 ,in fact1 it is not surprising to find that occasionally the elimination of daylighting--the reliance upon artificial light alone--has been seriously contemplated4 ,when the possibilities of the latter are considered1 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 systems4 ,naturally1 with the tremendous development of artificial light during the present age1 a new profession has arisen4 ,the lighting expert is evolving to fill the needs4 ,he is studying the problems of producing and utilizing artificial illumination4 ,he deals with the physics of light-production4 ,his studies of utilization carry him into the vast fields of physiology and psychology4 ,his is a profession which eventually will lead into numerous highways and byways of enterprise1 because the possibilities of lighting extend into all those activities which make their appeal to consciousness through the doorway of vision4 ,these possibilities are limited only by the boundaries of human endeavor and in the broadest sense extend even beyond them1 for light is one of the most prominent agencies in the scheme of creation4 ,it contributes largely to the safety1 the efficiency1 and the happiness of civilized beings and beyond all it is a powerful civilizing agency4 ,,ii ,,the ,,art ,,of ,,making ,,fire ,scattered over the earth at the present time various stages of civilization are to be found1 from the primitive savages to the most highly cultivated peoples4 ,although it is possible that there are tribes of lowly beings on earth to-day unfamiliar with fire or ignorant of its uses1 savages are generally able to make fire4 ,thus the use of fire may serve the purpose of distinguishing human beings from the lower animals4 ,surely the savage of to-day who is unable to kindle fire or who possesses a mind as yet insufficiently developed to realize its possibilities1 is quite at the mercy of nature's whims4 ,he lives merely by animal prowess and differs little in deeds and needs from the beasts of the jungle4 ,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 civilization4 ,in viewing the development of artificial light it is seen that preceding the modern electrical age1 man depended universally upon burning material4 ,obviously1 the course of civilization has been highly complex and cannot be symbolized adequately by the branching tree4 ,from its obscure beginning far in the impenetrable fog of prehistoric times1 it has branched here and there4 ,these various branches have been subjected to many different influences1 with the result that some flourished and endured1 some retrogressed1 some died1 some went to seed and fell to take root and to begin again the upward climb4 ,the ultimate result is the varied civilization of the present time1 a study of which aids in penetrating the veil that obscures the ages of unrecorded writing4 ,likewise1 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 begun4 ,throughout these various stages it becomes manifest that the development of artificial light is associated with the progress of mankind4 ,according to a certain myth1 ,prometheus stole fire from heaven and brought this blessing to earth4 ,throughout the mythologies of various races1 fire and1 as a consequence1 light have been associated with divinity4 ,they have been subjects of worship perhaps more generally than anything else1 and these early impressions have survived in the ceremonial uses of light and fire even to the present time4 ,the origin of fire as represented in any of the myths of the superstitious beings of early ages is as suitable as any other1 inasmuch as definite knowledge is unavailable4 ,active volcanoes1 spontaneous combustion1 friction1 accidental focusing of the sun's image1 and other means may have introduced primitive beings to fire4 ,a study of savage tribes of the present age combined with a survey of past history of mythology1 of material relics1 and of the absence of lamps or other lighting utensils leads to the conclusion that the earliest source of light was the wood fire4 ,illustration3 ,,primitive ,,fire-,,baskets ,illustration3 ,,crude ,,splinter-,,holders ,illustration3 ,,early ,,open-,,flame ,,oil ,,and ,,grease ,,lamps ,even to-day the savages of remote lands have not advanced further than the wood-fire stage1 and they may be found kneeling upon the ground energetically but skilfully rubbing sticks together until the friction kindles a fire4 ,in using these fire-sticks they convert mechanical energy into heat energy4 ,this is a fundamental principle of physics1 employed by them as necessity demands1 but they are totally ignorant of it as a scientific law4 ,the things which these savages learn are the result of accidental discovery4 ,until man pondered over such simple facts and cordinated them so that he could extend his knowledge by general reasoning1 his progress could not be rapid4 ,but the sluggish mind of primitive man is capable of devising improvements1 however slowly1 and the art of making fire by means of rubbing fire-sticks gradually became more refined4 ,mechanical improvements resulted from experience1 with the consequence that finally one stick was rubbed to and fro in a groove1 or was rapidly twirled between the palms of the hands while one end was pressed firmly into a hole in a piece of wood4 ,in the course of a few seconds or a minute1 depending upon skill and other conditions1 a fire was obtained4 ,it is interesting to note how civilized man is often compelled by necessity to adopt the methods of primitive beings4 ,the rubbing of sticks is an emergency measure of the master of woodcraft at the present time1 and the production of fire in this manner is the proud accomplishment or ambition of every ,boy ,scout4 ,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 place4 ,around this pyrtaneum the various civil1 political1 and religious affairs were carried on by the light and warmth of the public fire4 ,many quaint customs evolved1 apparently1 from this ancient procedure4 ,the tinder-box of modern centuries doubtless originated in very early times1 for it is inconceivable that the earliest beings did not become aware of the production of sparks when certain stones were struck together4 ,in the stone age1 when human beings spent much of their time chiseling implements and utensils from stone by means of tools of the same substance1 it appears certain that this means of producing fire was ever apparent4 ,many of their sharp implements1 such as knives and arrow-heads1 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 periods4 ,alaskan and ,aleutian tribes are known to have employed two pieces of quartz covered with native sulphur4 ,when these were struck together with skill1 excellent sparks were obtained4 ,later1 when iron and steel became available1 the more modern tinder-box was developed4 ,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 pyrites4 ,the latter is a yellow sulphide of iron1 of crystalline form1 best known as fool's gold4 ,doubtless1 the more primitive beings used dried grass1 leaves1 and moss as inflammable material upon which the sparks were showered4 ,in later centuries the tinder-box was filled with charred grass1 linen1 and paper4 ,there was a long interval between the development of fire-sticks and that of the tinder-box as measured by the progress of civilization4 ,during recent centuries ordinary brown paper soaked in saltpeter and dried was utilized satisfactorily as an inflammable material4 ,such devices have been employed in past ages in widely separated regions of the earth4 ,elaborate specimens of tinder-boxes from ,jamaica1 ,japan1 ,china1 ,europe1 and various other countries are now reposing in the collections in the possession of museums and of individuals4 ,if the radiant energy from the sun is sufficiently concentrated upon inflammable material1 the latter will ignite4 ,such concentration may be achieved by means of a convex lens or a concave mirror4 ,this method of producing fire does not antedate the more primitive methods such as striking quartz or rubbing wooden sticks1 because the materials required are not readily found or prepared1 but it is of very remote origin4 ,aristophanes in his comedy ,the ,clouds1 which is a satire aimed at the science and philosophy of his period 7#dhh-che ,b4 ,c471 mentions the burning lens4 ,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 mirror4 ,the ancient ,egyptians were proficient in the art of glass-making1 so it is likely that the burning-glass was employed by them4 ,even a crude lens of glass will focus an image of the sun sufficiently well to cause inflammable material to ignite4 ,the energy in sunlight varies enormously1 even on clear days1 because the water-vapor in the atmosphere absorbs some of the radiant energy emitted by the sun4 ,this absorbed radiation is chiefly known as infra-red energy1 which does not arouse the sensation of light4 ,when the water-vapor content of the atmosphere is high1 the sun1 though it may appear as bright to the eye1 in reality is not as hot as it would be if the water-vapor were not present4 ,however1 a fire may be kindled by concentrating only the visible rays in sunlight because of the enormous intensity of sunlight4 ,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 hands1 will kindle a fire in highly inflammable material if the sun is high and the atmosphere is fairly clear4 ,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 ,war4 ,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 ago4 ,as civilization advanced1 leading intellects began to inquire into the mysteries of nature and the periods of pure philosophy gave way to an era of methodical research4 ,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 laws4 ,in this manner the powerful sciences of physics and chemistry were born a few centuries ago4 ,among other things the production of fire and light received attention and the dark ages were doomed to end4 ,the crude1 uncertain1 and inconvenient methods of making fire were replaced by steadily improving scientific devices4 ,matches were at first cumbersome1 dangerous1 and expensive1 but these gradually evolved into the safety matches of the present time4 ,although they were primarily intended for lighting fires and various kinds of lamps1 billions of them are now used yearly as convenient light-sources4 ,smoldering hemp or other material treated with niter and other substances was an early form of match used especially for discharging firearms4 ,the modern wax-taper is an evolutionary form of this type of light-source4 ,phosphorus has long played a dominant rle in the preparation of matches4 ,the first attempt at making them in their modern form appears to have occurred about #afhj4 ,small pieces of phosphorus were used in connection with small splints of wood dipped in sulphur4 ,this type of match did not come into general use until after the beginning of the nineteenth century1 owing to its danger and expense4 ,white or yellow phosphorus is a deadly poison2 therefore the progress of the phosphorus match was inhibited until the discovery of the relatively harmless form known as red phosphorus4 ,the first commercial application of this form was made in about #ahej4 ,an early ingenious device consisted of a piece of phosphorus contained in a tube4 ,a piston fitted snugly into the tube1 by means of which the air could be compressed and the phosphorus ignited4 ,sulphur matches were ignited from the burning tinder1 the latter being fired by flint and steel4 ,in #ahbh another form of match consisted of a glass tube containing sulphuric acid and surrounded by a mixture of chlorate of potash and sugar4 ,a pair of nippers was supplied with each box of these matches1 by means of which the tip of the glass tube could be broken off4 ,this liberated the acid1 which upon mixing with the other ingredients set fire to them4 ,to this contrivance a roll of paper was attached which was ignited by the burning chemicals4 ,the lucifer or friction matches appeared in about #ahbg1 but successful phosphorus matches were first made in about #ahcc4 ,the so-called safety match of the present time was invented in the year #ahee4 ,to-day1 the total daily output of matches reaches millions and perhaps billions4 ,automatic machinery is employed in preparing the splints of wood and in dipping them into molten paraffin wax and finally into the igniting composition4 ,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 7a hydrous silicate of cerium and allied metals7 against steel4 ,these sparks ignite a gas-jet or a wick soaked in a highly inflammable liquid such as gasolene or alcohol4 ,this device is a tinder-box of the modern scientific age4 ,naturally with the advent of electricity1 electrical sparks came into use for lighting gas-jets and mantles and in isolated instances they have served as light-sources4 ,doubtless1 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-rug4 ,although many of these methods and devices have been used primarily for making fire1 they have served as emergency or momentary light-sources4 ,in the outskirts of civilization some of them are employed at the present time and various modern light-sources require a method of ignition4 ,,iii ,,primitive ,,light-,,sources ,many are familiar with the light of the firefly or of its larv1 the glow-worm1 but few persons realize that a vast number of insects and lower organisms are endowed with the superhuman ability of producing light by physiological processes4 ,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 predominantly4 ,that is1 these wonderful light-sources seem to be utilized more for signaling1 for luring prey1 and for protection than for strictly illuminating-purposes4 ,much study has been given to the production of light by animals1 because the secrets will be extremely valuable to mankind4 ,as one floats over tide-water on a balmy evening after dark and watches the pulsating spots of phosphorescent light emitted by the lowly jellyfishes1 his imaginative mood formulates the question1 ,why are these lowly organisms endowed with such a wonderful ability8 ,despite his highly developed mind and body and his boasted superiority1 man must go forth and learn the secrets of light-production before he may emancipate himself from darkness4 ,if man could emit light in relative proportion to his size as compared with the firefly1 he would need no other torch in the coal-mine4 ,how independent he would be in extreme darkness where his adapted eyes need only a feeble light-source6 ,primitive man1 desiring a light-source and having no means of making fire1 imprisoned the glowing insects in a perforated gourd or receptacle of clay1 and thus invented the first lantern perhaps before he knew how to make fire4 ,the fireflies of the ,west ,indies emit a continuous glow of considerable luminous intensity and the natives have used these imprisoned insects as light-sources4 ,thus mankind has exhibited his superiority by adapting the facilities at hand to the growing requirements which his independent nature continuously nourished4 ,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 ages4 ,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 tree4 ,however1 the crude lantern perhaps directed his primitive mind to the possibilities of artificial light4 ,the flaming fagot from the fire was the ancestor of the oil-lamp1 the candle1 the lantern1 and the electric flash-light4 ,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 inflammable4 ,nevertheless1 pine knots and similar resinous pieces of wood eventually were favored as torches and their use has persisted until the present time4 ,in some instances in ancient times resin was extracted from wood and burned in vessels4 ,this was the forerunner of the grease-and the oil-lamp4 ,in the woods to-day the craftsman of the wilds keeps on the lookout for live trees saturated with highly inflammable ingredients4 ,viewed from the present age1 these smoking1 flickering light-sources appear very crude2 nevertheless they represent a wide gulf between their users and those primitive beings who were unacquainted with the art of making fire4 ,although the wood fire prevailed as a light-source throughout uncounted centuries1 it was subjected to more or less improvement as civilization advanced4 ,when the wood fire was brought indoors the day was extended and early man began to develop his crude arts4 ,he thought and planned in the comfort and security of his cave or hut4 ,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 ago4 ,when it was too warm to have a roaring fire upon the hearth1 man devised other means for obtaining light without undue warmth4 ,he placed glowing embers upon ledges in the walls1 upon stone slabs1 or even upon suspended devices of non-inflammable material4 ,later he split long splinters of wood from pieces selected for their straightness of grain4 ,these burning splinters emitting a smoking1 feeble light were crude but they were refinements of considerable merit4 ,a testimonial of their satisfactoriness is their use throughout many centuries4 ,until very recent times the burning splinter has been in use in ,scotland and in other countries1 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 civilization4 ,scott1 in ,the ,legend of ,montrose1 describes a table scene during a feast4 ,behind each seat a giant ,highlander stood1 holding a blazing torch of bog-pine4 ,this was also the method of lighting in the ,homeric age4 ,crude clay relics representing a human head1 from the mouth of which the wood-splinters projected1 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 free4 ,splinter-holders of many types have survived1 but most of them are of the form of a crude pedestal with a notch or spring clip at its upper end4 ,the splinter was held in this clip and burned for a time depending upon its length and the character of the wood4 ,it was the business of certain individuals to prepare bundles of splinters1 which in the later stages of civilization were sold at the market-place or from house to house4 ,those who have observed the frontiersman even among civilized races will be quite certain that the wood for splinters was selected and split with skill1 and that the splinters were burned under conditions which would yield the most satisfactory light4 ,it is a characteristic of those who live close to nature1 and are thus limited in facilities1 to acquire a surprising efficiency in their primitive activities4 ,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 wall4 ,later when metal was available1 gratings or baskets were suspended from the ceiling or from brackets and glowing embers or flaming chips were placed upon them4 ,some of these were equipped with crude chimneys to carry away the smoke1 and perhaps to increase the draft4 ,in more recent centuries the first attempt at lighting outdoor public places was by means of metal baskets in which flaming wood emitted light4 ,it was the duty of the watchman to keep these baskets supplied with pine knots4 ,in early centuries street-lighting was not attempted1 and no serious efforts worthy of consideration as adequate lighting were made earlier than about a century ago4 ,as a consequence the link-boy came into existence4 ,with flaming torch he would escort pedestrians to their homes on dark nights4 ,this practice was in vogue so recently that the link-boy is remembered by persons still living4 ,in ,england the profession appears to have existed until about #ahdj4 ,somewhat akin to the wood-splinter1 and a forerunner of the candle1 was the rushlight4 ,in burning wood man noticed that a resinous or fatty material increased the inflammability and added greatly to the amount of light emitted4 ,it was a logical step to try to reproduce this condition by artificial means4 ,as a consequence rushes were cut and soaked in water4 ,they were then peeled1 leaving lengths of pith partially supported by threads of the skin which were not stripped off4 ,these sticks of pith were placed in the sun to bleach and to dry1 and after they were thoroughly dry they were dipped in scalding grease1 which was saved from cooking operations or was otherwise acquired for the purpose4 ,a reed two or three feet long held in the splinter-holder would burn for about an hour4 ,thus it is seen that man was beginning to progress in the development of artificial light4 ,in developing the rushlight he was laying the foundation for the invention of the candle4 ,pliny has mentioned the burning of reeds soaked in oil as a feature of funeral rites4 ,many crude forerunners of the candle were developed in various parts of the world by different races4 ,for example1 the ,malays made a torch by wrapping resinous gum in palm leaves1 thus devising a crude candle with the wick on the outside4 ,many primitive uses of vegetable and animal fats were forerunners of the oil-lamp4 ,in the ,east ,indies the candleberry1 which contains oily seeds1 has been burned for light by the natives4 ,in many cases burning fish and birds have served as lamps4 ,in the ,orkney ,islands the carcass of a stormy petrel with a wick in its mouth has been utilized as a light-source1 and in ,alaska a fish in a split stick has provided a crude torch for the natives4 ,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 civilization4 ,surely progress is limited where a burning fish serves as a torch1 or where1 at best1 the light-sources are feeble1 smoking1 flickering1 and ill-smelling6 ,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 thorough4 ,the early oil-lamps and candles did not emit much smoke1 but they were still feeble light-sources and not always without noticeable odors4 ,nevertheless1 they marked a tremendous advance in the production of artificial light4 ,although they were not scientific developments in the modern sense1 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 forms4 ,the advent of these two light-sources in reality marked the beginning of the civilization which was destined to progress and survive4 ,although such primitive light-sources as the flaming splinter and the glowing ember have survived until the present age1 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 times4 ,oil-lamps are to be seen in the earliest ,roman illustrations4 ,during the height of ancient civilization along the eastern shores of the ,mediterranean ,sea1 elaborate lighting was effected by means of the shallow grease-or oil-lamp4 ,it is difficult to estimate the age in which this form of light-source originated1 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 era4 ,it is noteworthy that such lamps did not differ materially in essential details from those in use as late as a few centuries ago4 ,at first the grease used was the crude fat from animals4 ,vegetable oils also were burned in the early lamps4 ,the ,japanese1 for example1 extracted oil from nuts4 ,when the demands of civilization increased1 extensive efforts were made to obtain the required fats and oils4 ,amphibious animals of the ,north and the huge mammals of the sea were slaughtered for their fat1 and vegetable sources were cultivated4 ,later1 sperm and colza were the most common oils used by the advanced races4 ,the former is an animal oil obtained from the head cavities of the sperm-whale2 the latter is a vegetable oil obtained from rape-seed4 ,mineral oil was introduced as an illuminant in #ahec1 and the modern lamp came into use4 ,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 securely4 ,the simplest forms had a single wick1 but in others many wicks dipped into the same receptacle4 ,the early ones were of stone1 but later1 lamps were modeled from clay or terra cotta and finally from metals4 ,they were usually covered and the wick projected through a hole in the top near the edge4 ,large stone vases filled with a hundred pounds of liquid fat are known to have been used in early times4 ,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 fat4 ,the ,esquimaux to-day use this form of lamp1 in which whale-oil and seal blubber is the fuel4 ,incidentally1 these lamps also supply the only artificial heat for their huts and igloos4 ,the heat from these feeble light-sources and from their bodies keeps these natives of the arctics warm within the icy walls of their abodes4 ,very beautiful oil-lamps of brass1 bronze1 and pewter evolved in such countries as ,egypt4 ,many of these were designed for and used in religious ceremonies4 ,the oil-lamps of ,china1 ,scotland1 and other countries in later centuries were improved by the addition of a pan beneath the oil-receptacle1 to catch drippings from the wick or oil which might run over during the filling4 ,the ,chinese lamps were sometimes made of bamboo1 but the ,scottish lamps were made of metal4 ,a flat metal lamp1 called a crusie1 was one of the chief products of blacksmiths and was common in ,scotland until the middle of the nineteenth century4 ,this type of lamp was used by many nations and has been found in the catacombs of ,rome4 ,the crusie was usually suspended by an iron hook and the flow of oil to the wick could be regulated by tilting4 ,the wick in the ,scottish lamps consisted of the pith of rushes1 cloth1 or twisted threads4 ,these early oil-lamps were almost always shallow vessels into which a short wick was dipped1 and it was not until the latter part of the eighteenth century that other forms came into general use4 ,the change in form was due chiefly to the introduction of scientific knowledge when mineral oil was introduced4 ,as early as #agha the burning of naptha obtained by distilling coal at low temperatures was first discussed1 but no general applications were made until a later period4 ,this was the beginning of many marked improvements in oil-lamps1 and was in reality the birth of the modern science of light-production4 ,illustration3 ,a ,,typical ,,metal ,,multiple-,,wick ,,open-,,flame ,,oil-,,lamp ,illustration3 ,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 lighting4 ,in consequence1 many ingenious devices for lighting were evolved4 ,for example1 in ,england in the seventeenth century man was already burrowing into the earth for coal and of course encountered coal-gases4 ,these inflammable gases were first known for the direful effects which they so often produced rather than for their useful qualities4 ,although they were known to miners long before they received scientific attention1 the earliest account of them in the ,transactions of the ,royal ,society was presented in the year #affg4 ,a description of early gas-lighting has been reserved for a later chapter1 but the foregoing is noted at this point to introduce a novel early method of lighting in coal-mines where inflammable gases were encountered4 ,in discussing this coal-gas another early writer stated that it will not take fire except by flame and that sparks do not affect it4 ,one of the early solutions of the problem of artificial lighting under such conditions is summarized as follows3 ,before the invention of ,sir ,humphrey ,davy's ,safety ,lamp1 this property of the gas gave rise to a variety of contrivances for affording the miners sufficient light to pursue their operations2 and one of the most useful of these inventions was a mill for producing light by sparks elicited by the collision of flint and steel4 ,such a stream of sparks may appear a very crude and unsatisfactory solution as judged by present standards1 but it was at least an ingenious application of the facilities available at that time4 ,various other devices were resorted to in the coal-mines before the introduction of a safety lamp4 ,in discussing the candle it is necessary again to go back to an early period1 for it slowly evolved in the course of many centuries4 ,it is the natural descendant of the rushlight1 the grease-lamp1 and various primitive devices4 ,until the advent of the more scientific age of artificial lighting1 the candle stood preminent among early light-sources4 ,it did not emit appreciable smoke or odor and it was conveniently portable and less fragile than the oil-lamp4 ,candles have been used throughout the ,christian era and some authorities are inclined to attribute their origin to the ,phoenicians4 ,it is known that the ,romans used them1 especially the wax-candles1 in religious ceremonies4 ,the ,phoenicians introduced them into ,byzantium1 but they disappeared under the ,turkish rule and did not come into use again until the twelfth century4 ,the wax-candle was very much more expensive than the tallow-candle until the fifteenth century1 when its relative cost was somewhat reduced1 bringing it within the means of a greater proportion of the people4 ,nevertheless it has long been used1 chiefly by the wealthy2 the departing guest of the early ,victorian inn would be likely to find an item on his bill such as this3 ,for a gentleman who called himself a gentleman1 wax-lights1 #e_/4 ,poor men used tallow dips or went to bed in the dark4 ,it is interesting to note the importance of the candle in the household budget of early times in various sayings4 ,for example1 ,the game is not worth the candle1 implies that the cost of candle-light was not ignored4 ,in these days little attention is given to the cost of artificial light under similar conditions4 ,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 energy4 ,with the rise of the ,christian church1 candles came to be used in religious ceremonies and many of the symbolisms1 meanings1 and customs survive to the present time4 ,some of the finest art of past centuries is found in the old candlesticks4 ,many of these antiques1 which ofttimes were gifts to the church1 have been preserved to posterity by the church4 ,the influence of these lighting accessories is often noted in modern lighting-fixtures1 but unfortunately early art often suffers from adaptation to the requirements of modern light-sources1 or the eyesight suffers from a senseless devotion to art which results in the use of modern light-sources1 unshaded and glaring1 in places where it was unnecessary to shade the feeble candle4 ,the oldest materials employed for making candles are beeswax and tallow4 ,the beeswax was bleached before use4 ,the tallow was melted and strained and then cotton or flax fibers were dipped into it repeatedly1 until the desired thickness was obtained4 ,in early centuries the pith of rushes was used for wicks4 ,tallow is now used only as a source of stearine4 ,spermaceti1 a fatty substance obtained from the sperm-whale1 was introduced into candle-making in about #agej and great numbers of men searched the sea to fill the growing demands4 ,paraffin wax1 a mixture of solid hydrocarbons obtained from petroleum1 came into use in #ahed and stearine is now used with it4 ,the latter increases the rigidity and decreases the brittleness of the candle4 ,some of the modern candles are made of a mixture of stearine and the hard fat extracted from cocoanut-oil4 ,modern candles vary in composition1 but all are the product of much experience and of the application of scientific knowledge4 ,the wicks are now made chiefly of cotton yarn1 braided or plaited by machinery and chemically treated to aid in complete combustion when the candle is burned4 ,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 consumed4 ,this eliminates the necessity of trimming4 ,candles have been made in various ways1 including dipping1 pouring1 drawing1 and molding4 ,wax-candles are made by pouring1 because wax cannot be molded satisfactorily4 ,drawing is somewhat similar to dipping1 except that the process is more or less continuous and is carried out by machinery4 ,molding1 as the term implies1 involves the use of molds1 of the size and shape desired4 ,the candlestick evolved from the most primitive wooden objects to elaborately designed and decorated works of art4 ,the primitive candlestick was crude and was no more than a holder of some kind for keeping the candle upright4 ,later a form of cup was attached to the stem of the holder1 to catch the dripping wax or fat4 ,the latter improvement has persisted throughout the centuries4 ,the modern candle is by no means an unsatisfactory light-source4 ,those who have had experience with it in the outskirts of civilization will testify that it possesses several desirable characteristics4 ,supplies of candles are transported without difficulty2 the lighted candle is easily carried about2 and the light in a quiescent atmosphere is quite satisfactory1 if common sense is used in shading and placing the candle4 ,although in a sense a primitive light-source1 it is a blessing in many cases and1 incidentally1 it is extensively used to-day in industries1 in religious ceremonies1 as a decorative element at banquets1 and in the outposts of civilization4 ,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-lamp4 ,there is a period of a century or more during which scientific progress was slow1 but those years paved the way for the extraordinary developments of the last few decades4 ,,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 mythology1 the early light-sources are associated more with this phase of artificial light than modern ones4 ,for this reason it appears appropriate to present this discussion before entering into the later stages of the development and utilization of artificial light4 ,furthermore1 many of the traditions of lighting at the present time are survivors of the early ages4 ,lighting-fixtures show the influence of this byway of lighting1 and in those cases where the ceremonial use of light has survived to the present time1 modern light-sources cannot be employed wisely in replacing more primitive ones without consideration of the origin and existence of the customs4 ,in fact1 candles are likely to be used for hundreds of years to come1 owing to the sentiment connected with them and to the established customs founded upon centuries of traditional use4 ,doubtless1 the sun as a source of heat and light and of the blessings which these bring to earth1 is responsible largely for the divine significance bestowed upon light4 ,darkness very deservingly acquired many uncomplimentary attributes1 for danger lurked behind its veil and it was the suitable abode of evil spirits4 ,it harbored all that was the antithesis of goodness1 happiness1 and security4 ,light naturally became sacred1 life-giving1 and symbolic of divine presence4 ,fire was to primitive beings the most impressive phenomenon over which they had any control1 and it was sufficiently mysterious in its operation to warrant a connection with the supernatural4 ,thus it was very natural that these earlier beings worshiped it as representing divine presence4 ,the sun1 as ,ra1 was one of the chief gods of the ancient ,egyptians2 and the ,assyrians1 the ,babylonians1 the ancient ,greeks1 and many other early peoples gave a high place to this deity4 ,among simpler races the sun was often the sole object of worship1 and those peoples who worship ,light as the god of all1 in a sense are not far afield4 ,fire-worshipers generally considered fire as the purest representation of heavenly fire1 the origin of everything that lives4 ,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 world4 ,this custom has prevailed widely but the fact that the lamps were unlighted indicates that only the material aspect was considered4 ,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 gods4 ,in later centuries a deeper symbolical meaning became attached to light and burning lamps were placed upon the tombs of important personages4 ,the burying of lamps with the dead appears to have originated in ,asia4 ,the ,phoenicians and ,romans apparently continued the custom1 but no traces of it have been found in ,greece and ,egypt4 ,fire and light have been closely associated in various religious creeds and their ceremonies4 ,the ,hindu festival in honor of the goddess of prosperity is attended by the burning of many lamps in the temples and homes4 ,the ,jewish synagogues have their eternal lamps and in their rituals fire and light have played prominent rles4 ,the devout ,brahman maintains a fire on the hearth and worships it as omniscient and divine4 ,he expects a brand from this to be used to light his funeral pyre1 whose fire and light will make his spirit fit to enter his heavenly abode4 ,he keeps a fire burning on the altar1 worships ,agni1 the god of fire1 and makes fire sacrifices on various occasions such as betrothals and marriages4 ,to the ,mohammedans lighted lamps symbolize holy places1 and the ,kaaba at ,mecca1 which contains a black stone supposed to have been brought from heaven1 is illuminated by thousands of lamps4 ,many of the uses to which light was put in ancient times indicate its rarity and sacred nature4 ,doubtless1 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 light4 ,certainly nothing is more generally appropriate in representing joy and prosperity4 ,throughout all countries ancient races had woven natural light and fire into their rites and customs1 so it became a natural step to utilize artificial light and fire in the same manner4 ,it would be tedious and monotonous to survey the vast field of ancient worship of light1 for the underlying ideas are generally similar4 ,the mythology of the ,greeks is illustrative of the importance attached to fire and light by the cultivated peoples of ancient times4 ,the myth of ,prometheus emphasizes the fact that in those remote periods fire and light were regarded as of prime importance4 ,according to this myth1 fire and light were contained in heaven and great cunning and daring were necessary in order to obtain it4 ,prometheus stole this heavenly fire1 for which act he was chained to the mountain and made to suffer4 ,the ,greeks mark this event as the beginning of human civilization4 ,all arts are traced to ,prometheus1 and all earthly woe likewise4 ,as past history is surveyed it appears natural to think of scientific men who have become martyrs to the quest of hidden secrets4 ,they have made great sacrifices for the future benefit of civilization and not a few of them have endured persecution even in recent times4 ,the ,greeks recognized that a new era began with the acquisition of artificial light4 ,its divine nature was recognized and it became a phenomenon for worship and a means for representing divine presence4 ,the origin of fire and light made them holy4 ,the fire on the altar took its place in religious rites and there evolved many ceremonial uses of lamps1 candles1 and fire4 ,the ,greeks and ,romans burned sacred lamps in the temples and utilized light and fire in many ceremonies4 ,the torch-race1 in which young men ran with lighted torches1 the winner being the one who reached the goal first with his torch still alight1 originated in a ,grecian ceremony of lighting the sacred fire4 ,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 heroes4 ,on birthdays and festivals the houses of the ,romans were specially ornamented with burning lamps4 ,the ,vestal ,virgins in ,rome maintained the sacred fire which had been brought by fugitives from ,troy4 ,in ancient ,rome when the fire in the ,temple of ,vesta became extinguished1 it was rekindled by the rubbing of a piece of wood upon another until fire was obtained4 ,this was carried into the temple by the ,vestal ,virgin and the sacred fire was rekindled4 ,the fire produced in this manner1 for some reason1 was considered holy4 ,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 ,eve4 ,candelabra1 of the form of the branching tree1 were commonly in use in the ,roman temples4 ,the ceremonial use of light in the ,christian church evolved both from adaptations of pagan customs and of the natural symbolisms of fire and light4 ,however1 these acquired a deeper meaning in ,christianity than in early times because they were primarily visible representations or manifestations of the divine presence4 ,the ,bible contains many references to the importance and symbolisms of light and fire4 ,according to the ,first ,book of ,moses1 the achievement of the ,creator immediately following the creation of the heavens and the earth was the creation of light4 ,the word light is the forty-sixth word in ,genesis4 ,christ is the true light and ,christians are children of light in war against the evil powers of darkness4 ,when ,st4 ,paul was converted there shined about him a great light from heaven4 ,the impressiveness and symbolism of fire and light are testified to in many biblical expressions4 ,christ stands in the midst of seven candle-sticks with his eyes as a flame of fire4 ,when the ,holy ,ghost appeared before the apostles there appeared unto them cloven tongues of fire4 ,when ,st4 ,paul was preaching the gospel of ,christ at ,alexandria there were many lights suggesting a festive illumination4 ,according to the ,bible1 the perpetual fire which came originally from heaven was to be kept burning on the altar4 ,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 extinguished4 ,if human hands were permitted to kindle it1 punishment was meted out4 ,the two sons of ,aaron who offered strange fire before the ,lord were devoured by fire from the ,lord4 ,the seven-branched candlestick was lighted eternally and these burning light-sources were necessary accompaniments of worship4 ,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 church4 ,the festive illumination of pagan temples in honor of gods was carried over into the ,christian era4 ,the ,christmas tree of to-day is incomplete without its many lights4 ,its illumination is a homage of light to the source of light4 ,the celebration of ,easter in the ,church of the ,holy ,sepulchre in ,jerusalem is a typical example of fire-worship retained from ancient times4 ,at the climax of the services comes the descent of the ,holy ,fire4 ,the central candelabra suddenly becomes ablaze and the worshipers1 each of whom carries a wax taper1 light their candles therefrom and rush through the streets4 ,the fire is considered to be of divine origin and is a symbol of resurrection4 ,the custom is similar in meaning to the light which in older times was maintained before gods4 ,during the first two or three centuries of the ,christian era the ceremonial use of light does not appear to have been very extensive4 ,writings of the period contain statements which appear to ridicule this use to some extent4 ,for example1 one writer of the second century states that ,on days of rejoicing 444 we do not encroach upon daylight with lamps4 ,another1 in the fourth century1 refers with sarcasm to the heathen practice in this manner3 ,they kindle lights as though to one who is in darkness4 ,can he be thought sane who offers the light of lamps and candles to the ,author and ,giver of all light8 ,that candles were lighted in cemeteries is evidenced by an edict which forbade their use during the day4 ,lamps of the early centuries of the ,christian era have been found in the catacombs of ,rome which are thought to have been ceremonial lamps1 for they were not buried with the dead4 ,they were found only in niches in the walls4 ,during these same centuries elaborate candelabra containing hundreds of candles were kept burning before the tombs of saints4 ,notwithstanding the doubt that exists as to the extent of ceremonial lighting in the early centuries of the ,christian era1 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 established4 ,that this is true and that there were still some objections is indicated by many controversies4 ,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 saints4 ,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 daytime4 ,passing beyond the early controversial period1 the ceremonial use of light is everywhere in evidence at ordinary church services4 ,on special occasions such as funerals1 baptisms1 and marriages1 elaborate altar-lighting was customary4 ,the gorgeous candelabra and the eternal lamp are noted in many writings4 ,early in the fifth century the pope ordered that candles be blessed and provided rituals for this ceremony4 ,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 blessed4 ,however1 it appears that the blessing of candles was not carried out in all churches4 ,altar lights were not generally used until the thirteenth century4 ,they were originally the seven candles carried by church officials and placed near the altar4 ,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 relation4 ,finally certain light-sources themselves became objects of worship and were surrounded by other lamps1 and the symbolisms of light grew apace4 ,a bishop in the sixth century heralded the triple offering to ,god represented by the burning wax-candle4 ,he pointed out that the rush-wick developed from pure water2 that the wax was the product of virgin bees2 and that the flame was sent from heaven4 ,each of these1 he was certain1 was an offering acceptable to ,god4 ,wax-candles became associated chiefly with religious ceremonies4 ,the wax later became symbolic of the ,blessed ,virgin and of the body of ,christ4 ,the wick was symbolical of ,christ's soul1 the flame represented his divine character1 and the burning candle thus became symbolical of his death4 ,the lamp1 lantern1 and taper are frequently symbols of piety1 heavenly wisdom1 or spiritual light4 ,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 love4 ,by the time the ,middle ,ages were reached the ceremonial uses of light became very complex1 but for the ,roman ,catholic ,church they may be divided into three general groups3 7#a7 ,they were symbolical of ,god's presence or of the effect of his presence2 of ,christ or of the children of light2 or of joy and content at festivals4 7#b7 ,they may be offered in fulfillment of a religious vow2 that is1 as an act of worship4 7#c7 ,they may possess certain divine power because of their being blessed by the church1 and therefore may be helpful to soul and body4 ,the three conceptions are indicated in the prayers offered at the blessing of the candles on ,candlemas as follows3 7#a7 ,o holy ,lord 444 who 444 by thy command didst cause this liquid to come by the labor of bees to the perfection of wax1 444 we beseech thee 444 to bless and sanctify these candles for the use of men1 and the health of bodies and souls4444 7#b7 444these candles1 which we thy servants desire to carry lighted to magnify thy name2 that by offering them to thee1 being worthily inflamed with the holy fire of thy most sweet charity1 we may deserve4444 7#c7 ,o ,lord ,jesus ,christ1 the true light1 444 mercifully grant1 that as these lights enkindled with visible fire dispel nocturnal darkness1 so our hearts illuminated by visible fire1 etc4 ,in general1 the ceremonial uses of lights in this church were originated as a forceful representation of ,christ and of salvation4 ,on the eve of ,easter a new fire1 emblematic of the arisen ,christ1 is kindled1 and all candles throughout the year are lighted from this4 ,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 one4 ,when but one remains burning it is carried behind the altar1 thus symbolizing the last days of ,christ on earth4 ,it is said that this ceremony has been traced to the eighth century4 ,on ,easter ,eve1 after the new fire is lighted and blessed1 certain ceremonies of light symbolize the resurrection of ,christ4 ,from this new fire three candles are lighted and from these the ,paschal ,candle4 ,the origin of the latter is uncertain1 but it symbolizes a victorious ,christ4 ,from it all the ceremonial lights of the church are lighted and they thereby are emblematic of the presence of the light of ,christ4 ,many interesting ceremonial uses may be traced out1 but space permits a glimpse of only a few4 ,at baptismal services the paschal candle is dipped into the water so that the latter will be effective as a regenerative element4 ,the baptized child is reborn as a child of light4 ,lighted candles are placed in the hands of the baptized persons or of their god-parents4 ,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 communion4 ,lights are placed around the bodies of the dead and are carried at the funeral4 ,they not only protect the dead from the powers of darkness but they symbolize the dead as still living in the light of ,christ4 ,the use of lighted candles around bodies of the dead still survives to some extent among ,protestants1 but their significance has been lost sight of4 ,even in the eighteenth century funerals in ,england were accompanied by lighted tapers1 but the carrying of lights in other processions appears to have ceased with the ,reformation4 ,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 funeral4 ,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 excommunication4 ,such a ceremony is described in an early writing thus3 ,twelve priests should stand about the bishop1 holding in their hands lighted torches1 which at the conclusion of the anathema or excommunication they should cast down and trample under foot4 ,when the excommunicant is reinstated1 a lighted candle is placed in his hands as a symbol of reconciliation4 ,these and many other ceremonial uses of light have been and are practised1 but they are not always mandatory4 ,furthermore1 the customs have varied from time to time1 but the few which have been touched upon illustrate the impressive part that light has played in religious services4 ,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 authority4 ,in the ,lutheran churches ceremonial lights were largely retained1 in the ,church of ,england they have been subjected to many changes largely through the edicts of the rulers4 ,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 ,commons4 ,many uses of light in religious ceremonies were revived in cathedrals after the ,restoration and they became wide-spread in ,england in the nineteenth century4 ,as late as #ahhi the ,archbishop of ,canterbury ruled that certain ceremonial candles were lawful according to the ,prayer-,book of ,edward ,,vi1 but the whole question was left open and unsettled4 ,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 race4 ,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 encountered4 ,although many ceremonial uses of light remain1 it is doubtful if their significance and especially their origin are appreciated by most persons4 ,nevertheless1 no more interesting phase of artificial light is encountered than this1 which reaches to the foundation of civilization4 ,v ,,oil-,,lamps ,,of ,,the ,,nineteenth ,,century ,it will be noted that the light-sources throughout the early ages were flames1 the result of burning material4 ,this principle of light-production has persisted until the present time1 but in the latter part of the nineteenth century certain departures revolutionized artificial lighting4 ,however1 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 development4 ,the oil-lamp and the candle were the mainstays of artificial lighting throughout many centuries4 ,the fats and waxes which these light-sources burned were many but in the later centuries they were chiefly tallow1 sperm-oil1 spermaceti1 lard-oil1 olive-oil1 colza-oil1 bees-wax and vegetable waxes4 ,those fuels which are not liquid are melted to liquid form by the heat of the flame before they are actually consumed4 ,the candle is of the latter type and despite its present lowly place and its primitive character1 it is really an ingenious device4 ,its fuel remains conveniently solid so that it is readily shipped and stored2 there is nothing to spill or to break beyond easy repair2 but when it is lighted the heat of its flame melts the solid fuel and thus it becomes an oil-lamp4 ,animal and vegetable oils were mainly used until the middle of the nineteenth century1 when petroleum was produced in sufficient quantities to introduce mineral oils4 ,this marked the beginning of an era of developments in oil-lamps1 but these were generally the natural offspring of early developments by ,ami ,argand4 ,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 light4 ,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 factor4 ,tallow was a by-product of the kitchen or of the butcher4 ,stearine1 a constituent of tallow1 is a compound of glyceryl and stearic acid4 ,it is obtained by breaking up chemically the glycerides of animal fats and separating the fatty acids from glycerin4 ,fats are glycerides2 that is1 combinations of oleic1 palmetic1 and stearic acids4 ,inasmuch as the former is liquid at ordinary temperatures and the others are solid1 it follows that the consistency or solidity of fats depend upon the relative proportions of the three constituents4 ,the sperm-whale1 which lives in the warmer parts of all the oceans1 has been hunted relentlessly for fuels for artificial lighting4 ,in its head cavities sperm-oil in liquid form is found with the white waxy substance known as spermaceti4 ,colza-oil is yielded by rape-seed and olive-oil is extracted from ripe olives4 ,the waxes are combinations of allied acids with bases somewhat related to glycerin but of complex composition4 ,fats and waxes are more or less related1 but to distinguish them carefully would lead far afield into the complexities of organic chemistry4 ,all these animal and vegetable products which were used as fuels for light-sources are rich in carbon1 which accounts for the light-value of their flames4 ,the brightness of such a flame is due to incandescent carbon particles1 but this phase of light-production is discussed in another chapter4 ,these oils1 fats1 and waxes are composed by weight of about #ge to #hj per cent4 carbon2 #aj to #ae per cent4 hydrogen2 and #e to #aj per cent4 oxygen4 ,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 projected4 ,the flame was feeble and smoky and the odors were sometimes very repugnant4 ,viewing such light-sources from the present age in which light is plentiful1 convenient1 and free from the great disadvantages of these early oil-lamps1 it is difficult to imagine the possibility of the present civilization emerging from that period without being accompanied by progress in light-production4 ,the improvements made in the eighteenth century paved the way for greater progress in the following century4 ,this is the case throughout the ages1 but there are special reasons for the tremendous impetus which light-production has experienced in the past half-century4 ,these are the acquirement of scientific knowledge from systematic research and the application of this knowledge by organized development4 ,the first and most notable improvement in the oil-lamp was made by ,argand in #aghd4 ,our nation was just organizing after its successful struggle for independence at the time when the production of light as a science was born4 ,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 lamp4 ,his burner consisted of two concentric metal tubes between which the wick was located4 ,the inner tube was open1 so that air could reach the inner surface of the wick as well as the outer surface4 ,the lamp chimney not only protected the flame from drafts but also improved combustion by increasing the supply of air4 ,it rested upon a perforated flange below the burner4 ,if the glass chimney of a modern kerosene lamp be lifted1 it will be noted that the flame flickers and smokes and that it becomes steady and smokeless when the chimney is replaced4 ,the advantages of such a chimney are obvious now1 but ,argand for his achievements is entitled to a place among the great men who have borne the torch of civilization4 ,he took the first step toward adequate artificial light and opened a new era in lighting4 ,the various improvements of the oil-lamp achieved by ,argand combined to effect complete combustion1 with the result that a steady1 smokeless lamp of considerable luminous intensity was for the first time available4 ,many developments followed1 among which was a combination of reservoir and gravity feed which maintained the oil at a constant level4 ,in later lamps1 upon the adoption of mineral oil1 this was found unnecessary1 perhaps owing to the construction of the wick and to the physical characteristics of the oil which favored capillary action in the wick4 ,however1 the height of the oil in the reservoir of modern oil-lamps makes some difference in the amount of light emitted4 ,the ,carcel lamp1 which appeared in #ahjj1 consisted of a double piston operated by clockwork4 ,this forced the oil through a tube to the burner4 ,franchot invented the moderator lamp in #ahcf1 which1 because of its simplicity and efficiency soon superseded many other lamps designed for burning animal and vegetable oils4 ,the chief feature of the moderator lamp is a spiral spring which forces the oil upward through a vertical tube to the burner4 ,these are still used to some extent in ,france1 but owing to the fact that mechanical lamps eventually were very generally replaced by more simple ones1 it does not appear necessary to describe these complex mechanisms in detail4 ,when coal is distilled at moderate temperatures1 volatile liquids are obtained4 ,these hydrocarbons1 being inflammable1 naturally attracted attention when first known1 and in #agha their use as fuel for lamps was suggested4 ,however1 it was not until #ahbj that the light oils obtained by distilling coal-tar1 a by-product of the coal-gas industry which was then in its early stage of development1 were burned to some extent in the ,holliday lamp4 ,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-burner4 ,the oil is heated by the flame and the vaporized mineral oil which escapes through small orifices is burned4 ,this type of lamp has undergone many physical changes1 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 stand4 ,although petroleum products were not used to any appreciable extent for illuminating-purposes until after the middle of the nineteenth century1 mineral oil is mentioned by ,herodotus and other early writers4 ,in #ahdg petroleum was discovered in a coal-mine in ,england1 but the supply failed in a short time4 ,however1 the discoverer1 ,james ,young1 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 deposits4 ,these were destined to form the corner-stone of the oil industry in ,scotland4 ,in #ahej he began producing petroleum in this manner1 but it was not seriously considered for illuminating-purposes4 ,however1 in ,germany about this time lamps were developed for burning the lighter distillates and these were introduced into several countries4 ,but the price of these lighter oils was so great that little progress was made until1 in #ahei1 ,col4 ,e4 ,l4 ,drake discovered oil in ,pennsylvania4 ,by studying the geological formations and concluding that oil should be obtained by boring1 ,drake gave to the world a means of obtaining petroleum1 and in quantities which were destined to reduce the price of mineral oil to a level undreamed of theretofore4 ,to his imagination1 which saw vast reservoirs of oil in the depths of the earth1 the world owes a great debt4 ,lamps were imported from ,germany to all parts of the civilized world and the kerosene lamp became the prevailing light-source4 ,hundreds of ,american patents were allowed for oil-lamps and their improvements in the next decade4 ,illustration3 ,,lamps ,,of ,a ,,century ,,or ,,two ,,ago ,illustration3 ,,elaborate ,,fixtures ,,of ,,the ,,age ,,of ,,candles ,the crude petroleum1 of course1 is not fit for illuminating purposes1 but it contains components which are satisfactory4 ,the various components are sorted out by fractional distillation and the oil for burning in lamps is selected according to its volatility1 viscosity1 stability1 etc4 ,it must not be so volatile as to have a dangerously low flashing-point1 nor so stable as to hinder its burning well4 ,in this fractional distillation a vast variety of products are now obtained4 ,gasolene is among the lighter products1 with a density of about #j4fe2 kerosene has a density of about #j4hj2 the lubricating-oils from #j4he to #j4ie2 and there are many solids such as vaseline and paraffin which are widely used for many purposes4 ,this process of refining oils is now the source of paraffin for making candles1 in which it is usually mixed with substances like stearin in order to raise its melting-point4 ,crude petroleum possesses a very repugnant odor2 it varies in color from yellow to black2 and its specific gravity ranges from about #j4hj to #a4jj1 but commonly is between #j4hj and #j4ij4 ,its chemical constitution is chiefly of carbon and hydrogen1 in the approximate ratio of about six to one respectively4 ,it is a mixture of paraffin hydrocarbons having the general formula of ,cn,h#bn#b and the individual members of this series vary from ,,ch#d 7methane7 to ,c#ae;,h#cb 7pentadecane71 although the solid hydrocarbons are still more complex4 ,petroleum is found in many countries and the ,united ,states is particularly blessed with great stores of it4 ,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 danger4 ,it requires care and may cause disaster if it is upset1 but it has been blamed unjustly in many accidents4 ,a disadvantage of the kerosene lamp over electric lighting1 for example1 is the relatively greater possibility of accidents through the carelessness of the user4 ,this point is brought out in statistics of fire-insurance companies1 which show that the fires caused by kerosene lamps are much more numerous than those from other methods of lighting4 ,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 chimney1 there is little danger in its use excepting accidental breakage or overturning4 ,in oil-lamps at the present time mineral oils are used which possess flashing-points above #ge;,f4 ,the highly volatile components of petroleum are dangerous because they form very explosive mixtures with air at ordinary temperatures4 ,a mineral oil like kerosene1 to be used with safety in lamps1 should not be too volatile4 ,it is preferable that an inflammable vapor should not be given off at temperatures under #abj;,f4 ,the oil must be of such physical characteristics as to be drawn up to the burner by capillarity from the reservoir which is situated below4 ,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 air4 ,the resulting products of this combustion1 if it is complete1 are carbon dioxide and water-vapor4 ,for each candle-power of light per hour about #j4bd cubic foot of carbon dioxide and #j4ah cubic foot of water-vapor are formed by a modern oil-lamp4 ,that an open flame devours something from the air is easily demonstrated by enclosing it in an air-tight space4 ,the flame gradually becomes feeble and smoky and finally goes out4 ,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 dioxide4 ,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 person4 ,inasmuch as oil-lamps are ordinarily of #aj to #bj candle-power1 it is seen that one lamp will consume as much oxygen as several persons4 ,in order that oil-lamps may produce a brilliant light free from smoke1 combustion must be complete4 ,the correct quantity of oil must be fed to the burner and it must be properly vaporized by heat4 ,if insufficient oil is fed1 the intensity of the light is diminished and if too much is available at the burner1 smoke and other products of incomplete combustion will be emitted4 ,the wick is an important factor1 for1 through capillarity1 it feeds oil forcefully to the burner against the action of gravity4 ,this action of a wick is commonly looked upon with indifference but in reality it is caused by an interesting and really wonderful phenomenon4 ,wicks are usually made of high-grade cotton fiber loosely spun into coarse threads and these are woven into a loose plait4 ,the wick must be dry before being inserted into the burner2 and it is desirable that it be considerably longer than is necessary merely to reach the bottom of the reservoir4 ,a flame burning in the open will smoke because insufficient oxygen is brought in contact with it4 ,the injurious products of this incomplete combustion are carbon monoxide and oil vapors1 which are a menace to health4 ,to supply the necessary amount of oxygen 7air7 to the flame1 a forced draft is produced4 ,chimneys are simple means of accomplishing this1 and this is their function whether on oil-lamps or factories4 ,other means of forced draft have been used1 such as small fans or compressed air4 ,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 stack4 ,with each noisy puff of smoke a quantity of air is forcibly drawn into the fire-box through the burning fuel4 ,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 burner4 ,these metal parts1 being hot1 also serve to warm the oil before it reaches the burning end of the wick1 thus serving to aid vaporization and combustion4 ,the consumption of oil per candle-power per hour varies considerably with the kind of lamp and with the character of the oil4 ,the average consumption of oil-lamps burning a mineral oil of about #j4hj specific gravity and a rather high flashing-point is about #ej to #fj grams of oil per candle-power per hour for well-designed flame-lamps4 ,kerosene weighs about #f4f pounds per gallon2 therefore1 about #hjj candle-power hours per gallon are obtained from modern lamps employing wicks4 ,kerosene lamps are usually of #aj to #bj candle-power1 although they are made up to #ajj candle-power4 ,these luminous intensities refer to the maximum horizontal candle-power4 ,the best practice now deals with the total light output1 which is expressed in lumens1 and on this basis a consumption of one gallon of kerosene per hour would yield about #hjjj lumens4 ,oil-lamps have been devised in which the oil is burned as a spray ejected by air-pressure4 ,these burn with a large flame2 however1 a serious feature is the escape of considerable oil which is not burned4 ,these lamps are used in industrial lighting1 especially outdoors1 and possess the advantage of consuming low-grade oils4 ,they produce about #gjj to #hjj candle-power hours per gallon of oil4 ,lamps of this type of the larger sizes burn with vertical flames two or three feet high4 ,the oil is heated as it approaches the nozzle and is fairly well vaporized on emerging into the air4 ,the names of ,lucigen1 ,wells1 ,doty1 and others are associated with this type of lamp or torch1 which is a step in the direction of air-gas lighting4 ,during the latter part of the nineteenth century numerous developments were made which paralleled the progress in gas-lighting4 ,experiments were conducted which bordered closely upon the next epochal event in light-production--the appearance of the gas mantle4 ,one of these was the use of platinum gauze by ,kitson4 ,he produced an apparatus similar to the oil-spray lamp1 on a small and more delicate scale4 ,the hot blue flame was not very luminous and he attempted to obtain light by heating a mantle of fine platinum gauze4 ,although these mantles emitted a brilliant light for a few hours1 their light-emissivity was destroyed by carbonization4 ,after the appearance of the ,welsbach mantle1 ,kitson's lamp and others met with success by utilizing it4 ,from this point1 attention was centered upon the new wonder1 which is discussed in a later chapter after certain scientific principles in light-production have been discussed4 ,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 homes1 especially in villages1 in the country1 and in the remote districts of civilization4 ,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 country4 ,it is convenient and safe when carelessness is avoided1 and is fairly free from odor4 ,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 overturning4 ,the kerosene lantern is widely used to-day1 but the danger due to accident is ever-present4 ,the consequences of such accidents are often serious and are exemplified in the terrible conflagration in ,chicago in #ahga1 when ,mrs4 ,o',leary's cow kicked over a lantern and started a fire which burned the city4 ,modern developments in lighting are gradually encroaching upon the territory in which the oil-lamp has reigned supreme for many years4 ,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 land4 ,,vi ,,early ,,gas-,,lighting ,owing to the fact that the smoky1 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-source1 the reader is prepared to suppose that gas-lighting is of recent origin4 ,apparently ,william ,murdock in ,england was the first to install pipes for the conveyance of gas for lighting purposes4 ,in an article in the ,philosophical ,transactions of the ,royal ,society of ,london dated ,february #be1 #ahjh1 in which he gives an account of the first industrial gas-lighting1 he states3 ,it is now nearly sixteen years1 since1 in a course of experiments ,i was making at ,redruth in ,cornwall1 upon the quantities and qualities of the gases produced by distillation from different mineral and vegetable substances1 ,i was induced by some observation ,i had previously made upon the burning of coal1 to try the combustible property of the gases produced from it4444 ,inasmuch as he is credited with having lighted his home by means of piped gas1 this experimental installation may be considered to have been made in #agib4 ,in his first trial he burned the gas at the open ends of the pipes2 but finding this wasteful1 he closed the ends and in each bored three small holes from which the gas-flames diverged4 ,it is said that he once used his wife's thimble in an emergency to close the end of the pipe2 and1 the thimble being much worn and consequently containing a number of small holes1 tiny gas-jets emerged from the holes4 ,this incident is said to have led to the use of small holes in his burners4 ,he also lighted a street lamp and had bladders filled with gas to carry at night1 with which1 and his little steam carriage running on the road1 he used to astonish the people4 ,apparently unknown to ,murdock1 previous observations had been made as to the inflammability of gas from coal4 ,long before this ,dr4 ,clayton described some observations on coal-gas1 which he called the spirit of coals4 ,he filled bladders with this gas and kept them for some time4 ,upon his pricking one of them with a pin and applying a candle1 the gas burned at the hole4 ,thus ,clayton had a portable gas-light4 ,he was led to experiment with distillation of coal from some experiences with gas from a natural coal bed1 and he thus describes his initial laboratory experiment3 ,i got some coal1 and distilled it in a retort in an open fire4 ,at first there came over only phlegm1 afterwards a black oil1 and then likewise1 a spirit arose which ,i could no ways condense2 but it forced my lute and broke my glasses4 ,once when it had forced my lute1 coming close thereto1 in order to try to repair it1 ,i observed that the spirit which issued out caught fire at the flame of the candle1 and continued burning with violence as it issued out in a stream1 which ,i blew out1 and lighted again alternately several times4 ,he then turned his attention to saving some of the gas and hit upon the use of bladders4 ,he was surprised at the amount of gas which was obtained from a small amount of coal2 for1 as he stated1 the spirit continued to rise for several hours1 and filled the bladders almost as fast as a man could have blown them with his mouth2 and yet the quantity of coals distilled was inconsiderable4 ,although this account appeared in the ,transactions of the ,royal ,society in #agci1 there is strong evidence that ,dr4 ,clayton had written it many years before1 at least prior to #afia4 ,but before entering further into the early history of gas-lighting1 it is interesting to inquire into the knowledge possessed in the seventeenth century pertaining to natural and artificial gas4 ,doubtless there are isolated instances throughout history of encounters with natural gas4 ,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 fireplace4 ,this is a gas-plant on a small scale2 for the gas is formed at the burning end of the wooden stick and is conducted through its hollow center to the cold end1 where it will burn if lighted4 ,if a piece of paper be rolled into the form of a tube and inclined somewhat from a horizontal position1 inflammable gas will emanate from the upper end if the lower end is burning4 ,by applying a match near the upper end1 we can ignite this jet of gas4 ,however1 it is certain that little was known of gas for illuminating purposes before the eighteenth century4 ,the literature of an ancient nation is often referred to as revealing the civilization of the period4 ,surely the scientific literature which deals with concrete facts is an exact indicator of the technical knowledge of a period6 ,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 ,candle1 by ,tho4 ,shirley in the ,transactions of the ,royal ,society in #affg4 ,much of the quaint charm of the original is lost by inability to present the text in its original form1 but it is reproduced as closely as practicable4 ,the report was as follows3 ,about the latter ,end of ,feb4 #afei1 returning from a ,journey to my ,house in ,wigan1 ,i was entertained with the ,relation of an odd ,spring situated in one ,mr4 ,hawkley's ,ground 7if ,i mistake not7 about a ,mile from the ,town1 in that ,road which leads to ,warrington and ,chester3 ,the ,people of this ,town did confidently affirm1 ,that the ,water of this ,spring did burn like ,oil4 ,when we came to the said ,spring 7being #e or #f in ,company together7 and applied a lighted ,candle to the ,surface of the ,water2 there was 'tis true1 a large ,flame suddenly produced1 which burnt the ,foot of a ,tree1 growing on the ,top of a neighbouring ,bank1 the ,water of which ,spring filled a ,ditch that was there1 and covered the ,burning-place2 ,i applied the lighted ,candle to divers ,parts of the ,water contained in the said ,ditch1 and found1 as ,i expected1 that upon the ,touch of the ,candle and the ,water the ,flame was extinct4 ,again1 having taken up a ,dish full of water at the flaming ,place1 and held the lighted ,candle to it1 it went out4 ,yet ,i observed that the ,water1 at the ,burning-place1 did boil1 and heave1 like ,water in a ,pot upon the ,fire1 tho' by putting my ,hand into it1 ,i could not perceive it so much as warm4 ,this ,boiling ,i conceived to proceed from the ,eruption of some bituminous or sulphureous ,fumes2 considering this ,place was not above #cj or #dj ,yards distant from the ,mouth of a ,coal-,pit there3 ,and indeed ,wigan1 ,ashton1 and the whole ,country1 for many ,miles compass1 is underlaid with ,coal4 ,then1 applying my ,hand to the ,surface of the ,burning-place of the ,water1 ,i found a strong ,breath1 as it were a ,wind1 to bear against my ,hand4 ,when the ,water was drained away1 ,i applied the ,candle to the ,surface of the dry ,earth1 at the same ,point where the ,water burned before2 the ,fumes took fire1 and burned very bright and vigorous4 ,the ,cone of the ,flame ascended a ,foot and a half from the ,superficies of the ,earth2 and the ,basis of it was of the ,compass of a ,man's ,hat about the ,brims4 ,i then caused a ,bucket full of ,water to be pour'd on the ,fire1 by which it was presently quenched4 ,i did not perceive the ,flame to be discoloured like that of sulphurous ,bodies1 nor to have any manifest ,scent with it4 ,the ,fumes1 when they broke out of the ,earth1 and press'd against my ,hand1 were not1 to my best ,remembrance1 at all hot4 ,turning again to ,dr4 ,clayton's experiments1 we see that he pointed out striking and valuable properties of coal-gas but apparently gave no attention to its useful purposes4 ,furthermore1 his account appears to have attracted no particular notice at the time of its publication in #agci4 ,dr4 ,richard ,watson in #agfg described the results of experiments which he had been making with the products arising from the distillation of coal4 ,in his process he permitted the gas to ascend through curved tubes1 and he particularly noted its great inflammability as well as elasticity4 ,he also observed that it retained the former property after it had passed through a great quantity of water4 ,his published account dealt with a variety of facts and computations pertaining to the quantities of coke1 tar1 etc41 produced from different kinds of coal and was a scientific work of value1 but apparently the usefulness of the property of inflammability of coal-gas did not occur to him4 ,it is usually the habit of the scientific explorer of nature to return from excursions into her unfrequented recesses with new knowledge1 to place it upon exhibition1 and to return for more4 ,the inventor passes by and sees applications for some of these scientific trophies which are productive of momentous consequences to mankind4 ,sir ,humphrey ,davy described his primitive arc-lamp three quarters of a century before ,brush developed an arc-lamp for practical purposes4 ,maxwell and ,hertz respectively predicted and produced electromagnetic waves long before ,marconi applied this knowledge and developed wireless telegraphy4 ,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 purposes4 ,up to the beginning of the nineteenth century the civilized world had only a faint glimpse of the illuminating property of gas1 but practicable gas-lighting was destined soon to be an epochal event in the progress of lighting4 ,the dawn of modern science was coincident with the dawn of a luminous era4 ,at ,soho foundry in #agih ,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 smoke4 ,soho was an unique institution described as a place to which men of genius were invited and resorted from every civilized country1 to exercise and to display their talents4 ,the perfection of the manufacturing arts was the great and constant aim of its liberal and enlightened proprietors1 ,messrs4 ,boulton and ,watt2 and whoever resided there was surrounded by a circle of scientific1 ingenious1 and skilful men1 at all times ready to carry into effect the inventions of each other4 ,the ,treaty of ,amiens1 which gave to ,england the peace she was sorely in need of1 afforded ,murdock an opportunity in #ahjb favorable for making a public display of gas-lighting4 ,the illumination of the ,soho works on this occasion is described as one of extraordinary splendour4 ,the fronts of the extensive range of buildings were ornamented with a large number of devices which displayed the variety of forms of gas-lights4 ,at that time this was a luminous spectacle of great novelty and the populace came from far and wide to gaze at1 and to admire1 this wonderful display of the combined effects of science and art4 ,naturally1 ,murdock had many difficulties to overcome in these early days1 but he possessed skill and perseverance4 ,his first retorts for distilling coal were similar to the common glass retort of the chemist4 ,next he tried cast-iron cylinders placed perpendicularly in a common furnace1 and in each were put about fifteen pounds of coal4 ,in #ahjd he constructed them with doors at each end1 for feeding coal and extracting coke respectively1 but these were found inconvenient4 ,in his first lighting installation in the factory of ,phillips and ,lee in #ahje he used a large retort of the form of a bucket with a cover on it4 ,inside he installed a loose cage of grating to hold the coal4 ,when carbonization was complete the coke could be removed as a whole by extracting this cage4 ,this retort had a capacity of fifteen hundred pounds of coal4 ,he labored with mechanical details1 varied the size and shape of the retorts1 and experimented with different temperatures1 with the result that he laid a solid foundation for coal-gas lighting4 ,for his achievements he is entitled to an honorable place among the torch-bearers of civilization4 ,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 utility4 ,in the early years of the nineteenth century the foundation was laid for the great public-utility organizations of the present time4 ,furthermore1 gas-lighting was an improvement over candles and oil-lamps from the standpoints of convenience1 safety1 and cost4 ,the latter points are emphasized by ,murdock in his paper presented before the ,royal ,society in #ahjh1 in which he describes the first industrial installation of gas-lighting4 ,he used two types of burners1 the ,argand and the cockspur4 ,the former resembled the ,argand lamp in some respects and the latter was a three-flame burner suggesting a fleur-de-lis4 ,in this installation there were #bga ,argand burners and #fcf cockspurs4 ,each of the former gave a light equal to that of four candles2 and each of the latter1 a light equal to two and a quarter of the same candles2 making therefore the total of the gas light a little more than #bejj candles4 ,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 #j4d oz4 7#age grains7 per hour4 ,thus the candle became very early a standard light-source and has persisted as such 7with certain variations in the specifications7 until the present time4 ,however1 during recent years other standard light-sources have been devised4 ,according to ,murdock1 the yearly cost of gas-lighting in this initial case was #fjj pounds sterling after allowing generously for interest on capital invested and depreciation of the apparatus4 ,the cost of furnishing the same amount of light by means of candles he computed to be #bjjj pounds sterling4 ,this comparison was on the basis of an average of two hours of artificial lighting per day4 ,on the basis of three hours of artificial lighting per day1 the relative cost of gas-and candle-lighting was about one to five4 ,murdock was characteristically modest in discussing his achievements and his following statement should be read with the conditions of the year #ahjh in mind3 ,the peculiar softness and clearness of this light with its almost unvarying intensity1 have brought it into great favour with the work people4 ,and its being free from the inconvenience and danger1 resulting from sparks and frequent snuffing of candles1 is a circumstance of material importance1 as tending to diminish the hazard of fire1 to which cotton mills are known to be exposed4 ,although this installation in the mill of ,phillips and ,lee is the first one described by ,murdock1 in reality it is not the first industrial gas-lighting installation4 ,during the development of gas apparatus at the ,soho works and after his luminous display in #ahjb1 he gradually extended gas-lighting to all the principal shops4 ,however1 this in a sense was experimental work4 ,others were applying their knowledge and ingenuity to the problem of making gas-lighting practicable1 but ,murdock has been aptly termed the father of gas-lighting4 ,among the pioneers was ,le ,bon in ,france1 ,becher in ,munich1 and ,winzler or ,winsor1 a ,german who was attracted to the possibilities of gas-lighting by an exhibition which ,le ,bon gave in ,paris in #ahjb4 ,winsor learned that ,le ,bon had been granted a patent in ,paris in #agii for making an illuminating gas from wood and tried to obtain the rights for ,germany4 ,being unsuccessful in this1 he set about to learn the secrets of ,le ,bon's process1 which he did1 perhaps largely owing to an accumulation of information directly from the inventor during the negotiations4 ,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 ,co4 ,winsor was primarily a promoter1 with little or no technical knowledge2 for in his claims and advertisements he disregarded facts with a facility possessed only by the ignorant4 ,he boasted of his inventions and discoveries in the most hyperbolical language1 which was bound to provoke a controversy4 ,nevertheless1 he was clever and in #ahjc he publicly exhibited his plan of lighting by means of coal-gas at the ,lyceum ,theatre in ,london4 ,he gave lectures accompanied by interesting and instructive experiments and in this manner attracted the public to his exhibition4 ,all this time he was promoting his company1 but his promoting instinct caused his representations to be extravagant and deceptive1 which exposed him to the ridicule and suspicion of learned men4 ,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-protection4 ,these years of controversy yield entertaining literature for those who choose to read it1 but unfortunately space does not permit dwelling upon it4 ,the investigations by committees of ,parliament also afford amusing side-lights4 ,throughout all this ,murdock appeared modest and conservative and had the support of reputable scientific men1 but ,winsor maintained extravagant claims4 ,during one of these investigations ,sir ,humphrey ,davy was examined by a committee from the ,house of ,commons in #ahji4 ,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 long4 ,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 practice4 ,as secretary of the ,society1 ,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 light4 ,winsor proceeded to float his company without awaiting the ,act of ,parliament and in #ahjg lighted a street in ,pall ,mall4 ,through the opposition which he aroused1 and owing to the just claims of priority on the part of ,murdock1 the bill to incorporate the ,national ,heat and ,light ,co4 with a capital of #bjj1jjj pounds sterling was thrown out4 ,however1 he succeeded in #ahab in receiving a charter very much modified in form1 for the ,chartered ,gas ,light and ,coke ,co4 which was the forerunner of the present ,london ,gas ,light and ,coke ,co4 ,the conditions imposed upon this company as presented in an early treatise on gas-lighting 7by ,accum in #ahah7 were as follows3 ,the power and authorities granted to this corporate body are very restricted and moderate4 ,the individuals composing it have no exclusive privilege2 their charter does not prevent other persons from entering into competition with them4 ,their operations are confined to the metropolis1 where they are bound to furnish not only a stronger and better light to such streets and parishes as chuse to be lighted with gas1 but also at a cheaper price than shall be paid for lighting the said streets with oil in the usual manner4 ,the corporation is not permitted to traffic in machinery for manufacturing or conveying the gas into private houses1 their capital or joint stock is limited to #bjj1jjj1 and his ,majesty has the power of declaring the gas-light charter void if the company fail to fulfil the terms of it4 ,the progress of this early company was slow at first1 but with the appointment of ,samuel ,clegg as engineer in #ahac an era of technical developments began4 ,new stations were built and many improvements were introduced4 ,by improving the methods of purifying the gas a great advance was made4 ,the utility of gas-lighting grew apace as the prejudices disappeared1 but for a long time the stock of the company sold at a price far below par4 ,about this time the first gas explosion took place and the members of the ,royal ,society set a precedent which has lived and thrived3 they appointed a committee to make an inquiry4 ,but apparently the inquiry was of some value1 for it led to some useful alterations and new modifications in its apparatus and machinery4 ,many improvements were being introduced during these years and one of them in #ahaf increased the gaseous product from coal by distilling the tar which was obtained during the first distillation4 ,in #ahaf ,clegg obtained a patent for a horizontal rotating retort2 for an apparatus for purifying coal-gas with cream of lime2 and for a rotative gas-meter4 ,before progressing too far1 we must mention the early work of ,william ,henry4 ,in #ahjd he described publicly a method of producing coal-gas4 ,besides making experiments on production and utilization of coal-gas for lighting1 he devoted his knowledge of chemistry to the analysis of the gas4 ,he also made analytical studies of the relative value of wood1 peat1 oil1 wax1 and different kinds of coal for the distillation of gas4 ,his chemical analyses showed to a considerable extent the properties of carbureted hydrogen upon which illuminating value depended4 ,the results of his work were published in various ,english journals between #ahje and #ahbe and they contributed much to the advancement of gas-lighting4 ,although ,clegg's original gas-meter was complicated and cumbersome1 it proved to be a useful device4 ,in fact1 it appears to have been the most original and beneficial invention occasioned by early gas-lighting4 ,later ,samuel ,crosley greatly improved it1 with the result that it was introduced to a considerable extent2 but by no means was it universally adopted4 ,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 tank4 ,clegg retired from the service of the gas company in #ahag after a record of accomplishments which glorifies his name in the annals of gas-lighting4 ,murdock is undoubtedly entitled to the distinction of having been the first person who applied gas-lighting to large private establishments1 but ,clegg overcame many difficulties and was the first to illuminate a whole town by this means4 ,in ,london in #ahag over #cjj1jjj cubic feet of coal-gas was being manufactured daily1 an amount sufficient to operate #gf1ejj ,argand burners yielding #f candle-power each4 ,gas-lighting was now exciting great interest and was firmly established4 ,westminster ,bridge was lighted by gas in #ahac1 and the streets of ,westminster during the following year4 ,gas-lighting became popular in ,london by #ahaf 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 ,continent4 ,it found its way into the houses rather slowly at first1 owing to apprehension of the attendant dangers1 to the lack of purification of the gas1 and to the indifferent service4 ,it was not until the latter half of the nineteenth century that it was generally used in residences4 ,the gas-burner first employed by ,murdock received the name cockspur from the shape of the flame4 ,this had an illuminating value equivalent to about one candle for each cubic foot of gas burned per hour4 ,the next step was to flatten the welded end of the gas-pipe and to bore a series of holes in a line4 ,from the shape of the flames this form of burner received the name cockscomb4 ,it was somewhat more efficient than the cockspur burner4 ,the next obvious step was to slit the end of the pipe by means of a fine saw4 ,from this slit the gas was burned as a sheet of flame called the bats-wing4 ,in #ahbj ,nielson made a burner which allowed two small jets to collide and thus form a flat flame4 ,the efficiency of this fish-tail burner was somewhat higher than that of the earlier ones4 ,its flame was steadier because it was less influenced by drafts of air4 ,in #ahec ,frankland showed an ,argand burner consisting of a metal ring containing a series of holes from which jets of gas issued4 ,the glass chimney surrounded these1 another chimney1 extending somewhat lower1 surrounded the whole1 and a glass plate closed the bottom4 ,the air to be fed to the gas-jets came downward between the two chimneys and was heated before it reached the burner4 ,this increased the efficiency by reducing the amount of cooling at the burner by the air required for combustion4 ,this improvement was in reality the forerunner of the regenerative lamps which were developed later4 ,in #ahed ,bowditch brought out a regenerative lamp and1 owing to the excessive publicity which this lamp obtained1 he is generally credited with the inception of the regenerative burner4 ,this principle was adopted in several lamps which came into use later4 ,they were all based upon the principle of heating both the gas and the air required for combustion prior to their reaching the burner4 ,the burner is something like an inverted ,argand arranged to produce a circular flame projecting downward with a central cusp4 ,the air- and gas-passages are directly above the flame and are heated by it4 ,in #ahgi ,friedrich ,siemens brought out a lamp of this type which was adapted from a device originally designed for heating purposes1 owing to the superior light which was produced4 ,this was the best gas-lamp up to that time4 ,later1 ,wenham1 ,cromartie1 and others patented lamps operating on this same principle4 ,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 burners4 ,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 metal1 which cooled the flame by conducting heat from it4 ,these were the early steps which led finally to the regenerative burner4 ,the increasing efficiency of the various gas-burners is indicated by the following1 which are approximately the candle-power based upon equal rates of consumption1 namely1 one cubic foot of gas per hour3 ,candle-power per cubic foot of gas per hour ,fish-tail flames1 depending upon size #j4f to #b4e ,argand1 depending upon improvements #b4i to #c4e ,regenerative #g to #aj ,it is seen that the possibilities of gas lighting were recognized in several countries1 all of which contributed to its development4 ,some of the earlier accounts have been drawn chiefly from ,england1 but these are intended merely to serve as examples of the difficulties encountered4 ,doubtless1 similar controversies arose in other countries in which pioneers were also nursing gas-lighting to maturity4 ,however1 it is certain that much of the early progress of lighting of this character was fathered in ,england4 ,gas-lighting was destined to become a thriving industry1 and is of such importance in lighting that another chapter is given its modern developments4 ,,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-sources4 ,many historical events remain to be touched upon in later chapters1 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 follow4 ,it is seen that from a standpoint of artificial lighting1 the dark age extended well into the nineteenth century4 ,oil-lamps and gas-lighting began to be seriously developed at the beginning of the last century1 but the pioneers gave attention chiefly to mechanical details and somewhat to the chemistry of the fuels4 ,it was not until the science of physics was applied to light-sources that rapid progress was made4 ,all the light-sources used throughout the ages1 and nearly all modern ones1 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 light4 ,this is due to various physical characteristics of carbon1 the chief one being its extremely high melting-point4 ,however1 most practicable light-sources of the past and present may be divided into two general classes3 7#a7 ,those in which solids or solid particles are heated by their own combustion1 and 7#b7 those in which the solids are heated by some other means4 ,some light-sources include both principles and some perhaps cannot be included under either principle without qualification4 ,the luminous flames of burning material such as those of wood-splinters1 candles1 oil-lamps1 and gas-jets1 and the glowing embers of burning material appear in the first class2 and incandescent gas-mantles1 electric filaments1 and arc-lamps to some extent are representative of the second class4 ,certain flaming arcs involve both principles1 but the light of the firefly1 phosphorescence1 and incandescent gas in vacuum tubes cannot be included in this simplified classification4 ,the status of these will become clear later4 ,it has been seen that flames have been prominent sources of artificial light2 and although of low luminous efficiency1 they still have much to commend them from the standpoints of portability1 convenience1 and subdivision4 ,the materials which have been burned for light1 whether solid or liquid1 are rich in carbon1 and the solid particles of carbon by virtue of their incandescence are responsible for the brightness of a flame4 ,a jet of pure hydrogen gas will burn very hot but with so low a brightness as to be barely visible4 ,if solid particles are injected into the flame1 much more light usually will be emitted4 ,a gas-burner of the ,bunsen type1 in which complete combustion is obtained by mixing air in proper proportions with the gas1 gives a hot flame which is of a pale blue color4 ,upon the closing of the orifice through which air is admitted1 the flame becomes bright and smoky4 ,the flame is now less hot1 as indicated by the presence of smoke or carbon particles1 and combustion is not complete4 ,however1 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 light4 ,a close observer will notice that the flame from a match1 a candle1 or a gas-jet1 is not uniformly bright4 ,the reader may verify this by lighting a match and observing the flame4 ,there is always a bluish or darker portion near the bottom4 ,in this less luminous part the air is combining with the hydrogen of the hydrocarbon which is being vaporized and disintegrated4 ,even the flame of a candle or of a burning splinter is a miniature gas-plant1 for the solid or liquid hydrocarbons are vaporized before being burned4 ,owing to the incoming colder air at this point1 the flame is not hot enough for complete combustion4 ,the unburned carbon particles rise in its draft and become heated to incandescence1 thus accounting for the brighter portion4 ,in cases of complete combustion they are eventually oxidized into carbon dioxide before they are able to escape4 ,if a piece of metal be held in the flame1 it immediately becomes covered with soot or carbon1 because it has reduced the temperature below the point at which the chemical reaction--the uniting of carbon with oxygen--will continue4 ,an ordinary flat gas-flame of the bats-wing type may vary in temperature in its central portion from #cjj;,f4 at the bottom to about #cjjj;,f4 at the top4 ,the central portion lies between two hotter layers in which the vertical variation is not so great4 ,the brightness of the upper portion is due to incandescent carbon formed in the lower part4 ,when scientists learned by exploring flames that brightness was due to the radiation of light by incandescent solid matter1 the way was open for many experiments4 ,in the early days of gas-lighting investigations were made to determine the relation of illuminating value to the chemical constitution of the gas4 ,the results combined with a knowledge of the necessity for solid carbon in the flame led to improvements in the gas for lighting purposes4 ,gas rich in hydrocarbons which in turn are rich in carbon is high in illuminating value4 ,heating-effect depends upon heat-units1 so the rating of gas in calories or other heat-units per cubic foot is wholly satisfactory only for gas used for heating4 ,the chemical constitution is a better indicator of illuminating value4 ,as scientific knowledge increased1 efforts were made to get solid matter into the flames of light-sources4 ,instead of confining efforts to the carbon content of the gas1 solid materials were actually placed in the flame1 and in this manner various incandescent burners were developed4 ,a piece of lime placed in a hydrogen flame or that of a ,bunsen burner is seen to become hot and to glow brilliantly4 ,by producing a hotter flame by means of the blowpipe1 in which hydrogen and oxygen are consumed1 the piece of lime was raised to a higher temperature and a more intense light was obtained4 ,in ,paris there was a serious attempt at street-lighting by the use of buttons of zirconia heated in an oxygen-coal-gas flame1 but it proved unsuccessful owing to the rapid deterioration of the buttons4 ,this was the line of experimentation which led to the development of the lime-light4 ,the incandescent burner was widely employed1 and until the use of electricity became common the lime-light was the mainstay for the stage and for the projection of lantern slides4 ,it is in use even to-day for some purposes4 ,the origin of the phrase in the lime-light is obvious4 ,the luminous intensity of the oxyhydrogen lime-light as used in practice was generally from #bjj to #djj candle-power4 ,the light decreases rapidly as the burner is used1 if a new surface of lime is not presented to the flame from time to time4 ,at the high temperatures the lime is somewhat volatile and the surface seems to change in radiating power4 ,zirconium oxide has been found to serve better than lime4 ,improvements were made in gas-burners in order to obtain hotter flames into which solid matter could be introduced to obtain bright light4 ,many materials were used1 but obviously they were limited to those of a fairly high melting-point4 ,lime1 magnesia1 zirconia1 and similar oxides were used successfully4 ,if the reader would care to try an experiment in verification of this simple principle1 let him take a piece of magnesium ribbon such as is used in lighting for photography and ignite it in a ,bunsen flame4 ,if it is held carefully while burning1 a ribbon of ash 7magnesia7 will be obtained intact4 ,placing this in the faintly luminous flame1 he will be surprised at the brilliance of its incandescence when it has become heated4 ,the simple experiment indicates the possibilities of light-production in this direction4 ,naturally1 metals of high melting-point such as platinum were tried and a network of platinum wire1 in reality a platinum mantle1 came into practical use in about #ahhj4 ,the town of ,nantes was lighted by gas-burners using these platinum-gauze mantles1 but the mantles were unsuccessful owing to their rapid deterioration4 ,this line of experimentation finally bore fruit of immense value for from it the gas-mantle evolved4 ,a group of so-called rare-earths1 among which are zirconia1 thoria1 ceria1 erbia1 and yttria 7these are oxides of zirconium1 etc47 possess a number of interesting chemical properties some of which have been utilized to advantage in the development of modern artificial light4 ,they are white or yellowish-white oxides of a highly refractory character found in certain rare minerals4 ,most of them are very brilliant when heated to a high temperature4 ,this latter feature is easily explained if the nature of light and the radiating properties of substances are considered4 ,suppose pieces of different substances1 for example1 glass and lime1 are heated in a ,bunsen flame to the same temperature which is sufficiently great to cause both of them to glow4 ,notwithstanding the identical conditions of heating1 the glass will be only faintly luminous1 while the piece of lime will glow brilliantly4 ,the former is a poor radiator2 furthermore1 the lime radiates a relatively greater percentage of its total energy in the form of luminous energy4 ,the latter point will become clearer if the reader will refresh his memory regarding the nature of light4 ,any luminous source such as the sun1 a candle flame1 or an incandescent lamp is sending forth electromagnetic waves not unlike those used in wireless telegraphy excepting that they are of much shorter wave-length4 ,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 energy4 ,the electromagnetic waves sent forth by a light-source like the sun are not all visible1 that is1 all of them do not arouse a sensation of light4 ,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 colors4 ,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 red4 ,between these two extremes of the visible spectrum1 the chief spectral colors are blue1 green1 yellow1 orange1 and red in the order of increasing wave-lengths4 ,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 energy4 ,those too short to be perceived as light are termed as a class ultraviolet radiant energy4 ,a solid body at a high temperature emits electro-magnetic energy of all wave-lengths1 from the shortest ultra-violet to the longest infra-red4 ,another complication arises in the variation in visibility or luminosity of energy of wave-lengths within the range of the visible spectrum4 ,obviously1 no amount of energy incapable of exciting the sensation of light will be visible4 ,the energy of those wave-lengths near the ends of the visible spectrum will be inefficient in producing light4 ,that energy which excites the sensation of yellow-green produces the greatest luminosity per unit of energy and is the most efficient light4 ,the visibility or luminous efficiency of radiant energy may be ranged approximately in this manner according to the colors aroused3 yellow-green1 yellow1 green1 orange1 blue-green1 red1 blue1 deep red1 violet4 ,newton1 an ,english scientist1 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 follows3 ,in the ,year #afff 7at which time ,i applied my self to the ,grinding of ,optick ,glasses of other ,figures than ,spherical7 ,i procured me a ,triangular ,glass-,prism1 to try therewith the celebrated ,phaenomena of ,colours4 ,and in order thereto1 having darkened my ,chamber1 and made a small ,hole in my ,window-,shuts1 to let in a convenient ,quantity of the ,sun's ,light1 ,i placed my ,prism at its ,entrance1 that it might be thereby refracted to the opposite ,wall4 ,it was at first a very pleasing ,divertisement1 to view the vivid and intense ,colours produced thereby2 but after a while applying my self to consider them more circumspectly1 ,i became surprised to see them in an oblong ,form2 which1 according to the receiv'd ,law of ,refractions1 ,i expected should have been circular4 ,they were terminated at the ,sides with streight ,lines1 but at the ,ends the ,decay of ,light was so gradual1 that it was difficult to determine justly what was the ,figure1 yet they seemed ,semicircular4 ,even ,newton could not have had the faintest idea of the great developments which were to be based upon the spectrum4 ,now to return to the peculiar property of rare-earth oxides--namely1 their unusual brilliance when heated in a flame--it is easy to understand the reason for this4 ,for example1 when a number of substances are heated to the same temperature they may radiate the same amount of energy and still differ considerably in brightness4 ,many substances are selective in their absorbing and radiating properties4 ,one may radiate more luminous energy and less infra-red energy1 and for another the reverse may be true4 ,the former would appear brighter than the latter4 ,the scientific worker in light-production has been searching for such selective radiators whose other properties are satisfactory4 ,the rare-earths possess the property of selectivity and are fortunately highly refractory4 ,welsbach used these in his mantle1 whose efficiency is due partly to this selective property4 ,recent work indicates that much higher efficiencies of light-production are still attainable by the principles involved in the gas-mantle4 ,turning again to flames1 another interesting physical phenomenon is seen on placing solutions of different chemical salts in the flame4 ,for example1 if a piece of asbestos is soaked in sodium chloride 7common salt7 and is placed in a ,bunsen flame1 the pale-blue flame suddenly becomes luminous and of a yellow color4 ,if this is repeated with other salts1 a characteristic color will be noted in each case4 ,the yellow flame is characteristic of sodium and if it is examined by means of a spectroscope1 a brilliant yellow line 7in fact1 a double line7 will be seen4 ,this forms the basis of spectrum analysis as applied in chemistry4 ,every element has its characteristic spectrum consisting usually of lines1 but the complexity varies with the elements4 ,the spectra of elements also exhibit lines in the ultra-violet region which may be studied with a photographic plate1 with a photo-electric cell1 and by other means4 ,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 absorbed4 ,spectrum analysis is far more sensitive than the finest weighing balance1 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 flame1 the yellow color characteristic of sodium will be detectable4 ,a wonderful example of the possibilities of this method is the discovery of helium in the sun before it was found on earth6 ,its spectral lines were detected in the sun's spectrum and could not be accounted for by any known element4 ,however1 it should be stated that the spectrum of an element differs generally with the manner obtained4 ,the electric spark1 the arc1 the electric discharge in a vacuum tube1 and the flame are the means usually employed4 ,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 developments4 ,although in lighting little use has been made of the injection of chemical salts into ordinary flames1 it appears certain that such developments would have risen if electric illuminants had not entered the field4 ,however1 the principle has been applied with great success in arc-lamps4 ,in the first arc-lamps plain carbon electrodes were used1 but in some of the latest carbon-arcs1 electrodes of carbon impregnated with various salts are employed4 ,for example1 calcium fluoride gives a brilliant yellow light when used in the carbons of the flame arc4 ,these are described in detail later4 ,following this principle of light-production the vacuum tubes were developed4 ,crookes studied the light from various gases by enclosing them in a tube which was pumped out until a low vacuum was produced4 ,on connecting a high voltage to electrodes in each end1 an electrical discharge passed through the residual gas making it luminous4 ,the different gases show their characteristic spectra and their desirability as light-producers is at once evident4 ,however1 the most general principle of light-production at the present time is the radiation of bodies by virtue of their temperature4 ,if a piece of wire be heated by electricity1 it will become very hot before it becomes luminous4 ,at this temperature it is emitting only invisible infra-red energy and has an efficiency of zero as a producer of light4 ,as it becomes hotter it begins to appear red1 but as its temperature is raised it appears orange1 until if it could be heated to the temperature of the sun1 about #aj1jjj;,f41 it would appear white4 ,all this time its luminous efficiency is increasing1 because it is radiating not only an increasing percentage of visible radiant energy but an increasing amount of the most effective luminous energy4 ,but even when it appears white1 a large amount of the energy which it radiates is invisible infra-red and ultra-violet1 which are ineffective in producing light1 so at best the substance at this high temperature is inefficient as a light-producer4 ,in this branch of the science of light-production substances are sought not only for their high melting-point1 but for their ability to radiate selectively as much visible energy as possible and of the most luminous character4 ,however1 at best the present method of utilizing the temperature radiation of hot bodies has limitations4 ,the luminous efficiencies of light-sources to-day are still very low1 but great advances have been made in the past half-century4 ,there must be some radical departures if the efficiency of light-production is to reach a much higher figure4 ,a good deal has been said of the firefly and of phosphorescence4 ,these light-sources appear to emit only visible energy and1 therefore1 are efficient as radiators of luminous radiant energy4 ,but much remains to be unearthed concerning them before they will be generally applicable to lighting4 ,if ultra-violet radiation is allowed to impinge upon a phosphorescent material1 it will glow with a considerable brightness but will be cool to the touch4 ,a substance of the same brightness by virtue of its temperature would be hot2 hence phosphorescence is said to be cold light4 ,an acquaintance with certain terms is necessary if the reader is to understand certain parts of the text4 ,the early candle gradually became a standard1 and uniform candles are still satisfactory standards where high accuracy is not required4 ,their luminous intensity and illuminating value became units just as the foot was arbitrarily adopted as a unit of length4 ,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 light4 ,but the luminous intensity of the candle was taken only in the horizontal direction4 ,in the same manner the luminous intensities of light-sources until a short time ago were expressed in candles as measured in a certain direction4 ,incandescent lamps were rated in terms of mean horizontal candles1 which would be satisfactory if the luminous intensity were the same in all directions1 but it is not4 ,therefore1 the candle-power in one direction does not give a measure of the total light-output4 ,if a source of light has a luminous intensity of one candle in all directions1 the illumination at a distance of one foot in any direction is said to be a foot-candle4 ,this is the unit of illumination intensity4 ,a lumen is the quantity of light which falls on one square foot if the intensity of illumination is one foot-candle4 ,it is seen that the area of a sphere with a radius of one foot is #d pi or #ab4eg square feet2 therefore1 a light-source having a luminous intensity of one candle in all directions emits #ab4eg lumens4 ,this is the satisfactory unit1 for it measures total quantity of light1 and luminous efficiencies may be expressed in terms of lumens per watt1 lumens per cubic foot of gas per hour1 etc4 ,of course1 the efficiencies of light-sources are usually of interest to the consumer if they are expressed in terms of cost4 ,but from a practical point of view there are many elements which combine to make another important factor1 namely1 satisfactoriness4 ,therefore1 the efficiency of artificial lighting from the standpoint of the consumer should be the ratio of satisfactoriness to cost4 ,however1 the scientist is interested chiefly in the efficiency of the light-source which may be expressed in lumens per watt1 or the amount of light obtained from a given rate of consumption or of emission of energy4 ,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 respect4 ,that radiant energy which is wholly of a wave-length of maximum visibility1 or1 in other words1 excites the sensation of yellow-green1 is the most efficient in producing luminous sensation4 ,of course1 no illuminants are available which approach this theoretical ideal and it is not likely that this would be a practical ideal4 ,under monochromatic yellow-green light the magical drapery of color would disappear and the surroundings would be a monochrome of shades of this hue4 ,having no colors with which to contrast this color1 the world would be colorless4 ,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 light4 ,the red under present conditions is kept alive by contrast with other colors1 because the latter live by virtue of the fact that most of our present illuminants contain their hues4 ,it is assumed that the reader knows that a red object1 for example1 appears red because it reflects 7or transmits7 red rays and absorbs the other rays in the illuminant4 ,in other words1 color is due to selective absorption reflection1 or transmission4 ,perhaps the ideal illuminant1 which is most generally satisfactory for general activities1 is a white light corresponding to noon sunlight4 ,if this is chosen as the scientific ideal1 the illuminants of the present time are much more efficient than if the most efficient light is the ideal4 ,the luminous efficiency of the radiant energy most efficient in producing the sensation of light 7yellow-green7 is about #fbe lumens per watt4 ,that is1 if energy of this wave-length alone were radiated by a hypothetical light-source1 each watt would produce #fbe lumens4 ,the luminous efficiency of the most efficient white light is about #bfe lumens per watt2 in other words1 if a hypothetical light-source radiated energy of only the visible wave-lengths and in proportions to produce the sensation of white1 each watt would produce #bfe lumens4 ,if such a white light were obtained by pure temperature radiation--that is1 by a normal radiator at a temperature of #aj1jjj;,f41 which is impracticable at present--the luminous efficiency would be about #ajj lumens per watt4 ,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 radiator4 ,modern illuminants have luminous efficiencies ranging from #e to #cj lumens per watt1 so it is seen that much is to be done before the limiting efficiencies are reached4 ,the amount of light obtained from various gas-burners for each cubic foot of gas consumed per hour varies for open gas-flames from #e to #cj lumens2 for ,argand burners from #ce to #dj lumens2 for regenerative lamps from #ej to #ge lumens2 and for gas-mantles from #bjj to #bej lumens4 ,in the development of light-sources1 of course1 any harmful effects of gases formed by burning or chemical action must be avoided4 ,some of the fumes from arcs are harmful1 but no commercial arc appears to be dangerous when used as it is intended to be used4 ,gas-burners rob the atmosphere of oxygen and vitiate it with gases1 which1 however1 are harmless if combustion is complete4 ,that adequate ventilation is necessary where oxygen is being consumed is evident from the data presented by authorities on hygiene4 ,a standard candle when burning vitiates the air in a room almost as much as an adult person4 ,an ordinary kerosene lamp vitiates the atmosphere as much as a half-dozen persons4 ,an ordinary single mantle burner causes as much vitiation as two or three persons4 ,in order to obtain a bird's-eye view of progress in light-production1 the following table of relative luminous efficiencies of several light-sources is given in round numbers4 ,these efficiencies are in terms of the most efficient 7yellow-green7 light4 ,efficiency in per cent4 ,sperm-candle #j4jb ,open gas-flame 4#jd ,incandescent gas-mantle 4#ai ,carbon filament lamp 4#je ,vacuum ,mazda lamp #a4c ,gas-filled ,mazda lamp #b to #c ,arc-lamps #b to #g ,white light radiated by black-body #af ,most efficient white light #dj ,firefly #ie ,most efficient light 7yellow-green7 #ajj ,the luminous efficiency of a light-source is distinguished from that of a lamp4 ,the former is the ratio of the light produced to the amount of energy radiated by the light-source4 ,the latter is the ratio of the light produced to the total amount of energy consumed by the device4 ,in other words1 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 account4 ,these additional losses are appreciable in the mechanisms of arc-lamps but are almost negligible in vacuum incandescent filament lamps4 ,they are unknown for the firefly1 so that its luminous efficiency only as a light-source can be determined4 ,its efficiency as a lighting-plant may be and perhaps is rather low4 ,,viii ,,modern ,,gas-,,lighting ,as has been seen1 the lighting industry1 as a public service1 was born in ,london about a century ago and companies to serve the public were organized on the ,continent shortly after4 ,from this early beginning gas-light remained for a long time the only illuminant supplied by a public-service company4 ,it has been seen that throughout the ages little advance was made in lighting until oil-lamps were improved by ,argand in the eighteenth century4 ,candles and open-flame oil-lamps were in use when the ,pyramids were built and these were common until the approach of the nineteenth century4 ,in fact1 several decades passed after the first gas-lighting was installed before this form of lighting began to displace the improved oil-lamps and candles4 ,it was not until about #ahej that it began to invade the homes of the middle and poorer classes4 ,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 residences2 still1 the total cost of lighting a residence has decreased considerably4 ,if the social and industrial activities of mankind are visualized for these various periods in parallel with the development of artificial lighting1 a close relation is evident4 ,did artificial light advance merely hand in hand with science1 invention1 commerce1 and industry1 or did it illuminate the pathway8 ,although gas-lighting was born in ,england it soon began to receive attention elsewhere4 ,in #ahae the first attempt to provide a gas-works in ,america was made in ,philadelphia2 but progress was slow1 with the result that ,baltimore and ,new ,york led in the erection of gas-works4 ,there are on record many protests against proposals which meant progress in lighting4 ,these are amusing now1 but they indicate the inertia of the people in such matters4 ,when ,bollman was projecting a plan for lighting ,philadelphia by means of piped gas1 a group of prominent citizens submitted a protest in #ahcc which aimed to show that the consequences of the use of gas were appalling4 ,but this protest failed and in #ahce a gas-plant was founded in ,philadelphia4 ,thus gas-lighting1 which to ,sir ,walter ,scott was a pestilential innovation projected by a madman1 weathered its early difficulties and grew to be a mighty industry4 ,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 cost4 ,think of the city of ,philadelphia in #ahjj1 with a population of about fifty thousand1 dependent for its lighting wholly upon candles and oil-lamps6 ,washington's birthday anniversary was celebrated in #ahag with a grand ball attended by five hundred of the lite4 ,an old report of the occasion states that the room was lighted by two thousand wax-candles4 ,the cost of this lighting was a hundred times the cost of as much light for a similar occasion at the present time4 ,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 ago8 ,to-day there are more than fifty thousand street lamps in the city--one for each inhabitant of a century ago4 ,of these street lamps about twenty-five thousand burn gas4 ,this single instance is representative of gas-lighting which initiated the light age and nursed it through the vicissitudes of youth4 ,the consumption of gas has grown in the ,united ,states during this time to three billion cubic feet per day4 ,for strictly illuminating purposes in #aiaj nearly one hundred billion cubic feet were used4 ,this country has been blessed with large supplies of natural gas2 but as this fails new oil-fields are constantly being discovered1 so that as far as raw materials are concerned the future of gas-lighting is assured for a long time to come4 ,the advent of the gas-mantle is responsible for the survival of gas-lighting1 because when it appeared electric lamps had already been invented4 ,these were destined to become the formidable light-sources of the approaching century and without the gas-mantle gas-lighting would not have prospered4 ,auer von ,welsbach was conducting a spectroscopic study of the rare-earths when he was confronted with the problem of heating these substances4 ,he immersed cotton in solutions of these salts as a variation of the regular means for studying elements by injecting them into flames4 ,after burning the cotton he found that he had a replica of the original fabric composed of the oxide of the metal1 and this glowed brilliantly when left in the flame4 ,this gave him the idea of producing a mantle for illuminating purposes and in #ahhe he placed such a mantle in commercial use4 ,his first mantles were unsatisfactory1 but they were improved in #ahhf by the use of thoria1 an oxide of thorium1 in conjunction with other rare-earth oxides4 ,his mantle was now not only stronger but it gave more light4 ,later he greatly improved the mantles by purifying the oxides and finally achieved his great triumph by adding a slight amount of ceria1 an oxide of cerium4 ,welsbach is deserving of a great deal of credit for his extensive work1 which overcame many difficulties and finally gave to the world a durable mantle that greatly increased the amount of light previously obtainable from gas4 ,the physical characteristics of a mantle depend upon the fabric and upon the rare-earths used4 ,it must not shrink unduly when burned1 and the ash should remain porous4 ,it has been found that a mantle in which thoria is used alone is a poor light-source1 but that when a small amount of ceria is added the mantle glows brilliantly4 ,by experiment it was determined that the best proportions for the rare-earth content are one part of ceria and ninety-nine parts of thoria4 ,greater or less proportions of ceria decreased the light-output4 ,the actual percentage of these oxides in the ash of the mantle is about #aj per cent41 making the content of ceria about one part in one thousand4 ,mantles are made by knitting cylinders of cotton or of other fiber and soaking these in a solution of the nitrates of cerium and thorium4 ,one end of the cylinder is then sewed together with asbestos thread1 which also provides the loop for supporting the mantle over the burner4 ,after the mantle has dried in proper form1 it is burned2 the organic matter disappears and the nitrates are converted into oxides4 ,after this burning off has been accomplished and any residual blackening is removed1 the mantle is dipped into collodion1 which strengthens it for shipping and handling4 ,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 drying4 ,the materials and structure of the fabric of mantles have been subjected to much study4 ,cotton was first used2 then ramie fibers were introduced4 ,the ramie mantle was found to possess a greater life than the cotton mantle4 ,later the mantles were mercerized by immersion in ammonia-water and this process yielded a stronger material4 ,the latest development is the use of an artificial silk as the base fabric1 which results in a mantle superior to previous mantles in strength1 flexibility1 permanence of form1 and permanence of luminous property4 ,this artificial silk mantle will permit of handling even after it has been in use for several hundred hours4 ,this great advance appears to be due to the fact that after the artificial-silk fibers have been burned off1 the fibers are solid and continuous instead of porous as in previous mantles4 ,the color-value of the light from mantles may be varied considerably by altering the proportions of the rare-earths4 ,the yellowness of the light has been traced to ceria1 so by varying the proportions of ceria1 the color of the light may be influenced4 ,the inverted mantle introduced greater possibilities into gas-lighting4 ,the light could be directed downward with ease and many units such as inverted bowls were developed4 ,in fact1 the lighting-fixtures and the lighting-effects obtainable kept pace with those of electric lighting1 notwithstanding the greater difficulties encountered by the designer of gas-lighting fixtures4 ,many problems were encountered in designing an inverted burner operating on the ,bunsen principle1 but they were finally satisfactorily solved4 ,in recent years a great deal of study has been given to the efficiency of gas-burners1 with the result that a high level of development has been reached4 ,several methods of electrical ignition have been evolved which in general employ the electric spark4 ,electrical ignition and developments of remote control have added great improvements especially to street-lighting by means of gas4 ,gas-valves for remote control are actuated by gas pressure and by electromagnets4 ,in general1 the gas-lighting engineers have kept pace marvelously with electric lighting1 when their handicaps are considered4 ,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 light4 ,these led to the development of the pressure system in which the pressure of gas was at first several times greater than usual4 ,the gas is fed into the mixing tube under this higher pressure in a manner which also draws in an adequate amount of air4 ,in this way the combustion at the burner is forced beyond the point reached with the usual pressure4 ,ordinary gas pressure is equal to that of a few inches of water1 but high-pressure systems employ pressures as great as sixty inches of water4 ,under this high-pressure system1 mantle-burners yield as high as #ejj lumens per cubic foot of gas per hour4 ,the fuels for gas-lighting are natural gas1 carbureted water-gas1 and coal-gas obtained by distilling coal1 but there are different methods of producing the artificial gases4 ,coal-gas is produced analytically by distilling certain kinds of coal1 but water-gas and producer-gas are made synthetically by the action of several constituents upon one another4 ,carbureted water-gas is made from fixed carbon1 steam1 and oil and also from steam and oil4 ,producer-gas is made by the action of steam or air or both upon fixed carbon4 ,water-gas made from steam and oil is usually limited to those places where the raw materials are readily available4 ,the composition of a gas determines its heating and illuminating values1 and constituents favorable to one are not necessarily favorable to the other4 ,coal-gas usually is of lower illuminating value than carbureted water-gas4 ,it contains more hydrogen1 for example1 than water-gas and it is well known that hydrogen gives little light on burning4 ,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 century4 ,from this beginning the manufacture of coal-gas has been developed to a great and complex industry4 ,the method is essentially destructive distillation4 ,the coal is placed in a retort and when it reaches a temperature of about #gjj;,f4 through heating by an outside fire1 the coal begins to fuse and hydrocarbon vapors begin to emanate4 ,these are generally paraffins and olefins4 ,as the temperature increases1 these hydrocarbons begin to be affected4 ,the chemical combinations which have long existed are broken up and there are rearrangements of the atoms of carbon and hydrogen4 ,the actual chemical reactions become very complex and are somewhat shrouded in uncertainty4 ,in this last stage the illuminating and heating values of the gas are determined4 ,usually about four hours are allowed for the complete distillation of the gaseous and liquid products from a charge of coal4 ,many interesting chemical problems arise in this process and the influences of temperature and time cannot be discussed within the scope of this book4 ,besides the coal-gas1 various by-products are obtained depending upon the raw materials1 upon the procedure1 and upon the market4 ,after the coal-gas is produced it must be purified and the sulphureted hydrogen at least must be removed4 ,one method of accomplishing this is by washing the gas with water and ammonia1 which also removes some of the carbon dioxide and hydrocyanic acid4 ,various other undesirable constituents are removed by chemical means1 depending upon the conditions4 ,the purified gas is now delivered to the gas-holder2 but1 of course1 all this time the pressure is governed1 in order that the pressure in the mains will be maintained constant4 ,much attention has been given to the enrichment of gas for illuminating purposes2 that is1 to produce a gas of high illuminating value from cheap fuel or by inexpensive processes4 ,this has been done by decomposing the tar obtained during the distillation of coal and adding these gases to the coal-gas2 by mixing carbureted water-gas with coal-gas2 by carbureting inferior coal-gases2 and by mixing oil-gas with inferior coal-gas4 ,water-gas is of low illuminating value1 but after it is carbureted it burns with a brilliant flame4 ,the water-gas is made by raising the temperature of the fuel bed of hard coal or coke by forced air1 which is then cut off1 while steam is passed through the incandescent fuel4 ,this yields hydrogen and carbon monoxide4 ,to make carbureted water-gas1 oil-gas is mixed with it1 the latter being made by heating oil in retorts4 ,a great many kinds of gas are made which are determined by the requirements and the raw materials available4 ,the amount of illuminating gas yielded by a ton of fuel1 of course1 varies with the method of manufacture1 with the raw material1 and with the use to which the fuel is to be put4 ,the production of coal-gas per ton of coal is of the order of magnitude of #aj1jjj cubic feet4 ,a typical yield by weight of a coal-gas retort is1 #aj1jjj cubic feet of gas #ag per cent4 coke #gj tar #e ammoniacal liquid #h ,the coke is not pure carbon but contains the non-volatile minerals which will remain as ash when the coke is burned1 just as if the original coal had been burned4 ,on the crown of the retort used in coal-gas production1 pure carbon is deposited4 ,this is used for electric-arc carbons and for other purposes4 ,from the tar many products are derived such as aniline dyes1 benzene1 carbolic acid1 picric acid1 napthalene1 pitch1 anthracene1 and saccharin4 ,a typical analysis of the gas distilled from coal is very approximately as follows1 ,hydrocarbons #dj per cent4 ,hydrogen #ej ,carbon monoxide #d ,nitrogen #d ,carbon dioxide #a ,various other gases #a ,it is seen that illuminating gas is not a definite compound but a mixture of a number of gases4 ,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 harmful4 ,the constituents are seen to consist of light-giving hydrocarbons1 of gases which yield chiefly heat1 and of impurities4 ,the chief hydrocarbons found in illuminating gas are1 ethylene ,c#b;,h#d crotonylene ,c#d;,h#f propylene ,c#c;,h#f benzene ,c#f;,h#f butylene ,c#d;,h#h toluene ,c#g;,h#h amylene ,c#e;,h#aj xylene ,c#h;,h#aj acetylene ,c#b;,h#b methane ,c ,h#d allylene ,c#c;,h#d ethane ,c#b;,h#f ,a gas which has played a prominent part in lighting is acetylene1 produced by the interaction of water and calcium carbide4 ,no other gas easily produced upon a commercial scale yields as much light1 volume for volume1 as acetylene4 ,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 gases4 ,the simplicity of the manufacture of acetylene from calcium carbide and water gives to this gas a great advantage in some cases4 ,it has served for individual lighting in houses and in other places where gas or electric service was unavailable4 ,where space is limited it also had an advantage and was adopted to some extent on automobiles1 motor-boats1 ships1 lighthouses1 and railway cars before electric lighting was developed for these purposes4 ,the color of the acetylene flame is satisfactory and it is extremely brilliant compared with most flames4 ,an interesting experiment is found in placing a spark-gap in the flame and sending a series of sparks across it4 ,if the conditions are proper the flame will became very much brighter4 ,when the gas issues from a proper jet under sufficient pressure1 the flame is quite steady4 ,its luminous efficiency gives it an advantage over other open gas-flames in lighting rooms1 because for the same amount of light it vitiates the air and exhausts the oxygen to a less degree than the others4 ,of course1 in these respects the gas-mantle is superior4 ,the reaction which takes place when water and calcium carbide are brought together is a double decomposition and is represented by1 ,ca,c#b ,h#b,o ,c#b;,h#b ,ca,o ,it will be seen that the products are acetylene gas and calcium oxide or lime4 ,the lime1 being hydroscopic and being in the presence of water or water-vapor in the acetylene generator1 really becomes calcium hydroxide ,ca7,,oh7#b1 commonly called slaked lime4 ,if there are impurities in the calcium carbide1 it is sometimes necessary to purify the gas before it may be safely used for interior lighting4 ,the burners and mantles used in acetylene lighting are essentially the same as those for other gas-lighting1 excepting1 of course1 that they are especially adapted for it in minor details4 ,the chief source of calcium carbide in this country is the electric furnace4 ,cheap electrical energy from hydro-electric developments1 such as the ,niagara plants1 have done much to make the earth yield its elements4 ,aluminum is very prevalent in the soil of the earth's surface1 because its oxide1 alumina1 is a chief constituent of ordinary clay4 ,but the elements1 aluminum and oxygen1 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 scale4 ,similarly1 calcium is found in various compounds over the earth's surface4 ,limestone abounds widely1 hence the oxide and carbonate of lime are wide-spread4 ,but calcium clings tightly to the other elements of its compounds and it has taken the electric furnace to bring it to submission4 ,the cheapness of calcium carbide is due to the development of cheap electric power4 ,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 process4 ,the discovery of a commercial scale of manufacture of calcium carbide has been a boon to isolated lighting4 ,electric lighting has usurped its place on the automobile and is making inroads in country-home lighting4 ,doubtless1 acetylene will continue to serve for many years1 but its future does not appear as bright as it did many years ago4 ,the ,pintsch gas1 used to some extent in railroad passenger-cars in this country1 is an oil-gas produced by the destructive distillation of petroleum or other mineral oil in retorts heated externally4 ,the product consists chiefly of methane and heavy hydrocarbons with a small amount of hydrogen4 ,in the early days of railways1 some trains were not run after dark and those which were operated were not always lighted4 ,at first attempts were made at lighting railway cars with compressed coal-gas1 but the disadvantage of this was the large tank required4 ,obviously1 a gas of higher illuminating-value per volume was desired where limited storage space was available1 and ,pintsch turned his attention to oil-gas4 ,gas suffers in illuminating-value upon being compressed1 but oil-gas suffers only about half the loss that coal-gas does4 ,in about #ahhj ,pintsch developed a method of welding cylinders and buoys which satisfied lighthouse authorities and he was enabled to furnish these filled with compressed gas4 ,thus the buoy was its own gas-tank4 ,he devised lanterns which would remain lighted regardless of wind and waves and thus gained a start with his compressed-gas systems4 ,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 inch4 ,this regulator served well throughout many years of exacting service4 ,the system began to be adopted on ships and railroads in #ahhj and for many years it has served well4 ,although gas-lighting has affected the activities of mankind considerably by intensifying commerce and industry and by advancing social progress1 the illuminants which eventually took the lead have extended the possibilities and influences of artificial light4 ,in the brief span of a century civilized man is almost totally independent of natural light in those fields over which he has control4 ,what another century will bring can be predicted only from the accomplishments of the past4 ,these indicate possibilities beyond the powers of imagination4 ,,ix ,,the ,,electric ,,arcs ,early in #ahjj ,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 pile4 ,this letter was published in the ,transactions and it created great excitement among scientific men1 who immediately began active investigations of certain electrical phenomena4 ,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 series4 ,he constructed a pile of metal disks consisting of zinc and copper alternated and separated by wet cloths4 ,at first he believed that mere contact was sufficient1 but when1 later1 it was shown that chemical action took place1 rapid progress was made in the construction of voltaic cells4 ,the next step after his pile was constructed was to place pairs of strips of copper and zinc in cups containing water or dilute acid4 ,volta received many honors for his discovery1 which contributed so much to the development of electrical science and art--among them a call to ,paris by ,bonaparte to exhibit his electrical experiments1 and to receive a medal struck in his honor4 ,while ,volta was being showered with honors1 various scientific men with great enthusiasm were entering new fields of research1 among which was the heating value of electric current and particularly of electric sparks made by breaking a circuit4 ,late in #ahjj ,sir ,humphrey ,davy was the first to use charcoal for the sparking points4 ,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 spheres4 ,apparently1 he was producing a feeble arc1 rather than a pure spark4 ,in the years which immediately followed many scientific men in ,england1 ,france1 and ,germany were publishing the results of their studies of electrical phenomena bordering upon the arc4 ,by subscription among the members of the ,royal ,society1 a voltaic battery of two thousand cells was obtained and in #ahjh ,davy exhibited the electric arc on a large scale4 ,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 arc4 ,certainly the descriptions indicate that the simple spark was not being experimented with1 but the source of electric current available at that time was of such high resistance that only feeble arcs could have been produced4 ,in #ahji ,davy demonstrated publicly an arc obtained by a current from a ,volta pile of one thousand plates4 ,this he described as a most brilliant flame1 of from half an inch to one and a quarter inches in length4 ,in the library of the ,royal ,society1 ,davy's notes made during the years of #ahje and #ahab are available in two large volumes4 ,these were arranged and paged by ,faraday1 who was destined to contribute greatly to the future development of the science and art of electricity4 ,in one of these volumes is found an account of a lecture-experiment by ,davy which certainly is a description of the electric arc4 ,an extract of this account is as follows3 ,the spark presumably the arc1 the light of which was so intense as to resemble that of the sun1 444 produced a discharge through heated air nearly three inches in length1 and of a dazzling splendor4 ,several bodies which had not been fused before were fused by this flame4444 ,charcoal was made to evaporate1 and plumbago appeared to fuse in vacuo4 ,charcoal was ignited to intense whiteness by it in oxymuriatic acid1 and volatilized by it1 but without being decomposed4 ,from a consideration of his source of electricity1 a voltaic pile of two thousand plates1 it is certain that this could not have been an electric spark4 ,later in his notes ,davy continued3 444the charcoal became ignited to whitness1 and by withdrawing the points from each other1 a constant discharge took place through the heated air1 in a space at least equal to four inches1 producing a most brilliant ascending arch of light1 broad and conical in form in the middle4 ,this is surely a description of the electric arc4 ,apparently the electrodes were in a horizontal position and the arc therefore was horizontal4 ,owing to the rise of the heated air1 the arc tended to rise in the form of an arch4 ,from this appearance the term arc evolved and ,davy himself in #ahbj definitely named the electric flame1 the arc4 ,this name was continued in use even after the two carbons were arranged in a vertical co-axial position and the arc no more arched4 ,an interesting scientific event of #ahbj 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 it4 ,this has been taken advantage of in certain modern arc-lamps in which inclined carbons are used4 ,in these arcs a magnet keeps the arc in place1 for without the magnet the arc would tend to climb up the carbons and go out4 ,in #ahch ,gassiot made the discovery that the temperature of the positive electrode of an electric arc is much greater than that of the negative electrode4 ,this is explained in electronic theory by the bombardment of the positive electrode by negative electrons or corpuscles of electricity4 ,this temperature-difference was later taken into account in designing direct-current arc-lamps1 for inasmuch as most of the light from an ordinary arc is emitted by the end of the positive electrode1 this was placed above the negative electrode4 ,in this manner most of the light from the arc is directed downward where desired4 ,in the few instances in modern times where the ordinary direct-current arc has been used for indirect lighting1 in which case the arc is above an inverted shade1 the positive carbon is placed below the negative one4 ,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 diameter4 ,after the arc operated for some time1 the positive wire was melted for such a distance that it bent downward1 but the negative remained quite straight4 ,charcoal was used for the electrodes in all the early experiments1 but owing to the intense heat of the arc1 it burned away rapidly4 ,a progressive step was made in #ahdc when electrodes were first made by ,foucault from the carbon deposited in retorts in which coal was distilled in the production of coal-gas4 ,however1 charcoal1 owing to its soft porous character1 gives a longer arc and a larger flame4 ,in #ahgg the cored carbons were introduced4 ,these consist of hard molded carbon rods in which there is a core of soft carbon4 ,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 center4 ,modern carbons for ordinary arc-lamps are generally made of a mixture of retort-carbon1 soot1 and coal-tar4 ,this paste is forced through dies and the carbons are baked at a fairly high temperature4 ,a variation in the hardness of the carbons may be obtained as the requirements demand by varying the proportions of soot and retort-carbon4 ,cored carbons are made by inserting a small rod in the center of the die and the carbons are formed with a hollow core4 ,this may be filled with a softer carbon4 ,if two carbons connected to a source of electric current are brought together1 the circuit is completed and a current flows4 ,if the two carbons are now slightly separated1 an arc will be formed4 ,as the arc burns the carbons waste away and in the case of direct current1 the positive decreases in length more rapidly than the negative one4 ,this is due largely to the extremely high temperature of the positive tip1 where the carbon fairly boils4 ,a crater is formed at the positive tip and this is always characteristic of the positive carbon of the ordinary arc1 although it becomes more shallow as the arc-length is increased4 ,the negative tip has a bright spot to which one end of the arc is attached4 ,by wasting away1 the length of the arc increases and likewise its resistance1 until finally insufficient current will pass to maintain the arc4 ,it then goes out and to start it the carbons must be brought together and separated4 ,the mechanisms of modern arc-lamps perform these functions automatically by the ingenious use of electromagnets4 ,the interior of the arc is of a violet color and the exterior is a greenish yellow4 ,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 carbons4 ,often material is deposited from the positive crater upon the negative tip and these accretions may build up a rounded tip4 ,this deposit sometimes interferes with the proper formation of the arc and also with the light from the arc4 ,it is often responsible for the hissing noise1 although this hissing occurs with any length of arc when the current is sufficiently increased4 ,the hissing seems to be due to the crater enlarging under excessive current until it passes the confines of the cross-section of the carbon4 ,it thus tends to run up the side1 where it comes in contact with oxygen of the air4 ,in this manner the carbon is directly burned instead of being vaporized1 as it is when the hot crater is small and is protected from the air by the arc itself4 ,the temperature of the positive crater is in the neighborhood of #fjjj to #gjjj;,f4 ,the brightness of the arc under pressure is the greatest produced by artificial means and is very intense4 ,by putting the arc under high pressure1 the brightness of the sun may be attained4 ,the temperature of the hottest spot on the negative tip is about a thousand degrees below that of the positive4 ,no great demand arose for arc-lamps until the development of the ,gramme dynamo in #ahgj1 which provided a practicable source of electric current4 ,in #ahgf ,jablochkov invented his famous electric candle consisting of two rods of carbon placed side by side but separated by insulating material4 ,in this country ,brush was the pioneer in the development of open arc-lamps4 ,in #ahgg he invented an arc-lamp and an efficient form of dynamo to supply the electrical energy4 ,the first arc-lamps were ordinary direct-current open arcs and the carbons were made from high-grade coke1 lampblack1 and syrup4 ,the upper positive carbon in these lamps is consumed at a rate of one to two inches per hour4 ,inasmuch as about #he per cent4 of the total light is emitted by the upper 7positive7 carbon and most of this from the crater1 the lower carbon is made as small as possible in order not to obstruct any more light than necessary4 ,the positive carbon of the open arc is often cored and the negative is a smaller one of solid carbon4 ,this combination operates quite satisfactorily1 but sometimes solid carbons are used outdoors4 ,the voltage across the arc is about #ej volts4 ,in #ahdf ,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 air4 ,after the appearance of the dynamo1 when increased attention was given to the development of arc-lamps1 this principle of enclosing the arcs was again considered4 ,the early attempts in about #ahhj 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 #fe volts1 that higher voltages were employed4 ,in #ahic marked improvements were consummated and ,jandus brought out a successful enclosed arc operating at #hj volts4 ,marks contributed largely to the success of the enclosed arc by showing that a small current and a high voltage of #hj to #he volts were the requisites for a satisfactory enclosed arc4 ,the principle of the enclosed arc is simple4 ,a closely fitting glass globe surrounds the arc1 the fit being as close as the feeding of the carbons will permit4 ,when the arc is struck the oxygen is rapidly consumed and the heated gases and the enclosure check the supply of fresh air4 ,the result is that the carbons are consumed about one tenth as rapidly as in the open arc4 ,there is no crater formed on the positive tip and the arc wanders considerably4 ,the efficiency of the enclosed arc as a light-producer is lower than that of the open arc1 but it found favor because of its slow rate of consumption of the carbons and consequent decreased attention necessary4 ,this arc operates a hundred hours or more without trimming1 and will therefore operate a week or more in street-lighting without attention4 ,when it is considered that open arcs for all-night burning were supplied with two pairs of carbons1 the second set going into use automatically when the first were consumed1 the value of the enclosed arc is apparent4 ,however1 the open arc has served well and has given way to greater improvements4 ,it is rapidly disappearing from use4 ,the alternating-current arc-lamp was developed after the appearance of the direct-current open-arc and has been widely used4 ,it has no positive or negative carbons1 for the alternating current is reversing in direction usually at the rate of #abj times per second2 that is1 it passes through #fj complete cycles during each second4 ,no marked craters form on the tips and the two carbons are consumed at about the same rate4 ,the average temperature of the carbon tips is lower than that of the positive tip of a direct-current arc1 with the result that the luminous efficiency is lower4 ,these arcs have been made of both the open and enclosed type4 ,they are characterized by a humming noise due to the effect of alternating current upon the mechanism and also upon the air near the arc4 ,this humming sound is quite different from the occasional hissing of a direct-current arc4 ,when soft carbons are used1 the arc is larger and apparently this mass of vapor reduces the humming considerably4 ,the humming is not very apparent for the enclosed alternating-current arc4 ,the alternating arc can easily be detected by closely observing moving objects4 ,if a pencil or coin be moved rapidly1 a number of images appear which are due to the pulsating character of the light4 ,at each reversal of the current1 the current reaches zero value and the arc is virtually extinguished4 ,therefore1 there is a maximum brightness midway between the reversals4 ,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 projection1 stage-equipment1 lighthouses1 search-lights1 and other applications4 ,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 carbon4 ,in fact1 the light from the arc itself is negligible4 ,a logical step in the development of the arc-lamp was to introduce salts in order to obtain a luminous flame4 ,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 carbons4 ,apparently ,bremer in #ahih was the first to introduce fluorides of calcium1 barium1 and strontium4 ,the salts deflagrate and a luminous flame envelops the ordinary feeble arc-flame4 ,from these arcs most of the light is emitted by the arc itself1 hence the name flame-arcs4 ,by the introduction of metallic salts into the carbons the possibilities of the arc-lamp were greatly extended4 ,the luminous output of such lamps is much greater than that of an ordinary carbon arc using the same amount of electrical energy4 ,furthermore1 the color or spectral character of the light may be varied through a wide range by the use of various salts4 ,for example1 if carbons are impregnated with calcium fluoride1 the arc-flame when examined by means of a spectroscope will be seen to contain the characteristic spectrum of calcium1 namely1 some green1 orange1 and red rays4 ,these combine to give to this arc a very yellow color4 ,as explained in a previous chapter1 the salts for this purpose may be wisely chosen from a knowledge of their fundamental or characteristic flame-spectra4 ,these lamps have been developed to meet a variety of needs and their luminous efficiencies range from #bj to #dj lumens per watt1 being several times that of the ordinary carbon open-arc4 ,the red flame-arc owes its color chiefly to strontium1 whose characteristic visible spectrum consists chiefly of red and yellow rays4 ,barium gives to the arc a fairly white color4 ,the yellow and so-called white flame-arcs have been most commonly used4 ,flame-arcs have been produced which are close to daylight in color1 and powerful blue-white flame-arcs have satisfied the needs of various chemical industries and photographic processes4 ,these arcs are generally operated in a space where the air-supply is restricted similar to the enclosed-arc principle4 ,inasmuch as poisonous fumes are emitted in large quantities from some flame-arcs1 they are not used indoors without rather generous ventilation4 ,in fact1 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 buildings4 ,they are made for both direct and alternating current and the mechanisms have been of several types4 ,the electrodes are consumed rather rapidly so they are made as long as possible4 ,in one type of arc1 the carbons are both fed downward1 their lower ends forming a narrow ,v with the arc-flame between their tips4 ,under these conditions the arc tends to travel vertically and finally to stretch itself to extinction4 ,however1 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 carbons4 ,the chief objection to the early flame-arcs was the necessity for frequent renewal of the carbons4 ,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 globe4 ,however1 in addition to the inner glass enclosure1 two cooling chambers of metal are attached to it4 ,air enters at the bottom and the fumes from the arc pass upward and into the cooling chambers1 where the solid products are deposited4 ,the air on returning to the bottom is thus relieved of these solids and the inner glass enclosure remains fairly clean4 ,the lower carbon is impregnated with salts for producing the luminous flame and the upper carbon is cored4 ,the life of the electrodes is about seventy-five hours4 ,the next step was the introduction of the so-called luminous-arc which is a flame-arc with entirely different electrodes4 ,the lower 7negative7 electrode consists of an iron tube packed chiefly with magnetite 7an iron oxide7 and titanium oxide in the approximate proportions of three to one respectively4 ,the magnetite is a conductor of electricity which is easily vaporized4 ,the arc-flame is large and the titanium gives it a high brilliancy4 ,the positive electrode1 usually the upper one1 is a short1 thick1 solid cylinder of copper1 which is consumed very slowly4 ,this lamp1 known as the magnetite-arc1 has a luminous efficiency of about #bj lumens per watt with a clear glass globe4 ,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 connected4 ,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 ago4 ,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-lamps4 ,there will be a continued demand for arc-lamps1 for scientific developments are opening new fields for them4 ,their value in photo-engraving1 in the moving-picture production studios1 in moving-picture projection1 and in certain aspects of stage-lighting is firmly established1 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 reactions4 ,the luminous efficiencies of arc-lamps depend upon so many conditions that it is difficult to present a concise comparison2 however1 the following may suffice to show the ranges of luminous output per watt under actual conditions of usage4 ,these efficiencies1 of course1 are less than the efficiencies of the arc alone1 because the losses in the mechanism1 globes1 etc41 are included4 ,lumens per watt ,open carbon arc #d to #h ,enclosed carbon arc #c to #g ,enclosed flame-arc 7yellow or white7 #ae to #be ,luminous arc #aj to #be ,another lamp differing widely in appearance from the preceding arcs may be described here because it is known as the mercury-arc4 ,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 electrodes4 ,the arc may be maintained of a length of several feet4 ,perhaps the first mercury-arc was produced in #ahfj by ,way1 who permitted a fine jet of mercury to fall from a reservoir into a vessel1 the reservoir and receiver being connected to the poles of a battery4 ,the electric current scattered the jet and between the drops arcs were formed4 ,he exhibited this novel light-source on the mast of a yacht and it received great attention4 ,later1 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 exhausted4 ,cooper ,hewitt was a successful pioneer in the production of practicable mercury-arcs4 ,he made them chiefly in the form of straight tubes of glass up to several feet in length1 with enlarged ends to facilitate cooling4 ,the tubes are inclined so that the mercury vapor which condenses will run back into the enlarged end1 where a pool of mercury forms the negative electrode4 ,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 iron4 ,the heat of the arc volatilizes the mercury so that an arc of considerable length is maintained4 ,the tilting is done by electromagnets4 ,starting has also been accomplished by means of a heating coil and also by an electric spark4 ,the lamps are stabilized by resistance and inductance coils4 ,one of the defects of the light emitted by the incandescent vapor of mercury is its paucity of spectral colors4 ,its visible spectrum consists chiefly of violet1 blue1 green1 and yellow rays4 ,it emits virtually no red rays1 and1 therefore1 red objects appear devoid of red4 ,the human face appears ghastly under this light and it distorts colors in general4 ,however1 it possesses the advantages of high efficiency1 of reasonably low brightness1 of high actinic value1 and of revealing detail clearly4 ,various attempts have been made to improve the color of the light by adding red rays4 ,reflectors of a fluorescent red dye have been used with some success1 but such a method reduces the luminous efficiency of the lamp considerably4 ,the dye fluoresces red under the illumination of ultra-violet1 violet1 and blue rays2 that is1 it has the property of converting radiation of these wave-lengths into radiant energy of longer wave-lengths4 ,by the use of electric incandescent filament lamps in conjunction with mercury-arcs1 a fairly satisfactory light is obtained4 ,many experiments have been made by adding other substances to the mercury1 such as zinc1 with the hope that the spectrum of the other substance would compensate the defects in the mercury spectrum4 ,however no success has been reached in this direction4 ,by the use of a quartz tube which can withstand a much higher temperature than glass1 the current density can be greatly increased4 ,thus a small quartz tube of incandescent mercury vapor will emit as much light as a long glass tube4 ,the quartz mercury-arc produces a light which is almost white1 but the actual spectrum is very different from that of white sunlight4 ,although some red rays are emitted by the quartz arc1 its spectrum is essentially the same as that of the glass-tube arc4 ,quartz transmits ultra-violet radiation1 which is harmful to the eyes1 and inasmuch as the mercury vapor emits such rays1 a glass globe should be used to enclose the quartz tube when the lamp is used for ordinary lighting purposes4 ,it is fortunate that such radically different kinds of light-sources are available1 for in the complex activities of the present time all are in demand4 ,the quartz mercury-arc finds many isolated uses1 owing to its wealth of ultra-violet radiation4 ,it is valuable as a source of ultra-violet for exciting phosphorescence1 for examining the transmission of glasses for this radiation1 for sterilizing water1 for medical purposes1 and for photography4 ,x ,,the ,,electric ,,incandescent ,,filament ,,lamps ,prior to #ahjj 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 electricity4 ,volta was not merely an inventor1 for he was one of the greatest scientists of his period1 endowed with an imagination which marked him as a genius in creative work4 ,by contributing the electric battery1 he added the greatest impetus to research in electrical science that it has ever received4 ,as has already been shown1 there began a period of enthusiastic research in the general field of heating effects of electric current4 ,the electric arc was born in the cradle of this enthusiasm1 and in the heating of metals by electricity the future incandescent lamp had its beginning4 ,between the years #ahda and #ahdh several inventors attempted to make light-sources by heating metals4 ,these crude lamps were operated by means of ,grove and ,bunsen electric cells1 but no practicable incandescent filament lamps were brought out until the development of the electric dynamo supplied an adequate source of electric current4 ,as electrical science progressed through the continued efforts of scientific men1 it finally became evident that an adequate supply of electric current could be obtained by mechanical means2 that is1 by rotating conductors in such a manner that current would be generated within them as they cut through a magnetic field4 ,even the pioneer inventors of electric lamps made great contributions to electrical practice by developing the dynamo4 ,brush developed a satisfactory dynamo coincidental with his invention of the arc-lamp1 and in a similar manner1 ,edison made a great contribution to electrical practice in devising means of generating and distributing electricity for the purpose of serving his filament lamp4 ,illustration3 ,,direct ,,current ,,arc ,most of the light being emitted by the positive 7upper7 electrode ,illustration3 ,,flame ,,arc ,most of the light being emitted by the flame ,illustration3 ,,on ,,the ,,testing-,,racks ,,of ,,the ,,manufacturer ,,of ,,incandescent ,,filament ,,lamps ,thousands of lamps are burned out for the sake of making improvements4 ,the electrical energy used is equivalent to that consumed by a city of #cj1jjj inhabitants ,edison in #ahgh attacked the problem of producing light from a wire or filament heated electrically4 ,he used platinum wire in his first experiments1 but its volatility and low melting-point 7#cbjj;,f47 limited the success of the lamps4 ,carbon with its extremely high melting-point had long attracted attention and in #ahgi ,edison produced a carbon filament by carbonizing a strip of paper4 ,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 glass4 ,platinum was used because its expansion and contraction is about the same as glass4 ,incidentally1 many improvements were made in incandescent lamps and thirty years passed before a material was found to replace the platinum leading-in wires4 ,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 glass4 ,in #ahgi and #ahhj ,edison had succeeded in overcoming the many difficulties sufficiently to give to the world a practicable incandescent filament lamp4 ,about this time ,swan and ,stearn in ,england had also produced a successful lamp4 ,in ,edison's early experiments with filaments he used platinum wire coated with carbon but without much success4 ,he also made thin rods of a mixture of finely divided metals such as platinum and iridium mixed with such oxides as magnesia1 zirconia1 and lime4 ,he even coiled platinum wire around a piece of one of these oxides1 with the aim of obtaining light from the wire and from the heated oxide4 ,however1 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 vessel4 ,one of the chief difficulties was to make the carbon filaments4 ,some of the pioneers1 such as ,sawyer and ,mann1 attempted to cut these from a piece of carbon4 ,however1 ,edison and also ,swan turned their attention to forming them by carbonizing a fiber of organic matter4 ,filaments cut from paper and threads of cotton and silk were carbonized for this purpose4 ,edison scoured the earth for better materials4 ,he tried a fibrous grass from ,south ,america and various kinds of bamboo from other parts of the world4 ,thin filaments of split bamboo eventually proved the best material up to that time4 ,he made many lamps containing filaments of this material1 and even until #aiaj bamboo was used to some extent in certain lamps4 ,of these early days1 ,edison said3 ,it occurred to me that perhaps a filament of carbon could be made to stand in sealed glass vessels1 or bulbs1 which we were using1 exhausted to a high vacuum4 ,separate lamps were made in this way independent of the air-pump1 and1 in ,october1 #ahgi1 we made lamps of paper carbon1 and with carbons of common sewing thread1 placed in a receiver or bulb made entirely of glass1 with the leading-in wires sealed in by fusion4 ,the whole thing was exhausted by the ,sprengel pump to nearly one-millionth of an atmosphere4 ,the filaments of carbon1 although naturally quite fragile owing to their length and small mass1 had a smaller radiating surface and higher resistance than we had dared hope4 ,we had virtually reached the position and condition where the carbons were stable4 ,in other words1 the incandescent lamp as we still know it to-day #aijd1 in essentially all its particulars unchanged1 had been born4 ,after ,edison's later success with bamboo1 ,swan invented a process of squirting filaments of nitrocellulose into a coagulating liquid1 after which they are carbonized4 ,very fine uniform filaments can be made by this process and although improvements have been made from time to time1 this method has been employed ever since its invention4 ,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 die4 ,this thread when hardened appears similar to cat-gut4 ,it is cut into proper lengths and bent upon a form4 ,it is then immersed in plumbago and heated to a high temperature in order to destroy the organic matter4 ,a carbon filament is the result4 ,from this point to the finished lamp many operations are performed1 but a discussion of these would lead far afield4 ,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 manufacturers4 ,at least1 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 war4 ,during the early years of incandescent lamps1 improvements were made from time to time which increased the life and the luminous efficiency of the carbon filaments1 but it was not until #aijf that any radical improvement was achieved4 ,in that year in this country a process was devised whereby the carbon filament was made more compact4 ,in fact1 from its appearance it received the name metallized filament4 ,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-gas4 ,the filament is heated by electric current and the heat breaks down the hydrocarbons1 with the result that carbon is deposited upon the filament4 ,this treated filament has a coating of hard carbon and its electrical resistance is greater than that of the untreated filament4 ,the luminous efficiency of a carbon filament is a function of its temperature and it increases very rapidly with increasing temperature4 ,for this reason it is a constant aim to reach high filament temperatures4 ,of all the materials used in filaments up to the present time1 carbon possesses the highest melting-point 7perhaps as high as #gjjj;,f471 but the carbon filament as operated in practice has a lower efficiency than any other filament4 ,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 filaments4 ,the incandescent carbon in the evacuated bulb sublimes or volatilizes and deposits upon the bulb4 ,this decreases the size of the filament eventually to the breaking-point and the blackening of the bulb decreases the output of light4 ,the treated filament was found to be a harder form of carbon that did not volatilize as rapidly as the untreated filament4 ,it immediately became possible to operate it at a higher temperature with a resulting increase of luminous efficiency4 ,this graphitized carbon filament lamp became known as the gem lamp in this country and many persons have wondered over the word gem4 ,the first two letters stand for ,general ,electric and the last for metallized4 ,this lamp was welcomed with enthusiasm in its day1 but the day for carbon filaments has passed4 ,the advent of incandescent lamps of higher efficiency has made it uneconomical to use carbon lamps for general lighting purposes4 ,although the treated carbon filament was a great improvement1 its reign was cut short by the appearance of metal filaments4 ,in #ahjc a new element was discovered and named tantalum4 ,it is a dark1 lustrous1 hard metal4 ,pure tantalum is harder than steel2 it may be drawn into fine wire2 and its melting-point is very high 7about #eajj;,f474 ,it is seen to possess properties desirable for filaments1 but for some reason it did not attract attention for a long time4 ,a century elapsed after its discovery before von ,bolton produced the first tantalum filament lamp4 ,owing to the low electrical resistance of tantalum1 a filament in order to operate satisfactorily on a standard voltage must be long and thin4 ,this necessitates storing away a considerable length of wire in the bulb without permitting the loops to come into contact with each other4 ,after the filaments have been in operation for a few hundred hours they become brittle and faults develop4 ,when examined under a microscope1 parts of the filament operated on alternating current appear to be offset4 ,the explanation of this defect goes deeply into crystalline structure4 ,the tantalum filament was quickly followed by osmium and by tungsten in this country4 ,the osmium filament appeared in #aije and its invention is due to ,welsbach1 who had produced the marvelous gas-mantle4 ,owing to its extreme brittleness1 osmium was finely divided and made into a paste of organic material4 ,the filaments were squirted through dies and1 after being formed and dried1 they were heated to a high temperature4 ,the organic matter disappeared and the fine metallic particles were sintered4 ,this made a very brittle lamp1 but its high efficiency served to introduce it4 ,in #ahgj when ,scheele discovered a new element1 known in this country as tungsten1 no one realized that it was to revolutionize artificial lighting and to alter the course of some of the byways of civilization4 ,this metal--which is known as wolfram in ,germany1 and to some extent in ,english-speaking countries--is one of the heaviest of elements1 having a specific gravity of #ai4a4 ,it is #ej per cent4 heavier than mercury and nearly twice as heavy as lead4 ,it was early used in ,german silver to the extent of #a or #b per cent4 to make platinoid1 an alloy possessing a high resistance which varies only slightly as the temperature changes4 ,this made an excellent material for electrical resistors4 ,the melting-point of tungsten is about #ecej;,f41 which makes it desirable for filaments1 but it was very brittle as prepared in the early experiments4 ,it unites very readily with oxygen and with carbon at high temperatures4 ,the first tungsten lamps appeared on the market in #aijf1 but these contained fragile filaments made by the squirting process4 ,when the squirted filament of tungsten powder and organic matter was heated in an atmosphere of steam and hydrogen to remove the binding material1 a brittle filament of tungsten was obtained4 ,the first lamps were costly and fragile4 ,after years of organized research tungsten is now drawn into the finest wires1 possessing a tensile strength perhaps greater than any other material4 ,filaments are now made into many shapes and the greatest strides in artificial lighting have been due to scientific research on a huge scale4 ,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 ,fame4 ,organization of scientific research in the industrial laboratories is such that often many persons contribute to the development of an improvement4 ,furthermore1 time is usually required for a full perspective of applications of scientific knowledge4 ,in the early days organized research was not practised and the great developments of those days were the works of individuals4 ,to-day1 even in pure science1 some of the greatest contributions are made by industrial laboratories2 but sometimes these do not become known to the public for many years4 ,the whole scheme of scientific development has changed materially4 ,for example1 the story of the development of ductile tungsten1 which has revolutionized lighting1 is complex and more or less shrouded in secrecy at the present time4 ,many men have contributed toward this accomplishment and the public at the present time knows little more than the fact that tungsten filaments1 which were brittle yesterday1 are now made of ductile tungsten wire drawn into the finest filaments4 ,the earlier tungsten filaments were made by three rival processes4 ,by the first1 a deposit of tungsten was flashed on a fine carbon filament1 the latter being eliminated finally by heating in an atmosphere of hydrogen and water-vapor4 ,by the second1 colloidal tungsten was produced by operating an arc between tungsten electrodes under water4 ,the finely divided tungsten was gathered1 partially dried1 and squirted through dies to form filaments4 ,these were then sintered4 ,the third was the paste process already described4 ,these methods produced fragile filaments1 but their luminous efficiency was higher than that of previous ones4 ,however1 in this country ductile tungsten was soon on its way4 ,an ingot of tungsten is subjected to vigorous swaging until it takes the form of a rod4 ,this is finally drawn into wire4 ,much of this development work was done by the laboratories of the ,general ,electric ,company and they were destined to contribute another great improvement4 ,the blackening of the lamp bulbs was due to the evaporation of tungsten from the filament4 ,all filaments up to this time had been confined in evacuated bulbs and the low pressure facilitates evaporation1 as is well known4 ,it had long been known that an inert gas in the bulb would reduce the evaporation and remedy other defects2 however1 under these conditions1 there would be a considerable loss of energy through conduction of heat by the gases4 ,in the vacuum lamp nearly all the electrical energy is converted into radiant energy1 which is emitted by the filament and any dissipation of heat is an energy loss4 ,a high vacuum was one of the chief aims up to this time1 but a radical departure was pending4 ,if an ordinary tungsten-lamp bulb be filled with an inert gas such as nitrogen1 the filament may be operated at a very much higher temperature without any more deterioration than takes place in a vacuum at a lower temperature4 ,this gives a more efficient light but a less efficient lamp4 ,the greater output of light is compensated by losses by conduction of heat through the gas4 ,in other words1 a great deal more energy is required by the filament in order to remain at a given temperature in a gas than in a vacuum4 ,however1 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 gas1 established the foundation for the gas-filled tungsten lamp4 ,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 light4 ,however1 a practical filament must have sufficient resistance to be used safely on lighting circuits already established and1 therefore1 the large diameter and high resistance were obtained by making a helical coil of a fine wire4 ,in fact1 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 gas4 ,this development was not accidental and from a scientific point of view it is not spectacular4 ,it did not mark a new discovery in the same sense as the discovery of ,x-rays4 ,however1 it is an excellent example of the great rewards which come to systematic1 thorough study of rather commonplace physical laws in respect to a given condition4 ,such achievements are being duplicated in various lines in the laboratories of the industries4 ,scientific research is no longer monopolized by educational institutions4 ,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 mankind4 ,the smoke-laden industrial district1 pulsating with life1 is the proud exhibit of the present civilization4 ,it is the creation of those who discover1 organize1 and apply scientific facts4 ,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 mankind8 ,a glimpse into a vast organization of research1 which1 for example1 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 companies4 ,the progress in the development of electric incandescent lamps is shown in the following table1 where the dates and values are more or less approximate4 ,it should be understood that from #ahhj to the present time there has been a steady progress1 which occasionally has been greatly augmented by sudden steps4 ,,approximate ,,values ,lumens per ,date ,filament ,temperature watt #ahhj ,carbon #ccjj;,f4 #c4j #aijf ,carbon 7graphitized7 #cdjj #d4e #aije ,tantalum #ceej #f4e #aije ,osmium #cfjj #g4e #aijf ,tungsten 7vacuum7 #cgjj #h4j #aiad ,tungsten 7gas-filled7 up to #ecjj;,f4 #aj to #be ,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 value4 ,one of the latest is the tungsten arc in an inert gas4 ,by means of a heating coil1 a small arc is started between two electrodes consisting of tungsten1 but this as yet has not been shown to be practicable4 ,another type of filament lamp was developed by ,nernst in #ahig4 ,it was an ingenious application of the peculiar properties of rare-earth oxides4 ,his first lamp consisted essentially of a slender rod of magnesia4 ,this substance does not conduct electricity at ordinary temperatures1 but when heated to incandescence it becomes conducting4 ,upon sufficient heating of this filament by external means while a proper voltage is impressed upon it1 the electric current passes through it and thereafter this current will maintain its temperature4 ,thus such a filament becomes a conductor and will continue to glow brilliantly by virtue of the electrical energy which it converts into heat4 ,later lamps consisted of glowers about one inch long made from a mixture of zirconia and yttria1 and finally a mixture of ceria1 thoria1 and zirconia was used4 ,the glower is heated initially by a coil of platinum wire located near it but not in contact with it4 ,owing to the fact that this glower decreases rapidly in resistance as its temperature is increased1 it is necessary to place in series with it a substance which increases in resistance with increasing current4 ,this is called a ballasting resistance and is usually an iron wire in a glass bulb containing hydrogen4 ,the heater is cut out by an electromagnet when the glower goes into operation4 ,this lamp is a marvel of ingenuity and when at its zenith it was installed to a considerable extent4 ,its light is considerably whiter than that of the carbon filament lamps4 ,however1 its doom was sounded when metallic filament lamps appeared4 ,an interesting filament was developed by ,parker and ,clark by using as a core a small filament of carbon4 ,this flashed in an atmosphere containing a vapor of a compound of silicon1 became coated with silicon4 ,this filament was of high specific resistance and appeared to have promise4 ,it has not been introduced commercially and doubtless it cannot compete with the latest tungsten lamps4 ,electric incandescent lamps are the present mainstay of electric illumination and1 it might be stated1 of progress in lighting4 ,wonderful achievements have been accomplished in other modes of lighting and the foregoing statement is not meant to depreciate those achievements4 ,however1 the incandescent filament lamp has many inherent advantages4 ,the light-source is enclosed in an air-tight bulb which makes for a safe1 convenient lamp4 ,the filament is capable of subdivision1 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 lamp4 ,the outputs of these are respectively a fraction of a lumen and twenty-five thousand lumens2 that is1 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 candles4 ,statistics are cold facts and are usually uninteresting in a volume of this character1 but they tell a story in a concise manner4 ,the development of the modern incandescent lamp has increased the intensity of light available with a great decrease in cost1 and this progressive development is shown easily by tables4 ,for example1 since the advent of the tungsten lamp the average candle-power and luminous efficiency of all the lamps sold in this country has steadily increased1 while the average wattages of the lamps have remained virtually stationary4 ,,average ,,candle-,,power1 ,,watts1 ,,and ,,efficiency ,,of ,,all ,,the ,,lamps ,,sold ,,in ,,this ,,country ,lumens ,year ,candle-power ,watts per watt #aijg #ah4j #ec #c4cc #aijh #ai4j #ec #c4eb #aiji #ba4j #eb #c4if #aiaj #bc4j #ea #d4db #aiaa #be4j #ea #d4hb #aiab #bf4j #di #e4bj #aiac #bi4d #dg #f4ac #aiad #ch4b #dh #g4hj #aiae #db4b #dg #h4gd #aiaf #de4h #di #i4fj #aiag #dh4g #ea #aj4ef ,it will be noted that the luminous intensity of incandescent filament lamps has steadily increased since the carbon lamp was superseded1 and that in a period of ten years of organized research behind the tungsten lamp the luminous efficiency 7lumens per watt7 has trebled4 ,in other words1 everything else remaining unchanged1 the cost of light in ten years was reduced to one third4 ,but the reduction in cost has been more than this1 as will be shown later4 ,during the same span of years the percentage of carbon filament lamps of the total filament lamps sold decreased from #ajj per cent4 in #aijg to #ac per cent4 in #aiag4 ,at the same time the percentage of tungsten 7,mazda7 lamps increased from virtually zero in #aijg to about #hg per cent4 in #aiag4 ,the tantalum lamp had no opportunity to become established1 because the tungsten lamp followed its appearance very closely4 ,in #aiaj the sales of the former reached their highest mark1 which was only #c4e per cent4 of all the lamps sold in the ,united ,states4 ,from a lowly beginning the number of incandescent filament lamps sold for use in this country has grown rapidly1 reaching nearly two hundred million in #aiai4 ,,xi ,,the ,,light ,,of ,,the ,,future ,in viewing the development of artificial light and its manifold effects upon the activities of mankind1 it is natural to look into the future4 ,jules ,verne possessed the advantage of being able to write into fiction what his riotous imagination dictated1 and so much of what he pictured has come true that his success tempts one to do likewise in prophesying the future of lighting4 ,surely a forecast based alone upon the past achievements and the present indications will fall short of the actual realizations of the future6 ,if the imagination is permitted to view the future without restrictions1 many apparently far-fetched schemes may be devised4 ,it may be possible to turn to nature's supply of daylight and to place some of it in storage for night use4 ,one millionth part of daylight released as desired at night would illuminate sufficiently all of man's nocturnal activities4 ,the fictionist need not heed the scientist's inquiry as to how this daylight would be bottled4 ,instead of giving time to such inquiries he would pass on to another scheme1 whereby earth would be belted with optical devices so that day could never leave4 ,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 darkness1 thus banishing night forever4 ,the writer of fiction need not bother with a consideration of the economic situation which would demand such efforts4 ,this line of conjecture is interesting1 for it may suggest possibilities toward which the present trend of artificial lighting does not point2 however1 the author is constrained to treat the future of light-production on a somewhat more conservative basis4 ,at the present time the light-source of chief interest in electric lighting is the incandescent filament lamp2 but its luminous efficiency is limited1 as has been shown in a previous chapter4 ,when light is emitted by virtue of its temperature much invisible radiant energy accompanies the visible energy4 ,the highest luminous efficiency attainable by pure temperature radiation will be reached when the temperature of a normal radiator reaches the vicinity of #aj1jjj;,f4 to #aa1jjj;,f4 ,the melting-points of metals are much lower than this4 ,the tungsten filament in the most efficient lamps employing it is operating near its melting-point at the present time4 ,carbon is a most attractive element in respect to melting-point1 for it melts at a temperature between #fjjj;,f4 and #gjjj;,f4 ,even this is far below the most efficient temperature for the production of light by means of pure temperature radiation4 ,there are possibilities of higher efficiency being obtained by operating arcs or filaments under pressure2 however1 it appears that highly efficient light of the future will result from a radical departure4 ,scientists are becoming more and more intimate with the structure of matter4 ,they are learning secrets every year which apparently are leading to a fundamental knowledge of the subject4 ,when these mysteries are solved1 who can say that man will not be able to create elements to suit his needs1 or at least to alter the properties of the elements already available8 ,if he could so alter the mechanism of radiation that a hot metal would radiate no invisible energy1 he would have made a tremendous stride even in the production of light by virtue of high temperature4 ,this property of selective radiation is possessed by some elements to a slight degree1 but if treatment could enhance this property1 luminous efficiency would be greatly increased4 ,certainly the principle of selectivity is a byway of possibilities4 ,a careful study of commonplace factors may result in a great step in light-production without the creation of new elements or compounds1 just as such a procedure doubled the luminous efficiency of the tungsten filament when the gas-filled lamp appeared4 ,there are a few elements still missing1 according to the ,periodic ,law which has been so valuable in chemistry4 ,when these turn up1 they may be found to possess valuable properties for light-production2 but this is a discouraging byway4 ,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 radiation4 ,the eye is able to convert radiant energy of different wave-lengths into certain fixed proportions of light4 ,for example1 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 #fbe lumens of light4 ,is this efficiency of conversion of the visual apparatus everlastingly fixed8 ,for the answer it is necessary to turn to the physiologist1 and doubtless he would suggest the curbing of the imagination4 ,but is it unthinkable that the visual processes will always be beyond the control of man8 ,however1 to turn again to the physics of light-production1 there are still several processes of producing light which are appealing4 ,many years ago ,geissler1 ,crookes1 and other scientists studied the spectra of gases excited to incandescence by the electric discharge in so-called vacuum tubes4 ,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 tubes4 ,when the pressure is sufficiently low1 the gases will glow and emit light4 ,twenty-eight years ago1 ,d4 ,mc,farlan ,moore developed the nitrogen tube1 which was actually installed in various places4 ,but there is such a loss of energy near the cathode that short vacuum tubes of this character are very inefficient producers of light4 ,efficiency is greatly increased by lengthening the tubes1 so ,moore used tubes of great length and a rather high voltage4 ,as a tube of this sort is used1 the gas gradually disappears and it must be replenished4 ,in order to replenish the gas1 ,moore devised a valve for feeding gas automatically4 ,an advantage of this mode of light-production is that the color or quality of the light may be varied by varying the gas used4 ,nitrogen yields a pinkish light2 neon an orange light2 and carbon dioxide a white light4 ,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 factor4 ,however1 for this purpose devices utilizing color-screens which alter the light from the tungsten lamp to a daylight quality are being used extensively4 ,the vacuum-tube method of producing light has an advantage in the selection of a gas among a large number of possibilities1 and some of the color effects of the future may be obtained by means of it4 ,claude has lately worked on light-production by vacuum tubes and has combined the neon tube with the mercury-vapor tube4 ,the spectrum of neon to a large extent compensates for the absence of red light in the mercury spectrum1 with a result that the mixture produces a more satisfactory light than that of either tube4 ,however1 this mode of light-production has not proved practicable in its present state of development4 ,fundamentally the limitations are those of the inherent spectral characteristics of gases4 ,doubtless the possibilities of the mechanisms of the tubes and of combining various gases have not been exhausted4 ,furthermore1 if man ever becomes capable of controlling to some extent the structure of elements and of compounds1 this method of light-production is perhaps more promising than others of the present day4 ,there is another attractive method of producing light and it has not escaped the writer of fiction4 ,h4 ,g4 ,wells1 with his rare skill and with the license so often envied by the writer of facts1 has drawn upon the characteristics of fluorescence and phosphorescence4 ,in his story ,the ,first ,men in the ,moon1 the inhabitants of the moon illuminate their caverns by utilizing this phenomenon4 ,a fluorescent liquid was prepared in large quantities4 ,it emitted a brilliant phosphorescent glow and when it splashed on the feet of the earth-men it felt cold1 but it glowed for a long time4 ,this is a possibility of the future and many have had visions of such lighting4 ,if the ceiling of a coal-mine was lined with glowing fireflies or with phosphorescent material excited in some manner1 it would be possible to see fairly well with the dark-adapted eyes4 ,this leads to the class of phenomena included under the general term luminescence4 ,the definition of this term is not thoroughly agreed upon1 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 hot4 ,a phosphorus match rubbed in the moist palm of the hand is seen to glow1 although it is at an ordinary temperature4 ,this may be termed chemi-luminescence4 ,sidot blende1 ,balmain's paint1 and many other compounds1 when illuminated with ordinary light1 and especially with ultra-violet and violet rays1 will continue to glow for a long time4 ,despite their brightness they will be cold to the touch4 ,this phenomenon would be termed photo-luminescence1 although it is better known as phosphorescence4 ,it should be noted that the latter term was carelessly originated1 for phosphorus has nothing to do with it4 ,the glow of the ,geissler tube or electrically excited gas at low pressure would be an example of electro-luminescence4 ,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 class4 ,inasmuch as light is emitted from comparatively cold bodies in these cases1 it is popularly known as cold light4 ,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 direction4 ,as yet little is known regarding the efficiency of light-production by phosphorescence4 ,the luminous efficiency of the radiant energy emitted by phosphorescent substances has been studied1 but it seems strange that among the vast works on phosphorescent phenomena1 scarcely any mention is made of the efficiency of producing light in this manner4 ,for example1 assume that phosphorescent zinc sulphide is excited by the light from a mercury-arc4 ,all the energy falling upon it is not capable of exciting phosphorescence1 as may be readily shown4 ,assuming that a known amount of radiant energy of a certain wave-length has been permitted to fall upon the phosphorescent material1 then in the dark the latter may be seen to glow for a long time4 ,an interesting point to investigate is the relation of the output to input2 that is1 the ratio of the total emitted light to the total exciting energy4 ,this is a neglected aspect in the study of light-production by this means4 ,the firefly has been praised far and wide as the ideal light-source4 ,it is an efficient radiator of light1 for its light is cold2 that is1 it does not appear to be accompanied by invisible radiant energy4 ,but little is said about its efficiency as a light-producer4 ,who knows how much fuel its lighting-plant consumes8 ,the chemistry of light-production by living organisms is being unraveled and this part of the phenomenon will likely be laid bare before long4 ,for an equal amount of energy radiated1 the firefly emits a great many times more light than the most efficient lamp in use at the present time1 but before the firefly is pronounced ideal1 the efficiency of its light-producing process must be known4 ,there are many ways of exciting phosphorescence and fluorescence1 the latter being merely an unenduring phosphorescence1 which ceases when the exciting energy is cut off4 ,ultra-violet1 violet1 and blue rays are generally the most effective radiant energy for excitation purposes4 ,x-rays and the high-frequency discharge are also powerful excitants4 ,as already stated1 virtually nothing is known of the efficiency of this mode of light-production or of the mechanism within the substance1 but on the whole it is a remarkable phenomenon4 ,radium is also a possibility in light-production and in fact has been practically employed for this purpose for several years4 ,it or one of its compounds is mixed with a phosphorescent substance such as zinc sulphide and the latter glows continuously4 ,inasmuch as the life of some of the radium products is very long1 such a method of illuminating watch-dials1 scales of instruments1 etc41 is very practicable where they are to be read by eyes adapted to darkness and consequently highly sensitive to light4 ,whether or not radium will be manufactured by the ton in the future can only conjectured4 ,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 #ae per cent4 of the luminous efficiency of the most luminous radiant energy4 ,at present there are no materials available which may be operated at the temperature necessary to reach even this efficiency4 ,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 energy4 ,at present such phenomena as fluorescence1 phosphorescence1 the light of the firefly1 chemi-luminescence1 etc41 are examples of this kind of light-production4 ,of course1 if science ever obtains control over the constitution of matter1 many difficulties will disappear2 for then man will not be dependent upon the elements and compounds now available but will be able to modify them to suit his needs4 ,,xii ,,lighting ,,the ,,streets ,in this age of brilliantly lighted boulevards and great white ways flooded with light from shop-windows1 electric signs1 and street-lamps1 it is difficult to visualize the gloom which shrouded the streets a century ago4 ,as the belated pedestrian walks along the suburban highways in comparative safety under adequate artificial lighting1 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 444 that a hundred or more in a company1 young and old1 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 streets4 ,inhabitants of the cities of the present time are inclined to think that crime is common on the streets at night1 but what would it be without adequate artificial light8 ,two centuries ago in a city like ,london a smoking grease-lamp1 a candle1 or a basket of pine knots here and there afforded the only street-lighting1 and these were extinguished by eleven o'clock4 ,lawlessness was hatched and hidden by darkness1 and even the lantern or torch served more to mark the victim than to protect him4 ,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 home4 ,by comparison with the present1 one is again encouraged to believe that the world grows better4 ,doubtless1 artificial light projected into the crannies has had something to do with this change4 ,adequate street-lighting is really a product of the twentieth century1 but throughout the nineteenth century progress was steadily made from the beginning of gas-lighting in #ahjg4 ,in preceding centuries crude lighting was employed here and there but not generally by the public authorities4 ,in the earliest centuries of written history little is said of street-lighting4 ,in those days man was not so much inclined to improve upon nature1 beyond protecting himself from the elements1 and he lighted the streets more as a festive outburst than as an economic proposition4 ,nevertheless1 in the early writings occasionally there are indications that in the centers of advanced civilization some efforts were made to light the streets4 ,the old ,syrian city of ,antioch1 which in the fourth century of the ,christian era contained about four hundred thousand inhabitants1 appears to have had lighted streets4 ,libanius1 who lived in the early years of that century1 wrote3 ,the light of the sun is succeeded by other lights1 which are far superior to the lamps lighted by ,egyptians on the festival of ,minerva of ,sais4 ,the night with us differs from the day only in the appearance of the light2 with regard to labor and employment1 everything goes on well4 ,although apparently labor was not on a strike1 the soldiers caused disturbances1 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-time1 to show that the ornaments of the city ought to give way to them4 ,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 up1 but not until they spat in each other's face and retired4 ,thus it is seen that artificial light and civilization may advance1 even though some human traits remain fundamentally unchanged4 ,throughout the next thousand years there was little attempt to light the streets4 ,iron baskets of burning wood1 primitive oil-lamps1 and candles were used to some extent1 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 manner4 ,in #adag the ,mayor of ,london ordained lanthorns with lights to bee hanged out on the winter evenings betwixt ,hallowtide and ,candlemasse4 ,this was during the festive season1 so perhaps street-lighting was not the sole aim4 ,early in the sixteenth century1 the streets of ,paris being infested with robbers1 the inhabitants were ordered to keep lights burning in the windows of all houses that fronted on the streets4 ,for about three centuries the citizens of ,london1 and doubtless of ,paris and of other cities1 were reminded from time to time in official mandates on pains and penalties to hang out their lanthorns at the appointed time4 ,the watchman in long coat with halberd and lantern in hand supplemented these mandates as he made his rounds by1 ,a light here1 maids1 hang out your lights1 ,and see your horns be clear and bright1 ,that so your candle clear may shine1 ,continuing from six till nine2 ,that honest men that walk along ,may see to pass safe without wrong4 ,in #affh1 when some regulations were made for improving the streets of ,london1 the inhabitants were ordered for the safety and peace of the city to hang out candles duly to the accustomed hour4 ,apparently this method of obtaining lighting for the streets was not met by the enthusiastic support of the people1 for during the next few decades the ,lord ,mayor was busy issuing threats and commands4 ,in #afgi he proclaimed the neglect of the inhabitants of this city in hanging and keeping out their lights at the accustomed hours1 according to the good and ancient usage of this ,city and ,acts of the ,common ,council on that behalf4 ,the result of this neglect was when nights darkened the streets then wandered forth the sons of ,belial1 flown with insolence and wine4 ,in #afid ,hemig patented a reflector which partially surrounded the open flame of a whale-oil lamp and possessed a hole in the top which aided ventilation4 ,he obtained the exclusive rights of lighting ,london for a period of years and undertook to place a light before every tenth door1 between the hours of six and twelve o'clock1 from ,michaelmas to ,lady ,day4 ,his effort was a worthy one1 but he was opposed by a certain faction1 which was successful in obtaining a withdrawal of his license in #agaf4 ,again the burden of lighting the streets was thrust upon the residents and fines were imposed for negligence in this respect4 ,but this procedure after a few more years of desultory lighting was again found to be unsatisfactory4 ,in #agbi certain individuals contracted to light the streets of ,london by taxing the residents and paid the city for this monopoly4 ,householders were permitted to hang out a lantern or a candle or to pay the company for doing so4 ,but robberies increased so rapidly that in #agcf the ,lord ,mayor and ,common ,council petitioned ,parliament to erect lamps for lighting the city4 ,an act was passed accordingly1 giving them the privilege to erect lamps where they saw fit and to burn them from sunset to sunrise4 ,a charge was made to the residents1 on a sliding scale depending upon the rate of rental of the houses4 ,as a consequence five thousand lamps were soon installed4 ,in #agch there were fifteen thousand street lamps in ,london and they were burned an average of five thousand hours annually4 ,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 crimes4 ,in appealing for more street-lamps in #agdd the ,lord ,mayor and aldermen of ,london in a petition to the king1 stated that divers confederacies of great numbers of evil-disposed persons1 armed with bludgeons1 pistols1 cutlasses1 and other dangerous weapons1 infest not only the private lanes and passages1 but likewise the public streets and places of public concourse1 and commit most daring outrages upon the persons of your ,majesty's good subjects1 whose affairs oblige them to pass through the streets1 by terrifying1 robbing and wounding them2 and these facts are frequently perpetrated at such times as were heretofore deemed hours of security4 ,it has already been seen that gas-lighting was introduced in the streets of ,london for the first time in #ahjg4 ,this marks the real beginning of public-service lighting companies4 ,in the next decade interest in street-lighting by means of gas was awakened on the ,continent1 and it was not long before this new phase of civilization was well under way4 ,although this first gas-lighting was done by the use of open flames1 it was a great improvement over all the preceding efforts4 ,lawlessness did not disappear entirely1 of course1 and perhaps it never will1 but it skulked in the back streets4 ,a controlling influence had now appeared4 ,but early innovations in lighting did not escape criticism and opposition4 ,in fact1 innovations to-day are not always received by unanimous consent4 ,there were many in those early days who felt that what was good for them should be good enough for the younger generation4 ,the descendants of these opponents are present to-day but fortunately in diminishing numbers4 ,it has been shown that in ,philadelphia in #ahcc a proposal to install a gas-plant was met with a protest signed by many prominent citizens4 ,a few paragraphs of an article entitled ,arguments against ,light which appeared in the ,cologne ,zeitung in #ahaf indicate the character of the objections raised against street-lighting4 #a ,from the theological standpoint3 ,artificial illumination is an attempt to interfere with the divine plan of the world1 which has preordained darkness during the night-time4 #b ,from the judicial standpoint3 ,those people who do not want light ought not to be compelled to pay for its use4 #c ,from the medical standpoint3 ,the emanations of illuminating gas are injurious4 ,moreover1 illuminated streets would induce people to remain later out of doors1 leading to an increase in ailments caused by colds4 #d ,from the moral standpoint3 ,the fear of darkness will vanish and drunkenness and depravity increase4 #e ,from the viewpoint of the police3 ,the horses will get frightened and the thieves emboldened4 #f ,from the point of view of national economy3 ,great sums of money will be exported to foreign countries4 #g ,from the point of view of the common people3 ,the constant illumination of streets by night will rob festive illuminations of their charm4 ,the foregoing objections require no comment1 for they speak volumes pertaining to the thoughts and activities of men a century ago4 ,it is difficult to believe that civilization has traveled so far in a single century1 but from this early beginning of street-lighting social progress received a great impetus4 ,artificial light-sources were feeble at that time1 but they made the streets safer and by means of them social intercourse was extended4 ,the people increased their hours of activity and commerce1 industry1 and knowledge grew apace4 ,the open gas-jet and kerosene-flame lamps held forth on the streets until within the memory of middle-aged persons of to-day4 ,the lamplighter with his ladder is still fresh in memory4 ,many of the towns and villages have never been lighted by gas1 for they stepped from the oil-lamp to the electric lamp4 ,the gas-mantle has made it possible for gas-lighting to continue as a competitor of electric-lighting for the streets4 ,in #ahgg ,mr4 ,brush illuminated the ,public ,square of ,cleveland with a number of arc-lamps1 and these met with such success that within a short time two hundred and fifty thousand open-arc lamps were installed in this country1 involving an investment of millions of dollars4 ,adding to this investment a much greater one in central-station equipment1 a very large investment is seen to have resulted from this single development in lighting4 ,this open-arc lamp was the first powerful light-source available and1 appearing several years before the gas-mantle1 it threatened to monopolize street-lighting4 ,it consumed about #ejj watts and had a maximum luminous intensity of about #abjj candles at an angle of about #de degrees4 ,its chief disadvantage was its distribution of light1 mainly at this angle of #de degrees1 which resulted in a spot of light near the lamp and little light at a distance4 ,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 reasons4 ,on referring to the chapter on the electric arc it will be seen that the upper 7positive7 carbon of the open-arc emits most of the light4 ,thus most of the light tends to be sent downward1 but the lower carbon obstructs some of this with a resulting dark spot beneath the lamp4 ,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 time4 ,it is a large source of light and therefore its light cannot be controlled by modern accessories as well as the light from smaller sources1 such as the arc or concentrated-filament lamp4 ,as a consequence1 there is marked unevenness of illumination along the streets unless the gas-mantle units are spaced rather closely4 ,even with the open-arc1 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 them4 ,in #ahgi the incandescent filament lamp was introduced and it began to appear on the streets in a short time4 ,it was a feeble1 inefficient light-source1 compared with the arc-lamp1 but it had the advantage of being installed on a small bracket4 ,as a consequence of simplicity of operation1 the incandescent lamp was installed to a considerable extent1 especially in the suburban districts4 ,illustration3 ,,the ,,moore ,,nitrogen ,,tube ,in lobby of ,madison ,square ,garden ,illustration3 ,,carbon-,,dioxide ,,tube ,,for ,,accurate ,,color-,,matching ,illustration3 ,,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 necessary4 ,in #ahic the enclosed arc appeared and although it consumed as much electrical energy as the open-arc and emitted considerably less light1 it possessed the great advantage of operating a week without requiring a renewal of carbons4 ,by surrounding the arc by means of a glass globe1 little oxygen could come in contact with the carbons and they were not consumed very rapidly4 ,the light was fairly steady and these arcs operated satisfactorily on alternating current4 ,the latter feature simplified the generating and distributing equipment of the central station4 ,the magnetite or luminous arc-lamp next appeared and met with considerable success4 ,it was more efficient than the preceding lamps but was handicapped by being solely a direct-current device4 ,those familiar with the generation and distribution of electricity will realize this disadvantage4 ,however1 its luminous intensity just below the horizontal was about #gjj candles and its general distribution of light was fairly satisfactory4 ,later the flame-arcs began to appear and they were installed to some extent4 ,the arc-lamp has served well in street-lighting from the year #ahgg1 when the open-arc was introduced1 until the present time1 when the luminous-arc is the chief survivor of all the arc-lamps4 ,the carbon incandescent filament lamp was used extensively until #aiji1 when the tungsten filament lamp began to replace it very rapidly4 ,however1 it was not until #aiad1 when the gas-filled tungsten lamp appeared1 that this type of light-source could compete with arc-lamps on the basis of efficiency4 ,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 possible4 ,prismatic refractors were designed1 somewhat on the principle of the lighthouse refractor1 so that the light would be emitted largely just below the horizontal4 ,this type of distribution builds up the illumination at distant points between successive street lamps1 which is very desirable in street-lighting4 ,the incandescent filament lamp possesses many advantages over other systems4 ,it is efficient2 capable of subdivision2 operates on direct and alternating current2 requires little attention2 and is capable of most successful use with light-controlling apparatus4 ,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 #cdh1fdc in #aiab to #bef1hch in #aiag1 while the number of electric incandescent filament lamps increased from #fha1ieg in #aiab to #a1chi1chb in #aiag4 ,street-lighting is not only a reinforcement for the police but it decreases accidents and has come to be looked upon as an advertising medium4 ,in the downtown districts the high-intensity white-way lighting is festive4 ,the ornamental street lamps have possibilities in making the streets attractive and in illuminating the buildings4 ,however1 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 companies4 ,these may be placed in the alleys or underground1 leaving the streets beautiful by day and glorified at night by the torches of advanced civilization4 ,,xiii ,,lighthouses ,at the present time thousands of lighthouses1 light-ships1 and light-buoys guide the navigator along the waterways and into harbors and warn him of dangerous shoals4 ,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 light4 ,many of these beacons of safety are automatic in operation and require little attention4 ,it has been said that nothing indicates the liberality1 prosperity1 or intelligence of a nation more clearly than the facilities which it affords for the safe approach of the mariner to its shores4 ,surely these marine lights are important factors in modern navigation4 ,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 ,sea4 ,as early as the seventh century before ,christ these beacon-fires were mentioned in writings4 ,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 ,,ii4 ,the tower was named ,pharos1 which is the origin of the term pharology applied to the science of lighthouse construction4 ,csar1 who visited ,alexandria two centuries later1 described the ,pharos as a tower of great height1 of wonderful construction4 ,fire was kept burning in it night and day and ,pliny said of it1 ,during the night it appears as bright as a star1 and during the day it is distinguished by the smoke4 ,apparently this tower served as a lighthouse for more than a thousand years4 ,it was found in ruins in #acdi4 ,throughout succeeding centuries many towers were built1 but little attention was given to the development of light-sources and optical apparatus4 ,the first lighthouse in the ,united ,states and perhaps on the ,western continents was the ,boston ,light1 which was completed in #agaf4 ,a few days after it was put into operation a news item in a ,boston paper heralded the noteworthy event as follows3 ,by virtue of an ,act of ,assembly made in the ,first ,year of ,his ,majesty's ,reign1 ,for ,building and ,maintaining a ,light ,house upon the ,great ,brewster 7called ,beacon-,island7 at the ,entrance of the ,harbour of ,boston1 in order to prevent the loss of the ,lives and ,estates of ,his ,majesty's ,subjects2 the said ,light ,house has been built2 and on ,fryday last the #adth ,currant the ,light was kindled1 which will be very useful for all ,vessels going out and coming in to the ,harbour of ,boston1 or any other ,harbours in the ,massachusetts ,bay1 for which all ,masters shall pay to the ,receiver of ,impost1 one ,penny per ,ton ,inwards1 and another ,penny ,outwards1 except ,coasters1 who are to pay ,two ,shillings each1 at their clearance ,out1 ,and all ,fishing ,vessels1 ,wood ,sloops1 etc4 ,five ,shillings each by the ,year4 ,this was the practical result of a petition of ,boston merchants made three years before4 ,the tower was built of stone1 at a cost of about ten thousand dollars4 ,two years later the keeper and his family were drowned and the catastrophe so affected ,benjamin ,franklin1 a boy of thirteen1 that he wrote a poem concerning it4 ,the lighthouse was badly damaged during the ,revolution1 by raiding-parties1 and in #aggf1 when the ,british fleet left the harbor1 a squad of sailors blew it up4 ,it was rebuilt in #aghc and has since been increased in height4 ,apparently oil-lamps were used in it from the beginning1 notwithstanding the fact that candles and coal fires served for years in many lighthouses of ,europe4 ,in #aghi sixteen lamps were used and in #ahaa ,argand lamps and reflectors were installed1 with a revolving mechanism4 ,it now ceased to be a fixed light and the day of flashing lights had arrived4 ,at the present time the ,boston ,light emits a beam of #ajj1jjj candle-power directed by modern lenses4 ,when the ,united ,states ,government was organized in #aghi there were ten lighthouses owned by the ,colonies1 but the ,boston ,light was in operation thirty years before the others4 ,sandy ,hook ,light1 ,new ,york ,harbor1 was established in #agfd and its original masonry tower is still standing and in use4 ,it is the oldest surviving lighthouse in this country4 ,it was built with funds raised by means of two lotteries authorized by the ,new ,york ,assembly4 ,a few days after it was lighted for the first time the following news item appeared in a ,new ,york paper3 ,on ,monday evening last the ,new ,york ,light-house erected at ,sandy ,hook was lighted for the first time4 ,the ,house is of an ,octagon ,figure1 having eight equal ,sides2 the ,diameter at the ,base #bi ,feet2 and at the top of the ,wall1 #ae ,feet4 ,the ,lanthorn is #g feet high2 the ,circumference #cc feet4 ,the whole ,construction of the ,lanthorn is ,iron2 the ,top covered with ,copper4 ,there are #dh ,oil ,blazes4 ,the ,building from the ,surface is ,nine ,stories2 the whole from ,bottom to ,top is #ajc ,feet4 ,from these early years the number of lighthouses has steadily grown1 until now the ,united ,states maintains lights along #ej1jjj miles of coast-line and river channels1 a distance equal to twice the circumference of the earth4 ,it maintains at the present time about #ae1jjj aids to navigation at an annual cost of about #e1jjj1jjj4 ,in #aiaf this country was operating #agjf major lights1 #ec light-ships1 and #eab light-buoys--a total of #ecbc4 ,the earliest lighthouses were equipped with braziers or grates in which coal or wood was burned4 ,these crude light-sources were used until after the advent of the nineteenth century and in one case until #ahdf4 ,in the famous ,eddystone tower off ,plymouth1 ,england1 candles were used for the first time4 ,the first ,eddystone tower was completed in #afih1 but it was swept away in #agjc4 ,another was built and destroyed by fire in #agee4 ,smeaton then built another in #agei4 ,inasmuch as ,smeaton is credited with having introduced the use of candles1 this must have occurred in the eighteenth century2 still it appears that1 as we have said1 the ,boston ,light1 built in #agaf1 used oil-lamps from its beginning4 ,however1 ,smeaton installed twenty-four candles of rather large size each credited with an intensity of #b4h candles4 ,the total luminous intensity of the light-source in this tower was about #fg candles4 ,inasmuch as this was before the use of efficient reflectors and lenses1 it is obvious that the early lighthouses were rather feeble beacons4 ,according to ,british records1 oil-lamps with flat wicks were first used in the ,liverpool lighthouses in #agfc4 ,the ,argand lamp1 introduced in about #aghd1 became widely used4 ,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-lamp4 ,later ,lange added an improvement by providing a contraction toward the upper part of the chimney4 ,rumford and also ,fresnel devised multiple-wick burners1 thus increasing the luminous intensity4 ,in these early lamps sperm-oil and colza-oil were burned and they continued to be until the middle of the nineteenth century4 ,cocoanut-oil1 lard-oil1 and olive-oil have also been used in lighthouses4 ,naturally1 mineral oil was introduced as soon as it was available1 owing to its lower cost2 but it was not until nearly #ahgj that a satisfactory mineral-oil lamp was in operation in lighthouses4 ,doty is credited with the invention of the first successful multiple-wick lighthouse lamp using mineral oil1 and his lamp and modifications of it were very generally used until the latter part of the nineteenth century4 ,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 level4 ,in some of the smallest lamps the ordinary capillarity of the wick is depended on to supply oil to the flame4 ,coal-gas was introduced into lighthouses in about the middle of the nineteenth century4 ,inasmuch as the gas-mantle had not yet appeared1 the gas was burned in jets4 ,various arrangements of the jets1 such as concentric rings forming a stepped cone1 were devised4 ,the gas-mantle was a great boon to the mariner as well as to civilized beings in general4 ,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 systems4 ,owing to the elaborate apparatus necessary for making coal-gas1 several other gases have been more desirable fuels for lighthouse lamps4 ,various simple gas-generators have been devised4 ,some of the high-flash mineral-oils are vaporized and burned under a mantle4 ,acetylene1 which is so simply made by means of calcium carbide and water1 has been a great factor in lighting for navigation4 ,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 candles4 ,these special gas-mantle light-sources have brightness as high as several hundred candles per square inch4 ,electric arc-lamps were first introduced into lighthouse service in about #ahfj1 but these lamps cannot be considered to have been really practicable until about #ahge4 ,in #ahhc the ,british lighthouse authorities carried out an extensive investigation of arc-lamps4 ,it was found that the whiter light from these lamps suffered a greater absorption by the atmosphere than the yellower light from oils1 but the much greater luminous intensity of the arc-lamp more than compensated for this disadvantage4 ,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-lamps2 but where great range was desired1 the latter were much more advantageous1 owing to their great luminous intensity4 ,electric incandescent filament lamps have been used for the less important lights1 and recently there has been some application of the modern high-efficiency filament lamps4 ,besides the high towers there are many minor beacons1 light-ships1 and light-buoys in use4 ,many of these are untended and therefore must operate automatically4 ,the light-ship is used where it is impracticable or too expensive to build a lighthouse4 ,inasmuch as it is anchored in fairly deep water1 it is safe in foggy weather to steer almost directly toward its position as indicated by the fog-signal4 ,light-ships are more expensive to maintain than lighthouses1 but they have the advantages of smaller cost and of mobility2 for sometimes it may be desired to move them4 ,the first light-ship was established in #agcb near the mouth of the ,thames1 and the first in this country was anchored in ,chesapeake ,bay near ,norfolk in #ahbj4 ,the early ships had no mode of self-propulsion1 but the modern ones are being provided with their own power4 ,oil and gas have been used as fuel for the light-sources and in #ahib the ,u4 ,s4 ,lighthouse ,board constructed a light-ship with a powerful electric light4 ,since that time several have been equipped with electric lights supplied by electric generators and batteries4 ,untended lights were not developed until about #ahhj1 when ,pintsch introduced his welded buoys filled with compressed gas and thereby provided a complete lighting-plant4 ,with improvements in lamps and controls the untended light-buoys became a success4 ,the lights burn for several months1 and even for a year continuously2 and the oil-gas used appears to be very satisfactory4 ,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-flame4 ,by this means a longer period of burning without attention may be obtained4 ,electric filament lamps supplied by batteries or by cables from the shore have been used1 but the oil-gas buoy still remains in favor4 ,acetylene has been employed as a fuel for light-buoys4 ,automatic generators have been devised1 but the high-pressure system is more simple4 ,in the latter case purified acetylene is held in solution under high pressure in a reservoir containing an asbestos composition saturated with acetone4 ,the light-sources of beacons have had the same history as those of other navigation lights4 ,many of these are automatic in operation1 sometimes being controlled by clockwork4 ,during the last twenty years the gas-mantle has been very generally applied to beacon-lights4 ,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 carbon4 ,the operation is such that this is not consumed and it prevents further burning of the wick4 ,the optical apparatus of navigation lights has undergone many improvements in the past century4 ,the early lights were not equipped with either reflecting or refracting apparatus4 ,in #ahbd ,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 person4 ,he was led by his experiments to suggest the application of mirrors to lighthouses4 ,his device was essentially a parabolic mirror similar to the reflectors now widely used in automobile head-lamps1 search-lights1 etc4 ,he employed the lime-light as a source of light and was enthusiastic over the results obtained4 ,his discussion published in #ahbf indicates that little practical work had been done up to that time toward obtaining beams or belts of light by means of optical apparatus4 ,however1 lighthouse records show that as early as #agfc small silvered plane glasses were set in plaster of ,paris in such a manner as to form a partially enveloping reflector4 ,spherical reflectors were introduced in about #aghj and parabolic reflectors about ten years later4 ,all the earlier lights were fixed1 but as it is desirable that the mariner be able to distinguish one light from another1 the revolving mechanism evolved4 ,by its agency characteristic flashes are obtained and from the time interval the light is recognized4 ,the first revolving mechanism was installed in #aghc4 ,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 pencil4 ,the type of parabolic reflector now in use does not differ essentially from that of an automobile head-lamp1 excepting that it is larger4 ,lenses appear to have been introduced in the latter part of the nineteenth century4 ,they were at first ground from a solid piece of glass1 in concentric zones1 in order to reduce the thickness4 ,they were similar in principle to some of the tail-light lenses used at present on automobiles4 ,later the lenses were built up by means of separate annular rings4 ,the name of ,fresnel is permanently associated with lighthouse lenses because in #ahbb he developed an elaborate built-up lens of annular rings4 ,the centers of curvature of the different rings receded from the axis as their distance from the center increased1 in such a manner as to overcome a serious optical defect known as spherical aberration4 ,fresnel devised many improvements in which he used refracting and reflecting prisms for the outer elements4 ,the optical apparatus of lighthouses usually aims 7#a7 to concentrate the rays of light into a pencil of light1 7#b7 to concentrate them into a belt of light1 or 7#c7 to concentrate the rays over a limited azimuth4 ,in the first case a single lens or a parabolic reflector suffices1 but in the second case a cylindrical lens which condenses the light vertically into a horizontal sheet of light is essential4 ,the third case is a combination of the first two4 ,the modern lighthouse lenses are very elaborate in construction1 being built up by means of many elements into several sections4 ,for example1 the central section may consist of a spherical lens ground with annular rings4 ,in the next section refracting prisms may be used and in the outer section reflecting glass prisms are employed4 ,the various elements are carefully designed according to the laws of geometrical optics4 ,the flashing light has such advantages over the fixed that it is generally used for important beacons4 ,a variety of methods of obtaining intermittent light have been employed1 but they are not of particular interest4 ,sometimes the lens or reflector is revolved and in other types an opaque screen containing slits is revolved4 ,in the larger lighthouses the optical apparatus and its structure sometimes weigh several tons4 ,when it is necessary to revolve apparatus of this weight1 the whole mechanism is floated upon mercury contained in a cast-iron vessel of suitable size1 and by an ingenious arrangement only a small portion of mercury is required4 ,the characteristics of navigation lights are varied considerably in order to enable the mariner to distinguish them and thereby to learn exactly where he is4 ,the fixed light is liable to be confused with others1 so it has now become a minor light4 ,flashes of short duration followed by longer periods of darkness are extensively used4 ,the mariner by timing the intervals is able to recognize the light4 ,this method is extended to groups of short flashes followed by longer intervals of darkness4 ,in fact1 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 watch4 ,however1 a time element is generally used4 ,a combination of fixed light upon which is superposed a flash or a group of flashes of white or of colored light has been used1 but it is in disrepute as being unreliable4 ,a type known as occulating lights consists of a fixed light which is momentarily eclipsed1 but the duration of the eclipse is usually less than that of the light4 ,obviously1 groups of eclipses may be used4 ,sometimes lights of different colors are alternated without any dark intervals4 ,the colored ones used are generally red and green1 but these are short-range lights at best4 ,colored sectors are sometimes used over portions of the field1 in order to indicate dangers1 and white light shows in the fairway4 ,these are usually fixed lights for marking the channel4 ,the distance at which a light may be seen at sea depends upon its luminous intensity1 upon its color or spectral composition1 upon its height and that of the observer's eyes above the sea-level1 and upon the atmospheric conditions4 ,assuming a perfectly clear atmosphere1 the visibility of a light-source apparently depends directly upon its candle-power4 ,the atmosphere ordinarily absorbs the red1 orange1 and yellow rays less than the green1 blue1 and violet rays4 ,this is demonstrated by the setting sun1 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 increases4 ,for this reason a red light would have a greater range than a blue light of the same luminous intensity4 ,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 earth4 ,for the uncolored illuminants the range in nautical miles appears to be at least equal to the square root of the candle-power4 ,a real practical limitation which still exists is the curvature of the earth1 and the distance an object may be seen by the eye at sea-level depends upon the height of the object4 ,the relation is approximately expressed thus1-- ,range in nautical miles #h_/g square root of ,height of object in feet4 ,for example1 the top of a tower #ajj feet high is visible to an eye at sea-level a distance of #h_/g square root of #ajj #hj_/g #aa4dc miles4 ,now if the eye is #di feet above sea-level1 a similar computation will show how far away it may be seen by the original eye at sea-level4 ,this is #h_/g square root of #di #h miles4 ,hence an eye #di feet above sea-level will be able to see the top of the #ajj-;foot tower at a distance of #aa4dc #h or #ai4dc nautical miles4 ,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 #h miles from the eye and #aa4dc miles from the tower4 ,the luminous intensity of a light-source or of the beam of light is directly responsible for the range4 ,the luminous intensity of the early beacon-fires and oil-lamps was equivalent to a few candles4 ,the improvements in light-sources and also in reflecting and refracting optical systems have steadily increased the candle-power of the beams1 until to-day the beams from gas-lamps have intensities as high as several hundred thousand candle-power4 ,the beams sent forth by modern lighthouses equipped with electric lamps and enormous light-gathering devices are rated in millions of candle-power4 ,in fact1 ,navesink ,light at the entrance of ,new ,york ,bay is rated as high as #fj1jjj1jjj candle-power4 ,of course1 light-production has increased enormously in efficiency in the past century1 but without optical devices for gathering the light1 the enormous beam intensity would not be obtained4 ,for example1 consider a small source of light possessing a luminous intensity of one candle in all directions4 ,if all this light which is emitted in all directions is gathered and sent forth in a beam of small angle1 say one thousandth of the total angle surrounding a point1 the intensity of this beam would be #ajjj candles4 ,it is in this manner that the enormous beam intensities are built up4 ,there is an interesting point pertaining to short flashes of light4 ,to the dark-adapted eye a brief flash is registered as of considerably higher intensity than if the light remained constant4 ,in other words1 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 steadily4 ,this is a physiological phenomenon which operates in favor of the flashing light4 ,illustration3 ,a4 ,a ,,completed ,,lighthouse ,,lens ,illustration3 ,b4 ,,torro ,,point ,,lighthouse1 ,,panama ,,canal ,illustration3 ,,american ,,search-,,light ,,position ,,on ,,western ,,front ,,in #aiai ,illustration3 ,,american ,,standard ,,field ,,search-,,light ,,and ,,power ,,unit ,doubtless1 the reader has noted that reliability1 simplicity1 and low cost of operation are the primary considerations for light-sources used as aids to navigation4 ,this accounts for the continued use of oil and gas4 ,from an optical standpoint the electric arc-lamps and concentrated-filament lamps are usually superior to the earlier sources of light1 but the complexity of a plant for generating electricity is usually a disadvantage in isolated places4 ,the larger light-ships are now using electricity generated by apparatus installed in the vessels4 ,there seems to be a tendency toward the use of more buoys and fewer lighthouses1 but the beam-intensities of the latter are increasing4 ,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 mariner4 ,the development of these aids to navigation has been wonderful1 but it must go on and on4 ,the surface of the earth comprises #ea1hhf1jjj square statute miles of land and #ade1jed1jjj square miles of water4 ,three fourths of the earth's surface is water and the oceans will always be highways of world commerce4 ,all the dangers cannot be overcome1 but human ingenuity is capable of great achievements4 ,wreckage will appear along the shore-lines despite the lights1 but the harvest of the shoals has been much reduced since the time described by ,robert ,louis ,stevenson1 when the coast people in the ,orkneys looked upon wrecks as a source of gain4 ,he states3 ,it had become proverbial with some of the inhabitants to observe that if wrecks were to happen1 they might as well be sent to the poor island of ,sanday as anywhere else4 ,on this and the neighboring island1 the inhabitants have certainly had their share of wrecked goods4 ,on complaining to one of the pilots of the badness of his boat's sails1 he replied with some degree of pleasantry1 ,had it been ,his ,god's will that you come na here wi these lights1 we might a' had better sails to our boats and more o' other things4 ,in the leasing of farms1 a location with a greater probability of shipwreck on the shore brought a much higher rent4 ,,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 years4 ,the airplane1 in #aiad a doubtful plaything of daredevils1 emerged from the war a perfected thing of the air4 ,lighting did not have the glamor of flying or the novelty of chemical warfare1 but it progressed greatly in certain directions and served well4 ,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 transportation1 it was also doing its part at the battle front4 ,huge search-lights revealed the submarine and the arial bomber2 flares exposed the manoeuvers of the enemy2 rockets brought aid to beleaguered vessels and troops2 pistol lights fired by the arial observer directed artillery fire2 and many other devices of artificial light were in the fray4 ,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 warfare4 ,night after night along the battle front flares were sent up to reveal patrols and any other enemy activity4 ,on the slightest suspicion great swarms of these brilliant lights would burst forth as though flocks of huge fireflies had been disturbed4 ,they were even used as light barrages1 for movements could be executed in comparative safety when a large number of these lights lay before the enemy's trenches sputtering their brilliant light4 ,the airman dropped flares to illuminate his target or his landing field4 ,the torches of past parades aided the soldier in his night operations and rockets sent skyward radiated their messages to headquarters in the rear4 ,the star-shell had the same missions as other flares1 but it was projected by a charge of powder from a gun4 ,these and many modifications represent the useful applications of what formerly were mere fireworks4 ,those which are primarily signaling devices are discussed in another chapter1 but the others will be described sufficiently to indicate the place which artificial light played in certain phases of warfare4 ,the illuminating compounds used in these devices are not particularly new1 consisting essentially of a combustible powder and chemical salts which make the flame luminous and give it color when desired4 ,among the ingredients are barium nitrate1 potassium perchlorate1 powdered aluminum1 powdered magnesium1 potassium nitrate1 and sulphur4 ,one of the simplest mixtures used by the ,english is1 ,barium nitrate #cg per cent4 ,powdered magnesium #cd per cent4 ,potassium nitrate #bi per cent4 ,the magnesium is coated with hot wax or paraffin1 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 stored4 ,the barium and potassium nitrates supply the oxygen to the magnesium1 which burns with a brilliant white flame4 ,the potassium nitrate takes fire more readily than the barium nitrate1 but it is more expensive than the latter4 ,owing to the cost of magnesium1 powdered aluminum has been used to some extent as a substitute4 ,aluminum does not have the illuminating value of magnesium and it is more difficult to ignite1 but it is a good substitute in case of necessity4 ,an ,english mixture containing these elements is1 ,barium nitrate #eh per cent4 ,magnesium #bi per cent4 ,aluminum #ac per cent4 ,mixtures which are slow to ignite must be supplemented by a primary mixture which is readily ignited4 ,for obtaining colored lights it is only necessary to add chemicals which will give the desired color4 ,the mixtures can be proportioned by means of purely theoretical considerations2 that is1 just enough oxygen can be present to burn the fuel completely4 ,however1 usually more oxygen is supplied than called for by theory4 ,the illuminating shell is perhaps the most useful of these devices to the soldier4 ,it has been constructed with and without parachutes1 the former providing an intense light for a brief period because it falls rapidly4 ,these shells of the larger calibers are equipped with time-fuses and are generally rather elaborate in construction4 ,the shell is of steel1 and has a time-fuse at the tip4 ,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 casing4 ,at the same time the black powder ignites the priming mixture next to it1 which in turn ignites the slow-burning illuminating compound4 ,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 it4 ,the time of burning varies1 but is ordinarily less than a minute4 ,certain structural details must be such as to endure the stresses of a high muzzle velocity4 ,furthermore1 a velocity of perhaps #ajjj feet per second still obtains when the star-shell with its parachute is ejected at the desired point in the air4 ,the non-parachute illuminating shell is designed to give an intense light for a brief interval and is especially applicable to defense against air raids4 ,such a light aims to reveal the aircraft in order that the gunners may fire at it effectively4 ,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 gun4 ,the contents of the shell are thereby ejected and ignited4 ,the container for the illuminating material is so designed that there is rapid combustion and consequently a brilliant light for about ten seconds4 ,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 him4 ,the rifle-light which resembles an ordinary rocket1 is fired from a rifle and is designed for short-range use4 ,it consists of a steel cylindrical shell a few inches long fastened to a steel rod4 ,a parachute is attached to the cardboard container in which the illuminating mixture is packed and the whole is stowed away in the steel shell4 ,shore delay-fuses are used for starting the usual cycle of events after the rifle-light has been fired from the gun4 ,the steel rod is injected into the barrel of a rifle and a blank cartridge is used for ejecting this rocket-like apparatus4 ,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 pulled4 ,illuminating bombs of the same general principles are used by airmen in search of a landing for himself or for a destructive bomb2 in signaling to a gunner1 and in many other ways4 ,they are simple in construction because they need not withstand the stresses of being fired from a gun2 they are merely dropped from the aircraft4 ,the mechanism of ignition and the cycle of events which follow are similar to those of other illuminating shells4 ,the value of such artificial-lighting devices depends both upon luminous intensity and time of burning4 ,although long-burning is not generally required in warfare1 it is obvious that more than a momentary light is usually needed4 ,in general1 high candle-power and long-burning are opposed to each other1 so that the most intense lights of this character usually are of short duration4 ,typical performances of two flares of the same composition are as follows3 ,flare ,no4 #a ,flare ,no4 #b ,average candle-power #bgj1jjj #ie1jjj ,seconds of burning #aj #ce ,candle-seconds #b1gjj1jjj #c1cbe1jjj ,cubic inches of compound #f #g ,candle-seconds per cubic inch #dej1jjj #dge1jjj ,candle-hours per cubic inch #abe #acb ,the illuminating compound was the same in these two flares1 which differed only in the time allowed for burning4 ,of course1 the measurements of the luminous intensity of such flares is difficult because of the fluctuations1 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 burning4 ,the light-source in the case of burning powders is really a flame1 and inasmuch as the burning end hangs downward1 more light is emitted in the lower hemisphere than in the upper4 ,the candle-power of the largest flares equals the combined luminous intensities of #bjj street arc-lamps or of #aj1jjj ordinary #dj-watt tungsten lamps such as are used in residence lighting4 ,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 lighting4 ,illuminating shells in use during the recent war were designed for muzzle velocities as high as #bgjj feet per second and were gaged to ignite at any distance from a quarter of a mile to several miles4 ,the maximum range of illuminating shells fired from rifles was about #bjj yards2 for trench mortars about one mile2 and from field and naval guns about four miles4 ,the search-light has long been a valuable aid in warfare and during the recent conflict considerable attention was given to its development and application4 ,it is used chiefly for detecting and illuminating distant targets1 but this covers a wide range of conditions and requirements4 ,in order that a search-light may be effective at a great distance1 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 obtained4 ,reflectors are usually employed in military search-lights1 and in order that the beam may be as nearly parallel 7minimum divergence7 as possible1 the light must be emitted by the smallest source compatible with high intensity4 ,this source is placed at the proper point in respect to a large parabolic reflecter which renders the rays parallel or nearly so4 ,ever since its advent the electric arc has been employed in large search-lights1 with which the army and the navy were supplied2 however1 the greatest improvements have been made under the stress of war4 ,the science of aronautics 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 concern4 ,the rapidly moving aircraft and its high altitude brought new factors into the design of these lights4 ,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 apparatus1 for the targets were sometimes minute specks moving at high speed at altitudes as high as five miles4 ,furthermore1 owing to the shifting battle areas1 mobile apparatus was necessary4 ,the control of light by means of reflectors has been studied for centuries1 but until the advent of the electric arc the light-sources were of such large areas that effective control was impossible4 ,optical devices generally are considered in connection with point sources1 but inasmuch as no light can be obtained from a point1 a source of small dimensions and of high brightness is the most effective compromise4 ,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 #ahbe by ,drummond1 who used as a source of light a piece of lime heated to incandescence in a blast flame4 ,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 projection4 ,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 #ahfc4 ,in #ahdh the first electric arc lamp used for general lighting was installed in ,paris4 ,it was supplied with current by a large voltaic cell1 but the success of the electric arc was obliged to await the development of a more satisfactory source of electricity4 ,a score of years was destined to elapse1 after the public was amazed by the first demonstration1 before a suitable electric dynamo was invented4 ,with the advent of the dynamo1 the electric arc was rapidly developed and thus there became available a concentrated light-source of high intensity and great brilliancy4 ,gradually the size was increased1 until at the present time mirrors as large as seven feet in diameter and electric currents as great as several hundred amperes are employed4 ,the beam intensities of the most powerful search-lights are now as great as several hundred million candles4 ,the most notable advance in the design of arc search-lights was achieved in recent years by ,beck1 who developed an intensive flame carbon-arc4 ,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 arc4 ,in the ordinary arc excessive current causes the carbons to disintegrate rapidly unless they are of large diameter4 ,beck directed a stream of alcohol vapor at the arc and they were kept from oxidizing4 ,he thus achieved a high current-density and much greater beam intensities4 ,he also used cored carbons containing certain metallic salts which added to the luminous intensity1 and by rotation of the positive carbon so that the crater was kept in a constant position1 greater steadiness and uniformity were obtained4 ,tests show that1 in addition to its higher luminous efficiency1 an arc of this character directs a greater percentage of the light into the effective angle of the mirror4 ,the small source results in a beam of small divergence2 in other words1 the beam differs from a cylinder by only one or two degrees4 ,if the beam consisted entirely of parallel rays and if there were no loss of light in the atmosphere by scattering or by absorption1 the beam intensity would be the same throughout its entire length4 ,however1 both divergence and atmospheric losses tend to reduce the intensity of the beam as the distance from the search-light increases4 ,inasmuch as the intensity of the beam depends upon the actual brightness of the light-source1 the brightness of a few modern light-sources are of interest4 ,these are expressed in candles per square inch of projected area2 that is1 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 measured1 the brightness of the hole is easily determined in candles per square inch4 ,,brightness ,,of ,,light-,,sources ,,in ,,candles ,,per ,,square ,,inch ,kerosene flame #e to #aj ,acetylene #cj to #fj ,gas-mantle #cj to #ejj ,tungsten filament 7vacuum7 lamp #gej to #a1bjj ,tungsten filament 7gas-filled7 lamp #c1ejj to #ah1jjj ,magnetite arc #d1jjj to #f1jjj ,carbon arc for search-lights #hj1jjj to #ij1jjj ,flame arc for search-lights #bej1jjj to #cej1jjj ,sun 7computed mean7 about #a1jjj1jjj ,as the reflector of a search-light is an exceedingly important factor in obtaining high beam-intensities1 considerable attention has been given to it since the practicable electric arc appeared4 ,the parabolic mirror has the property of rendering parallel1 or nearly so1 the rays from a light-source placed at its focus4 ,if the mirror subtends a large angle at the light-source1 a greater amount of light is intercepted and rendered parallel than in the case of smaller subtended angles2 hence1 mirrors are large and of as short focus as practicable4 ,search-light projectors direct from #cj to #fj per cent4 of the available light into the beam1 but with lens systems the effective angle is so small that a much smaller percentage is delivered in the beam4 ,mangin in #ahgd made a reflector of glass in which both outer and inner surfaces were spherical but of different radii of curvature1 so that the reflector was thicker in the middle4 ,this device was silvered on the outside and the refraction in the glass1 as the light passed through it to the mirror and back again1 corrected the spherical aberration of the mirrored surface4 ,these have been extensively used4 ,many combinations of curved surfaces have been developed for special projection purposes1 but the parabolic mirror is still in favor for powerful search-lights4 ,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 #abe degrees4 ,within this angle is included a large portion of the light emitted by the light-source in the case of direct-current arcs4 ,if this angle is increased for a mirror of a given diameter by decreasing its focal length1 the divergence of the beam is increased and the beam-intensity is diminished4 ,this is due to the fact that the light-source now becomes apparently larger2 that is1 being of a given size it now subtends a larger angle at the reflector and departs more from the theoretical point4 ,when the recent war began the search-lights available were intended generally for fixed installations4 ,these were barrel lights with reflectors several feet in diameter1 the whole output sometimes weighing as much as several tons4 ,shortly after the entrance of this country into the war1 a mobile barrel search-light five feet in diameter was produced1 which1 complete with carriage1 weighed only #ahjj pounds4 ,later there were further improvements4 ,an example of the impetus which the stress of war gives to technical accomplishments is found in the development of a particular mobile searchlight4 ,two months after the ,war ,department submitted the problems of design to certain large industrial establishments a new #fj-;inch search-light was placed in production4 ,it weighed one fifth as much as the previous standard2 it had one twentieth the bulk2 it was much simpler2 it could be built in one fourth the time2 and it cost half as much4 ,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 unit4 ,if he is near the search-light1 this veil of diffused light very seriously interferes with his vision4 ,mobile power-units were necessary and the types developed used the automobile engine as the prime mover4 ,in one the generator is located in front of the engine and supported beyond the automobile chassis4 ,in another type the generator is located between the automobile transmission and the differential4 ,a standard clutch and gear-shift lever is employed to connect the engine either with the generator or with the propeller shaft of the truck4 ,the first type included a #aae-volt1 #ae-kilowatt generator1 a #cf-;inch wheel barrel search-light1 and #ejj feet of wire cable4 ,the second type included a #aje-volt1 #bj-kilowatt generator1 a #fj-;inch open searchlight1 and #fjj feet of cable4 ,this type has been extended in magnitude to include a #ej-kilowatt generator4 ,when these units are moved1 the search-light and its carriage are loaded upon the rear of the mobile generating equipment4 ,an idea of the intensities obtainable with the largest apparatus is gained from illumination produced at a given distance4 ,for example1 the #ae-kilowatt search-light with highly concentrated beam1 produced an illumination at #icj feet of #bhj foot-candles4 ,at this point this is the equivalent of the illumination produced by a source having a luminous intensity of nearly #bej1jjj1jjj candles4 ,of course1 the range at which search-lights are effective is the factor of most importance1 but this depends upon a number of conditions such as the illumination produced by the beam at various distances1 the atmospheric conditions1 the position of the observer1 the size1 pattern1 color1 and reflection-factor of the object1 and the color1 pattern1 and reflection-factor of the background4 ,these are too involved to be discussed here1 but it may be stated that under ordinary conditions these powerful lights are effective at distances of several miles4 ,according to recent work1 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 intensity4 ,although the metallic parabolic reflector is used in the most powerful search-lights1 there have been many other developments adapted to warfare4 ,fresnel lenses have been used above the arc for search-lights whose beams are directed upward in search of aircraft1 thus replacing the mirror below the arc1 which1 owing to its position1 is always in danger of deterioration by the hot carbon particles dropping upon it4 ,for short ranges incandescent filament lamps have been used with success4 ,oxyacetylene equipment has found application1 owing to its portability4 ,the oxyacetylene flame is concentrated upon a small pellet of ceria1 which provides a brilliant source of small dimensions4 ,a tank containing about #ajjj liters of dissolved acetylene and another containing about #aajj liters of oxygen supply the fuel4 ,a beam having an intensity of about #a1ejj1jjj candles is obtained with a consumption of #dj liters of each of the gases per hour4 ,at this rate the search-light may be operated twenty hours without replenishing4 ,although the beacon-light for nocturnal airmen is a development which will assume much importance in peaceful activities1 it was developed chiefly to meet the requirements of warfare4 ,these do not differ materially from those which guide the mariner1 except that the traveler in the arial ocean is far above the plane on which the beacon rests4 ,for this reason the lenses are designed to send light generally upward4 ,in foreign countries several types of beacons for arial navigation have been in use4 ,in one the light from the source is freely emitted in all upward directions1 but the light normally emitted into the lower hemisphere is turned upward by means of prisms4 ,in a more elaborate type1 belts of lenses are arranged so as to send light in all directions above the horizontal plane4 ,a flashing apparatus is used to designate the locality by the number or character of the flashes4 ,electric filaments and acetylene flames have been used as the light-sources for this purpose4 ,in another type the light is concentrated in one azimuth and the whole beacon is revolved4 ,portable beacons employing gas were used during the war on some of the flying-fields near the battle front4 ,all kinds of lighting and lighting-devices were used depending upon the needs and material available4 ,even self-luminous paint was used for various purposes at the front1 as well as for illuminating watch-dials and the scales of instruments4 ,wooden buttons two or three inches in diameter covered with self-luminous paint could be fixed wherever desired and thus serve as landmarks4 ,they are visible only at short distances and the feebleness of their light made them particularly valuable for various purposes at the battle front4 ,they could be used in the hand for giving optical signals at a short distance where silence was essential4 ,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 friends4 ,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 enemy4 ,several years ago a ,brazilian battle-ship built in this country was equipped with a dual lighting-system4 ,the extra one used deep-blue light1 which is very effective for eyes adapted to darkness or to very low intensities of illumination and is a short-range light4 ,owing to the low luminous intensity of the blue lights they do not carry far2 and furthermore1 it is well established that blue light does not penetrate as far through ordinary atmosphere as lights of other colors of the same intensity4 ,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 purposes4 ,,xv ,,signaling ,from earliest times the beacon-fire has sent forth messages from hilltops or across inaccessible places4 ,in this country1 when the ,indian was monarch of the vast areas of forest and prairie1 he spread news broadcast to roving tribesmen by means of the signal-fire1 and he flashed his code by covering and uncovering it4 ,castaways1 whether in fiction or in reality1 instinctively turn to the beacon-fire as a mode of attracting a passing ship4 ,on every hand throughout the ages this simple means of communication has been employed2 therefore1 it is not surprising that mankind has applied his ingenuity to the perfection of signaling by means of light1 which has its own peculiar fields and advantages4 ,of course1 wireless telephony and telegraphy will replace light-signaling to some extent1 but there are many fields in which the last-named is still supreme4 ,in fact1 during the recent war much use was made of light in this manner and devices were developed despite the many other available means of signaling4 ,one of the chief advantages of light as a signal is that it is so easily controlled and directed in a straight line4 ,wireless waves1 for example1 are radiated broadcast to be intercepted by the enemy4 ,the beginning of light-signaling is hidden in the obscurity of the past4 ,of course1 the most primitive light-signals were wood fires1 but it is likely that man early utilized the mirror to reflect the sun's image and thus laid the foundation of the modern heliograph4 ,the ,book of ,job1 which is probably one of the oldest writings available1 mentions molten mirrors4 ,the ,egyptians in the time of ,moses used mirrors of polished brass4 ,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 mirrors4 ,john ,peckham1 ,archbishop of ,canterbury in the thirteenth century1 described mirrors of polished steel and of glass backed with lead4 ,mirrors of glass coated with an alloy of tin and mercury were made by the ,venetians in the sixteenth century4 ,huygens in the seventeenth century studied the laws of refraction and reflection and devised optical apparatus for various purposes4 ,however1 it was not until the eighteenth century that any noteworthy attempts were made to control artificial light for practical purposes4 ,dollond in #ageg was the first to make achromatic lenses by using combinations of different glasses4 ,lavoisier in #aggd made a lens about four feet in diameter by constructing a cell of two concave glasses and filling it with water and other liquids4 ,it is said that he ignited wood and melted metals by concentrating the sun's image upon them by means of this lens4 ,about that time ,buffon made a built-up parabolic mirror by means of several hundred small plane mirrors set at the proper angles4 ,with this he set fire to wood at a distance of more than two hundred feet by concentrating the sun's rays4 ,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 later4 ,these are examples of the early work which laid the foundation for the highly perfected control of light of the present time4 ,while engaged in the survey of ,ireland1 ,thomas ,drummond in #ahbf devised apparatus for signaling many miles1 thus facilitating triangulation4 ,distances as great as eighty miles were encountered and it appeared desirable to have some method for seeing a point at these great distances4 ,gauss in #ahbb used the reflection of the sun's image from a plane mirror and ,drummond also tried this means4 ,the latter was successful in signaling #de miles to a station which because of haze could not be seen1 or even the hill upon which it rested4 ,having demonstrated the feasibility of the plan1 he set about making a device which would include a powerful artificial light in order to be independent of the sun4 ,in earlier geodetic surveys ,argand lamps had been employed with parabolic reflectors and with convex lenses1 but apparently these did not have a sufficient range4 ,fresnel and ,arago constructed a lens consisting of a series of concentric rings which were cemented together1 and on placing this before an ,argand lamp possessing four concentric wicks1 they obtained a light which was observed at forty-eight miles4 ,despite these successes1 ,drummond believed the parabolic mirror and a more powerful light-source afforded the best combination for a signal-light4 ,in searching for a brilliant light-source he experimented with phosphorus burning in oxygen and with various brilliant pyrotechnical preparations4 ,however1 flames were unsteady and generally unsuitable4 ,he then turned in the direction which led to his development of the lime-light4 ,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 lime4 ,he thereby obtained1 according to his own description in #ahbf1 a light so intense that when placed in the focus of a reflector the eye could with difficulty support its splendor1 even at a distance of forty feet1 the contour being lost in the brilliancy of the radiation4 ,he then continued to experiment with various oxides1 including zirconia1 magnesia1 and lime from chalk and marble4 ,this was the advent of the lime-light1 which should bear ,drummond's name because it was one of the greatest steps in the evolution of artificial light4 ,by means of this apparatus in the survey1 signals were rendered visible at distances as great as one hundred miles4 ,drummond proposed the use of this light-source in the important lighthouses at that time and foresaw many other applications4 ,the lime-light eventually was extensively used as a light-signaling device4 ,the heliograph1 which utilizes the sun as a light-source1 has been widely used as a light-signaling apparatus and ,drummond perhaps was the first to utilize artificial light with it4 ,the disadvantage of the heliograph is the undependability of the sun4 ,with the adoption of artificial light1 various optical devices have come into use4 ,philip ,colomb perhaps is deserving of the credit of initiating modern signaling by flashing a code4 ,he began work on such a system in #aheh and as an officer in the ,british ,navy worked hard to introduce it4 ,finally1 in #ahfg1 the ,british ,navy adopted the flashing-system1 in which a light-source is exposed and eclipsed in such a manner as to represent dots and dashes analogous to the ,morse code4 ,at first the rate of transmission of words was from seven to ten per minute4 ,recently much more sensitive apparatus is available1 and with such devices the rate is limited only by the sluggishness of the visual process4 ,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 fog4 ,inasmuch as the dot-and-dash system requires only two elements1 it may be transmitted by various means4 ,a lantern may be swung in short and long arcs or dipped accordingly4 ,the blinker or pulsating light-signal consists of a single light-source mechanically occulted4 ,it is controlled by means of a telegraph-key and the code may be rapidly transmitted4 ,the search-light affords a means for signaling great distances1 even in the daytime4 ,the light is usually mechanically occulted by a quick-acting shutter1 but recently another system has been devised4 ,in the latter the light itself is controlled by means of an electrical shunt across the arc4 ,in this manner the light is dimmed by shunting most of the current1 thereby producing the same effect as actually eclipsing the light with a mechanical shutter4 ,by means of the search-light signals are usually visible as far as the limitations of the earth's curvature will permit4 ,by directing the beam against a cloud1 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 surface4 ,by means of small search-lights it is easy to send signals ten miles4 ,this kind of apparatus has the advantage of being selective2 that is1 the signals are not visible to persons a few degrees from the direction of the beam4 ,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 mirror4 ,the beam is directed by means of sights and the flashes are obtained by interrupting the current by means of a trigger-switch4 ,the filament is so sensitive that signals may be sent faster than the physiological process of vision will record4 ,with the advent of wireless telegraphy light-signaling for long distances was temporarily eclipsed1 but during the recent war it was revived and much development work was prosecuted4 ,the ,ardois system consists of four lamps mounted in a vertical line as high as possible4 ,each lamp is double1 containing a red and a white light1 and these lights are controlled from a keyboard4 ,a red light indicates a dot in the ,morse code and a white light indicates a dash4 ,the keys are numbered and lettered1 so that the system may be operated by any one4 ,various other systems employing colored lights have been used1 but they are necessarily short-range signals4 ,another example is the semaphore4 ,when used at night1 tungsten lamps in reflectors indicate the positions of the arms4 ,the advantage of these signals over the flashing-system is that each signal is complete and easy to follow4 ,the flashing-system is progressive and must be carefully followed in order to obtain the meaning of the dots and dashes4 ,smaller signal-lamps using acetylene have been employed in the forestry service and in other activities where a portable device is necessary4 ,in one type1 a mixture-tank containing calcium carbide and water is of sufficient capacity for three hours of signaling4 ,a small pilot-light is permitted to burn constantly and the flashes are obtained by operating a key which increases the gas-pressure4 ,the light flares as long as the key is depressed4 ,the range of this apparatus is from ten to twenty miles4 ,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 miles4 ,tests show that this device is a hundred and fifty times more powerful than the ordinary acetylene signal-lamp1 and it is thought that with this new electric lamp haze and smoke will seldom prevent observations4 ,certain fixed lights are required by law on a vessel at night4 ,when it is under way there must be a white light at the masthead1 a starboard green light1 a port red light1 a white range-light1 and a white light at the stern4 ,the masthead light is designed to emit light through a horizontal arc of twenty points of the compass1 ten on each side of dead ahead4 ,this light must be visible at a distance of five miles4 ,the port and starboard lights operate through a horizontal arc of twenty points of the compass1 the middle of which is dead ahead4 ,they are screened so as not to be visible across the bow and they must be intense enough to be visible two miles ahead4 ,the masthead light is carried on the foremast and the range-light on the mainmast1 at an elevation fifteen feet higher than the former4 ,the range-light emits light toward all points of the compass and must be intense enough to be seen at a distance of three miles4 ,the stern light is similar to the masthead1 but its light must not be visible forward of the beam4 ,when a vessel is towing another it must display two or three lights in a vertical line with the masthead light and similar to it4 ,the lights are spaced about six feet apart1 and two extra ones indicate a short tow and three a long one4 ,a vessel over a hundred and fifty feet long when at anchor is required to display a white light forward and aft1 each visible around the entire horizon4 ,these and many other specifications indicate how artificial light informs the mariner and makes for order in shipping4 ,without artificial light the waterways would be trackless and chaos would reign4 ,the distress signals of a vessel are rockets1 but any burning flame also serves if rockets are unavailable4 ,fireworks were known many centuries ago and doubtless the possibilities of signaling by means of rockets have long been recognized4 ,an early instance of scientific interest in rockets and their usefulness is that of ,benjamin ,robins in #agdi4 ,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 visible4 ,his measurements indicated that the rockets ascended usually to a height of #ddj yards1 but some of them attained altitudes as high as #fae yards4 ,he then had some special ones made and despatched letters to friends in three different localities1 at distances as great as #ej miles1 asking them to observe at a certain time1 when the rockets were to be sent up in the outskirts of ,london4 ,some of these rockets rose to altitudes as great as #fjj yards and were distinctly seen by observers #ch miles away4 ,later he made rockets which ascended as high as #abjj yards and concluded that this was a practical means of signaling4 ,since that time and especially during the recent war1 rockets have served well in signaling messages4 ,the self-propelled rockets have not been altered in essential features since the remote centuries when the ,chinese first used them in celebrations4 ,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 upward4 ,at a certain point in the air1 various signals burst forth1 which vary in character and color4 ,one of the advantages of the rocket is that it contains within itself the force of propulsion2 that is1 no gun is necessary to project it4 ,the illuminating compounds and various details are similar to those of the illuminating shells described in another chapter4 ,at present the rocket is not scientifically designed to obtain the greatest efficiency of propulsion1 but its simplicity in this respect is one of its chief advantages4 ,if the self-propelled rocket becomes the projectile of the future1 as some have ventured to predict1 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 attained4 ,there are other details in which improvements may be made4 ,the combustion products of the black powder which are not gaseous equal about one third the weight of the powder4 ,this represents inefficient propulsion4 ,furthermore1 during recent years much information has been gained pertaining to the air-resistance which can be applied to advantage in designing the form of rockets4 ,besides the various rockets1 signal-lights have been constructed to be fired from guns and pistols4 ,during the recent war the airman in the dark heights used the pistol signal-light effectively for communication4 ,these devices emitted stars either singly or in succession1 and the color of these stars as well as their number and sequence gave significance to the signal4 ,some of these light-signals were provided with parachutes and were long-burning2 that is1 light was emitted for a minute or two4 ,there are many variations possible and a great many different kinds of light-signals of this character were used4 ,in the front-line trenches and in advances they were used when telephone service was unavailable4 ,the airman directed artillery fire by means of his pistol-light4 ,rockets brought aid to the foundered ship or to the life-boats4 ,the signal-tube which burned red1 green1 or white was held in the hand or laid on the ground and it often told its story4 ,for many years such a device dropped from the rear of the railroad train has kept the following train at a safe distance4 ,a device was tried out in the trenches1 during the war1 which emitted a flame4 ,this could be varied in color to serve as a signal and the apparatus had sufficient capacity for thirty hours' burning4 ,this could also be used as a weapon1 or when reduced in intensity it served as a flash-light4 ,for many years experiments have been made upon the use of the invisible rays which accompany visible rays4 ,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 them4 ,some successful results were obtained with a #f-volt electric lamp possessing a coiled filament at the focus of a lens three inches in diameter and twelve inches in focal length4 ,this gave a very narrow beam visible only in the neighborhood of the observation post to which the signals were directed4 ,the beam was directed by telescopic sights4 ,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 daylight4 ,it is said that signals were distinguished at a distance of six miles4 ,by night a screen was used which transmitted only the ultraviolet rays1 and the observer's telescope was provided with a fluorescent screen in its focal plane4 ,the ultraviolet rays falling upon this screen were transformed into visible rays by the phenomenon of fluorescence4 ,the range of this device was about six miles4 ,for naval convoys lamps are required to radiate toward all points of the compass4 ,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 light4 ,the lamp appeared a deep violet color at close range1 but the faintly visible light which it transmitted was not seen at a distance4 ,a distant observer picks up the invisible ultraviolet light by means of a special optical device having a fluorescent screen of barium-platino-cyanide4 ,this device had a range of about four miles4 ,light-signals are essential for the operation of railways at night and they have been in use for many years4 ,in this field the significance of light-signals is based almost universally on color4 ,the setting of a switch is indicated by the color of the light that it shows4 ,with the introduction of the semaphore system1 in which during the day the position of the arm is significant1 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 arm4 ,a kerosene flame behind a glass lens was the lamp used1 and1 for example1 red meant ,stop1 green counseled ,caution1 and clear or white indicated ,all clear4 ,for many years the kerosene lamp has been used1 but recently the electric filament lamp is being installed to some extent for this purpose4 ,in fact1 on one railroad at least1 tungsten lamps are used for light-signals by day as well as by night4 ,three signals--red1 green1 and white--are placed in a vertical line and behind each lens are two lamps1 one operating at high efficiency and one at low efficiency to insure against the failure of the signal4 ,the normal daylight range is about three thousand feet and under the worst conditions when opposed to direct sunlight1 the range is not less than two thousand feet4 ,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-storm4 ,the standard colors for light-signals as adopted by the ,railway ,signal ,association are red1 yellow1 green1 blue1 purple1 and lunar white4 ,these are specified as to the amount of the various spectral colors which they transmit when the light-source is the kerosene flame4 ,obviously1 the colors generally appear different when another illuminant is used4 ,the blue and purple are short-range signals1 but the effective range of the best railway signal employing a kerosene flame is only about four miles4 ,it has been shown that the visibility of point sources of white light in clear atmosphere1 for distances up to a mile at least1 is proportional to their candle-power and inversely proportional to the square of the distance4 ,apparently the luminous intensities of signal-lamps required in clear weather in order that they may be visible must be #j4dc candles for one nautical mile1 #a4ge candles for two nautical miles1 and #aa candles for five nautical miles4 ,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 direction4 ,the range in nautical miles of a green light apparently is proportional to the cube root of the candle-power4 ,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 determined1 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 #gjjj4 ,could this light be seen at a distance of seven thousand miles through ordinary atmosphere8 ,the most distinctive colored lights are red1 yellow1 green1 and blue4 ,to these white 7clear7 and purple have been added for signaling-purposes4 ,yellow is intense1 but it may be confused with white or clear4 ,blue and purple as obtained from the present practicable light-sources are of low intensity4 ,this leaves red1 green1 and clear as the most generally satisfactory signal-lights4 ,there are numerous other applications1 especially indoors4 ,some of these have been devised for special needs1 but there are many others which are general1 such as for elevators1 telephones1 various call systems1 and traffic signals4 ,light has the advantages of being silent and controllable as to position and direction1 and of being a visible signal at night4 ,thus1 in another field artificial light has responded to the demands of civilization4 ,,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 fallen1 a result of which has brought forth the issue known as daylight saving4 ,doubtless1 daylight should be used whenever possible1 but there are two sides to the question4 ,in the first place1 it costs something to bring daylight indoors4 ,the architectural construction of windows and skylights increases the cost of daylight4 ,light-courts1 by sacrificing valuable floor-area1 add to the expense4 ,the maintenance of windows and sky lights is an appreciable item4 ,considering these and other factors1 it can be seen that daylight indoors is expensive2 and as it is also undependable1 a supplementary system of artificial lighting is generally necessary4 ,in fact1 it is easy to show in some cases that artificial lighting is cheaper than natural lighting4 ,the average middle-class home is now lighted artificially for about #ae4jj to #be4jj per year1 with convenient light-sources which are available at all times4 ,there is no item in the household budget which returns as much satisfaction1 comfort1 and happiness in proportion to its cost as artificial light4 ,it is an artistic medium of great potentiality1 and light in a narrow utilitarian sense is always a by-product of artistic lighting4 ,the insignificant cost of modern lighting may be emphasized in many ways4 ,the interest on the investment in a picture or a vase which cost #be4jj will usually cover the cost of operating any decorative lamp in the home4 ,a great proportion of the investment in personal property in a home is chargeable to an attempt to beautify the surroundings4 ,the interest on only a small portion of this investment will pay for artistic and utilitarian artificial lighting in the home4 ,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 latter4 ,it would become monotonous to cite the various examples of the insignificant cost of artificial light and its high return to the user4 ,the example of the home has been chosen because the reader may easily carry the analysis further4 ,the industries where costs are analyzed are now looking upon adequate and proper lighting as an asset which brings in profits by increasing production1 by decreasing spoilage1 and by decreasing the liability of accidents4 ,inasmuch as daylight saving became an issue during the recent war and is likely to remain a matter of concern1 its history is interesting4 ,one of the outstanding differences between primitive and civilized beings is their hours of activities4 ,the former automatically adjusted themselves to daylight1 but as civilization advanced1 the span of activities began to extend more and more beyond the coming of darkness4 ,finally in many activities the work-day was extended to twenty-four hours4 ,there can be no insurmountable objection to working at night with a proper arrangement of the periods of work2 in fact1 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 production4 ,there cannot be any basic objection to artificial lighting1 because most factories1 for example1 may be better illuminated by artificial than by natural light4 ,of course1 the lag of comfortable temperature behind daylight is responsible to some extent for a natural shifting of the ordinary working-day somewhat behind the sun4 ,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 bed4 ,there are powerful influences always at work and despite the desirable features of daylight-saving1 mankind will always tend to lag4 ,as years go by1 doubtless it will be necessary to make the shift again and again4 ,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 ahead4 ,among the earliest advocates of daylight saving during modern times1 when it became important enough to be considered as an economic issue1 was ,benjamin ,franklin4 ,in #aghd he wrote a masterful serio-comic essay entitled ,an ,economical ,project which was published in the ,journal of ,paris4 ,the article1 which appeared in the form of a letter1 began thus3 ,,messieurs3 ,you often entertain us with accounts of new discoveries4 ,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 utility4 ,i was the other evening in a grand company where the new lamp of ,messrs4 ,quinquet and ,lange was introduced and much admired for its splendor2 but a general inquiry was made whether the oil it consumed was not in exact proportion to the light it afforded1 in which case there would be no saving in the use of it4 ,no one present could satisfy us on that point1 which all agreed ought to be known1 it being a very desirable thing to lessen1 if possible1 the expense of lighting our apartments1 when every other article of family expense was so much augmented4 ,i was pleased to see this general concern for economy1 for ,i love economy exceedingly4 ,i went home1 and to bed1 three or four hours after midnight1 with my head full of the subject4 ,an accidental sudden noise waked me about #f in the morning1 when ,i was surprised to find my room filled with light1 and ,i imagined at first that a number of those lamps had been brought into it2 but1 rubbing my eyes1 ,i perceived the light came in at the windows4 ,i got up and looked out to see what might be the occasion of it1 when ,i saw the sun just rising above the horizon1 from whence he poured his rays plentifully into my chamber1 my domestic having negligently omitted the preceding evening to close the shutters4 ,i looked at my watch1 which goes very well1 and found that it was but #f o'clock2 and1 still thinking it something extraordinary that the sun should rise so early1 ,i looked into the almanac1 where ,i found it to be the hour given for his rising on that day4 ,i looked forward1 too1 and found he was to rise still earlier every day till toward the end of ,june1 and that at no time in the year he retarded his rising so long as till #h o'clock4 ,your readers who1 with me1 have never seen any signs of sunshine before noon1 and seldom regard the astronomical part of the almanac1 will be as much astonished as ,i was when they hear of his rising so early1 and especially when ,i assure them that he gives light as soon as he rises4 ,i am convinced of this4 ,i am certain of my fact4 ,one cannot be more certain of any fact4 ,i saw it with my own eyes4 ,and1 having repeated this observation the three following mornings1 ,i found always precisely the same result4 ,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 encounters4 ,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-light4 ,he then mustered the little arithmetic he was master of and made some serious computations4 ,he assumed as the basis of his computations that a hundred thousand families lived in ,paris and each used a half-pound of candles nightly4 ,he showed that between ,march #bjth and ,september #bjth1 #fd1jjj1jjj pounds of wax and tallow could be saved1 which was equivalent to #ah1jjj1jjj4 ,after these serious computations he amusingly proposed the means for enforcing the daylight saving4 ,obviously1 it was necessary to arouse the sluggards and his proposals included the use of cannons and bells4 ,besides1 he proposed that each family be restricted to one pound of candles per week1 that coaches would not be allowed to pass after sunset except those of physicians1 etc41 and that a tax be placed upon every window which had shutters4 ,his closing paragraph was as follows3 ,for the great benefit of this discovery1 thus freely communicated and bestowed by me on the public1 ,i demand neither place1 pension1 exclusive privilege1 nor any other regard whatever4 ,i expect only to have the honor of it4 ,and yet ,i know there are little1 envious minds who will1 as usual1 deny me this and say that my invention was known to the ancients1 and perhaps they may bring passages out of the old books in proof of it4 ,i will not dispute with these people that the ancients knew not the sun would rise at certain hours2 they possibly had1 as we have1 almanacs that predicted it2 but it does not follow thence that they knew he gave light as soon as he rose4 ,that is what ,i claim as my discovery4 ,if the ancients knew it1 it might have been long since forgotten2 for it certainly was unknown to the moderns1 at least to the ,parisians1 which to prove ,i need use but one plain simple argument4 ,they are as well instructed1 judicious and prudent a people as exist anywhere in the world1 all professing1 like myself1 to be lovers of economy1 and1 for the many heavy taxes required from them by the necessities of the ,state have surely an abundant reason to be economical4 ,i say it is impossible that so sensible a people1 under such circumstances1 should have lived so long by the smoky1 unwholesome and enormously expensive light of candles1 if they had really known that they might have had as much pure light of the sun for nothing4 ,franklin's amusing letter had a serious aim1 for in #aghd family expenses were much augmented and adequate lighting by means of candles was very costly in those days4 ,however1 conditions have changed enormously in the past hundred and thirty-five years4 ,a great proportion of the population lives in the darker cities4 ,the wheels of progress must be kept going continuously in order to curb the cost of living1 which is constantly mounting higher owing to the addition of conveniences and luxuries4 ,furthermore1 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 industry4 ,it is paying dividends of another kind in the social and educational aspects of the home1 library1 church1 and art museum4 ,daylight saving has much to commend it1 but the cost of daylight and the value of artificial light are important considerations4 ,the cost of fuels for lighting purposes cannot be thoroughly compared throughout a span of years without regard to the fluctuating purchasing power of money1 which would be too involved for consideration here4 ,however1 it is interesting to make a brief survey throughout the past century4 ,from #ahjj until #ahde whale-oil sold for about 4#hj per gallon1 but after this period it increased in value1 owing apparently to its growing scarcity1 until it reached a price of #a4ge per gallon in #ahee4 ,fortunately1 petroleum was discovered about this time1 so that the oil-lamp did not become a luxury4 ,from #ahjj to #ahej tallow-candles sold at approximately #bj cents a pound4 ,there being six candles to the pound1 and inasmuch as each candle burned about seven hours1 the light from a candle cost about #a_/b cent per hour4 ,from #ahej to #ahge tallow-candles sold at an average price of approximately #be cents a pound4 ,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 much4 ,a candle-hour is the total amount of light emitted by a standard candle in one hour1 and candle-hours in any case are obtained by multiplying the candle-power of the source by the hours of burning4 ,in a similar manner1 lumens output multiplied by hours of operation give the lumen-hours4 ,a standard candle may be considered to emit an amount of light approximately equal to #aj lumens4 ,a wax-candle will emit about as much light as a sperm candle but will consume about #aj per cent4 less weight of material4 ,a tallow candle will emit about the same amount of light with a consumption about #ej per cent4 greater4 ,the tallow-candle has disappeared from use4 ,with the appearance of kerosene distilled from petroleum the camphene lamp came into use4 ,the kerosene cost about #hj cents per gallon during the first few years of its introduction4 ,the price of kerosene averaged about #ee cents a gallon between #ahfe and #ahge4 ,during the next decade it dropped to about #bb cents a gallon and between #ahhe and #ahie it sold as low as #ac cents4 ,artificial gas in #ahfe sold approximately at #b4ej per thousand cubic feet2 between #ahge and #ahhe at #b4jj2 between #ahhe and #ahie at #a4ej4 ,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 householder1 for example1 a constantly increasing amount of light for the same expenditure4 ,for example1 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 price4 ,it is interesting to trace the influence of this greatly diminishing cost of light in the home4 ,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 considered4 ,in fact1 the amount of money that an average householder spends for lighting has remained fairly constant throughout the past century1 but he has enjoyed a longer period of artificial light and a greater amount of light as the years advanced4 ,the following is a table of approximate values which shows the lighting obtainable for #bj4jj per year throughout the past century exclusive of electricity3 ,hours ,equivalent of ,candle-hours ,year per night light in candles per night per year #ahjj #c #e #ae #e1ejj #ahej #c #h #bd #h1gjj #ahfj #c #aa #cc #ab1jjj #ahgj #c #bb #ff #bd1jjj #ahhj #c4e #cf #abf #df1jjj #ahij #d #ej #bjj #gc1jjj #aijj #e #aed #ggj #bhj1jjj ,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 times1 while the hours during which this light is used have nearly doubled4 ,in other words1 in the nineteenth century the candle-hours obtainable for #bj4jj per year increased about fifty times4 ,stated in another manner1 the cost of light at the end of the century was about one fiftieth that of candle light at the beginning of the century4 ,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 #agjj per cent4 in the amount of night lighting of an ,american family1 in average circumstances1 using gas for light1 there has come a reduction in the cost of the year's lighting of #cd per cent4 or approximately #g4ej per year2 and that the cost of lighting per unit of light--the candle-hour--is now but #b4h per cent4 of what it was in the first half of the nineteenth century4 ,no other necessity of household use has been so cheapened and improved during the last century4 ,in general1 the light-user has taken advantage of the decrease by increasing the amount of light used and the period during which it is used4 ,in this manner the greatly diminished cost of light has been a marked sociological and economic influence4 ,after ,murdock made his first installation of gas-lighting in an industrial plant early in the nineteenth century1 he published a comparison of the expense of operation with that of candle-lighting4 ,he arrived at the costs of light equivalent to #ajjj candle-hours as follows3 #ajjj candle-hours ,gas-lighting at a rate of two hours per day #a4ie three #a4dj ,candle-lighting #f4ej ,it is seen that the longer hours of burning reduce the cost of gas-lighting by reducing the percentage of overhead charges4 ,there are no such factors in lighting by candles because the whole installation is consumed4 ,this is an early example of which an authentic record is available4 ,at the present time a certain amount of light obtained for #a4jj with efficient tungsten filament lamps1 costs #b4jj if obtained from kerosene flames and about #ej4jj if obtained by burning candles4 ,in order to obtain the cost of an equivalent amount of light throughout the past century a great many factors must be considered4 ,obviously1 the results obtained by various persons will differ owing to the unavoidable factor of judgment2 however1 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-production4 ,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 computations4 ,the figures apply particularly to this country4 ,,table ,,showing ,,the ,,approximate ,,total ,,cost ,,of #ajjj ,,candle-,,hours ,,for ,,various ,,periods ,per #ajjj candle-hours #ahjj to #ahej1 sperm-oil #b4dj tallow candle #e4jj #ahej to #ahfe1 kerosene #a4fe tallow candle #f4he #ahfe to #ahge1 kerosene 4#ge tallow candle #f4be gas1 open-flame 4#ij #ahge to #ahhe1 kerosene 4#be gas1 open-flame 4#fj #ahhe to #ahie1 kerosene 4#ae gas1 open-flame 4#dj #ahie to #aiae1 gas mantle 4#jg carbon filament 4#ch metallized filament 4#bh tungsten filament 7vacuum7 4#ab tungsten filament 7gas-filled7 4#jg ,in these days the cost of living has claimed considerable attention and it is interesting to compare that of lighting4 ,in the following table the price of food and of electric lighting are compared for twenty years preceding the recent war4 ,the great disturbance due to the war is thereby eliminated from consideration1 but it should be noted that since #aiad the price of food has greatly increased but that of electric lighting has not changed materially4 ,the cost of each commodity is taken as one hundred units for the year #ahid but1 of course1 the actual cost of living for the householder is perhaps a hundred times greater than the cost of electric lighting4 ,year ,food ,electric lighting #ahid #ajj #ajj #ahif #hj #ib #ahih #ib #ij #aijj #ajj #he #aijb #aac #gg #aijd #aaj #gg #aijf #aae #eg #aijh #abh #cj #aiaj #ach #bh #aiab #add #bc #aiad #ade #ag ,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 rates4 ,there is no discrimination or injustice when the householder1 for example1 must pay more for his lighting than a factory pays4 ,the rates are not only affected by demand but by the period in which the demand comes4 ,residence lighting is chiefly confined to certain hours from #e to #i ,p4 ,m4 and there is a great peak of demand at this time4 ,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 day4 ,the factory which uses electricity throughout the day or night or both is helping to keep the central-station operating efficiently4 ,the equipment necessary to supply electricity to the factory is operating long hours4 ,not only is this overhead charge much less for factories and many other consumers than for the householder1 but the expense of accounting1 of reading meters1 etc41 is about the same for all classes of consumers4 ,therefore1 this is an appreciable item on the bill of the small consumer4 ,doubtless1 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 large4 ,increased production is responsible for some of this decrease and science for much of it4 ,the latter1 having been called to the aid of the manufacturers1 who are better able by virtue of their magnitude to spend time and resources upon scientific developments1 has responded with many improvements which have increased the efficiency of light-production4 ,some figures of the ,census ,bureau may be of interest4 ,these are given for #aiad in order that the abnormal conditions due to the recent war may be avoided4 ,the figures pertaining to the manufacture of gas for sale which do not include private plants are as follows for the year #aiad for this country3 ,number of establishments #a1bhd ,capital #a1beb1dba1ehd ,value of products 7gas1 coke1 tar1 etc47 #bbj1bcg1gij ,cost of materials #gf1ggi1bhh ,value added by manufacture #adc1deh1ejb ,value of gas #age1jfe1ibj ,coal used 7tons7 #f1aaf1fgb ,coke used 7tons7 #ifd1hea ,oil used 7gallons7 #gae1dah1fbc ,length of gas mains 7miles7 #eh1gbg ,manufactured products sold ,total gas 7cubic feet7 #bjc1fci1bfj1jjj ,straight coal gas 7cubic feet7 #aj1eji1idf1jjj ,carbureted water gas 7cubic feet7 #ij1jag1gbe1jjj ,mixed coal- and water-gas 7cubic feet7 #hf1bha1cci1jjj ,oil gas 7cubic feet7 #af1eab1bgd1jjj ,acetylene 7cubic feet7 #acf1efd1jjj ,other gas1 chiefly gasolene 7cubic feet7 #aha1dab1jjj ,coke 7bushels7 #aad1jia1gec ,tar 7gallons7 #abe1ich1fjg ,ammonia liquors 7gallons7 #ej1gcg1gfb ,ammonia1 sulphate 7pounds7 #f1baf1fah ,of course1 only a small fraction of the total gas manufactured is used for lighting4 ,according to the ,u4 ,s4 ,geological ,survey1 the quantities of gas sold in this country in the year #aiag were as follows3 ,coal-gas #db1ibg1gbh1jjj cubic feet ,water-gas #aec1deg1cah1jjj ,oil-gas #ad1gci1ejh1jjj ,byproduct gas #aca1jbf1ege1jjj ,natural gas #gie1aaj1cgf1jjj ,in #aiad there were #ch1gje1dif barrels 7each fifty gallons7 of illuminating oils refined in this country and the value was #if1hjf1deb4 ,about half of this quantity was exported4 ,in #aiad the value of all candles manufactured in this country was about #b1jjj1jjj1 which was about half that of the candles manufactured in #aiji and in #aijd4 ,in #aiad the value of the matches manufactured in this country was #ab1eef1jjj4 ,this has increased steadily from #dbi1jjj in #ahdi4 ,in #aiad the glass industries in this country made #g1jjj1jjj lamps1 #gj1jjj1jjj chimneys1 #af1cjj1jjj lantern globes1 #bd1jjj1jjj shades1 globes1 and other gas goods4 ,many millions of other lighting accessories were made1 but unfortunately they are not classified4 ,some figures pertaining to public electric light and power stations of the ,united ,states for the years #aijg and #aiag are as follows3 #aiag #aijg ,number of establishments #f1eda #d1gad ,commercial #d1bbd #c1dfb ,municipal #b1cag #a1efb ,income #ebf1hhf1djh #age1fdb1cch ,total horse-power of plants #ab1heg1iih #d1jih1ahh ,steam engines #h1chi1chi #b1fic1bgc ,internal combustion engines #bag1ahf #ee1hbh ,water-wheels #d1bea1dbc #a1cdi1jhg ,kilowatt capacity of generators #i1jja1hgb #b1gji1bbe ,output in millions of kilowatt-hours #be1dch #e1hfc ,motors served 7horse-power7 #i1baf1cbc #a1fdi1jbf ,electric-arc street-lamps served #bef1hch 4444 ,electric-filament street-lamps served #a1chi1chb 4444 ,in general1 there is a large increase in the various items during the decade represented4 ,the output of the central stations doubled in the five years from #aijg to #aiab1 and doubled again in the next five years from #aiab to #aiag4 ,street lamps were not reported in #aijg1 but in #aiab there were #cdh1fdc arc-lamps served by the public companies4 ,the number of arc-lamps decreased to #bef1hch in #aiag4 ,on the other hand1 there were #fha1ieg electric filament street lamps served in #aiab1 which doubled in number to #a1chi1chb in #aiag4 ,the cost of construction and equipment of these central stations totaled more than #c1jjj1jjj1jjj in #aiag4 ,although there is no immediate prospect of the failure of the coal and oil supplies1 exhaustion is surely approaching4 ,and as the supplies of fuel for the production of gas and electricity diminish1 the cost of lighting may advance4 ,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 #e1jjj1jjj1jjj and #bj1jjj1jjj1jjj barrels1 the best estimate being about #g1jjj1jjj1jjj4 ,the annual consumption is now about #djj1jjj1jjj barrels4 ,these figures do not take into account the oil which may be distilled from the rich shale deposits4 ,apparently this source will yield a hundred billion barrels of oil4 ,in a similar manner the coal-supply is diminishing and the consumption is increasing4 ,in #aiah more than a half-billion tons of coal were shipped from the mines4 ,the production of natural gas perhaps has reached its peak1 and1 owing to its relation to the coal and oil deposits1 its supply is limited4 ,although only a fraction of the total production of gas1 oil1 and coal is used in lighting1 the limited supply of these products emphasizes the desirability of developing the enormous water-power resources of this country4 ,the present generation will not be hard pressed by the diminution of the supply of gas1 oil1 and coal1 but it can profit by encouraging and even demanding the development of water-power4 ,furthermore1 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 possible4 ,science will continue to produce more efficient light-sources1 but the cost of light finally is dependent upon the cost of the energy supplied to these lamps4 ,at the present time water-power is the anchor to the windward4 ,,xvii ,,light ,,and ,,safety ,it is established that outdoors life and property are at night safer under adequate lighting than they are under inadequate lighting4 ,police departments in the large cities will testify that street-lighting is a powerful ally and that crime is fostered by darkness4 ,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 towns8 ,owing to the necessity of darkening the streets in order to reduce the hazards of air-raids1 ,london experienced a great increase in accidents on the streets1 which demonstrated the practical value of street-lighting from the standpoint of accident prevention4 ,during the war1 when dastardly traitors and agents of the enemy were striking at industry1 the value of lighting was further recognized by the industries1 with the result that flood-lighting was installed to protect them4 ,by common consent this new phase was termed protective lighting4 ,soon after the entrance of this country into the recent war1 the ,u4 ,s4 ,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 materials4 ,protective lighting was early recognized by this section as a very potential agency for defense1 and extensive use was made of it4 ,for example1 ,edmund ,leigh1 chief of the section1 in discussing the value of outdoor lighting stated3 ,an illustration of our work in this connection is the case of an #hj1jjj1jjj powder plant of recent construction4 ,we arranged to have all wires buried4 ,in addition to the ordinary lighting on an adjacent hill there is a large searchlight which will command any part of the buildings and grounds4 ,every three hundred yards there is a watch-tower with a searchlight on top4 ,these searchlights are for use only in emergency4 ,each tower has a telephone service1 one connected with the other4 ,the men in the towers have a view of the building exteriors1 which are all well lighted1 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 between4 ,the most vital parts of the buildings are surrounded by three fences4 ,in the near-by woods the underbrush has been cleared out and destroyed4 ,the trunks and limbs of trees have been whitewashed4 ,no one can walk among these trees or between the trees and the plant without being seen in silhouette4444 ,i say flatly that ,i know nothing that is so potential for good defense as good illumination and at the same time so little understood4 ,without such protective lighting an army of men would have been required to insure the safety of this one vital plant2 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 destruction4 ,the ,united ,states participated for nineteen months in the recent war and during that time about #djj1jjj casualties were suffered by its forces4 ,this was at the rate of about #bej1jjj per year1 which included casualties in battle1 at sea1 and from sickness1 wounds1 and accidents4 ,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 months4 ,however1 ,r4 ,e4 ,simpson of the ,travelers ,insurance ,company has stated that3 ,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 casualties4 ,this is a startling comparison1 which emphasizes a phase of lighting that has long been recognized by experts but has been generally ignored by the industries and by the public4 ,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 places4 ,accident prevention is an important phase of modern life which must receive more attention4 ,from published statistics and conservative estimates it has been concluded that there are approximately #be1jjj persons killed or permanently disabled1 #ejj1jjj seriously injured1 and #a1jjj1jjj slightly injured each year in this country4 ,translating these figures by means of the accident severity rates1 ,mr4 ,simpson has found that there is a total of #ahj1jjj1jjj days of time lost per year4 ,this is equivalent to the loss of services of #fjj1jjj men for a full year of #cjj work-days4 ,this loss is distributed over the entire country and consequently its magnitude is not demonstrated excepting by statistics4 ,of course1 the causes of the accidents are numerous1 but1 among the means of prevention1 proper lighting is important4 ,according to some authorities at least #ah per cent4 of these accidents are due to defects in lighting4 ,on this basis the services of #ajh1jjj 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 workers4 ,if the full year's labor of #ajh1jjj men could be applied to the mining of coal1 #acj1jjj1jjj million tons of coal would be added to the yearly output2 and only #aj1jjj tons would be necessary to supply adequate lighting for this army of men working for a full year for ten hours each day4 ,statistics obtained under the ,british workmen's compensation system show that #be per cent4 of the accidents were caused by inadequate lighting of industrial plants4 ,much has been said and actually done regarding the saving of fuel by curtailing lighting1 but the saving may easily be converted into a great loss4 ,for example1 a #be-watt electric lamp may be operated ten hours a day for a whole year at the expense of one eighth of a ton of coal4 ,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 worker4 ,if this one day's time could have produced coal1 there would have been enough coal mined in the ten hours to operate the lamp for thirty-two years4 ,the insignificant cost of lighting is also shown by the distribution of the consumption of fuel for heating1 cooking1 and lighting in the home4 ,of the total amount of fuel consumed in the home for these purposes1 #hg per cent4 is for heating1 #aa per cent4 for cooking and #b per cent4 for lighting4 ,the amount of coal used for lighting purposes in general is about #b4e per cent4 of the total consumption of coal1 so it is seen that the curtailment of lighting at best cannot save much fuel2 and it may actually result in a great economic loss4 ,by replacing inefficient lamps and accessories with efficient lighting-equipment and by washing windows and artificial lighting devices1 a real saving can be realized4 ,improper lighting may be as productive of accidents as inadequate lighting1 and throughout the industries and upon the streets the misuse of light is in evidence4 ,the blinding effect of a brilliant light-source is easily proved by looking at the sun4 ,after a few moments great discomfort is experienced1 and on looking away from this brilliant source the eyes are temporarily blinded by the after-images4 ,when this happens in a factory as the result of gazing into an unshielded light-source1 the workman may be injured by moving machinery1 by stumbling over objects1 and in many other ways4 ,unshaded light-sources are too prevalent in the industries4 ,improper lighting is likely to cause deep shadows wherein many dangers may be hidden4 ,on the street the glare from automobile head-lamps is very prevalent and nearly everybody may testify from experience to the dangers of glare4 ,even the glaring locomotive head-lamp has been responsible for many casualties4 ,unfortunately1 natural lighting outdoors has not been under the control of man and he has accepted it as it is4 ,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 it4 ,it is so intensely glaring that man unconsciously avoids looking directly at it4 ,these conditions are responsible to an extent for man's indifference and even ignorance of the rudiments of safe lighting4 ,when he has artificial light1 over which he may exercise control1 he either ignores it or owing to the less striking glare he misuses it and his eyesight without realizing it4 ,a great deal of eye-strain and permanent eye trouble arises from the abuse of the eyes by improper lighting4 ,for example1 near-sightedness is often due to inadequate illumination1 which makes it necessary for the eyes to be near the work or the reading-page4 ,improper or inadequate lighting especially influences eyes that are immature in growth and in function1 and it has been shown that with improvements in lighting the percentage of short-sightedness has decreased in the schools4 ,furthermore1 it has been shown that where no particular attention has been given to lighting and vision1 the percentage of short-sightedness has increased with the grade4 ,there are twenty million school children in this country whose future eyesight is in the hands of those who have jurisdiction over lighting and vision4 ,there are more than a hundred million persons in this country whose eyes are daily subjected to improper lighting-conditions1 either through their own indifference or through the negligence of others4 ,of a certain group of #ia1jjj purely industrial accidents in the year #aiaj1 ,mr4 ,simpson has stated that #bc4h per cent4 were due1 directly or indirectly1 to the lack of proper illumination4 ,these may be further divided into two approximately equal groups1 one of which comprises the accidents due to inadequate illumination and the other to those toward which improper lighting was a contributing cause4 ,the seasonal variation of these accidents is given in the following table1 both for those due directly or indirectly to inadequate and improper lighting and those due to other causes4 ,,seasonal ,,distribution ,,of ,,industrial ,,accidents ,,due ,,to ,,lighting ,,conditions ,,and ,,to ,,other ,,causes ,percentage due to ,lighting conditions ,other causes ,july #d4h #e4i ,august #e4b #f4b ,september #f4a #f4i ,october #h4f #h4e ,november #aj4i #aj4e ,december #ae4f #ab4b ,january #af4a #aa4i ,february #aj4j #aj4e ,march #g4f #h4h ,april #f4a #f4i ,may #e4b #e4h ,june #c4h #e4i ,the figures in one column have no direct relation to those in the other2 that is1 each column must be considered by itself4 ,it is seen from the foregoing that about half the number of the accidents due to poor illumination occurred in the months of ,november1 ,december1 ,january1 and ,february4 ,these are the months of inadequate illumination unless artificial lighting has been given special attention4 ,the same general type of seasonal distribution of accidents due to other causes is seen to exist but not so prominently4 ,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 conditions4 ,this ratio reduces to about twice in the case of accidents due to other causes4 ,looking at the data from another angle1 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 months4 ,doubtless1 this may be explained largely upon the basis of morale4 ,the winter months are more dreary than those of summer and the workman's general outlook is different in winter than in summer4 ,in the former season he goes back and forth to work in the dark1 or at best1 in the cold twilight4 ,he is not only more depressed but he is clumsier in his heavier clothing4 ,if the enervating influence of these factors is combined with a greater clumsiness due to cold and perhaps to colds1 it is not difficult to account for this type of seasonal distribution of accidents4 ,a study of the accidents of #aiag indicated that #ac per cent4 occurred between #e and #f ,p4 ,m4 when artificial lighting is generally in use to help out the failing daylight4 ,only #g4c per cent4 occurred between #ab ,m4 and #a ,p4 ,m4 ,illustration3 ,,signal-,,light ,,for ,,airplane ,illustration3 ,,trench ,,light-,,signaling ,,outfit ,illustration3 ,,aviation ,,field ,,light-,,signal ,,projector ,illustration3 ,,signal ,,search-,,light ,,for ,,airplane ,illustration3 ,,unsafe1 ,,unproductive ,,lighting ,,worthy ,,of ,,the ,,dark ,,ages ,illustration3 ,,the ,,same ,,factory ,,made ,,safe1 ,,cheerful1 ,,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 lighting4 ,as each innovation in lighting appeared during the past century there immediately arose the question of safety4 ,the fire-hazard of open flames received attention in early days1 and when gas-lighting appeared it was condemned as a poison and an explosive4 ,mineral-oil lamps introduced the danger of explosions of the vapors produced by evaporation4 ,when electric lighting appeared it was investigated thoroughly4 ,the result of all this has been an effort to make lamps and methods safe4 ,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 taken4 ,when electric lighting was first introduced the public looked upon electricity as dangerous and naturally many questions pertaining to hazards arose4 ,the distribution of electricity has been so highly perfected that little is heard of the hazards which were so magnified in the early years4 ,data gathered between #ahhd and #ahhi showed that about #ac1jjj fires took place in a certain district4 ,of these1 #db were attributed to electric wires2 #bb times as many to breakage and explosion of kerosene lamps2 and ten times as many through carelessness with matches4 ,these figures cannot be taken at their face value because of the absence of data showing the relative amount of electric and kerosene lighting2 nevertheless they are interesting because they represent the early period4 ,there are industries where unusual care must be exercised in regard to the lighting4 ,in certain chemical industries no lamps are used excepting the incandescent lamp and this is enclosed in an air-tight glass globe4 ,even a public-service gas company cautions its employees and patrons thus3 ,do not look for a gas-leak with a naked light6 ,use electric light4 ,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 general1 with the additional difficulties attending the presence or possible presence of explosive gas4 ,the surroundings in a coal-mine reflect a small percentage of the light1 so that much light is wasted unless the walls are whitewashed4 ,this is a practical method for increasing safety in coal-mines4 ,however1 the most dangerous feature is the light-source itself4 ,according to the ,bureau of ,mines during the years #aiaf and #aiag about #fj per cent4 of the fatalities due to gas and coal-dust explosions were directly traceable to the use of defective safety lamps and to open flames4 ,in the early days of coal-mining it was found that the flame of a candle occasionally caused explosions in the mines4 ,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-source4 ,of course1 statistics are unavailable concerning the casualties in coal-mines throughout the past centuries1 but with the accidents not uncommon in this scientific age1 with its elaborate organizations striving to stamp out such casualties1 there is good reason to believe that previous to a century or two ago the risks of coal-mining must have been great4 ,open flames have been widely used in this industry1 but there has always been the risk of the presence or the appearance of gas or explosive dust4 ,the early open-flame lamps not only were sources of danger but their feeble varying intensity caused serious damage to the eyesight of miners4 ,this factor is always present in inadequate and improper lighting1 but its influence is noticeable in coal-mining in the nervous disease affecting the eyes which is known as nystagmus4 ,the symptoms of the disease are inability to see at night and the dazzling effect of ordinary lamps4 ,finally objects appear to the sufferer to dance about and his vision is generally very much disturbed4 ,the oil-lamps used in coal-mining have a luminous intensity equivalent to about one to four candles1 but owing to the atmospheric conditions in the mines a flame does not burn as brightly as in the fresh air4 ,the possibility of explosion due to the open flame was eliminated by surrounding it with a metal gauze4 ,davy was the inventor of this device and his safety lamp introduced about a hundred years ago has been a boon to the coal-miner4 ,various improvements have been devised1 but ,davy's lamp contained the essentials of a safety device4 ,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 explode4 ,this device not only keeps the flame from igniting the gas but it also serves as an indicator of the amount of gas present1 by the variation in the size and appearance of the tip of the flame4 ,however1 the gauze reduces the luminous output1 and as it accumulates soot and dust the light is greatly diminished4 ,one of these lamps is about as luminous as a candle1 initially1 but its intensity is often reduced by accumulations upon the gauze to only one fifth of the initial value4 ,the acetylene lamp is the best open-flame light-source available to the miner1 for several reasons4 ,it is of a higher candle-power than the others and as it is a burning gas1 there is not the danger of flying sparks as in the case of burning wicks4 ,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 him4 ,however1 this lamp may be a source of danger1 owing to the fact that it will burn more brilliantly in a vitiated atmosphere than other flame-lamps4 ,another disadvantage is the possibility of calcium carbide accidentally spilt coming in contact with water and thereby causing the generation of acetylene gas4 ,if this is produced in the mine in sufficient quantities it is a danger which may not be suspected4 ,if ignited it will explode and may also cause severe burns4 ,the electric lamp1 being an enclosed light-source capable of being subdivided and fed by a small portable battery1 early gave promise of solving the problem of a safe mine-lamp of adequate candle-power4 ,much ingenuity has been applied to the development of a portable electric safety mine-lamp1 and several such lamps are now approved by the ,bureau of ,mines4 ,two general types are being manufactured1 the cap outfit and the hand outfit4 ,they consist essentially of a lamp in a reflector whose aperture is closed with a sheet or a lens of clear glass4 ,the battery may be of the dry or storage type and in the case of the cap outfit the battery is carried on the back4 ,the specifications for these lamps demand that a luminous intensity averaging at least #j4d candle be maintained throughout twelve consecutive hours of operation4 ,at no time during this period shall the output of light fall below #a4be lumens for a cap-lamp and below #c lumens for a hand-lamp4 ,inasmuch as these are equipped with reflectors1 the specifications insist that a circle of light at least seven feet in diameter shall be cast on a wall twenty inches away4 ,it appears that a portable lamp is an economic necessity in the coal-mines1 on account of the expense1 inconvenience1 and possible dangers introduced by distribution systems such as are used in most places4 ,although the major defects in lighting are due to absence of light in dangerous places1 to glare1 and to other factors of improper lighting1 there are many minor details which may contribute to safety4 ,for example1 low lamps are useful in making steps in theaters and in other places1 in drawing attention to entrances of elevators1 in lighting the aisles of ,pullman cars1 under hand-rails on stairways1 and in many other vital places4 ,a study of accidents indicates that simple expedients are effective preventives4 ,,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 living4 ,to-day mankind enjoys conveniences and luxuries that were undreamed of by the past generations4 ,for example1 a certain town in ,iowa1 a score of years ago1 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 underwriters4 ,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-day4 ,there are economists who would argue that the automobile has paid for itself by its usefulness1 but the fact still exists that a great amount of labor has been diverted from producing food1 clothing1 and fuel to the production of pleasure automobiles4 ,and this is the case with many other conveniences and luxuries4 ,it is admitted that mankind deserves these refinements of modern civilization1 but he must expect the cost of living to increase unless counteracting measures are taken4 ,the economics of the increasing cost of living and the analysis of the relations of necessities1 conveniences1 and luxuries are too complex to be thoroughly discussed here4 ,in fact1 the most expert economists would disagree on many points4 ,however1 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 increase4 ,increased production is an anchor to the windward4 ,it may drag and give way to some extent1 but it will always oppose the course of the cost of living4 ,when the first industrial plant was lighted by gas1 early in the nineteenth century1 the aim was merely to reinforce daylight toward the end of the day4 ,continuous operation of industrial plants was not practised in those days1 excepting in a very few cases where it was essential4 ,to-day some industries operate continuously1 but most of them do not4 ,in the latter case the consumer pays more for the product because the percentage of fixed or overhead charge is greater4 ,investment in ground1 buildings1 and equipment exacts its toll continuously and it is obvious that three successive shifts producing three times as much as a single day shift1 or as much as a trebled day shift1 will produce the less costly product4 ,in the former case the fixed charge is distributed over the production of continuous operation1 but in the latter case the production of a single day shift assumes the entire burden4 ,of course1 there are many factors which enter into such a consideration and an important one is the desirability of working at night4 ,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 production4 ,in the first place1 it has been proved that in factories proper lighting as obtained by artificial means is generally more satisfactory than the natural lighting4 ,of course1 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 light1 but these buildings are the exception and they will grow rarer as industrial districts become more congested4 ,artificial light may be controlled so that light of a satisfactory quality is properly directed and diffused4 ,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 light4 ,with increasing cost of ground space1 factories are built of several stories and with less space given to light courts1 with the result that the ratio of window area to that of the floor is reduced4 ,these tendencies militate against satisfactory daylighting4 ,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 daylight4 ,it has been proved that proper artificial lighting--and there is no excuse for improper artificial lighting--is superior to most interior daylighting conditions4 ,illustration3 ,,locomotive ,,electric ,,headlight ,illustration3 ,,search-,,light ,,on ,a ,,fire-,,boat ,illustration3 ,,building ,,ships ,,under ,,artificial ,,light ,,at ,,hog ,,island ,,shipyard ,although it is difficult to present figures in a brief discussion of this character1 it may be stated that1 in general1 the cost of adequate artificial light is about #b per cent4 of the pay-roll of the workers2 about #aj per cent4 of the rental charges2 and only a fraction of #a per cent4 of the cost of the manufactured products4 ,these figures vary considerably1 but they represent conservative average estimates4 ,from these it is seen that artificial lighting is a small factor in adding to the cost of the product4 ,but does artificial lighting add to the cost of a product8 ,many examples could be cited to prove that proper artificial lighting may be responsible for an actual reduction in the cost of the product4 ,in a certain plant it was determined that the workmen each lost an appreciable part of an hour per day because of inadequate lighting4 ,a properly designed and maintained lighting-system was installed and the saving in the wages previously lost1 more than covered the operating-expense of the artificial lighting4 ,besides really costing the manufacturer less than nothing1 the new artificial lighting system was responsible for better products1 decreased spoilage1 minimized accidents1 and generally elevated spirits of the workmen4 ,in some cases it is only necessary to save one minute per hour per workman to offset entirely the cost of lighting4 ,the foregoing and many other examples illustrate the insignificance of the cost of lighting4 ,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 respectively4 ,in a well-lighted factory which operated day and night shifts1 the cost of adequate lighting was #g cents per square foot per year4 ,if this factory1 operating only in the daytime1 were to maintain the same output1 it would be necessary to double its size4 ,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 equipment4 ,a fair rental value for plant and equipment is #ej cents per square foot per year2 but of course this varies considerably1 depending upon the type of plant and the character of the equipment4 ,an investigation showed that this value varies usually between #cj to #gj cents per square foot per year4 ,using the mean value1 #ej cents1 it is seen that the rental charge is about seven times the cost of lighting4 ,furthermore1 there is a saving of #dc cents per square foot per year during the night operation by operating the night shift4 ,of course1 this is not strictly true because a depreciation of machinery during the night shift should be allowed for4 ,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 shift4 ,incidentally1 the two-shift factory need not be a hardship for the workers1 for1 if the eight-hour shifts are properly arranged1 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 eliminated4 ,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 lighting4 ,about one fourth of the total number of accidents may be charged to defective lighting4 ,the consumer bears the burden of the support of an unproducing army of idle men4 ,according to some experts an average of about #aej1jjj men are continuously idle in this country owing to inadequate and improper lighting4 ,this is an appreciable factor in the cost of living1 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 lighting4 ,the standard of artificial-lighting intensity possessed by the average person at the present time is an inheritance from the past4 ,in those days when artificial light was much more costly than at present the tendency naturally was to use just as little light as necessary4 ,that attitude could not have been severely criticized in those early days of artificial lighting1 but it is inexcusable to-day4 ,eyesight and greater safety from accidents are in themselves valuable enough to warrant adequate lighting1 but besides these there is the appeal of increased production4 ,outdoors on a clear summer day at noon the intensity of daylight illumination at the earth's surface is about #aj1jjj foot-candles2 in other words1 it is equal to the illumination on a surface produced by a light-source equivalent to #aj1jjj candles at a distance of one foot from the surface4 ,this will be recognized as an enormous intensity of illumination4 ,on a cloudy day the intensity of illumination at the earth's surface may be as high as #cjjj foot-candles and on a gloomy day the illumination at the earth's surface may be #ajjj foot-candles4 ,when it is considered that mankind works under artificial light with an intensity of only a few foot-candles1 the marvels of the visual apparatus are apparent4 ,but it should be noted that the eyes of the human race evolved under natural light4 ,they have been used to great intensities when called upon for their greatest efforts4 ,the human being is wonderfully adaptive1 but it could scarcely be hoped that the eyes could readjust themselves in a few generations to the changed conditions of low-intensity artificial lighting4 ,there is no complaint against the range of intensities to which the eye responds1 for in range of sensibility it is superior to any man-made device4 ,for extremely low brightnesses another set of physiological processes come into play4 ,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 past4 ,with this principle of vision as a foundation1 experiments have been made with greater intensities of illumination in the industries and elsewhere and increased production has been the result4 ,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 #d to #ab foot-candles increased the production in various operations4 ,the lowest increase in production was #h per cent41 the highest was #bg per cent41 and the average was #ae per cent4 ,the original lighting in this case was better than that of the typical industrial conditions1 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 illumination4 ,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 used4 ,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 #cj per cent4 for the least increase to #ajj per cent4 for the greatest increase4 ,inasmuch as the energy consumption in the latter case was increased seven times and the illumination twenty-five times1 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-system4 ,in another case a #aj per cent4 increase in production was obtained by increasing the intensity of illumination from #c foot-candles to about #ab foot-candles4 ,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 #a4b per cent4 of the pay-roll4 ,in another test an increase of #aj per cent4 in production was obtained at an increase in cost equal to less than #a per cent4 of the payroll4 ,the efficiency of well-designed lighting installations is illustrated in this case1 for the illumination intensity was increased six times by doubling the consumption of electrical energy4 ,various other tests could be cited1 but these would merely emphasize the same results4 ,however1 it may be stated that the factory superintendents involved are convinced that adequate and proper artificial lighting is a great factor in increasing production4 ,mr4 ,w4 ,a4 ,durgin1 who conducted the tests1 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 #ae per cent4 increase in production at an increased cost of not more than #e per cent4 of the pay-roll4 ,this is apparently a conservative statement4 ,when it is considered that generally the cost of lighting is only a fraction of #a per cent4 of the cost of products to the consumer1 it is seen that the additional cost of obtaining an increase of #ae per cent4 in production is inappreciable4 ,industrial superintendents are just beginning to see the advantage of adequate artificial lighting1 but the low standards of lighting which were inaugurated when artificial light was much more costly than it is to-day persist tenaciously4 ,when high intensities of proper illumination are once tried1 they invariably prove successful in the industries4 ,not only does the worker see all his operations better1 but there appears to be an enlivening effect upon individuals under the higher intensities of illumination4 ,mankind chooses a dimly lighted room in which to rest and to dream4 ,a room intensely lighted by means of well-designed units which are not glaring is comfortable but not conducive to quiet contemplation4 ,it is a place in which to be active4 ,this is perhaps one of the factors which makes for increased production under adequate lighting4 ,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 time4 ,if high-intensity artificial lighting was installed in all the industries and a #ae per cent4 increase in production resulted1 as tests appear to indicate1 the increased production would be equal to that of nearly two million workers4 ,this great increase in output is brought about by lighting at an insignificant increase in cost but without the additional consumption of food or clothing4 ,besides this increase in production there is the decrease in spoilage4 ,the saving possible in this respect through adequate lighting has been estimated for the industries of this country at #ajj1jjj1jjj4 ,if mankind is to have conveniences and luxuries1 efficiency in production must be practised to the utmost and in the foregoing a proved means has been discussed4 ,there are many other ways in which artificial light may serve in increasing production4 ,man has found that eight hours of sleep is sufficient to keep him fit for work if he has a sufficient amount of recreation4 ,before the advent of artificial light the activities of the primitive savage were halted by darkness4 ,this may have been ,nature's intention1 but civilized man has adapted himself to the changed conditions brought about by efficient and adequate artificial light4 ,there appears to be no fundamental reason for not imposing an artificial day upon plants1 animals1 chemical processes1 etc42 and1 in fact1 experiments are being prosecuted in these directions4 ,the hen1 when permitted to follow her natural course1 rises with the sun and goes to roost at sunset4 ,during the winter months she puts in short days off the roost4 ,it has been shown that an artificial day1 made by piecing out daylight by means of artificial light1 might keep the hen scratching and feeding longer1 with an increased production of eggs as a result4 ,many experiments of this character have been carried out1 and there appears to be a general conclusion that the use of artificial light for this purpose is profitable4 ,experiments conducted recently by the agricultural department of a large university indicate that in poultry husbandry1 when artificial light is applied to the right kind of stock with correct methods of feeding1 the distribution of egg-production throughout the whole year can be radically changed4 ,the supply of eggs may be increased in autumn and winter and decreased in spring and summer4 ,data on the amount of illumination have not been published1 but it is said that the most satisfactory results have been obtained when the artificial illumination is used from sunset until about #i ,p4 ,m4 throughout the year4 ,an increase of #cj to #dj per cent4 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 #aiac4 ,on this farm there were nearly #bjj yards of hen-houses containing about #fjjj hens1 and the runs were lighted on dark mornings and early nights of the year preceding the report4 ,about #cjj small lamps varying from #h to #cb candle-power were used in the houses4 ,it was found that an imitation of sunset was necessary by switching off the #cb candle-power lamps at #f ,p4 ,m4 and the #af candle-power lamps at #i3cj4 ,this left only the #h candle-power lamps burning1 and in the faint illumination the hens sought the roosting-places4 ,at #aj ,p4 ,m4 the remaining lights were extinguished4 ,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 parasites4 ,the increase in production of eggs is brought about merely by keeping the fowls awake longer4 ,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 longer4 ,many fishermen will testify that artificial light seems to attract fish1 and various reports have been circulated regarding the efficacy of using artificial light for this purpose on a commercial scale4 ,one report which bears the earmarks of authenticity is from ,italy1 where it is said that electric lights were successfully used as bait to augment the supply of fish during the war4 ,the lamps were submerged to a considerable depth and the fish were attracted in such large numbers that the use of artificial light was profitable4 ,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 war4 ,an interesting incident pertaining to fish1 but perhaps not an important factor in production1 is the use of electric lights in the summer over the reservoirs of a fish hatchery4 ,these lights1 which hang low1 attract myriads of bugs1 many of which fall in the water and furnish natural and inexpensive food for the fish4 ,many experiments have been carried out in the forcing of plants by means of artificial light4 ,some of these were conducted forty years ago1 when artificial light was more costly than at the present time4 ,of course1 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 plants4 ,in greenhouses the forcing of plants is desirable1 owing to the restricted area for cultivation4 ,it has been established that some of the ultra-violet rays which are absorbed or not transmitted by glass are harmful to growing plants4 ,for this reason an arc-lamp designed for forcing purposes should be equipped with a glass globe4 ,f4 ,w4 ,rane reported in #ahid upon some experiments with electric carbon-filament lamps in greenhouses in which satisfactory results were obtained by using the artificial light several hours each night4 ,prof4 ,l4 ,h4 ,bailey also conducted experiments with the arc-lamp and concluded that there were beneficial results if the light was filtered through clear glass4 ,without considering the details of the experiment1 we find some of ,rane's conclusions of interest1 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 time4 ,some of his conclusions were as follows3 ,the incandescent electric light has a marked effect upon greenhouse plants4 ,the light appears to be beneficial to some plants grown for foliage1 such as lettuce4 ,the lettuce was earlier1 weighed more and stood more erect4 ,flowering plants blossomed earlier and continued to bloom longer under the light4 ,the light influences some plants1 such as spinach and endive1 to quickly run to seed1 which is objectionable in forcing these plants for sale4 ,the stronger the candle-power the more marked the results1 other conditions being the same4 ,most plants tended toward a taller growth under the light4 ,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 plants2 and at present prices 7#ahid7 it is a question if it will pay to employ it even for these4 ,there are many points about the incandescent electric light that appear to make it preferable to the arc light for greenhouse use4 ,although we have not yet thoroughly established the economy and practicability of the electric light upon plant growth1 still ,i am convinced that there is a future in it4 ,these are encouraging conclusions1 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 time4 ,in an experiment conducted in ,england in #aiac mercury glass-tube arcs were used in one part of a hothouse and the other part was reserved for a control test4 ,the same kind of seeds were planted in the two parts of the hothouse and all conditions were maintained the same1 excepting that a mercury-vapor lamp was operated a few hours in the evening in one of them4 ,miss ,dudgeon1 who conducted the test1 was enthusiastic over the results obtained4 ,ordinary vegetable seeds and grains germinated in eight to thirteen days in the hothouse in which the artificial light was used to lengthen the day4 ,in the other1 germination took place in from twelve to fifty-seven days4 ,in all cases at least several days were saved in germination and in some cases several weeks4 ,flowers also increased in foliage1 and a #be per cent4 increase in the crop of strawberries was noted4 ,seedlings produced under the forcing by artificial light needed virtually no hardening before being planted in the open4 ,professor ,priestley of ,bristol ,university said of this work3 ,the light seems to have been extraordinarily efficacious1 producing accelerated germination1 increased growth1 greater depth of color1 and more important still1 no signs of lanky1 unnatural extension of plant usually associated with forcing4 ,rather the plants exposed to the radiation seem to have grown if anything more sturdy than the control plants4 ,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 plants4 ,unfortunately there is much confusion amid the results of experiments pertaining to the effects of different rays1 including ultra-violet1 visible and infra-red1 upon plant growth4 ,if this aspect was thoroughly established1 investigations could be outlined to greater advantage and efficient light-sources could be chosen with certainty4 ,there is the discouraging feature that the average intensity of daylight illumination from sunrise to sunset in the summer-time is several thousand foot-candles4 ,the cost of obtaining this great intensity by means of artificial light would be prohibitive4 ,however1 the daylight illumination in a greenhouse in winter is very much less than the intensity outdoors in summer4 ,indeed1 this intensity perhaps averages only a few hundred foot-candles in winter4 ,there is encouragement in this fact and there is hope that a little light is relatively much more effective than a great amount4 ,expressed in another manner1 it is possible that a little light is much more effective than no light at all4 ,experiments with artificial light indicate very generally an increased growth4 ,recently ,hayden and ,steinmetz experimented with a plot of ground #e feet by #i feet1 over which were hung five #ejj-watt gas-filled tungsten lamps #c feet above the ground and #ag inches apart4 ,the lamps were equipped with reflectors and the resulting illumination was #gjj foot-candles4 ,this is an extremely high intensity of artificial illumination and is comparable with daylight in greenhouses4 ,the only seeds planted were those of string beans and two beds were carried through to maturity1 one lighted by daylight only and the other by daylight and artificial light1 the latter being in operation twenty-fours hours per day4 ,the plants under the additional artificial light grew more rapidly than the others1 and of the various records kept the gain in time was in all cases about #ej per cent4 ,from the standpoint of profitableness the artificial lighting was not justified4 ,however1 there are several points to be brought out before considering this conclusion too seriously4 ,first1 it appears unwise to use the artificial light during the day2 second1 it appears possible that a few hours of artificial light in the evening would suffice for considerable forcing2 third1 it is possible that a much lower intensity of artificial light might be more effective per lumen than the great intensity used2 fourth1 it is quite possible that some other efficient light-source may be more effective in forcing the growth of plants4 ,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 direction4 ,certainly1 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 manner4 ,many other instances could be cited in which artificial light is very closely associated with the cost of living4 ,overseas shipment of fruit from the ,canadian ,northwest is responsible for a decided innovation in fruit-picking4 ,in searching for a cause of rotting during shipment it was finally concluded that the temperature at the time of picking was the controlling factor4 ,as a consequence1 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 night4 ,this change is said to have remedied the situation4 ,cases of threshing and other agricultural operations being carried on at night are becoming more numerous4 ,these are just the beginnings of artificial light in a new field or in a new relation to civilization4 ,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 territory4 ,the modern illuminants have been developed so recently that the new possibilities have not yet been established4 ,however1 artificial light is already a factor on the side of the people in the struggle against the increasing cost of living1 and its future in this direction is still more promising4 ,,xix ,,artificial ,,light ,,and ,,chemistry ,some one in an early century was the first to notice that the sun's rays tanned the skin1 and this unknown individual made the initial discovery in what is now an extensive branch of science known as photo-chemistry4 ,the fading of dyes1 the bleaching of textiles1 the darkening of silver salts1 the synthesis and decomposition of compounds are common examples of chemical reactions induced by light4 ,there are thousands of other examples of the chemical effects of light some of which have been utilized by mankind4 ,others await the development of more efficient light-sources emitting greater quantities of active rays1 and many still remain interesting scientific facts without any apparent practical applications at the present time4 ,visible and ultra-violet rays are the radiations almost entirely responsible for photochemical reactions1 but the most active of these are the blue1 violet1 and ultra-violet rays4 ,these are often designated chemical or actinic rays in order to distinguish the group as a whole from other groups such as ultra-violet1 visible1 and infra-red4 ,light is a unique agent in chemical reactions because it is not a material substance4 ,it neither contaminates nor leaves a residue4 ,although much information pertaining to photochemistry has been available for years1 the absence of powerful light-sources emitting so-called chemical rays in large quantities inhibited the practical development of the science of photochemistry4 ,even to-day1 with vast applications of light in this manner1 mankind is only beginning to utilize its chemical powers4 ,illustration3 ,in a moving-picture studio ,in a portrait studio ,,artificial ,,light ,,in ,,photography ,illustration3 ,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 ancients1 the earliest photochemical investigations which could be considered scientific and systematic were those of ,k4 ,w4 ,scheele in #aggg on silver salts4 ,an extract from his own account is as follows3 ,i precipitated a solution of silver by sal-ammoniac2 then ,i edulcorated 7washed7 it and dried the precipitate and exposed it to the beams of the sun for two weeks2 after which ,i stirred the powder and repeated the same several times4 ,hereupon ,i poured some caustic spirit of sal-ammoniac 7strong ammonia7 on this1 in all appearance1 black powder1 and set it by for digestion4 ,this menstruum 7solvent7 dissolved a quantity of luna cornua 7horn silver71 though some black powder remained undissolved4 ,the powder having been washed was1 for the greater part1 dissolved by a pure acid of nitre 7nitric acid71 which1 by the operation1 acquired volatility4 ,this solution ,i precipitated again by means of sal-ammoniac into horn silver4 ,hence it follows that the blackness which the luna cornua acquires from the sun's light1 and likewise the solution of silver poured on chalk1 is silver by reduction4 ,i mixed so much of distilled water with the well-washed horn silver as would just cover this powder4 ,the half of this mixture ,i poured into a white crystal phial1 exposed it to the beams of the sun1 and shook it several times each day2 the other half ,i set in a dark place4 ,after having exposed the one mixture during the space of two weeks1 ,i filtrated the water standing over the horn silver1 grown already black2 ,i let some of this water fall by drops in a solution of silver1 which was immediately precipitated into horn silver4 ,this extract shows that ,scheele dealt with the reducing action of light4 ,he found that silver chloride was decomposed by light and that there was a liberation of chlorine4 ,however1 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 chlorine4 ,scheele's work aroused much interest in photochemical effects and many investigations followed4 ,in many of these the superiority of blue1 violet1 and ultra-violet rays was demonstrated4 ,in #ahjb the first photograph was made by ,wedgwood1 who copied paintings upon glass and made profiles by casting shadows upon a sensitive chemical compound4 ,however1 he was not able to fix the image4 ,much study and experimentation were expended upon photochemical effects1 especially with silver compounds1 before ,niepce developed a method of producing pictures which were subsequently unaffected by light4 ,later ,daguerre became associated with ,niepce and the famous daguerreotype was the result4 ,apparently the latter was chiefly responsible for the development of this first commercial process1 the products of which are still to be found in the family album4 ,a century has elapsed since this earliest period of commercial photography1 and during each year progress has been made1 until at the present time photography is thoroughly woven into the activities of civilized mankind4 ,in those earliest years a person was obliged to sit motionless in the sun for minutes in order to have his picture taken4 ,the development of a century is exemplified in the snapshot of the present time4 ,photographic exposures outdoors at present are commonly one thousandth of a second1 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 second4 ,artificial light is playing a great part in this branch of photochemistry1 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 power4 ,the intensity of illumination due to sunlight on a clear day when the sun is near the zenith is commonly #aj1jjj foot-candles on a surface perpendicular to the direct rays4 ,this is equivalent to the illumination due to a source #ij1jjj candle-power at a distance of three feet4 ,the sun delivers about #bjj1jjj1jjj1jjj horse-power to the earth continuously1 which is estimated to be about one million times the amount of power generated artificially on the earth4 ,of this inconceivable quantity of energy a small part is absorbed by vegetation1 some is reflected and radiated back into space1 and the balance heats the earth4 ,to store some of this energy so that it may be utilized at will in any desired form is one of the dreams of science4 ,however1 artificial light-sources are depended upon at present in many photographic and other chemical processes4 ,although two illuminants may be of the same luminous intensity1 they may differ widely in actinic value4 ,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-length4 ,nearly all human eyes see visible rays in approximately the same manner1 but the multitude of chemical reactions show a wide variation in sensitivity to the various rays4 ,for example1 one photographic emulsion may be sensitive only to ultra-violet1 violet1 and blue rays and another to all these rays and also to the green1 yellow1 and red4 ,therefore1 one illuminant may be superior to another for one photochemical reaction1 while the reverse may be true in the case of another reaction4 ,in general1 it may be said that the arc-lamps including the mercury-arcs provide the most active illuminants for photochemical processes2 however1 a large number of electric incandescent filament lamps are used in photographic work4 ,the photo-engraver has been independent of sunlight since the practical development of his art4 ,in fact1 the printer could not depend upon sunlight for making the engravings which are used to illustrate the magazines and newspapers4 ,the newspaper photographer may make a flashlight exposure1 develop his negative1 and make a print from it under artificial light4 ,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 streets4 ,the moving-picture studio is independent of daylight in indoor settings and there is a tendency toward the exclusive use of artificial light4 ,in this field mercury-vapor lamps1 arc-lamps1 and tungsten photographic lamps are used4 ,similarly1 in the portrait studio there is a tendency for the photographer to leave the skylighted upper floors and to utilize artificial light4 ,in this field the tungsten photographic lamp is gaining in popularity1 owing to its simplicity and to other advantages4 ,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 obtained4 ,in ordinary photographic printing tungsten lamps are widely used1 but in blue-printing the white flame-arc and the mercury-vapor lamp are generally employed4 ,not many years ago the blue-printer waited for the sun to appear in order to make his prints1 but to-day large machines operate continuously under the light of powerful artificial sources4 ,how many realize that the blue-print is almost universally at the foundation of everything at the present time8 ,not only are products made from blue-prints but the machinery which makes the products is built from blue-prints4 ,even the building which houses the machinery is first constructed from blue-prints4 ,they form an endless chain in the activities of present civilization4 ,artificial light has been a great factor in the practical development of photography and it is looked upon for aid in many other directions4 ,although there is a multitude of reactions in photographic processes which are brought about by exposure to light1 these represent relatively few of the photochemical reactions4 ,in general1 it may be stated that light is capable of causing nearly every type of reaction4 ,the chemical compounds which are photo-sensitive are very numerous4 ,many of the compounds of silver1 gold1 platinum1 mercury1 iron1 copper1 manganese1 lead1 nickel1 and tin are photo-sensitive and these have been widely investigated4 ,light and oxygen cause many oxidation reactions and1 on the other hand1 light reduces many compounds such as silver salts1 even to the extent of liberating the metal4 ,oxygen is converted partially into ozone under the influence of certain rays and there are many examples of polymerization caused by light4 ,various allotropic changes of the elements are due to the influence of light2 for example1 a sulphur soluble in carbon disulphide is converted into sulphur which is insoluble1 and the rate of change of yellow phosphorus into the red variety is greatly accelerated by light4 ,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 light4 ,carbon monoxide and chlorine combine to form phosgene and the combination of chlorine1 bromine1 and iodine1 with organic compounds1 is much hastened by exposing the mixture to light4 ,in a similar manner many decompositions are due to light2 for example1 hydrogen peroxide is decomposed into water and oxygen4 ,this suggests the reason for the use of brown bottles as containers for many chemical compounds4 ,such glass does not transmit appreciably the so-called actinic or chemical rays4 ,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 chlorophyll1 the green coloring matter in vegetation4 ,no permanent change takes place in the chlorophyll1 but by the action of light it enables the plant to absorb oxygen1 carbon dioxide1 and water and to use these to build up the complex organic substances which are found in plants4 ,radiant energy or light is absorbed and converted into chemical energy4 ,this use of radiant energy occurs only in those parts of the plant in which chlorophyll is present1 that is1 in the leaves and stems4 ,these parts absorb the radiant energy and take carbon dioxide from the air through breathing openings4 ,they convert the radiant energy into chemical energy and use this energy in decomposing the carbon dioxide4 ,the oxygen is exhausted and the carbon enters into the structure of the plant4 ,the energy of plant life thus comes from radiant energy and with this aid the simple compounds1 such as the carbon dioxide of the air and the phosphates and nitrates of the soil1 are built into complex structures4 ,thus plants are constructive and synthetic in operation4 ,it is interesting to note that the animal organism converts complex compounds into mechanical and heat energy4 ,the animal organism depends upon the synthetic work of plants1 consuming as food the complex structures built by them under the action of light4 ,for example1 plants inhale carbon dioxide1 liberate the oxygen1 and store the carbon in complex compounds1 while the animal uses oxygen to burn up the complex compounds derived from plants and exhales carbon dioxide4 ,it is a beautiful cycle1 which shows that ultimately all life on earth depends upon light and other radiant energy associated with it4 ,contrary to most photochemical reactions1 it appears that plant life utilize yellow1 red1 and infra-red energy more than the blue1 violet1 and ultra-violet4 ,in general1 great intensities of blue light and of the closely associated rays are necessary for most photochemical reactions with which man is industrially interested4 ,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 chloroform4 ,one advantage of the radiation from this light-source is that it does not extend far into the ultra-violet1 for the ultra-violet rays of short wave-lengths decompose some compounds4 ,in other words1 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 reaction4 ,by the use of a shunt across the arc the light can be gradually varied over a considerable range of intensity4 ,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 carbons4 ,for example1 strontium fluoride is used in the red flame-arc whose radiant energy is rich in red and yellow4 ,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 color4 ,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 rays4 ,its carbons contain rare-earths4 ,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 quality4 ,a million white flame-carbons are being used annually in this country for various photochemical processes4 ,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 materials4 ,as a consequence such tests could not be carried out very systematically until a powerful artificial source of light resembling daylight was available4 ,it appears that the white flame-arc is quite satisfactory in this field1 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 #bh-;ampere arc4 ,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 country4 ,inasmuch as the fastness of colors in daylight is usually of interest1 the artificial illuminant used for color-fading should be spectrally similar to daylight4 ,apparently the white flame-arc fulfils this requirement as well as being a powerful source4 ,lithopone1 a white pigment consisting of zinc sulphide and barium sulphate1 sometimes exhibits the peculiar property of darkening on exposure to sunlight4 ,this property is due to an impurity and apparently cannot be predicted by chemical analysis4 ,during the cloudy days and winter months when powerful sunlight is unavailable1 the manufacturer is in doubt as to the quality of his product and he needs an artificial light-source for testing it4 ,in such a case the white flame-arc is serving satisfactorily1 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 lens4 ,in fact1 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 lens4 ,in special cases of this sort the use of a focused image is far superior to the ordinary illumination from the light-source1 but1 of course1 this is impracticable when testing a large number of samples simultaneously4 ,incidentally1 lithopone which turns gray or nearly black in the sunlight regains its whiteness during the night4 ,an amusing incident is told of a young man who painted his boat one night with a white paint in which lithopone was the pigment4 ,on returning home the next afternoon after the boat had been exposed to sunlight all day1 he was astonished to see that it was black4 ,being very much perturbed1 he telephoned to the paint store1 but the proprietor escaped a scathing lecture by having closed his shop at the usual hour4 ,the young man telephoned in the morning and told the proprietor what had happened1 but on being asked to make certain of the facts he went to the window and looked at his boat and behold6 it was white4 ,it had regained whiteness during the night but would turn black again during the day4 ,although pigments and dyes are not generally as peculiar as lithopone1 much uncertainty is eliminated by systematic tests under constant1 continuous1 and controllable artificial light4 ,the sources of so-called chemical rays are numerous for laboratory work1 but there is a need for highly efficient powerful producers of this kind of energy4 ,in general the flame-arcs perhaps are foremost sources at the present time1 with other kinds of carbon arcs and the quartz mercury-arc ranking next4 ,one advantage of the mercury-arc is its constancy4 ,furthermore1 for work with a single wave-length it is easy to isolate one of the spectral lines4 ,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 processes4 ,an excellent source for experimental work can be made easily by producing an arc between two small iron rods4 ,the electric spark has served in much experimental work1 but the total radiant energy from it is small4 ,by varying the metals used for electrodes a considerable variety in the radiant energy is possible4 ,this is also true of the electric arcs1 and the flame-arcs may be varied widely by using different chemical compounds in the carbons4 ,there are other effects of light which have found applications but not in chemical reactions4 ,for example1 selenium changes its electrical resistance under the influence of light and many applications of this phenomenon have been made4 ,another group of light-effects forms a branch of science known as photo-electricity4 ,if a spark-gap is illuminated by ultra-violet rays1 the resistance of the gap is diminished4 ,if an insulated zinc plate is illuminated by ultra-violet or violet rays1 it will gradually become positively charged4 ,these effects are due to the emission of electrons from the metal4 ,violet and ultra-violet rays will cause a colorless glass containing manganese to assume a pinkish color4 ,the latter is the color which manganese imparts to glass and under the influence of these rays the color is augmented4 ,certain ultra-violet rays also ionize the air and cause the formation of ozone4 ,this can be detected near a quartz mercury-arc1 for example1 by the characteristic odor4 ,the foregoing are only a few of the multitude of photochemical reactions and other effects of radiant energy4 ,the development of this field awaits to some extent the production of so-called actinic rays more efficiently and in greater quantities1 but there are now many practical applications of artificial light for these purposes4 ,in the extensive fields of photography various artificial light-sources have served for many years and they are constantly finding more applications4 ,artificial light is now used to a considerable extent in the industries in connection with chemical processes1 but little information is available1 owing to the secrecy attending these new developments in industrial processes4 ,however1 this brief chapter has been introduced in order to indicate another field of activity in which artificial light is serving4 ,it is agreed by scientists that photochemistry has a promising future4 ,mankind harnesses nature's forces and produces light and this light is put to work to exert its influence for the further benefit of mankind4 ,science has been at work systematically for only a century1 but the accomplishments have been so wonderful that the imagination dares not attempt to prophesy the achievements of the next century4 ,,xx ,,light ,,and ,,health ,the human being evolved without clothing and the body was bathed with light throughout the day1 but civilization has gone to the other extreme of covering the body with clothing which keeps most of it in darkness4 ,inasmuch as light and the invisible radiant energy which is associated with it are known to be very influential agencies in a multitude of ways1 the question arises3 ,has this shielding of the body had any marked influence upon the human organism8 ,although there is a vast literature upon the subject of light-therapy1 the question remains unanswered1 owing to the conflicting results and the absence of standardization of experimental details4 ,in fact1 most investigations are subject to the criticism that the data are inadequate4 ,throughout many centuries light has been credited with various influences upon physiological processes and upon the mind4 ,but most of the early applications had no foundation of scientific facts4 ,unfortunately1 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 foundation4 ,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 chaos4 ,this does not mean that many of the effects are not real1 for radiant energy is known to cause certain effects1 and viewing the subject broadly it appears that light is already serving humanity in this field and that its future is promising4 ,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 involved4 ,for example1 it is easy to err by attributing an effect to visible rays when the effect may be caused by accompanying invisible rays4 ,furthermore1 it may be possible that certain rays counteract or aid the effective rays without being effective alone4 ,in other words1 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 action4 ,radiant energy of all kinds and wave-lengths has played a part in therapeutics1 so it is of interest to indicate them according to wave-length or frequency4 ,these groups vary in range of wave-length1 but the actual intervals are not particularly of interest here4 ,beginning with radiant energy of highest frequencies of vibration and shortest wave-lengths1 the following groups and subgroups are given in their order of increasing wave-length3 ,rntgen or ,x-rays1 which pass readily through many substances opaque to ordinary light-rays4 ,ultra-violet rays1 which are divided empirically into three groups1 designated as extreme1 middle1 and near in accordance with their location in respect to the visible region4 ,visible rays producing various sensations of color1 such as violet1 blue1 green1 yellow1 orange1 and red4 ,infra-red or the invisible rays bordering on the red rays4 ,an unknown1 unmeasured1 or unfilled region between the infra-red and the electric waves4 ,electric waves1 which include a class of electromagnetic radiant energy of long wave-length4 ,of these the ,herzian waves are of the shortest wave-length and these are followed by wireless waves4 ,electric waves of still greater wave-length are due to the slower oscillations in certain electric circuits caused by lightning discharges1 etc4 ,the ,rntgen rays were discovered by ,rntgen in #ahif and they have been studied and applied very widely ever since4 ,their great use has been in ,x-ray photography1 but they are also being used in therapeutics4 ,the extreme ultra-violet rays are not available in sunlight and are available only near a source rich in ultra-violet rays1 such as the arc-lamps4 ,they are absorbed by air1 so that they are studied in a vacuum4 ,these are the rays which convert oxygen into ozone because the former strongly absorbs them4 ,the middle ultra-violet rays are not found in sunlight1 because they are absorbed by the atmosphere4 ,they are also absorbed by ordinary glass but are freely transmitted by quartz4 ,the nearer ultra-violet rays are found in sunlight and in most artificial illuminants and are transmitted by ordinary glass4 ,next to this region is the visible spectrum with the various colors1 from violet to red1 induced by radiant energy of increasing wave-length4 ,the infra-red rays are sometimes called heat-rays1 but all radiant energy may be converted into heat4 ,various substances transmit and absorb these rays in general quite differently from the visible rays4 ,water is opaque to most of the infra-red rays4 ,next there is a region of wave-lengths or frequencies for which no radiant energy has been found4 ,the so-called electric waves vary in wave-length over a great range and they include those employed in wireless telegraphy4 ,all these radiations are of the same general character1 consisting of electromagnetic energy1 but differing in wave-length or frequency of vibration and also in their effects4 ,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 work4 ,illustration3 ,in art work ,in a haberdashery ,,judging ,,color ,,under ,,artificial ,,daylight ,illustration3 ,in an underground tunnel ,in an art gallery ,,artificial ,,daylight ,it has been conclusively shown that radiant energy kills bacteria4 ,the early experiments were made with sunlight and the destruction of micro-organisms is generally attributed to the so-called chemical rays1 namely1 the blue1 violet1 and ultra-violet rays4 ,it appears in general that the middle ultra-violet rays are the most powerful destroyers4 ,it is certainly established that sunlight sterilizes water1 for example1 and the quartz mercury-lamp is in daily use for this purpose on a practicable scale4 ,however1 there still appears to be a difference of opinion as to the destructive effect of radiant energy upon bacteria in living tissue4 ,it has been shown that the middle ultra-violet rays destroy animal tissue and1 for example1 cause eye-cataracts4 ,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 sunlight4 ,this is one of the reasons for the use of blue glass in light-therapy1 which isolates the blue1 violet1 and near ultra-violet rays from the other visible rays4 ,if the infra-red rays are not desired they can be readily eliminated by the use of a water-cell4 ,there is a vast amount of testimony which proves the bactericidal action of light4 ,bacteria on the surface of the body are destroyed by ultra-violet rays4 ,typhus and tubercle bacilli are destroyed equally well by the direct rays from the sun and from the electric arcs4 ,cultures of diphtheria develop in diffused daylight but are destroyed by direct sunlight4 ,lower organisms in water are readily killed by the radiation from any light-source emitting ultra-violet rays comparable with those in direct sunlight4 ,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 rays4 ,it appears also that no bacteria can resist these rays if they are intense enough and are permitted to play upon the bacteria long enough4 ,the destruction of these organisms appears to be a phenomenon of oxidation1 for the presence of oxygen appears to be necessary4 ,the foregoing remarks about the bactericidal action of radiant energy apply only to bacteria in water1 in cultures1 and on the surface of the body4 ,there is much uncertainty as to the ability of radiant energy to destroy bacteria within living tissue4 ,the active rays cannot penetrate appreciably into such tissue and many authorities are convinced that no direct destruction takes place4 ,in fact1 it has been stated that the so-called chemical rays are more destructive to the tissue cells than to bacteria4 ,finsen1 a pioneer in the use of radiant energy in the treatment of disease1 effected many wonderful cures and believed that the bacteria were directly destroyed by the ultra-violet rays4 ,however1 many have since come to the conclusion that the beneficent action of the rays is due to the irritation which causes an outflow of serum1 thus bringing more antibodies in contact with the bacilli1 and causing the destruction of the latter4 ,hot applications appear to work in the same manner4 ,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 kind4 ,these wounds are usually infected and the sun's rays render them aseptic and they heal readily4 ,many cases of sores and surgical wounds have been quickly healed by exposure to sunlight4 ,even red light has been effective1 so it has been concluded by some that rays of almost any wave-length1 if intense enough1 will effect a cure of this character by causing an effusion of serum4 ,it has also been stated that the chemical rays have ansthetic powers and have been used in this rle for many minor operations4 ,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 uncommon4 ,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 light4 ,it is also stated that this treatment was administered throughout the reigns of ,elizabeth and of ,charles ,,ii4 ,another account states that a few soldiers confined in dark dungeons recovered from smallpox without pitting4 ,finsen also obtained excellent results in the treatment of this disease by means of red light4 ,however1 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-therapy4 ,in other words1 the red light plays no part except in furnishing a light which does not inhibit healing4 ,although the so-called actinic rays have curative value in certain cases1 there are some instances where light-baths are claimed to be harmful4 ,it is said that sun-baths to the naked body are not so popular as they were formerly1 except for obesity1 gout1 rheumatism1 and sluggish metabolism1 because it is felt that the shorter ultra-violet rays may be harmful4 ,these rays are said to increase the pulse1 respiration1 temperature1 and blood-pressure and may even start hemorrhages and in excessive amounts cause headache1 palpitation1 insomnia1 and anemia4 ,these same authorities condemn sun-baths to the naked body of the tuberculous1 claiming that any cures effected are consummated despite the injury done by the energy of short wave-length4 ,there is no doubt that these rays are beneficial in local lesions1 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 serum1 and not to any direct beneficial result on the tissue-cells4 ,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-lengths4 ,these conclusions by a few authorities are submitted for what they are worth and to show that this phase of light-therapy is also unsettled4 ,any one who has been in touch with light-therapy in a scientific rle is bound to note that much ignorance is displayed in the use of light in this manner4 ,in fact1 it appears safe to state that light-therapy often smacks of quackery4 ,very mysterious effects are sometimes attributed to radiant energy1 which occasionally border upon superstition4 ,nevertheless1 this kind of energy has value1 and notwithstanding the chaos which still exists1 it is of interest to note some of the equipment which has been used4 ,some practitioners have great confidence in the electric bath1 and elaborate light-baths have been devised4 ,in the earlier years of this kind of treatment the electric arc was conspicuous4 ,electrodes of carbon1 carbon and iron1 and iron have been used when intense ultra-violet rays were desired4 ,the quartz mercury-arc of later years supplies this need admirably4 ,dr4 ,cleaves1 after many years of experience with the electric-arc bath1 has stated3 ,from the administration of an electric-arc bath there is obtained an action upon the skin1 the patient experiences a pleasant and slightly prickly sensation4 ,there is produced1 even from a short exposure1 upon the skin of some patients a slight erythema1 while with others there is but little such effect even from long exposures4 ,the face assumes a normal rosy coloring and an appearance of refreshment and repose on emerging from the bath is always observed4 ,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 action1 as evidenced by improved volume and slower pulse rate1 the augmentation of the temperature1 increased activity of the skin1 fuller and slower respiration1 gradually increased respiratory capacity1 and diminished irritability of the mucous membrane in tubercular1 bronchitic1 or asthmatic patients4 ,there is also lessened discharge in those patients suffering from catarrhal conditions of the nasal passages4 ,in diseases of the respiratory system1 a soothing effect upon the mucous membranes is always experienced1 while cough and expectoration are diminished4 ,the cabinet used by ,dr4 ,cleaves was large enough to contain a cot upon which the patient reclined4 ,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 cabinet4 ,by means of mirrors the light from the arcs could be concentrated upon any desired part of the patient4 ,finsen1 who in #ahie published his observations upon the stimulating action of light1 is considered the pioneer in the use of so-called chemical rays in the treatment of disease4 ,he had a circular room about thirty-seven feet in diameter1 in which two powerful #ajj-;ampere arc-lamps about six feet from the floor were suspended from the ceiling4 ,low partitions extended radially from the center1 so that a number of patients could be treated simultaneously4 ,the temperature of the room was normal1 so that the treatment was essentially by radiant energy and not by heat4 ,the chemical action upon the skin was said to be quite as strong as under sunlight4 ,the exposures varied from ten minutes to an hour4 ,light-baths containing incandescent filament lamps are also used4 ,in some cases the lamp1 sometimes having a blue bulb1 is merely contained as a reflector and the light is applied locally as desired4 ,light-cabinets are also used1 but in these there is considerable effect due to heat4 ,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 feeble4 ,the glass bulbs do not transmit the extreme ultra-violet rays responsible for the production of ozone1 or the middle ultra-violet rays which are effective in destroying animal tissue4 ,the cabinets contain from twenty to one hundred incandescent filament lamps of the ordinary sizes1 from #be to #fj watts4 ,in the days of the carbon filament lamp the #af-;candle-power lamp was used4 ,certainly the heating effect has advantages in some cases over other methods of heating4 ,the light-rays penetrate the tissue and are absorbed and transformed into heat4 ,other methods involve conduction of heat from the hot air or other hot applications4 ,of course1 it is also contended that the light-rays are directly beneficial4 ,light is also concentrated upon the body by means of lenses and mirrors4 ,for this purpose the sun1 the arc1 the quartz mercury-arc1 and the incandescent lamp have been used4 ,besides these1 vacuum-tube discharges and sparks have been utilized as sources for radiant energy and electrical treatment4 ,rntgen rays and radium have also figured in recent years in the treatment of disease4 ,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 others4 ,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 properties4 ,finsen in his early experiments cured a case of lupus1 a tuberculous skin disease1 by means of the visible and near ultra-violet rays in sunlight4 ,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 water4 ,this was really a lens made of glass and water4 ,the glass absorbed the ultra-violet rays of shorter wave-length and the water absorbed the infra-red rays4 ,thus he was able to concentrate upon the diseased skin radiant energy consisting of visible and near ultra-violet rays4 ,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 lenses4 ,this gave him a powerful source of so-called chemical rays1 which could be concentrated wherever desired4 ,however1 when science contributed the mercury-vapor arc1 developments were immediately begun which aimed to utilize this artificial source of steady powerful ultra-violet rays in light-therapy4 ,as a consequence1 there are now available very compact quartz mercury-arcs designed especially for this purpose4 ,apparently their use has been very effective in curing many skin diseases4 ,certainly if radiant energy is effective1 it has a great advantage over drugs4 ,an authority has stated in regard to skin diseases that1 treatment with the ultra-violet rays1 especially in conjunction with the ,rntgen rays1 radium and mesothorium is that treatment which in most instances holds rank as the first1 and in many as the only and often enough the most effective mode of handling the disease4 ,sterilization by means of the radiation from the quartz mercury-arc has been practised successfully for several years4 ,compact apparatus is in use for the sterilization of water for drinking1 for surgical purposes1 and for swimming-pools1 and the claims made by the manufacturers of the apparatus apparently are substantiated4 ,one type of apparatus withstands a pressure of one hundred pounds per square inch and may be connected in series with the water-main4 ,the water supplied to the sterilizer should be clear and free of suspended matter1 in order that the radiant energy may be effective4 ,such apparatus is capable of sterilizing any quantity of water up to a thousand gallons an hour1 and the lamp is kept burning only when the water is flowing4 ,it is especially useful in hotels1 stores1 factories1 on ships1 and in many industries where sterile water is needed4 ,water is a vital necessity in every-day life1 whether for drinking1 cooking1 or industrial purposes4 ,it is recognized as a carrier of disease and the purification of water-supply in large cities is an important problem4 ,chlorination processes are in use which render the treated water disagreeable to the taste and filtration alone is looked upon with suspicion4 ,the use of chemicals requires constant analysis1 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 clear1 or if it has been properly filtered before treating4 ,the system of sterilization by ultra-violet rays is the natural way1 for the sun's rays perform this function in nature4 ,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 cities4 ,large mechanical filters are used in conjunction with these sterilizers1 and thus mankind copies nature's way1 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 life4 ,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 factory1 hospital1 store1 or office building4 ,these were used in some ,american hospitals during the recent war1 where they supplied sterilized water for drinking and for the antiseptic bathing of wounds4 ,in warfare the water supply is exceedingly important4 ,for example1 the ,japanese in their campaign in ,manchuria boiled the water to be used for drinking purposes4 ,the mortality of armies in many previous wars was often much greater from preventable diseases than from bullets1 but the ,japanese in their war with ,russia reversed the mortality statistics4 ,of a total mortality of #ha1jjj more than #fj1jjj died of casualties in battle4 ,the sterilization of water for swimming-pools is coming into vogue4 ,heretofore it was the common practice to circulate the water through a filter1 in order to remove the impurities imparted to it by the bathers and to return it to the pool4 ,it is insisted by the adherents of sterilization that filtration of this sort is likely to leave harmful bacteria in the water4 ,sterilizers in which ultra-violet rays are the active rays are now in use for this purpose1 being connected beyond the outflow from the filter4 ,the effectiveness of the apparatus has been established by the usual method of counting the bacteria4 ,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 origin4 ,then a sterilizer was installed in which the effective elements were two quartz mercury-lamps which consumed #b4b amperes each at #bbj volts4 ,a count of bacteria in the water leaving the sterilizer showed that these organisms had been reduced to #e per cent4 and finally to a smaller percentage of their original value1 and that all those of intestinal origin had been destroyed4 ,in fact1 the water which was returned to the pool was better than that which most persons drink4 ,radiant energy possesses advantages which are unequaled by other bactericidal agents1 in that it does not contaminate or change the properties of the water in any way4 ,it does its work of destroying bacteria and leaves the water otherwise unchanged4 ,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 correlated4 ,the sun is of primary importance to mankind1 but it serves in so many ways that it is naturally a compromise4 ,it cannot supply just the desired radiant energy for one purpose and at the same time serve for another purpose in the best manner4 ,it is obscured on cloudy days and disappears nightly4 ,these absences are beneficial to some processes1 but man in the highly organized activity of present civilization desires radiant energy of various qualities available at any time4 ,in this respect artificial light is superior to the sun and is being improved continually4 ,,xxi ,,modifying ,,artificial ,,light ,in a single century science has converted the dimly lighted nights with their feeble flickering flames into artificial daytime4 ,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 century1 but1 as has been noted in another chapter1 great improvements in light-production are still possible4 ,nevertheless1 the wonderful developments in the last four decades1 which created the arc-lamps1 the gas-mantle1 the mercury-vapor lamps1 and the series of electric incandescent-filament lamps1 have contributed much to the efficiency1 safety1 health1 and happiness of mankind4 ,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 desired4 ,to-day light alone is not sufficient4 ,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 stage4 ,man now desires lights of various colors for their expressive effects4 ,he is no longer satisfied with mere light in adequate quantities2 he desires certain qualities4 ,furthermore1 he no longer finds it sufficient to be independent of daylight merely in quantity of light4 ,in fact1 he has demanded artificial daylight4 ,doubtless the future will see the production of efficient light of many qualities or colors1 but to-day many of the demands must be met by modifying the artificial illuminants which are available4 ,vision is accomplished entirely by the distinction of brightness and color4 ,an image of any scene or any object is focused upon the retina as a miniature map in light1 shade1 and color4 ,although the distinction of brightness is a more important function in vision than the ability to distinguish colors1 color-vision is far more important in daily life than is ordinarily appreciated4 ,one may go through life color-blind without suffering any great inconvenience1 but the divine gift of color-vision casts a magical drapery over all creation4 ,relatively few are conscious of the wonderful drapery of color1 except for occasional moments when the display is unusual4 ,nevertheless a study of vision in nearly all crafts reveals the fact that the distinction of colors plays an important part4 ,in the purchase of food and wearing-apparel1 in the decoration of homes and throughout the arts and industries1 mankind depends a great deal upon the appearance of colors4 ,he depends upon daylight in this respect and unconsciously often1 when daylight fails1 ceases work which depends upon the accurate distinction of colors4 ,his color-vision evolved under daylight2 arts and industries developed under daylight2 and all his associations of color are based primarily upon daylight4 ,for these reasons1 adequate artificial illumination does not make mankind independent of daylight in the practice of arts and crafts and in many minor activities4 ,in quality or spectral character1 the unmodified illuminants used for general lighting purposes differ from daylight and therefore do not fully replace it4 ,noon sunlight contains all the spectral colors in approximately the same proportions1 but this is not true of these artificial illuminants4 ,for these reasons there is a demand for artificial daylight4 ,the vacuum tube affords a possibility of an extensive variety of illuminants differing widely in spectral character or color4 ,every gas when excited to luminescence by an electric discharge in the vacuum tube 7containing the gas at a low pressure7 emits light of a characteristic quality or color4 ,by varying the gas a variety of illuminants can be obtained1 but this means of light-production has not been developed to a sufficiently practicable state to be satisfactory for general lighting4 ,nitrogen yields a pinkish light and the nitrogen tube as developed by ,dr4 ,moore was installed to some extent a few years ago4 ,neon yields an orange light and has been used in a few cases for displays4 ,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 essential4 ,the flame-arcs afford a means of obtaining a variety of illuminants differing in spectral character or color4 ,by impregnating the carbons with various chemical compounds the color of the flame can be widely altered4 ,the white flame-arc obtained by the use of rare-earth compounds in the carbons provides an illuminant closely approximating average daylight4 ,by using various substances besides carbon for the electrodes1 illuminants differing in spectral character can be obtained4 ,these are usually rich in ultra-violet rays and therefore have their best applications in processes demanding this kind of radiant energy4 ,the arc-lamp is limited in its application by its unsteadiness1 its bulkiness1 and the impracticability of subdividing it into light-sources of a great range of luminous intensities4 ,the most extensive applications of artificial daylight have been made by means of the electric incandescent filament lamp1 equipped with a colored glass which alters the light to the same quality as daylight4 ,the light from the electric filament lamp is richer in yellow1 orange1 and red rays than daylight1 and by knowing the spectral character of the two illuminants and the spectral characteristics of colored glasses in which various chemicals have been incorporated1 it is possible to develop a colored glass which will filter out of the excess of yellow1 orange1 and red rays so that the transmitted light is of the same spectral character as daylight4 ,thousands of such artificial daylight units are now in use in the industries1 in stores1 in laboratories1 in dye-works1 in print-shops1 and in many other places4 ,currency and ,liberty ,bonds have been made under artificial daylight and such units are in use in banks for the detection of counterfeit currency4 ,the diamond expert detects the color of jewels and the microscopist is certain of the colors of his stains under artificial daylight4 ,the dyer mixes his dyes for the coloring of tons of valuable silk and the artist paints under this artificial light4 ,these are only a few of a vast number of applications of artificial daylight1 but they illustrate that mankind is independent of natural light in another respect4 ,there are various kinds of daylight1 two of which are fairly constant in spectral character4 ,these are noon sunlight and north skylight4 ,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 proportions4 ,north skylight contains an excess of violet1 blue1 and blue-green rays and as a consequence is a bluish white4 ,noon sunlight on a clear day is fairly constant in spectral character1 but north skylight varies somewhat depending upon the absence or presence of clouds and upon the character of the clouds4 ,if large areas of sunlit clouds are present1 the light is largely reflected sunlight4 ,if the sky is overcast1 the north skylight is a result of a mixture of sunlight and blue skylight filtered through the clouds and is slightly bluish4 ,if the sky is clear1 the light varies from light blue to deep blue4 ,illustration3 ,,fireworks ,,and ,,illuminated ,,battle-,,fleet ,,at ,,hudson-,,fulton ,,celebration ,illustration3 ,,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 vegetation1 and after it enters a room it is sometimes modified by reflection from colored surroundings4 ,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 yellow4 ,besides these alterations1 sunlight varies in color from the yellow or red of dawn through white at noon to orange or red at sunset4 ,throughout the day the amount of light from the sky does not change nearly as much as the amount of sunlight1 so there is a continual variation in the proportion of direct sunlight and skylight reaching the earth4 ,this is further varied by the changing position of the sun4 ,for example1 at a north window in which the direct sunlight may not enter throughout the day1 the amount of sunlight which enters by reflection from adjacent buildings and other objects may vary greatly4 ,thus it is seen that daylight not only varies in quantity but also in quality1 and an artificial daylight1 which is based upon an extensive analysis1 has the advantage of being constant in quantity and quality as well as correct in quality4 ,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 daylight4 ,although there are many expert colorists who require an accurate artificial daylight1 there are vast fields of lighting where a less accurate daylight quality is necessary4 ,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 matching4 ,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 stores1 offices1 and industries4 ,in order to make an accurate artificial north skylight for color-work by means of colored glass1 from #ge to #he per cent4 of the light from a tungsten lamp must be filtered out4 ,this absorption in a broad sense increases the efficiency of the light1 for the fraction that remains is now satisfactory1 whereas the original light is virtually useless for accurate color-discrimination4 ,about one third of the original light is absorbed by the bulb of the tungsten daylight lamp1 with a resultant light which is an approximation to average daylight4 ,old illuminants such as that emitted by the candle and oil-lamp were used for centuries in interiors4 ,all these illuminants were of a warm yellow color4 ,even the earlier modern illuminants were not very different in color1 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 illuminants4 ,the psychological effect of warmth and cheerfulness due to such illuminants or colors is well established4 ,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 tint4 ,the white light is excellent for the kitchen1 laundry1 and bath-room1 and for reading-lamps1 but the warm yellow light is best suited for making cozy and cheerful the environment of the interiors in which mankind relaxes4 ,an illuminant of this character can be obtained efficiently by using a properly tinted bulb on tungsten filament lamps4 ,by absorbing about one fourth to one third of the light 7depending upon the temperature of the filament7 the color of the candle flame may be simulated by means of a tungsten filament lamp4 ,some persons are still using the carbon-filament lamp despite its low efficiency1 because they desire to retain the warmth of tint of the older illuminants4 ,however1 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 light4 ,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 lamp4 ,thus the high efficiency of the modern illuminants is utilized to advantage even though their color is maintained the same as the old illuminants4 ,all modern illuminants emit radiant energy1 which does not affect the ordinary photographic plate4 ,this superfluous visible energy merely contributes toward glare or a superabundance of light in photographic studios4 ,a glass has been developed which transmits virtually all the rays that affect the ordinary photographic plate and greatly reduces the accompanying inactive rays4 ,such a glass is naturally blue in color1 because it must transmit the blue1 violet1 and near ultra-violet rays4 ,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 photography4 ,this glass1 it is seen1 transmits the so-called chemical rays and is useful in other activities where these rays alone are desired4 ,it is used in light-therapy and in some other activities in which the chemical effects of these rays are utilized4 ,in the photographic dark-room a deep red light is safe for all emulsions excepting the panchromatic1 and lamps of this character are standard products4 ,an orange light is safe for many printing papers4 ,panchromatic plates and films are usually developed in the dark where extreme safety is desired1 but a very weak deep red light is not unsafe if used cautiously4 ,however1 many photographic emulsions of this character are not very sensitive to green rays1 so a green light has been used for this purpose4 ,a variety of colored lights are in demand for theatrical effects1 displays1 spectacular lighting1 signaling1 etc41 and there are many superficial colorings available for this purpose4 ,few of these show any appreciable degree of permanency4 ,permanent superficial colorings have recently been developed1 but these are secret processes unavailable for the market4 ,for this reason colored glass is the only medium generally available where permanency is desired4 ,for permanent lighting effects1 signal glasses1 colored caps1 and sheets of colored glass may be used4 ,tints may be obtained by means of colored reflectors4 ,other colored media are dyes in lacquers and in varnishes1 colored inks1 colored textiles1 and colored pigments4 ,inasmuch as colored glass enters into the development of permanent devices1 it may be of interest to discuss briefly the effects of various metallic compounds which are used in glass4 ,the exact color produced by these compounds1 which are often oxides1 varies slightly with the composition of the glass and method of manufacture1 but this phase is only of technical interest4 ,the coloring substances in glass may be divided into two groups4 ,the first and largest group consists of those in which the coloring matter is in true solution2 that is1 the coloring is produced in the same manner as the coloring of water in which a chemical salt is dissolved4 ,in the second group the coloring substances are present in a finely divided or colloidal state2 that is1 the coloring is due to the presence of particles in mechanical suspension4 ,in general1 the lighter elements do not tend to produce colored glasses1 but the heavier elements in so far as they can be incorporated into glass tend to produce intense colors4 ,of course1 there are exceptions to this general statement4 ,the alkali metals1 such as sodium1 potassium1 and lithium1 do not color glass appreciably1 but they have indirect effects upon the colors produced by manganese1 nickel1 selenium1 and some other elements4 ,gold in sufficient amounts produces a red in glass and in low concentration a beautiful rose4 ,it is present in the colloidal state4 ,in the manufacture of gold red glass1 the glass when first cooled shows no color1 but on reheating the rich ruby color develops4 ,the glass is then cooled slowly4 ,the gold is left in a colloidal state4 ,copper when added to a glass produces two colors1 blue-green and red4 ,the blue-green color1 which varies in different kinds of glasses1 results when the copper is fully oxidized1 and the red by preventing oxidation by the presence of a reducing agent4 ,this red may be developed by reheating as in the case of making gold ruby glass4 ,selenium produces orange and red colors in glass4 ,silver when applied to the surface of glass produces a beautiful yellow color and it has been widely used in this manner4 ,it has little coloring effect in glass1 because it is so readily reduced1 resulting in a metallic black4 ,uranium produces a canary yellow in soda and potash-lime glasses1 which fluoresce1 and these glasses may be used in the detection of ultra-violet rays4 ,the color is topaz in lead glass4 ,both sulphur and carbon are used in the manufacture of pale yellow glasses4 ,antimony has a weak effect1 but in the presence of much lead it is used for making opaque or translucent yellow glasses4 ,chromium produces a green color1 which is reddish in lead glass1 and yellowish in soda1 and potash-lime glasses4 ,iron imparts a green or bluish green color to glass4 ,it is usually present as an impurity in the ingredients of glass and its color is neutralized by adding some manganese1 which produces a purple color complementary to the bluish green4 ,this accounts for the manganese purple which develops from colorless glass exposed to ultra-violet rays4 ,iron is used in bottle green glass4 ,its color is greenish blue in potash-lime glass1 bluish green in soda-lime glass1 and yellowish green in lead glass4 ,cobalt is widely used in the production of blue glasses4 ,it produces a violet-blue in potash-lime and soda-lime glasses and a blue in lead glasses4 ,it appears blue1 but it transmits deep red rays4 ,for this reason when used in conjunction with a deep red glass1 a filter for only the deepest red rays is obtained4 ,nickel produces an amethyst color in potash-lime glass1 a reddish brown in soda-lime glass1 and a purple in lead glass4 ,manganese is used largely as a decolorizing agent in counteracting the blue-green of iron4 ,it produces an amethyst color in potash-lime glass and reddish violet in soda-lime and lead glasses4 ,these are the principal coloring ingredients used in the manufacture of colored glass4 ,the staining of glass is done under lower temperatures1 so that a greater variety of chemical compounds may be used4 ,the resulting colors of metals and metallic oxides dissolved in glass depend not only upon the nature of the metal used1 but also partly upon the stage of oxidation1 the composition of the glass and even upon the temperature of the fusion4 ,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 obtained4 ,it is seen that the coloring elements are limited and the combination of these is further limited by chemical considerations4 ,in combining various colored glasses or various coloring elements in the same glass the subtractive method of color-mixture is utilized4 ,for example1 if a green glass is desired1 yellowish green chromium glass may be used as a basis4 ,by the addition of some blue-green due to copper1 the yellow rays may be further subdued so that the resulting color is green4 ,the primary colors for this method of color-mixture are the same as those of the painter in mixing pigments--namely1 purple1 yellow1 and blue-green4 ,various colors may be obtained by superposing or intimately mixing the colors4 ,the resulting transmission 7reflection in the case of reflecting media such as pigments7 are those colors commonly transmitted by all the components of a mixture4 ,thus1 ,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 colors4 ,these primaries are red1 green1 and blue and it will be noted that they are the complementaries of the subtractive primaries4 ,by the use of red1 green1 and blue lights in various proportions1 all colors may be obtained in varying degrees of purity4 ,the chief mixtures of two of the additive primaries produce the subtractive primaries4 ,thus1 ,red and blue purple ,red and green yellow ,green and blue blue-green ,although the coloring media which are permanent under the action of light1 heat1 and moisture are relatively few1 by a knowledge of their spectral characteristics and other principles of color the expert is able to produce many permanent colors for lighting effects4 ,the additive and subtractive methods are chiefly involved1 but there is another method which is an averaging additive one4 ,for example1 if a warm tint of yellow is desired and only a dense yellow glass is available1 the yellow glass may be cut into small pieces and arranged upon a colorless glass in checker-board fashion4 ,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 glass4 ,if this light is properly mixed by a diffusing glass the effect is satisfactory4 ,these are the principal means of obtaining colored light by means of filters and by mixing colored lights4 ,by using these in conjunction with the array of light-sources available it is possible to meet most of the growing demands4 ,of course1 the ideal solution is to make the colored light directly at the light-source1 and doubtless future developments which now appear remote or even impossible will supply such colored illuminants4 ,in the meantime1 much is being accomplished with the means available4 ,,xxii ,,spectacular ,,lighting ,artificial light is a natural agency for producing spectacular effects4 ,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 sky4 ,it surpasses other decorative media by the extreme range of values which may be obtained4 ,the decorator and painter are limited by a range of values from black to white pigments1 which ordinarily represents an extreme contrast of about one to thirty4 ,the brightnesses due to light may vary from darkness to those of the light-sources themselves4 ,the decorator deals with secondary light--that is1 light reflected by more or less diffusely reflecting objects4 ,the lighting expert has at his command not only this secondary light but the primary light of the sources4 ,lighting effects everywhere attract attention and even the modern merchant testifies that adequate lighting in his store is of advertising value4 ,in all the field of spectacular lighting the superiority of artificial light over natural light is demonstrated4 ,light is a universal medium with which to attract attention and to enthrall mankind4 ,the civilizations of all ages have realized this natural power of light4 ,it has played a part in the festivals and triumphal processions from time immemorial and is still the most important feature of many celebrations4 ,in the early festivals fires1 candles1 and oil-lamps were used and fireworks were invented for the purpose4 ,even to-day the pyrotechnical displays against the dark depths of the night sky hold mankind spellbound4 ,but these evanescent notes of light have been improved upon by more permanent displays on a huge scale4 ,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 ,england4 ,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 ,exposition4 ,some who saw that original display of gas-jets totaling a few hundred candle-power described it as an occasion of extraordinary splendour4 ,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 #b1fjj1jjj1jjj beam candle-power6 ,no other comparison exemplifies more strikingly the progress of artificial lighting in the hundred years which have elapsed since it began to be developed4 ,the nature of the light-sources in the first half of the nineteenth century did not encourage spectacular or display lighting4 ,in fact1 this phase of lighting chiefly developed along with electric lamps4 ,of course1 occasionally some temporary effect was attempted as in the case of illuminating the dome of ,st4 ,paul's ,cathedral in ,london in #ahgb1 but continued operation of the display was not entertained4 ,in the case of lighting this dome a large number of ship's lanterns were used1 but the result was unsatisfactory4 ,after this unsuccessful attempt at lighting ,st4 ,paul's1 a suggestion was made of flooding it with electric light projected from various quarters4 ,spectacular lighting outdoors really began in earnest in the dawn of the twentieth century4 ,although some of the first attempts at spectacular lighting outdoors were made with search-lights1 spectacular lighting did not become generally popular until the appearance of incandescent filament lamps of reasonable efficiency and cost4 ,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 monuments4 ,the effect was almost wholly that of light1 for the glare from the visible lamps obscured the buildings or other objects4 ,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 lamps4 ,however1 the method has limitations from an artistic point of view because the artistic effects of painting1 sculpture1 and architecture cannot be combined with it very effectively4 ,for example1 the details of a monument or of a building cannot be seen distinctly enough to be appreciated4 ,the effect is merely that of outlines or lines and patterns of points of light and is usually glaring4 ,the next step was to conceal these lamps behind the cornices or other projections or in nooks constructed the purpose4 ,light now began to mold and to paint the objects4 ,the structures began to be visible2 at least the important cornices and other details were no longer mere outlines4 ,the introduction of the drawn-wire tungsten lamp is responsible for an innovation in spectacular lighting of this sort1 for now it became possible to make concentrated light-sources so essential to projectors4 ,furthermore1 these lighting units require very little attention after once being located4 ,with the introduction of electric-filament lamps of this character small projectors came into use1 and by means of concentrated beams of light whole buildings and monuments could be flooded with light from remote positions4 ,the effects obtained by concealing lamps behind cornices had demonstrated that the lighting of the surfaces was the object to be realized in most cases1 and when small projectors not requiring constant attention became available1 a great impetus was given to flood-lighting4 ,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 ,liberty4 ,this torch was modified at the time of the erection of the statue to accommodate the lamps available1 with the result that it was merely a lantern containing a number of electric lamps4 ,at night it was a speck of light more feeble than many surrounding shore lights4 ,the statue had been lighted during festivals with festoons and outlines of lamps1 but in #aiae1 when the freedom of the generous donor of the statue appeared to be at stake1 a movement was begun which culminated in a fund for flood-lighting ,liberty4 ,the broad foundation of the statue made the lighting comparatively easy by means of banks of incandescent filament search-lights4 ,about #bbe of these units were used with a total beam candle-power of about #bj1jjj1jjj4 ,the original idea of an imitation flame for the torch was restored by building this from pieces of yellow cathedral glass of three densities4 ,about six hundred pieces of glass were used1 the upper ones being generally of the lighter tints and the lower ones of the darker tints4 ,a lighthouse lens was placed in this lantern so that an intense beam of light would radiate from it4 ,the flood-lighted ,statue of ,liberty is now visible by night as well as by day and it has a double significance at night1 for light also symbolizes independence4 ,just as the ,statue of ,liberty stands alone in the ,new ,york ,harbor so does the ,woolworth ,building reign supreme on lower ,manhattan4 ,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 nature4 ,this building with its cream terra-cotta surface and intricate architectural details touched here and there with buff1 blue1 green1 red1 and gold1 rises #gib feet or sixty stories above the street and typifies the ,american spirit of conceiving and of executing great undertakings4 ,in it are blended art1 utility1 and majesty4 ,viewed by multitudes during the day1 it is a valuable advertisement for the name which stands for a national institution4 ,but by day it shares attention with its surroundings4 ,if lighted at night it would stand virtually alone against the dark sky and the investment would not be wholly idle during the evening hours4 ,mr4 ,h4 ,h4 ,magdsick1 who designed the lighting for ,liberty1 planned the lighting for the ,woolworth ,tower1 which rises #djg feet or thirty-one stories above the main building4 ,five hundred and fifty projectors containing tungsten filament lamps were distributed about the base of the tower and among some of the architectural details4 ,the main architectural features of the mansard roof extending from the fifty-third to the fifty-seventh floor1 the observation balcony at the fifty-eighth and the lantern structures at the fifty-ninth and sixtieth floors are covered with gold-leaf4 ,by proper placing of the projectors a glittering effect is obtained from these gold surfaces4 ,the crowning features of the lighting effect are the lanterns in the crest of the spire4 ,twenty-four #ajjj-watt tungsten lamps were placed behind crystal diffusing glass1 which transmits the light predominantly in a horizontal direction4 ,thus at long distances1 from which the architectural details cannot be distinguished1 the brilliant crowning light is visible4 ,an automatic dimmer was devised so that the effect of a huge varying flame was obtained4 ,at close range1 owing to the nature of the glass panels1 this portion is not much brighter than the remainder of the surfaces4 ,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 civilization4 ,many prominent buildings and monuments have burst forth in a flood of light1 and their beauty and symbolism have been appreciated at night by many persons who do not notice them by day4 ,not only are the beautiful structures of man lighted permanently but many temporary effects are devised4 ,artificial lighting effects have become a prominent part in outdoor festivals1 pageants1 and theatricals4 ,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 years4 ,the ,municipal ,christmas ,tree in ,chicago in #aiaf was ninety feet high and was lighted with projectors4 ,thousands of gems taken from the ,tower of ,jewels at the ,san ,francisco ,exposition added life and sparkle to that of the other decorations4 ,illustration3 ,the ,capitol flooded with light ,luna ,park1 ,coney ,island1 studded with #fj1jjj incandescent filament lamps ,,the ,,new ,,flood ,,lighting ,,contrasted ,,with ,,the ,,old ,,outline ,,lighting ,illustration3 ,,niagara ,,falls ,,flooded ,,with ,,light ,after the close of the recent war artificial light played a prominent part throughout the country in the joyful festivals4 ,a jeweled arch erected in ,new ,york in honor of the returning soldiers rivaled some of the spectacles of the ,panama-,pacific ,exposition4 ,the arch hung like a gigantic curtain of jewels between two obelisks1 which rose to a height of eighty feet and were surmounted by jeweled forms in the shape of sunbursts4 ,approximately thirty thousand jewels glittered in the beams of batteries of arc-projectors4 ,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 permanency4 ,the equipment of a large building consisted of more than five thousand #aj-watt lamps1 the entire building being outlined with stars consisting of eleven lamps each4 ,the ,brighten ,up campaign spread throughout the country4 ,the lighting and installation of signs and special patriotic displays1 the flooding of streets and shop-windows with light without stint1 produced an inspiring and uplifting effect which did much to restore cheerfulness and optimism4 ,a glowing example was set in ,washington1 where the flood-lighting of the ,capitol1 discontinued shortly after our entrance into the war1 was resumed4 ,in ,chicago a ,victory ,way was established1 with street-lighting posts on both sides of the street equipped with red1 white1 and blue globes surmounted by a golden goddess of ,victory4 ,one hundred and seventy-five projectors were installed along the way on the roofs and in the windows of office buildings4 ,a brilliant1 scintillating ,altar of ,victory was erected at the center of the ,way4 ,it was composed of two enormous candelabra erected one on each side of a platform ninety feet high4 ,these were studded with jewels and supported a curtain of jewels suspended from the altar4 ,in the center of the curtain was a huge jeweled eagle bearing the ,allied flags4 ,this was illuminated by arc-projectors which delivered #bjj1jjj1jjj beam candle-power4 ,in addition to these there were many smaller projectors4 ,in the top of each candelabra six large red-and-orange lamps were installed in reflectors4 ,these illuminated live steam which issued from the top4 ,surmounting the whole was a huge luminous fan formed by beams from large arc search-lights4 ,these are only a few of the many lighting effects which welcomed the returning soldiers1 but they illustrate how much modern civilization depends upon artificial light for expressing its feelings and emotions4 ,throughout all these festivals light silently symbolized happiness1 freedom1 and advancement4 ,projectors were used on a large scale in several cases before the advent of the concentrated filament lamp4 ,w4 ,d',a4 ,ryan1 the leader in spectacular lighting1 lighted the ,niagara ,falls in #aijg with batteries of arc-projectors aggregating #a1aae1jjj1jjj-;beam candle-power4 ,in #aijh 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 diameter4 ,many flags waved throughout the war in the beams of search-lights1 symbolizing a patriotism fully aroused4 ,the search-light beam as it bores through the atmosphere at night is usually faintly bright1 owing to the small amount of fog1 dust1 and smoke in the air4 ,by providing more substance in the atmosphere1 the beams are made to appear brighter4 ,following this reasoning1 ,ryan developed his scintillator consisting of a battery of search-light beams projected upward through clouds of steam which provided an artificial fog4 ,this was first displayed at the ,hudson-,fulton celebration with a battery of arc search-lights totaling #a1jjj1jjj1jjj-;candle-power4 ,all these effects despite their magnitude were dwarfed by those at the ,panama-,pacific ,exposition1 and inasmuch as this up to the present time represents the crowning achievement in spectacular lighting1 some of the details worked out by ,ryan may be of interest4 ,in general1 the lighting effects departed from the bizarre outline lighting in which glaring light-sources studded the structures4 ,the radiant grandeur and beauty of flood-lighting from concealed light-sources was the key-note of the lighting4 ,in this manner wonderful effects were obtained1 which not only appealed to the eye and to the artistic sensibility but which were free from glare4 ,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 preserved4 ,a great many different kinds of devices and lamps were used to make the night effects superior in grandeur to those of daytime4 ,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 future4 ,in another section the visitor was greeted with a gorgeous display of carnival spirit4 ,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 height4 ,the ,tower of ,jewels with more than a hundred thousand dangling gems was flood-lighted1 and the myriads of minute reflected images of light-sources glittering against the dark sky produced an effect surpassing the dreams of imagination4 ,shadows and high-lights of striking contrasts or of elusive colors greeted the visitor on every hand4 ,individual isolated effects of light were to be found here and there4 ,fire hissed from the mouths of serpents and cast the spell of mobile light over the composite ,spanish-,gothic-,oriental setting4 ,a colored beam of a search-light played here and there4 ,mysterious vapors rising from caldrons were in reality illuminated steam4 ,symbolic fountain groups did not escape the magic touch of the lighting wizard4 ,in the ,court of the ,universe great areas were illuminated by two fountains rising about a hundred feet above the sunken gardens4 ,one of these symbolized the setting sun1 the other the rising sun4 ,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 #ejj1jjj4 ,the balustrade seventy feet above the sunken gardens was surmounted by nearly two hundred incandescent filament search-lights4 ,light was everywhere1 either varying in color into a harmonious scene or changing in light and shadow to mold the architecture and sculpture4 ,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 revolved2 rings and comets which appeared at the horizon passed on their way through the heavens1 changing in color and disappearing again at the horizon4 ,all these effects and many more were mirrored in the waters of the lagoons and the whole was a ,wonderland indeed4 ,the scintillator consisted of #dh arc search-lights three feet in diameter totaling #b1fjj1jjj1jjj beam candle-power4 ,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 locomotive4 ,the latter was so arranged that the wheels could be driven at a speed of sixty miles per hour under brake1 thereby emitting great volumes of steam and smoke1 which when illuminated with various colors produced a magnificent spectacle4 ,over three hundred scintillator effects were worked out and this feature of fireless fireworks was widely varied4 ,the aurora borealis and other effects created by this battery of search-lights extended for many miles4 ,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 devices4 ,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 unlimited4 ,it represented the power of light to beautify and to awe4 ,it showed the feebleness of the decorator's media in comparison with light pulsating with life4 ,it consisted of a great variety of direct1 masked1 concealed1 and projected effects1 but these were blended harmoniously with one another and with the decorative and architectural details of the structures4 ,it was a crowning achievement of a century of public lighting which began with ,murdock's initial display of a hundred flickering gas-jets4 ,it demonstrated the powers of science in the production of light and of genius and imagination in the utilization of light4 ,it was a silent but pulsating display of grandeur dwarfing into insignificance the aurora borealis in its most resplendent moments4 ,,xxiii ,,the ,,expressiveness ,,of ,,light ,from an esthetic or1 more broadly1 a psychological point of view no medium rivals light in expressiveness4 ,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 attributes4 ,in fact1 it is possible that light1 color1 and darkness possess certain fundamentally innate powers2 at least1 they have acquired expressive and impressive powers through the many associations in mythology1 religion1 nature1 and common usage4 ,besides these attributes1 light possesses a great advantage over the media of decoration in obtaining brightness and color effects4 ,for example1 the landscape artist cannot reproduce the range of values or brightnesses in most of nature's scenes1 for if black is used to represent a deep shadow1 white is not bright enough to represent the value of the sky4 ,in fact1 the range of brightnesses represented by the deep shadow and the sky extends far beyond the range represented by black and white pigments4 ,the extreme contrast ordinarily available by means of artist's colors is about thirty to one1 but the sky is a thousand times brighter than a shadow1 a sunlit cloud is thousands of times brighter than the deep shadows of woods1 and the sun is millions of times brighter than the shadows in a landscape4 ,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 themselves4 ,in the matter of purity of colors1 light surpasses reflecting media1 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 light4 ,it is impossible to obtain pure hues by means of pigments or of other reflecting media4 ,these advantages of light are very evident on turning to spectacular lighting effects1 and even the lighting of interiors illustrates a potentiality in light superior to other media4 ,for example1 in a modern interior in which concealed lighting produces brilliantly illuminated areas above a cornice and dark shadows on the under side1 the range in values is often much greater than that represented by black and white1 and still there remains the possibility of employing the light-sources themselves in extending the scale of brightness4 ,superposing color upon the whole it is obvious that the combination of primary light with reflected light possesses much greater potentiality than the latter alone4 ,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 pigments1 etc4 ,the expressive possibilities of lighting find extensive applications in relation to painting1 sculpture1 and architecture4 ,a painting is an expression of light and the sculptor's product finally depends upon lighting for its effectiveness4 ,lighting is the master painter and sculptor4 ,it may affect the values of a painting to some extent and it is a great influence upon the colors4 ,it molds the model from which the sculptor works and it molds the completed work4 ,the direction1 distribution1 and quality of light influence the appearance of all objects and groups of them4 ,aside from the modeling of ornament1 the light and shade effects of relatively large areas in an interior such as walls and ceiling1 the contrasts in the brightnesses of alcoves with that of the main interior1 and the shadows under cornices1 beams1 and arches are expressions of light4 ,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 likewise1 but the latter is even able to alter the mood produced by the decorator4 ,for example1 a large interior flooded with light from concealed sources has the airiness and extensiveness of outdoors4 ,if lighted solely by means of sources concealed in an upper cornice1 the ceiling may be bright and the walls may be relatively dark by contrast4 ,such a lighting effect may produce a feeling of being hemmed in by the walls without a roof4 ,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 defined1 the feeling produced may be that of being hemmed in by crowding darkness4 ,thus lighting is productive of moods and illusions ranging from the mystery of crowding darkness to the extensiveness of outdoors4 ,future lighting of interiors doubtless will provide an adequacy of lighting effects which will meet the respective requirements of various occasions4 ,a decorative scheme in which light and medium grays are employed produces an interior which is very sensitive to lighting effects4 ,to these light-and-shade effects colored light may add its charming effectiveness4 ,not only are colored lighting effects able to add much to the beauty of the setting but they possess certain other powers4 ,blue tints produce a cold effect and the yellow and orange tints a warm effect4 ,for example1 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 summer4 ,how tinted illuminants fit the spirit of an occasion or the mood of a room may be fully appreciated only through experiments1 but these are so effective that the future of lighting will witness the application of the idea of painting with light to its fullest extent4 ,color is demanded in other fields1 and1 considering its effectiveness and superiority in lighting1 it will certainly be demanded in lighting when its potentiality becomes appreciated and readily utilized4 ,the expressiveness of light is always evident in a landscape4 ,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 evening4 ,the artist in painting a desert scene employs short harsh shadows if he desires to suggest the excessive heat4 ,these shadows suggest the relentless noonday sun4 ,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 sun4 ,nature's lighting varies from moment to moment1 from day to day1 and from season to season4 ,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 altitude4 ,they are harshest at noon and gradually fade as they lengthen1 until at sunset they disappear4 ,the colors of sunlit surfaces and of shadows vary from sunrise to sunset4 ,these are the fundamental variations in the lighting1 but in the various scenes the lighting effects are further modified by clouds and by local conditions or environment4 ,the vast outdoors provides a fruitful field for the study of the expressiveness of light4 ,having become convinced of this power of light1 the lighting expert may turn to artificial light1 which is so easily controlled in direction1 distribution1 and color1 and draw upon its potentiality4 ,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 occasion4 ,a study of nature's lighting reveals one great principle1 namely1 variety4 ,mankind demands variety in most of his activities4 ,work is varied and alternated with recreation4 ,meals are not always the same4 ,clothing1 decorations1 and furnishings are relieved of monotony4 ,one of the most potent features of artificial light is the ease with which variety may be obtained4 ,in obtaining relief from the monotony of decorations and furnishings1 considerable expense and inconvenience are inevitably encountered4 ,with an adequate supply of outlets1 circuits1 and controls a wide variety of lighting effects may be obtained with perhaps an insignificant increase in the initial investment4 ,variety is the spice of lighting as well as of life4 ,these various principles of lighting are readily exemplified in the lighting of the home1 which is discussed in another chapter4 ,the church is even a better example of the expressive possibilities of lighting4 ,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 scheme4 ,obviously1 the dark-stained ceiling of a certain type of church would not be flooded with light4 ,the fact that it is made dark by staining precludes such a procedure in lighting4 ,the characteristics of creeds are distinctly different and these are to some extent exemplified by the lines of the architecture of their churches4 ,in the same way the lighting effect may be harmonized with the creed and the spirit of the interior4 ,the lighting may always be dignified1 impressive1 and congruous4 ,few churches are properly lighted with a high intensity of illumination2 moderate lighting is more appropriate1 for it is conducive to the spirit of worship4 ,in some creeds a dominant note is extreme penitence and severity4 ,the architecture may possess harsh outlines1 and this severity or extreme solemnity may be expressed in lighting by harsher contrasts1 although this does not mean that the lighting must be glaring4 ,on the other hand1 in a certain modern creed the dominant note appears to be cheerfulness4 ,the spacious interiors of the churches of this creed are lacking in severe lines and the walls and ceilings are highly reflecting4 ,adequate illumination by means of diffused light without the production of severe contrasts expresses the creed1 modernity1 and enlightenment4 ,on the altar of certain churches the expressiveness of light is utilized in the ceremonial uses which vary with the creed4 ,even the symbolism of color may be appropriately woven into the lighting of the church4 ,the expressiveness of light and color originated through the contact of primitive man with nature4 ,sunlight meant warmth and a bountiful vegetation1 but darkness restricted his activities and harbored manifold dangers4 ,many associations thus originated and they were extended through ignorance and superstition4 ,yellow is naturally emblematical of the sun and it became the symbol of warmth4 ,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 winter4 ,the first signs of green vegetation in the spring were welcomed as an end of winter and a beginning of another bountiful summer2 hence green symbolized youth and hope4 ,it became associated with the springtime of life and thus signified inexperience1 but as the color of vegetation it also meant life itself and became a symbol of immortality4 ,blue acquired certain divine attributes because1 as the color of the sky1 it was associated with the abode of the gods or heaven4 ,also a blue sky is the acme of serenity and this color acquired certain appropriate attributes4 ,associations of this character became woven into mythology and thus became firmly established4 ,poets have felt these influences of light and color in nature and have given expression to them in words4 ,they also have entwined much of the mythology of past civilizations and these repetitions have helped to establish the expressiveness of light and color4 ,early ecclesiasts employed these symbolisms in religious ceremonies and dictated the garbs of saints and other religious personages in the paintings which decorated their edifices4 ,thus there were many influences at work during the early centuries when intellects were particularly susceptible through superstition and lack of knowledge4 ,the result has been an extensive symbolism of light1 color1 and darkness4 ,at the present time it is difficult to separate the innate appeal of light1 color1 and darkness from those attributes which have been acquired through associations4 ,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 consent4 ,space does not permit a discussion of this point1 but the chief aim is consummated if the existence of an expressiveness and impressiveness of light is established4 ,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 them4 ,psychological investigations reveal many interesting facts pertaining to the influence of light and color upon mankind4 ,when choosing color for color's sake alone1 that is1 divorced from any associations of usage1 mankind prefers the pure colors to the tints and shades4 ,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 surroundings4 ,civilized mankind chooses tints and shades predominantly to live with1 that is1 for the decoration of his surroundings4 ,however1 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 with4 ,this is an interesting discovery and it has its applications in lighting1 especially in spectacular and stage-lighting4 ,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 spectrum1 such as red and blue4 ,red is favored by women1 with blue a close second1 but the reverse is true for men4 ,it is also thoroughly established that red1 orange1 and yellow exert an exciting influence2 yellow-green1 green1 and blue-green1 a tranquilizing influence1 and blue and violet a subduing influence upon mankind4 ,all these results were obtained with colors divorced from surroundings and actual usage4 ,in the use of light and color the laws of harmony and esthetics must be obeyed1 but the sensibility of the lighting artist is a satisfactory guide4 ,harmonies are of many varieties1 but they may be generally grouped into two classes1 those of analogy and those of contrast4 ,the former includes colors closely associated in hue and the latter includes complementary colors4 ,no rules in simplified form can be presented for the production of harmonies in light and color4 ,these simplifications are made only by those who have not looked deeply enough into the subject through observation and experiment to see its complexity4 ,the expressiveness of light finds applications throughout the vast field of lighting1 but the stage offers great opportunities which have been barely drawn upon4 ,when one has awakened to the vast possibilities of light1 shade1 and color as a means of expression it is difficult to suppress a critical attitude toward the crudity of lighting effects on the present stage1 the lack of knowledge pertaining to the latent possibilities of light1 and the superficial use of this potential medium4 ,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-day4 ,one turns hopefully toward the gallant though small band of stage artists who are striving to realize a harmony of lighting1 setting1 and drama in the so-called modern theater4 ,unappreciated by a public which flocks to the melodramatic movie1 whose scenarios produced upon the legitimate stage would be jeered by the same public1 the modern stage artist is striving to utilize the potentiality of light4 ,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 effectively4 ,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 sensibility4 ,science and art must be linked in lighting4 ,the worthy efforts of stage artists in some of the modern theaters lack the support of the producers1 who cater to the taste of the public which pays the admission fees4 ,apparently the modern theater must first pass through a period in which financial support must be obtained from those who are able to give it1 just as the symphony orchestra has been supported for the sake of art4 ,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 commercialism4 ,those who have not viewed stage-lighting from behind the scenes would often be surprised at the crudity of the equipment1 and especially at the superficial intellects which are responsible for some of the realistic effects obtained4 ,but these are the result usually of experiment1 not of directed knowledge4 ,furthermore1 little thought is given to the emotional value of light1 shade1 and color4 ,the flood of light and the spot of light are varied with gaudy color-effects1 but how seldom is it possible to distinguish a deep relation between the lighting and the dramatic incidents6 ,illustration3 ,soldiers' and ,sailors' ,monument ,jeweled portal welcoming returned soldiers ,,artificial ,,light ,,honoring ,,those ,,who ,,fell ,,and ,,those ,,who ,,returned ,illustration ,illustration3 ,,the ,,expressiveness ,,of ,,light ,,in ,,churches ,in much of the foregoing discussion the present predominating theatrical productions are not considered1 for the lighting effects are good enough for them4 ,many ingenious tricks and devices are resorted to in these productions1 and as a whole lighting is serving effectively enough4 ,but in considering the expressiveness of light the deeper play is the medium necessary for utilizing the potentiality of light4 ,these are rare and unfortunately the stage artist appreciative of the significations and emotional value of light and color is still rarer4 ,the equipment of the present stage consists of footlights1 side-lights1 border-lights1 flood-lights1 spot-lights1 and much special apparatus4 ,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 light4 ,this is directed upward and the effect is an unnatural and even a grotesque modeling of the actors' features4 ,the shadows produced are incongruous1 for they are opposed to the other real and painted effects of light and shade4 ,the only excuse for such lighting is that it is easily done and that proper lighting is difficult to obtain1 owing to the fact that it involves a change in construction4 ,by no means should the footlights be abandoned1 for they would still be invaluable in obtaining diffused light even when the dominant light is directed from above the horizontal4 ,in the present stage-lighting1 in which the footlights generally predominate1 the expressiveness of light is not satisfactory4 ,perhaps they are a necessary compromise1 but inasmuch as their effect is unnatural they should not be accepted until it is thoroughly proved that ingenuity cannot eliminate the present defects4 ,the stage as a whole is a mobile picture in light1 shade1 and color with the addition of words and music4 ,excepting the latter1 it is an expression of light worthy of the same care and consideration that the painting1 which is also an expression of light1 receives from the artist4 ,the scenery and costumes should be considered in terms of the lighting effects because they are affected by changes in the color of the light4 ,in fact1 the author showed a number of years ago that by carefully relating the colors of the light with the colors used in painting the scenery1 a complete change of scene can be obtained by merely changing the color of the light4 ,rather wonderful dissolving effects can be produced in this manner without shifting scenery4 ,for example1 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 leaves4 ,but before such accomplishments can be realized upon the stage1 scientific knowledge must be available behind the scenes4 ,the art museum affords a multitude of opportunities for utilizing the expressiveness of light4 ,this is more generally true of sculptured objects than of paintings because the latter may be treated as a whole4 ,the artist almost invariably paints a picture by daylight and unless it is illuminated by daylight it is altered in appearance1 that is1 it becomes another picture4 ,the great difference in the appearance of a painting under daylight and ordinary artificial light is quite startling1 when demonstrated by means of apparatus in which the two effects may be rapidly alternated4 ,art museums are supposed to exhibit the works of artists and1 therefore1 no changes in these works should be tolerated if they can be avoided4 ,the modern artificial-daylight lamps make it possible to illuminate galleries with light at night which approximates daylight4 ,a further advantage of artificial light is that it may be easily controlled and a more satisfactory lighting may be obtained than with natural light4 ,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 galleries4 ,if the works of artists are really prized for their appearance1 the lighting of them is very important4 ,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 satisfaction1 it is possible to give the best consideration to its lighting in its final place of exhibition4 ,the appearance of a sculpture depends upon the dominant direction of the light1 the solid-angle subtended by the light-source 7skylight1 area of sky1 etc47 and the amount of scattered light4 ,the direction of dominant light determines the general direction of the shadows2 the solid-angle of the light-source affects the character of the edges of the shadows2 and the scattered light accounts for the brightness of the shadows4 ,it should be obvious that variations of these factors affect the appearance or expression of three-dimensional objects4 ,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 important4 ,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 appearances1 for they can arouse the emotions only through the doorway of vision4 ,a century ago mankind gave no thought to utilizing the expressive and impressive powers of light except in religious ceremonies4 ,it was not practicable to utilize light from the feeble flames of those days in the elaborate manner necessary to draw upon these powers4 ,man was concerned with the more pressing needs4 ,he wanted enough light to make the winter evenings endurable and the streets reasonably safe4 ,the artists of those days saw the wonderful expressions of light exhibited by ,nature1 but they dared not dream of rivaling these with artificial light4 ,to-day ,nature surpasses man in the production of lighting effects only in magnitude4 ,man surpasses her artistically4 ,in fact1 the artist becomes a master only when he can improve upon her settings2 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 reality4 ,but everywhere ,nature is the great teacher1 for her world is full of an everchanging infinitude of expressions of light4 ,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 sense4 ,,xxiv ,,lighting ,,the ,,home ,in the home artificial light exerts its influence upon every one4 ,without artificial lighting the family circle may not have become the important civilizing influence that it is to-day4 ,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 splinter4 ,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 lighting4 ,he flees from his home to that of his more fortunate neighbor1 or he retires in his helplessness to awaken in the morning with a blessing for daylight4 ,he cannot conceive of happiness and recreation in the homes of a century or two ago1 when a few candles or an oil-lamp or two were the sole sources of light4 ,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 age4 ,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 lighting4 ,his chief aim was to utilize as little as possible1 for cost was always foremost in his mind4 ,the development of the science of light-production has been so rapid during the past generation that adequate1 efficient1 and cheap artificial light finds mankind unconsciously viewing lighting with the same attitude as he displays toward his food and fuel bills4 ,another consequence of this rapid development is that mankind does not know how to extract the joy from modern artificial light4 ,this is readily demonstrated by analyzing the lighting of middle-class homes4 ,the cost of light has been discussed in another chapter and it has been shown that it has decreased enormously in a century4 ,it is now the most potential agency in the home when viewed from the standpoint of cost4 ,the average householder pays less than twenty dollars per year for ever-ready light throughout his home4 ,for about five cents per day the average family enjoys all the blessings of modern lighting1 which is sufficient proof that cost is an insignificant item4 ,in order to simplify the discussion of lighting the home the terminology of electric-lighting will be used4 ,the principles expounded apply as well to gas as to electricity1 and owing to the ingenuity of the gas-lighting experts1 the possibilities of gas-lighting are extensive despite its handicaps4 ,there are some places in the home1 such as the kitchen and basement1 where lighting is purely utilitarian in the narrow sense1 but in most of the rooms the esthetic or1 more broadly1 the psychological aspects of lighting should dominate4 ,pure utility is always a by-product of artistic lighting and furthermore1 the lighting effects will be without glare when they satisfy all the demands of esthetics4 ,in dealing with lighting in the home the householder should concentrate his attention upon lighting effects4 ,unfortunately1 he is not taught to do so1 for everywhere he turns for help he finds the discussion directed toward fixtures and lamps instead of toward lighting effects4 ,however1 these are merely links in the chain from the meter to the eye4 ,lamps are of interest from the standpoint of quantity and quality of light1 and fixtures are of importance chiefly as distributers of light4 ,these details are merely means to an end and the end is the lighting effect4 ,of course1 the fixtures are more important as objects than the wires because they are visible and should harmonize with the general decorative and architectural scheme4 ,the home is the theater of life full of various moods and occasions2 hence the lighting of a home should be flexible4 ,a degree of variety should be possible4 ,controls1 wiring1 outlets1 and fixtures should conspire to provide this variety4 ,at the present time the average householder does not give much attention to lighting until he purchases fixtures4 ,it is probable that he thought of it when he laid out or approved the wiring1 but usually he does not consider it seriously until he visits the fixture-dealer to purchase fixtures4 ,and then unfortunately the fixture-dealer does not light his home2 he does not sell the householder lighting-effects designed to meet the requirements of the particular home2 he sells merely fixtures4 ,unfortunately there are few fixtures available which have definite aims in lighting as demanded by the home4 ,of the great variety of fixtures available there are many artistic objects1 but it is obvious that little attention is given to their design from the standpoint of lighting4 ,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 display4 ,he exhibits fixtures usually en masse and seldom attempts to illustrate the lighting effects produced in the room4 ,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 appreciated4 ,the point at which to begin to design the lighting for a home is the wiring4 ,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 them4 ,at this point the householder should attempt to form an opinion as to the relative values4 ,is artificial lighting important enough to warrant an expenditure of two per cent4 of the total investment in the home and its furnishings8 ,the answer will depend upon the extent to which artificial light is appreciated4 ,it appears that four or five per cent4 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 residence4 ,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 convenience4 ,it appears best to take up this subject room by room because the requirements vary considerably1 but in order to be specific in the discussions1 a middle-class home will be chosen4 ,the more important rooms will be treated first and various simple details will be touched upon because1 after all1 the proper lighting of a home is realized by attention to small details4 ,the living-room is the scene of many functions4 ,it serves at times for the quiet gathering of the family1 each member devoted to reading4 ,at another time it may contain a happy company engaged at cards or in conversation4 ,the lighting requirements vary from a spot or two of light to a flood of light4 ,excepting in the small living-rooms there does not appear to be a single good reason for a ceiling fixture4 ,it is nearly always in the field of vision when occupants are engaged in conversation1 and for reading purposes the portable lamp of satisfactory design has no rival4 ,wall brackets cannot supply general lighting without being too bright for comfort4 ,if they are heavily shaded they may still emit plenty of light upward1 but the adjacent spots on the walls or ceiling will generally be too bright4 ,wall brackets may be beautiful ornaments and decorative spots of light and have a right to exist as such1 but they cannot be safely depended upon for adequate general lighting on those occasions which demand such lighting4 ,as a general principle1 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 scale4 ,by placing these on the drawings the furnished room is readily visualized and the locations of baseboard outlets become evident4 ,it appears that the best method of lighting a living-room is by means of decorative portable lamps4 ,such lamps are really lighting-furniture1 for they aid in decorating and in furnishing the room at all times4 ,a number of these lamps in the living-room insures great flexibility in the lighting1 and the light may be kept localized if desired so that the room is restful4 ,a room whose ceiling and walls are brilliantly illuminated is not so comfortable for long periods as one in which these areas are dimly lighted4 ,furthermore1 the latter is more conducive to reading and to other efforts at concentration4 ,the furniture may be readily shifted as desired and the portable lamps may be rearranged4 ,such lighting serves all the purposes of the living-room excepting those requiring a flood of light1 but it is easy to conceal elaborate lighting mechanisms underneath the shades of portable lamps4 ,several types of portable lamps are available which supply an indirect component as well as direct light4 ,the former illuminates the ceiling with a flood of light without any discomforting glare4 ,such a lighting-unit is one of the most satisfactory for the home1 for two distinct effects and a combination of these introduce a desirable element of variety into the lighting4 ,not less than four and preferably six baseboard outlets should be provided in a living-room of moderate size4 ,one outlet on the mantel is also to be desired for connecting decorative candlesticks1 and brackets above the fireplace are of ornamental value4 ,although the absence of ceiling fixtures improves the appearance of the room1 wiring may be provided for ceiling outlets in new houses as a matter of insurance against the possible needs of the future4 ,when ceiling fixtures are not used1 switches may be provided for the mantel brackets or certain baseboard outlets in order that light may be had upon entering the room4 ,the merits of a portable lamp may be ascertained before purchasing by actual demonstration4 ,some of them are not satisfactory for reading-lamps1 owing to the shape of the shade or to the position of the lamps4 ,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 it4 ,a floor lamp may also be tested very easily4 ,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 furniture4 ,a tall floor lamp often serves for lighting the piano1 but small piano lamps may be found which are decorative as well as serviceable in illuminating the music without glare4 ,the dining-room presents an entirely different problem for the setting is very definite4 ,the dining-table is the most important area in the room and it should be the most brilliantly illuminated area in the room4 ,a demonstration of this point is thoroughly convincing4 ,the decorator who designs wall brackets for the dining-room is interested in beautiful objects of art and not in a proper lighting effect4 ,the fixture-dealer1 having fixtures to sell and not recognizing that he could fill a crying need as a lighting specialist1 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 illuminated4 ,the indirect and semi-indirect units illuminate the ceiling predominantly with the result that this bright area distracts attention from the table4 ,a brightly illuminated table holds the attention of the diners4 ,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 light4 ,the old-fashioned dome which hung over the dining-table has served well1 for it illuminated the table and left the remainder of the room dimly lighted4 ,but its wide aperture made it necessary to suspend it rather low in order that the lamps within should not be visible4 ,it is an obtrusive fixture and despite its excellent lighting effect1 it went out of style4 ,but satisfactory lighting principles never become antiquated1 and as taste in fixtures changes the principles may be retained in new fixtures4 ,modern domes are available which are excellent for the dining-room if the lamps are well concealed4 ,the so-called showers are satisfactory if the shades are dense and of such shape as to conceal the lamps from the eyes4 ,various modifications readily suggest themselves to the alert fixture-designer4 ,even the housewife can do much with silk shades when the principle of lighting the dining-table is understood4 ,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 downward4 ,semi-indirect and indirect fixtures have many applications in lighting1 but they do not provide the proper effect for a dining-room4 ,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 walls4 ,if a daylight lamp is used for the direct component1 the table will appear very beautiful4 ,under this light the linen and china are white1 flowers and decorations on the china appear in their full colors1 the silver is attractive1 and the various color-harmonies such as butter1 paprika1 and baked potato are enticing4 ,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 shades4 ,the ceiling fixture should be provided with two circuits and switches4 ,in some cases it is easy to provide a dangling plug for connecting such electric equipment as a toaster1 percolator1 or candlesticks4 ,two candlesticks are effective on the buffet1 but usually the smallest normal-voltage lamps available give too much light4 ,miniature lamps may be used with a small transformer1 or two regular lamps may be connected in series4 ,at least two baseboard outlets are convenient4 ,the foregoing deals with the more or less essential lighting of a dining-room1 but there are various practicable additional lighting effects which add much charm to certain occasions4 ,colored light of low intensity obtained from a cove or from flower-boxes fastened upon the wall is very pleasing4 ,if a cove is provided around the room1 two circuits containing orange and blue lamps respectively will supply two colors widely differing in effect4 ,by mixing the two a beautiful rose tint may be obtained4 ,this equipment has been installed with much satisfaction4 ,a simpler method of obtaining a similar effect is to use imitation flower-boxes plugged into wall outlets4 ,artificial foliage adds to the charm of these boxes4 ,the colored light is merely to add another effect on special occasions and its intensity should never be high4 ,in the dining-room such unusual effects are not out of place and they need not be garish4 ,the sun-room partakes of the characteristics of the living-room to some extent1 but1 it being smaller1 a semi-indirect fixture may be satisfactory for general illumination4 ,however1 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 necessary4 ,two or three baseboard outlets are desirable for attaching decorative or even purely utilitarian lamps4 ,the sun-room is an excellent place for utilizing flower-box fixtures decorated with artificial foliage4 ,in fact1 a central fixture may assume the appearance of a hanging basket of foliage4 ,the library and den offer no problems differing from those already discussed in the living-room4 ,a careful consideration of the disposition of the furniture will reveal the best positions for the outlets4 ,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 purposes4 ,in both these rooms an excellent reading-lamp is desired1 but it may be decorative as well4 ,wall outlets may be desired for decorative portable lamps upon the bookcases4 ,the sleeping-room1 which commonly is also a dressing-room1 often exhibits the errors of a lack of foresight in lighting4 ,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 located4 ,the windows may usually be arranged for twin beds as well as for a single one with obvious advantages of flexibility in arrangement4 ,with the position of the bureau determined it is easy to locate outlets for two wall brackets1 one on each side1 about sixty-six inches above the floor and about five feet apart4 ,when the brackets are equipped with dense upright shades1 the figure before the mirror is well illuminated without glare and sufficient light reaches the ceiling to illuminate the whole room4 ,a baseboard outlet should be available for small portable lamps which may be used upon the bureau or for electric heating devices4 ,the same is true for the dressing-table2 indeed1 two small decorative lamps on the table serve better than high wall brackets owing to the fact that the user is seated4 ,a baseboard outlet near the head of the bed or between the beds is convenient for a reading-lamp and for other purposes4 ,an outlet in the center of the ceiling controlled by a convenient switch may be installed on building1 as insurance against future needs or desires4 ,but a single lighting-unit in the center of the ceiling does not serve adequately the needs at the bureau and dressing-table4 ,in fact1 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 fixture4 ,in the bath-room the principal problem is to illuminate the person1 especially the face1 before the mirror4 ,many mistakes are made at this point1 despite the simplicity of the solution4 ,in order to see the image of an object in a mirror1 the object must be illuminated4 ,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 feet4 ,both sides of the face will be well illuminated and the light-sources are low enough to eliminate objectionable shadows4 ,the units may be merely pull-chain sockets containing frosted or opal lamps4 ,a center bracket or a single unit suspended from the ceiling is not as satisfactory as the two brackets4 ,these afford enough light for the entire bath-room4 ,a baseboard or wall outlet is convenient for connecting a heater1 curling-iron1 and other electrically heated devices4 ,the sewing-room1 which in the middle-class home is usually a small room1 is sometimes used as a bedroom4 ,a ceiling fixture will supply adequate general lighting1 but a baseboard outlet should be available for a short floor lamp or a table lamp for sewing purposes4 ,an intense local light is necessary for this occupation1 which severely taxes the eyes4 ,a so-called daylight lamp serves very well in this case4 ,illustration3 ,,obtaining ,,two ,,different ,,moods ,,in ,a ,,room ,,by ,a ,,portable ,,lamp ,,which ,,supplies ,,direct ,,and ,,indirect ,,components ,,of ,,light ,illustration3 ,,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 range1 work-table1 sink1 etc41 are determined4 ,a bracket for each is advisable unless they are so located that one will serve two purposes4 ,it is customary to have a combination fixture for gas and electricity4 ,this is often suspended from the center of the ceiling1 but inasmuch as the gas-light cannot be close to the ceiling1 the fixture extends so far downward as to become a nuisance4 ,furthermore1 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 shadow4 ,if a ceiling outlet is used it should be an electrical socket at the ceiling4 ,the combination fixture is best placed on the wall as a bracket4 ,the so-called daylight lamps are valuable in the kitchen4 ,in the basement a generous supply of ceiling outlets adds much to the satisfaction of a basement4 ,one in each locker1 one before the furnace1 and a large daylight lamp above but to one side of the laundry trays are worth many times their cost4 ,furthermore1 a wall socket for the electric iron and washing-machine is a convenience very much appreciated4 ,in the stairways convenient three-way switches for each of the ceiling fixtures represents the best practice4 ,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 served4 ,in vestibules and on porches ceiling fixtures controlled by means of convenient switches are satisfactory4 ,the entrance hall may be made to express hospitality by means of lighting which should be adequate and artistic4 ,an adequate supply of outlets and wall switches is not costly and they pay generous dividends4 ,with a scanty supply of these1 the possibilities of lighting are very much curtailed4 ,there is nothing intricate about locating switches and outlets1 so the householder may do this himself1 or he may view critically the plans as submitted4 ,the chief difficulties are to throw aside his indifference and to readjust his ideas and values4 ,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 furnishings4 ,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 displays1 but he should insist upon a demonstration4 ,if the dealer is not equipped with a room for this purpose1 he should be asked to demonstrate in the rooms to be lighted4 ,if the fixture-dealer does not realize that he should be selling lighting effects1 the householder should make him understand that lighting effects are of primary importance and the fixtures themselves are of secondary interest in most cases4 ,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 desired4 ,an advantage of portable lamps is that they may be taken away on moving4 ,in fact1 when lighting is eventually considered a powerful decorative medium1 as it should be1 it is probable that fixtures will be personal property attached to ceiling1 wall1 and floor outlets by means of plugs4 ,a variety of incandescent lamps are available4 ,for the home1 opal1 frosted1 or bowl-frosted lamps are usually more satisfactory than clear lamps4 ,bare filaments should not be visible1 for they not only cause discomfort and eye-strain but they spoil what might otherwise be an artistic effect4 ,lamps with diffusing bulbs do much toward eliminating harsh shadows cast by the edges of the shades1 by the chains of the fixtures1 etc4 ,these lamps are available in many shapes and sizes and the householder should make a record of voltage1 wattage1 and shape of the lamps which he finds satisfactory in the various fixtures4 ,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 lamps4 ,in brackets and other purely decorative lighting-units small frosted lamps are usually the most satisfactory4 ,there is a general desire for the warm yellowish light of the candle-flame1 and this may be obtained by a tinted shade but usually more satisfactorily by means of a tinted lamp4 ,the householder will find it interesting to become intimate with lighting1 for it can serve him well4 ,the housewife will often find much interest in making shades of textiles and of parchment4 ,charming glassware in appropriate tints and painted designs is available for all rooms4 ,in the bedchamber and the nursery some of these painted designs are exceedingly effective4 ,fixtures should shield the lamps from the eyes1 and the diffusing media whether glass or textile should be dense enough to prevent glare4 ,no fixture can be beautiful and no lighting effect can be artistic if glare is present4 ,if the architect and the householder will realize that light is a medium comparable with the decorator's media1 better lighting will result4 ,light has the great advantage of being mobile and with adequate outlets and controls supplemented by fixtures from which different effects are available1 the householder will find in lighting one of the most fruitful sources of interest and pleasure4 ,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 furnishing4 ,artificial lighting1 softly diffused and properly localized1 is one of the most important factors in making a house a home4 ,,xxv ,,lighting--,a ,,fine ,,art8 ,in the preceding chapters the progress of light has been sketched from its obscure infancy to its vigorous youth of the present time4 ,it has been seen that progress was slow until the beginning of the nineteenth century1 after which it began to gain momentum until the present century has witnessed tremendous advances4 ,until the latter part of the nineteenth century artificial light was considered an expensive utility1 but as modern lamps appeared which supplied adequate light at reasonable cost attention began to be centered upon utilization1 and the lighting engineer was born4 ,gradually it is being realized that artificial light is no longer a luxury1 that it may be used in great quantity1 and that it may be directed1 diffused1 and altered in color as desired4 ,although the potentiality of light has been barely drawn upon1 the present usages surpass the most extravagant dreams of civilized beings a half-century ago4 ,mere light of that time was changed into more light as gas-lighting developed1 and more light has increased to adequate light of the present time through the work of scientists4 ,it is apparent that a sudden enforced reversion to the primitive flames of fifty years ago would paralyze many activities4 ,much of interest and beauty would be blotted out of this brilliant1 pulsating1 productive age4 ,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 period4 ,in fact1 its development since it began in earnest has gone forward with ever-increasing momentum4 ,on viewing the wonders of modern artificial lighting on every hand it is not difficult to muster the courage necessary to venture into its future4 ,the lighting engineer has been a natural evolution of the present age1 for the economic aspects of lighting have demanded attention4 ,he is increasing the safety1 efficiency1 and happiness of mankind and civilization is beginning to feel his influence economically4 ,however1 with the advent of adequate1 efficient1 and controllable light1 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 opportunity4 ,but the artist who believes that a new art may be evolved to perfection in a few years is doomed to disappointment1 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 contact4 ,will lighting ever become a fine art8 ,will it ever be able alone to arouse emotional man as do the fine arts8 ,are the powers of light sufficiently great to enthrall mankind without the aid of form1 music1 action1 or spoken words8 ,it is safer to answer yes than no to these questions4 ,painting has reached a high place as an art and this art is the expressiveness of secondary or reflected light reinforced by imitation forms1 which by a combination of light and drawing comprise the subjects4 ,a painting is a momentary expression of light1 a cross-section of something mobile1 such as nature1 thought1 or action4 ,light has the essential qualifications of painting with the advantages of a greater range of brightness1 of greater purity of colors1 and the great potentiality of mobility4 ,if lighting becomes a fine art it will doubtless be related to painting somewhat in the same manner that architecture is akin to sculpture4 ,with the introduction of mobility it will borrow something from the arts of succession and especially from music4 ,the art of lighting in its present infancy is leaning upon established arts1 just as the infant learns to walk alone by first depending upon support4 ,the use of color in painting developed slowly1 being supported for centuries by the strength of drawing or subject4 ,the landscapes of a century ago were dull1 for color was employed hesitatingly and sparingly4 ,the colors in the portraits of the past merely represented the gorgeous dress of bygone days4 ,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 drawing4 ,drafting and coloring are now in partnership1 the former having given up guardianship when the latter reached maturity4 ,lighting is now an accompaniment of the drama1 of the dance1 of architecture1 of decoration1 and of music4 ,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 rle4 ,even in its infancy it has on occasions performed admirably almost without any aid4 ,the bursting rocket1 the marvelous effects at the ,panama-,pacific ,exposition1 and some of the exhibitions on the theatrical stage are glimpses of the potentiality of light4 ,to fall back upon the terminology of music1 these may be glimmerings of light-symphonies4 ,harmony is simultaneity and a painting in this respect is a chord--a momentary expression fixed in material media4 ,a melody of light requires succession just as the melody in music4 ,the restless colors of the opal comprise a light melody like the songs of birds4 ,the gorgeous splendor of the sunset compares in magnitude and in its various moods with the symphony orchestra and its powers4 ,throughout nature are to be found gentle chords1 beautiful melodies and powerful symphonies of light and this music of light exhibits the complexity and structure analogous to music4 ,there is no physical relation between music1 poetry1 and light1 but it is easy to lean upon the established terminology for purposes of discussion4 ,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 light4 ,in other words1 a relation between light and music can exist only in the psychological realm4 ,these melodies and symphonies of light in nature are admittedly pleasing or impressive as the case may be1 but are they as appealing as music1 poetry1 painting1 or sculpture8 ,the consensus of opinion of a large group of average persons might indicate a negative reply1 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 light4 ,the unprejudiced opinion of artists is that light is a powerfully expressive and impressive medium4 ,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 things4 ,but he has experimented only with single colors or with simple patterns and his subjects are selected more or less at random from the multitude4 ,what would be his conclusion if he examined painters and others who have developed their sensibilities to a deep appreciation of light and color8 ,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 sounds4 ,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 old4 ,would the primitive savage appreciate the modern symphony orchestra8 ,even the majority of civilized beings prefer the modern ragtime or jazz to the exquisite art of the symphony4 ,an appreciation of the opera and the symphony is reached by educational methods extending over long periods4 ,an appreciation of the expressiveness of light cannot be expected to be realized by any short-cut4 ,most persons to-day enjoy the melodramatic movie more than the drama and relatively few experience the deep appeal of the fine arts4 ,surely the symphony of light cannot be justly condemned because of a lack of appreciation and understanding of it1 for it has not been introduced to the public4 ,furthermore1 the expressiveness of music is still indefinite at best despite the many centuries of experimenting on the part of musicians4 ,if poetry is to be believed1 the symphonies of light as rendered by nature in the sunsets1 in the aurora borealis1 and in other sky-effects of great magnitude have deeply impressed the poet4 ,if his descriptions are to be accepted at their face-value1 the melodies of light rendered in the precious stone1 in the ice-crystal1 and in the iridescence of bird-plumage please his finer sensibilities4 ,if he is sincere1 mobile light is a seductive agency4 ,the painter has contributed little of direct value in developing the music of light4 ,he is concerned with an instantaneous expression4 ,he waits for it patiently and1 while waiting1 learns to appreciate the fickleness of mood in nature1 but when he fixes one of these moods he has contributed very little to the art of mobile light4 ,unfortunately the art schools teach the student little or nothing pertaining to color for color's sake4 ,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 masters4 ,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 ,corot4 ,the world moves and has only a position in the rank and file for imitators4 ,occasionally an artist goes to work with a vim and indulges in research1 thereby demonstrating originality in two respects4 ,painting is just as much a field for research as light-production4 ,recently experiments are being made in the production of color-harmonies devoid of form4 ,surely there is a field for pure color-composition and this the field of the painter which leads toward the art of mobile light4 ,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 light4 ,being formless1 they are devoid of subject in the ordinary sense and cannot be more or less than a fixed expression of light4 ,naturally they have received much criticism and have been ridiculed1 but they can expect nothing else until they are understood4 ,they cannot be understood until mankind learns their language and then they must be understandable4 ,in other words1 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 taken4 ,this army of camp-followers will not advance the art of mobile light1 but the sincere seekers after the principles of light-expression who form the foundation of the various isms may contribute much4 ,the painter will always be available with his finer sensibility to appreciate and to aid in developing the art of mobile light1 but his direct contribution appears most likely to come from the present chaos of experiments in pure color-composition1 in the psychology of light1 or1 more broadly1 in the expressiveness of light4 ,the decorator and the designer of gowns and costumes do not arrogate to themselves the name artist1 but they are daily creating something which is leading toward a fuller appreciation of the expressiveness of light4 ,if they do not contribute directly to the development of the art of mobile light1 they are at least aiding in developing what may eventually be an appreciative public4 ,the artist paints a still-life1 the decorator creates a color-harmony of abstract or conventional forms1 and the costumer produces a color-composition in textiles4 ,the decorator and costumer approach closer to pure color-composition than the artist in his still-life4 ,the latter is a grouping of objects primarily for their color-notes4 ,why bother with a banana when a yellow-note is desired8 ,why utilize the abstract or conventional forms of the decorator8 ,why not follow this lead further to the less definite forms employed by the costumer8 ,why not eliminate form even more completely8 ,this is an important point and an interesting lead1 for to become rid of form has been one of the perplexing problems encountered by those who have dreamed of an art of mobile light4 ,the painter who uses line and color imitatively has perhaps acquired skill in depicting objects and more or less appreciation of the beautiful4 ,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 objects4 ,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-harmonies4 ,from these momentary expressions of light and from the experience gained1 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 called4 ,the development of taste for abstract art is needed in order that the art of mobile light may develop and1 incidentally1 an appreciation of the abstract in art is needed in all arts4 ,science has contributed much by way of clearing the decks4 ,it has produced the light-sources and the apparatus for controlling light4 ,it has analyzed the physical aspects of color-mixture and has accumulated extensive data pertaining to color-vision4 ,it has pointed out pitfalls and during recent years has been delving further by investigating the psychology of light and color4 ,the latter field is looked to for valuable information1 but1 after all1 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 light4 ,some of these have been made1 but unfortunately they have been heralded as finished products4 ,perhaps the most general mistake made is in relating sounds and colors by stressing a mere analogy too far4 ,notwithstanding the vibratory nature of the propagation of sound and light1 this is no reason for stressing a helpful analogy4 ,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 quantities4 ,no space will be given to such a relation because it is so absurdly superficial2 however1 the language of music will be borrowed with the understanding that no relation is assumed4 ,a few facts pertaining to vision will indicate the trend of developments necessary in the presentation of mobile light4 ,the visual process synthesizes colors and at this point departs widely from the auditory process4 ,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 blue1 of red1 green1 and blue1 of purple and green1 and a vast array of other combinations4 ,a mixture of red and green lights may produce an exact match for a pure yellow4 ,thus it is seen that the mixture of lights will cause some difficulty4 ,for example1 the components of a musical chord may be picked out one by one by the trained ear1 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 components4 ,in music of light1 the components of color-chords must be kept separated1 for if they are intermingled like those of musical chords they are indistinguishable4 ,therefore1 the elements of harmony in mobile light must be introduced by giving the components different spatial positions4 ,the visual process is more sluggish than the auditory process2 that is1 lights must succeed each other less rapidly than musical notes if they are to be distinguished separately4 ,the ear can follow the most rapid execution of musical passages1 but there is a tendency for colors to blend if they follow one another rapidly4 ,this critical frequency or rate at which successive colors blend decreases with the brightness of the components4 ,if red and green are alternated at a rate exceeding the critical frequency1 a sensation of yellow will result2 that is1 neither component will be distinguishable and a steady yellow or a yellow of flickering brightness will be seen4 ,the hues blend at a lower frequency than the brightness components of colors2 hence there may be a blend of color which still flickers in brightness4 ,many weird results may be obtained by varying the rate of succession of colors4 ,if this rate is so low that the colors do not tend to merge1 they are much enriched by successive contrast4 ,it is known that juxtaposed colors generally enrich one another and this phenomenon is known as simultaneous contrast4 ,successive contrast causes a similar effect of heightened color4 ,an effect analogous to dynamic contrast in music may be obtained with mobile light by varying the intensity of the light or possibly the area4 ,melody may be simply obtained by mere succession of lights4 ,tone-quality has an analogy in the variation of the purity of color4 ,for example1 a given spectral hue may be converted into a large family of tints by the addition of various amounts of white light4 ,rhythm is as easily applied to light as to music1 to poetry1 to pattern1 or to the dance1 but in mobile lights its limitations already have been suggested4 ,however1 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-rhythmic4 ,rhythm abounds everywhere and nothing so stirs mankind from the lowliest savage to the highly cultivated being as rhythmic sequences4 ,many psychological effects of light have been recorded from experiment and observation and affective values of light have been established in various other byways4 ,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 music4 ,however1 if this were true it would offer no discouragement1 because absolute values play a small part in life4 ,two events when directly compared apparently may differ enormously in their ability to arouse emotions1 but the human organism is so adaptive that each in its proper environment may powerfully affect the emotions4 ,for example1 those who have sported in arial 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 dusk4 ,the wonderful adaptability of the inner being is the salvation of art as well as of life4 ,in the rendition of mobile light it is fair to give the medium every advantage4 ,sometimes this means to eliminate competitors and sometimes it means to remove handicaps4 ,on the stage light has had competitors which are better understood4 ,for example1 in the drama words and action are easily understood1 and regardless of the effectiveness of light it would not receive much credit for the emotive value of the production4 ,in the wonderful harmony of music1 dance1 and light in certain recent exhibitions1 the dance and music overpowered the effects of lights because they speak familiar languages4 ,illustration3 ,a community ,christmas tree ,a community song-festival ,,artificial ,,light ,,in ,,community ,,affairs ,illustration3 ,,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 creditable1 but a much-heralded exhibition on a large scale a few years ago was not the product of deep thought and sincere effort4 ,for example1 colored lights thrown upon a screen having an area of perhaps twenty square feet were expected to compete with a symphony orchestra in ,carnegie ,hall4 ,the music reached the most distant auditor in sufficient volume1 but the lighting effect dwindled to insignificance4 ,without entering into certain details which condemned the exhibition in advance1 the method of rendition of the light-accompaniment revealed a lack of appreciation of the problems involved on the part of those responsible4 ,incidentally1 it has been shown that the composer of this particular musical selection with its light accompaniment was psychologically abnormal2 that is1 he was affected with colored audition4 ,it is not yet established to what extent normal persons are similarly affected by light and color4 ,certainly there is no similarity among the abnormal and none between the abnormal and normal4 ,if light is to be used as an accompaniment to music1 it must be given an opportunity to supply atmosphere4 ,this it cannot do if confined to an insignificant spot2 it must be given extensity4 ,furthermore1 by the use of diaphanous hangings1 form will be minimized and the evanescent effects surely can be charming4 ,but finally the lighting effects must fill the field of vision just as the music fills the field of audition in order to be effective4 ,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 music4 ,if it progresses through its relation with music1 so much is gained2 if not1 the relation may be broken for music is quite capable of standing alone4 ,there is a tendency on the part of some revolutionary stage artists to give to lighting an emotional part in the play1 or1 in other words1 to utilize lighting in obtaining the proper mood for the action of the play4 ,color and purely pictorial effect are the dominant notes of some of them4 ,all of these modern stage-artists are abandoning the intricately realistic setting1 and1 as a consequence1 light is enjoying a greater opportunity4 ,in the more common and shallow theatrical production1 lighting and color effects have many times saved the day1 and1 although these effects are not of the deeper emotional type1 they may add a spectacular beauty which brings applause where the singing is mediocre and the comedy isn't comedy4 ,the potentiality of lighting effects for the stage has been barely drawn upon1 but as the expressiveness of light is more and more utilized on the stage1 the art of mobile light will be advanced just so much more4 ,light1 color1 and darkness have many emotional suggestions which are easily understood and utilized1 but the blending of mobile light with the action is difficult because its language is only faintly understood4 ,it is futile to attempt to describe a future composition of mobile light4 ,certainly there is an extensive variety of possibilities4 ,a sunset may be compressed into minutes or an opalescent sky may be a motif4 ,varying intensities of a single hue or of allied hues may serve as a gentle melody4 ,realistic effects may be introduced4 ,the expressiveness of individual colors may be taken as a basis for constructing the various motifs4 ,these may be woven into melody in which rhythm both in time and in intensity may be introduced4 ,action may be easily suggested and the number of different colors1 in a broad sense1 which are visible is comparable to the audible tones4 ,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-sources4 ,the tools will be forthcoming if the conscientious artist requests them4 ,whatever the future of the art of mobile light may be1 it is certain that the utilization of the expressiveness of light has barely begun4 ,it may be that light-music must pass through the ragtime stage of fireworks and musical-revue color-effects4 ,if so1 it is gratifying to know that it is on its way4 ,certainly it has already served on a higher level in some of the artistic lighting effects in which mobility has featured to some extent4 ,if the art does not develop rapidly it will be merely following the course of other arts4 ,a vast amount of experimenting will be necessary and artists and public alike must learn4 ,but if it ever does develop to the level of a fine art its only rival will be music1 because the latter is the only other abstract art4 ,material civilization has progressed far and artificial light has been a powerful influence4 ,may it not be true that artificial light will be responsible for the development of spiritual civilization to its highest level8 ,if mobile light becomes a fine art1 it will be man's most abstract achievement in art and it may be incomparably finer and more ethereal than music4 ,if this is realized1 artificial light in every sense may well deserve to be known as the torch of civilization4 ,,reading ,,references ,no attempt will be made to give a pretentious bibliography of the literature pertaining to the various aspects of artificial lighting1 for there are many articles widely scattered through many journals4 ,the ,transactions of the ,illuminating ,engineering ,society afford the most fruitful source of further information2 the ,illuminating ,engineer 7,london71 contains much of interest2 and ,zeitschrift fr ,beleuchtungswesen deals with lighting in ,germany4 ,h4 ,r4 ,d',allemagne has compiled an elaborate ,historie du ,luminaire which is profusely illustrated1 and ,l4 von ,benesch in his ,beleuchtungswesen has presented many elaborate charts4 ,in both these volumes lighting devices and fixtures from the early primitive ones to those of the nineteenth century are illustrated4 ,a few of the latest books on lighting1 in the ,english language1 are ,the ,art of ,illumination1 by ,bell2 ,modern ,illuminants and ,illuminating ,engineering1 by ,gaster and ,dow2 ,radiation1 ,light and ,illumination1 by ,steinmetz2 ,the ,lighting ,art1 by ,luckiesh2 ,illuminating ,engineering ,practice1 consisting of a course of lectures presented by various experts under the joint auspices of the ,university of ,pennsylvania and the ,illuminating ,engineering ,society2 ,lectures on ,illuminating ,engineering1 comprising a series of lectures presented under the joint auspices of ,johns ,hopkins ,university and the ,illuminating ,engineering ,society2 and ,the ,range of ,electric ,searchlight ,projectors1 by ,rey2 ,the ,electric ,arc1 by ,mrs4 ,ayrton2 ,electric ,arc ,lamps1 by ,zeidler and ,lustgarten1 and ,the ,electric ,arc1 by ,child treat the scientific and technical aspects of the arc4 ,g4 ,b4 ,barham has furnished a book on ,the ,development of the ,incandescent ,electric ,lamp4 ,color and ,its ,applications1 and ,light and ,shade and ,their ,applications1 are two books by ,luckiesh which deal with lighting from unique points of view4 ,the ,language of ,color1 by ,luckiesh1 aims to present what is definitely known regarding the expressiveness and impressiveness of color4 ,w4 ,p4 ,gerhard has supplied a volume on ,the ,american ,practice of ,gaspiping and ,gas ,lighting in ,buildings1 and ,leeds and ,butterfield one on ,acetylene4 ,a recent book in ,french by ,v4 ,trudelle treats ,lumire ,electrique et ses diffrentes ,applications au ,thatre4 ,many books treat of photometry1 power-plants1 etc41 but these are omitted because they deal with phases of light which have not been discussed in the present volume4 ,light ,energy1 by ,cleaves1 is a large volume devoted to light-therapy1 germicidal action of radiant energy1 etc4 ,references to individual articles will often be found in the various indexes of publications4 ,,the ,,end ,,index ,aaron1 #dc ,accidents3 #h2 street-lighting in relation to1 #bbe et seq42 percentage 7table7 of1 due to improper lighting1 #bca ,acetylene3 #fb2 light-yield of1 #ajf1 #ajg1 #agj1 #ahg1 #aia ,actinic rays3 effect of1 upon human organism1 #bge ,africa1 public lighting in ancient1 #ca ,agni1 god of fire1 #dj ,air-pump1 #acj ,air-raids1 #bbe ,alaska1 #ah1 #bi ,alchemy1 #bj ,aleutians1 #ah ,alexandria1 #dc1 #afc ,allylene1 #ajf ,aluminum1 #ajh1 #agi1 #ahj ,amiens1 ,treaty of1 #fi ,amylene1 #ajf ,aniline dyes1 #ajf ,animal3 distinction between1 and human being1 #c2 #ae2 production of light1 #bd et seq42 sources of light1 #cj1 #ca2 oils1 #ea ,antimony1 #bid ,antioch1 #aec ,arago1 #aad1 #aif ,archbishop of ,canterbury1 #di ,archimedes1 #ai ,arc3 lamps1 #fi1 #hi2 electric1 #aaa et seq42 distinction between spark and1 #aab2 ,davy's notes on electric1 #aac2 formation of1 #aae1 #aaf2 ,staite and enclosed1 #aag1 #aah2 principle of enclosed1 #aah1 #aai2 types of1 #abj2 flame-1 #aba1 #abb2 luminous1 #abb2 electric1 #abg2 luminous efficiency of electric 7table71 #abd2 #afj et seq42 -lamp in lighthouses1 #afh et seq42 magnetite-1 #ahg2 #bfa ,ardois system of signaling1 #aii ,argand1 ,ami3 #eb2 inaugurates new era in artificial lighting1 #ec1 #ed2 #fc1 #gj1 #gf1 #gg1 #gh1 #ig1 #afg1 #aif ,argon1 #acg ,aristophanes1 ,the ,clouds1 #ai ,art ,museums1 #i1 #ac1 #cbb1 #cbc ,asbestos1 #agj ,asia3 public lighting in ancient1 #ca1 #ci ,automobiles1 #bch ,babylon1 #ci ,bacteria3 effect of artificial light upon1 #bgb et seq42 #bha1 #bhb ,bailey1 ,prof4 ,l4 ,h41 #bej ,baltimore1 #ih ,bamboo3 carbon filaments1 #afi ,bartholdi1 #cjb1 #cjc ,beacons4 ,see ,lighthouses4 ,beck1 #ahf ,beecher1 #gb ,beeswax1 #ce1 #ea ,benzene1 #ajf ,bible1 cited on importance of artificial light1 #db-dd ,bluebird1 ,the1 ,maeterlinck1 #i ,blue-prints1 #bfa ,bollman1 #ih ,bolton1 von1 #acb1 #acc ,bombs1 illuminating1 #ahb et seq4 ,boston ,light1 #afd1 #afe1 #aff1 #agg ,bowditch1 production of regenerative lamp by1 #gh1 #gi ,boy ,scouts1 #ag ,bremer1 #abj ,bristol ,university1 #beb ,brush1 #fh1 #aei ,building1 #h ,bunsen1 #ha1 #he1 #hi1 #adh1 #adi ,bureau of ,mines3 cited on open flames1 #bcd2 #bcf ,burning-glasses1 #ai1 #bj4 ,see also ,lenses4 ,butylene1 #ajf ,byzantium1 #cd ,csar1 #afc ,canada1 #bed ,candle-hour1 defined1 #bae ,candles3 progress and1 #g2 #be1 #bh1 #bi1 #cj1 #cc2 religious uses of1 #cd1 #ce2 as a modern light-source1 #cf1 #cg2 ceremonial uses of1 #ch et seq42 #dd1 #dh1 #eg1 #hb1 #ig1 #bbb1 #bii1 #cjd ,calcium1 #ajg1 #ajh ,carbolic acid1 #ajf ,carbon3 #ec1 #hj1 #ha2 physical characteristics of1 #hj1 #ha2 #ij1 #ajd1 #aje1 #abh1 #abi1 #add1 #agj ,carbon filament3 #abg et seq42 preparation of1 #abi1 #acj1 #aca2 luminous efficiency of1 #aca1 #acb2 lamps1 #afa2 lamps in greenhouses1 #bej et seq4 ,carbons1 formation of1 #aae1 #aaf ,carbureted hydrogen1 #ge ,carcel1 invention of clockwork lamp by1 #ed1 #ee ,cat-gut1 #acj ,ceria1 #he1 #aja ,charleston1 ,s4 ,c41 #ahe ,charcoal3 #aac2 uses of1 for electrodes1 #aae ,chartered ,gas ,light and ,coke ,co41 ,london1 #gd ,chemistry3 artificial light and1 #bef-bfh ,chicago1 #fb1 #cjd1 #cje ,chimneys1 #ed1 #fj1 #fb ,china1 #ai1 #ca1 #cb ,chlorate of potash1 #bb ,christ1 #cc1 #df1 #dg ,christians1 children of light1 #db ,christmas trees1 #dc1 #cjd ,chromium1 #bid ,church of ,england1 #di ,cities3 economy of artificial lighting in congested1 #ac ,civilization3 effect of artificial light upon1 #d et seq42 fire and1 #ae ,clark1 ,parker and1 #aci ,clayton1 ,dr43 invention of portable gas-light by1 #fd2 quoted1 #fd1 #fe2 experiments of1 with coal-gas1 #fg ,claude1 #adg ,cleaves1 ,dr41 quoted1 #bgf1 #bgg ,clegg1 ,samuel3 #gd2 gas-lighting accomplishments of1 #ge1 #gf ,cleveland1 #aei ,clouds1 ,the1 ,aristophanes1 #ai ,coal3 #cb2 as a light-source1 #ee2 supply1 #bbc2 #bbh ,coal-gas3 #fc et seq42 public lighting by1 developed1 #gj et seq42 analytical production of1 #ajc1 #ajd2 yield of1 retort 7table71 #aje2 analysis of1 #ajf ,coal-mines1 #bcd et seq4 ,cobalt1 #bid ,coke1 #fh1 #aje ,cologne1 #aeg1 #aeh ,colomb1 ,philip1 #aig ,color3 #i2 relation of artificial light to1 #bhd et seq4 ,colza1 #ca1 #eb1 #afg ,combustion1 #hb et seq4 ,commerce1 #h1 #ig ,constantine1 #db ,copper1 #bfb1 #bie ,cornwall1 #fc ,cotton3 #aja2 carbon filaments1 #abi1 #acj ,cromartie1 #gh ,crookes1 #ij1 #adf ,crosley1 ,samuel1 improvement of gas-meter by1 #gf ,crusies1 #cb ,daguerre1 #beh ,dancing1 #cdf ,davy1 ,sir ,humphrey3 #cc1 #fh1 #gc2 first use by1 of charcoal for sparking points1 #aab2 notes of1 on electric arc1 #aac2 #aad ,daylight1 artificial1 #ab3 #bhd et seq42 application of1 #bhg ,daylighting1 #ab-ad ,dollond1 #aie ,doty1 #fa1 #afg ,drake1 ,col4 ,e4 ,l41 discovery of oil in ,pennsylvania by1 #ef ,drummond1 ,thomas3 #aga1 #ahe1 #aif2 quoted on signaling1 #aig ,dudgeon1 ,miss1 #bea1 #beb ,dyes1 #bef1 #bfe ,east ,indies1 #bi ,eddystone ,light1 #aff1 #afg ,edison3 and problem of electric incandescent filament lamps1 #abh et seq42 #abi2 quoted on birth of incandescent lamp1 #acj ,edward ,i1 #bgd ,edward ,,vi1 #di ,efficiency1 effect of artificial light upon1 #ad ,eggs3 relation of artificial light to production of1 #bdg1 #bdh ,egypt3 #ca2 sacredness of light in ancient1 #ci2 #aec1 #aie ,electric filament3 #ha1 #abg et seq43 approximate value of1 lamps 7table71 #ach ,electric pile3 construction of1 #aaa2 #abg ,electricity3 #ac1 #bb2 as a light-source1 #eg2 for home-lighting1 #fb1 #hd2 #hg1 #hi2 ignition of gas by1 #ajb2 lighting by1 #aji et seq4 ,electromagnetic waves1 #fh1 #hf1 #hg ,electromagnets1 #aad1 #aaf ,electrodes1 #aac1 #aad1 #aae et seq42 life of1 #abb ,elizabeth1 ,queen1 #bgd ,england3 #cb2 petroleum discovered in1 #ef2 gas-lighting in1 #fc et seq42 #aff1 #bea1 #bgd ,erbia1 #he ,esquimaux3 #ah2 use of artificial light by1 #ca ,ethylene1 #ajf ,factories3 #ac2 artificial light in1 #bci et seq4 ,faraday1 #aac ,filaments1 carbon1 #abi et seq4 ,finsen3 #bgc1 #bgd1 #bge2 on stimulating action of artificial light1 #bgg2 #bgi1 #bhj ,fire3 importance of1 to man1 #e et seq42 man's dependence upon1 #ae2 mythical origin of1 #af2 making1 #ag et seq42 production of1 in the stone age1 #ah2 in early civilization1 #ai2 ancient worship of1 #bi1 #bii ,fireflies3 #bd1 #ha1 #if1 #adh1 #adi1 #aej ,first ,men in the ,moon1 ,the1 ,h4 ,g4 ,wells1 cited1 #adh ,fish3 artificial light as bait for1 #bdi ,flame-arcs1 #abj1 #aba1 #abb1 #ahg ,flames3 #hf1 #hh1 #hi2 open1 #bcc1 #bcd et seq4 ,flint1 #cc ,fool's gold1 #ah ,fort ,wagner1 #ahe ,france3 lamps in1 #ee2 early gas-light in1 #gb ,franchot1 invention of moderator lamps by1 #ee ,frankland1 #gg ,franklin1 ,benjamin3 #afe2 quoted1 #baj-bab2 #bac ,fresnel1 #afg1 #aif ,friction1 #af1 #ag ,gas3 #ac1 #bb2 discovery of coal1 #cb1 #cc2 early uses of1 as light-source1 #fc et seq42 installment of1 pipes in ,england1 #fc1 #fd2 ,shirley's report on ,natural1 #ff1 #fg2 first public display of1 lighting1 #fi2 cost of1 lighting1 #ga2 first attempt at industrial1 lighting1 #gb2 first ,english1 company1 #gd2 first1 explosion1 #ge2 house1 lighting1 #gf1 #gg2 #hj1 #hb2 spectrum of1 #ij2 modern1 lighting industry1 #ig et seq42 origin of lighting by1 #ih2 first1 works in ,america1 #ih2 growth of1 consumption in ,united ,states1 #ii2 electrical ignition applied to1 lighting1 #ajb2 pressure1 #ajb1 #ajc2 water1 #aje2 carbons in1 #ajf2 production of ,pintsch1 #aji1 #aaj2 salts applied to1 flames1 #abj2 #aeg2 ,census ,bureau figures on cost of1 plants1 #bba1 #bbb2 #bbd1 #cda ,gas-burners3 #fc1 #fd1 #gg2 candle-power of pioneer 7table71 #gi2 improvements in1 #hd ,gas-mantle3 #fa1 #ha2 influence of1 #ii2 characteristics of1 #ajj et seq42 #ahg ,gas-meter1 ,clegg's1 #gf ,gasolene3 lamps1 #ee2 #eg ,gassiot1 #aad ,gauss1 #aif ,geissler1 #adf ,general ,electric ,company1 #acb1 #ace1 #acf ,germany3 development of lamps in1 #ef2 early gas-lighting in1 #gb ,glass1 #aie1 #bij et seq4 ,glowers1 #aci ,glow-worms1 #bd ,glycerides1 #eb ,gold1 #bic ,gout1 #bge ,gramme dynamo1 #aag ,grass3 #ah2 carbon filaments1 #abi ,greece3 #ci2 sacred lamps in ancient1 #da2 #db ,greenhouses1 carbon-filament lamps in1 #bej et seq4 ,hall of ,fame1 #acd ,happiness1 effect of artificial light upon1 #ad ,hayden and ,steinmetz1 #bec ,health1 artificial light in relation to1 #bfi-bhc ,helium1 #hi ,hemig1 #aee ,hemp1 #ba ,henry1 ,william1 #ge ,herodotus1 #ef ,hertz1 #fh ,hertzian waves1 #bga ,hewitt1 ,cooper1 produces mercury-arcs1 #abd1 #abe ,home3 artificial light in relation to1 #f2 lighting1 #cbe et seq4 ,hindu3 light in1 ceremonials1 #dj ,hudson-,fulton ,celebration1 #cjf ,huygens1 #aie ,hydrocarbons1 #hb ,hydrogen1 #ha ,illiteracy1 artificial light and1 #i ,invention1 #g1 #ig ,iowa1 #bch ,iridium1 #abi ,iron1 #ah1 #bfb1 #bid ,iron pyrites1 #ah ,italy1 #bdi ,jablochkov3 electric candle of1 #aag ,jamaica1 #ai ,jandus1 #aah1 #abb ,japan3 #ai2 use of oil in1 #cj2 #bha ,jerusalem1 #dc ,jews3 artificial light among1 #dj ,journal1 ,paris1 quoted1 #baj-bab ,kerosene3 #eg2 weight of1 lumens1 #fj2 #fb1 #ahg1 #bcc ,kitson1 platinum-gauze mantle applied by1 #fa ,laboratories3 achievements of1 #acg ,lamps3 #af1 #be2 ,roman1 #cj2 #ca2 invention of safety1 #cc2 ancient funereal1 #ci2 sacred1 of antiquity1 #da2 ceremonial1 #dd2 scientific development of oil1 #ea et seq42 ,holliday1 #ee2 ,carcel1 #ed1 #ee2 ,franchot's moderator1 #ee2 gasolene1 #ee2 development of1 in ,germany1 #ef2 air pressure1 #fa2 supremacy of oil1 ends1 #fb2 ,bowditch's1 #gg1 #gh2 #hj1 #ig2 mercury-arc1 #abf2 electric incandescent filament1 #abg et seq42 gem1 #acb2 tungsten1 #acc et seq42 luminous efficiency 7table7 of incandescent filament1 #ada2 #bii2 in home1 #cbh-ccc ,lange1 #afg ,lard-oil1 #ea ,lavoisier1 #aie ,lead1 #bfb1 #bid ,le ,bon1 #gb ,legend of ,montrose1 ,the1 ,scott1 cited on primitive lighting1 #bg ,leigh1 ,edmund1 quoted1 #bbf ,lenses1 #bj1 #aga et seq4 ,libanius1 quoted1 #aec1 #aed ,liberty1 ,statue of1 #cja1 #cjb1 #cjc ,libraries1 #i ,light3 relation of artificial1 to progress1 #c et seq42 as a civilizing agency1 #c-ad2 primitive man and artificial1 #d2 ,milton1 quoted on importance of1 #e2 artificial1 and science1 #g2 artificial1 and industrial development1 #h2 ,maeterlinck's tribute to1 #i2 ,lincoln's debt to artificial1 #i2 symbolism of1 #i1 #aj2 therapy1 #aj2 in war1 #aa2 adaptations of1 #ab2 #ac2 mythical origin of artificial1 #af2 earliest source of1 #af2 production of1 in stone age1 #ah2 matches as source of1 #ba2 animals as1 sources1 #bd1 #be2 primitive sources of1 #bd-cg2 evolution of artificial1 sources1 #bd-cg2 development1 #bh et seq42 early outdoor use of artificial1 #bh2 ,roman uses of artificial1 #cj2 beginning of scientific1 #cc1 #cd2 candles as modern1 source1 #cf1 #cg2 symbolism and religious uses of1 #ch et seq42 ,bible cited on artificial1 #db-dd2 in relation to worship1 #dc1 #de1 #df2 ,argand's contribution to1 #ec1 #ed2 coal as1 source1 #ee2 early uses of gas as1 source1 #fc et seq42 as a public utility1 #gj2 first installation of industrial gas1 #gb2 science of1 production1 #hj et seq42 causes of1 radiation1 #hj1 #ha2 #hc2 lime1 #hd2 electric1 #hi et seq42 principle of1 production1 #ij1 #ia2 sources1 #ic2 various gas-burners'1 supply1 #ie2 relative efficiency of1 sources1 #ie1 #if2 in the home1 #ig2 influence of1 upon science1 invention1 and commerce1 #ig et seq42 yield of acetylene1 #ajf1 #ajg2 electric1 #aji2 influence of gas upon development of artificial1 #aaj2 development of artificial1 #aaa et seq42 efforts to improve color of mercury-arc1 #abe2 electric-incandescent-filament1 #abg et seq42 effect of tungsten1 upon1 #acc et seq42 of the future1 #adc-aeb2 in warfare1 #agh-aic2 signaling1 #aid-bjg2 cost of1 #bjh-bbd2 and safety1 #bbe et seq42 improper use of1 #bbi1 #bcj2 comparison of daylight and artificial1 #bdj2 reducing action of1 #beh2 bactericidal action of1 #bgb et seq42 modifying1 #bhd et seq42 spectacular uses of1 #bih-cji2 expressiveness of1 #caj-cbd2 utility of modern1 #cbe-cdj2 evolution of the art of applying1 #cda-cef2 mobile1 #cdg1 #cdh1 #cdi1 #cej2 psychological effect of1 #cea et seq42 as an accompaniment to music1 #ceb-ced ,light-buoys1 #aj1 #afi ,lighthouses3 #aj1 #afc-agg2 optical apparatus of1 #agb et seq4 ,light-ships1 #aj1 #afi ,lighting-systems3 comparison of1 #ab-ad ,lime1 #hd1 #ajg1 #ajh1 #bid ,lincoln1 ,abraham1 #i ,linen1 #ah ,link-buoys1 #bh ,lithopone1 #bfe1 #bff ,liverpool1 #afg ,living3 comparison of1 standards1 #bch et seq4 ,london1 #aeb1 #aed1 #aee1 #aef1 #aeg1 #bjb ,london ,gas ,light and ,coke ,company1 #gd ,lucigen1 #fa ,lumen-hour3 defined1 #bae ,lumens3 #fj1 #id1 #bae ,lutheran ,church1 #di ,lyceum ,theatre1 ,london1 #gc ,maeterlinck1 ,maurice1 #i ,magazines1 #h ,magdsick1 ,h4 ,h41 #cjc ,magnesia3 #hd2 ,nernst's application of1 #ach ,magnesium1 #agi1 #ahj ,magnetite arc1 #ahg ,man3 distinction between1 and animal1 #c2 artificial light and early1 #d2 light-sources of primitive1 #be ,manganese1 #bfb1 #bfh1 #bid ,mangin1 #ahh ,mann1 #abi ,mantles1 #ie ,manufacturing1 #h ,marconi1 #fh ,marks1 #aah ,matches3 as light-sources1 #ba2 #bb1 #hb ,maxwell1 #fh ,mazda lamps1 #bhi1 #cci ,mecca1 #dj ,mediterranean ,sea1 #afc ,mercury-arc3 ,way's1 #abd2 #abe1 #abf2 quartz1 #abe1 #abf2 attempts to improve color of1 light1 #abe ,middle ,ages1 #df1 #dg1 #dgd ,milton1 quoted1 #e ,mirror1 #ai ,mohammedans1 #dj ,moore1 ,dr4 ,mc,farlan1 #adf1 #adg ,morality1 effect of light upon1 #i ,morse code3 application of1 to light-signaling1 #aih1 #aii ,moses1 #aie ,moving-pictures1 #i1 #bfj1 #bfa ,munich1 #gb ,murdock1 ,william3 installment of gas-pipes by1 #fc2 #fh1 #fi1 #gj2 quoted on industrial use of artificial1 #ga2 #gb1 #gc1 #gd1 #gf1 #gh1 #bag1 #cji ,museums3 #ac2 utilization of artificial light by1 #cbb1 #cbc ,music3 light as an accompaniment to1 #ceb-ced ,mythology1 #af ,nantes1 #he ,napoleon1 #aaa ,napthalene1 #ajf ,national ,heat and ,light ,co41 #gb1 #gd ,natural gas1 #ii ,navesink ,light1 #bjf ,nernst1 #ach1 #aci ,newspapers1 #h ,newton1 ,sir ,isaac3 #g2 quoted on discovery of visible spectrum1 #hg2 #hh ,new ,york1 #ih1 #afe1 #aff1 #bjf1 #cjb1 #cjd ,niagara ,falls1 #ajh1 #cjf ,nickel1 #bfb ,nielson1 #gg ,niepce1 #beh ,niter1 #ba ,nitrogen1 #acg ,norfolk1 #afi ,obesity1 #bge ,offices1 #ac ,oil3 as a light-source1 #bi et seq42 development of1 lamps1 #ea et seq42 #aee2 in lighthouse1 #afe et seq42 #bbb1 #bbd1 #bii ,o',leary1 ,mrs41 and her lamp1 #fb ,olive-oil1 #ea1 #eb1 #afg ,orkney ,islands1 #bi1 #agg ,osmium1 #acc ,oxygen3 relative consumption of1 by oil-lamps1 #eh1 #ei2 #bfb ,ozone1 #bfb ,painting1 #cdb1 #cdc1 #cdg1 #cdh1 #cdi ,pall ,mall1 #gd ,panama-,pacific ,exposition3 #cjd2 artificial lighting of1 #cjf1 #cjg1 #cjh1 #cji ,paper3 #ah2 carbon filaments1 #abi1 #acj ,paraffin1 #ce1 #eg ,parker and ,clark1 #aci ,paris3 experimental gas-lighting in1 #hc1 #hd2 ,volta in1 #aaa2 #aed1 #ahe1 #baj1 #bab1 #bac ,peckham1 ,john1 #aie ,pennsylvania3 discovery of oil in1 #ef ,periodic ,law1 #ade ,petroleum3 #ce1 #ea1 #ee2 discovery of1 #ef2 constitution of crude1 #eg2 #eh1 #bad ,pharos1 #afc ,philadelphia1 #ih1 #ii1 #aeg ,phillips and ,lee1 #gj1 #gb ,philosophical ,transactions of the ,royal ,society of ,london1 #cc2 quoted on industrial lighting1 #fc2 ,shirley's report on natural gas in1 #ff1 #fg2 quoted1 #hg ,phoenicians1 #cd1 #ci ,phosphorus1 #ba ,photo-micrography1 #ab ,photography3 #abf2 early experiments in1 #beh2 development of1 #bei2 #bia1 #bib ,picric acid1 #ajf ,pigments1 #bfe ,pintsch3 production of1 gas1 #aji1 #aaj1 #agj ,pitch1 #ajf ,plant-growth3 artificial light and1 #aa1 #bdi et seq4 ,platinum1 #he1 #abh1 #abi1 #bfb ,plumbago1 #aac1 #acj ,plymouth1 #aff ,poetry1 #cdf ,police1 #afb ,potash1 chlorate of1 #bb ,priestley1 ,professor1 quoted1 #beb ,printing1 #h ,progress3 influence of fire upon1 #ae et seq4 ,prometheus1 #af1 #da ,propylene1 #ajf ,ptolemy ,,ii1 #afc ,quartz3 #ah1 #ai2 mercury-arcs1 #abe2 uses of1 #abf2 in skin diseases1 #bgh1 #bgi ,radiators1 energy1 #hh et seq4 ,radium1 #aej ,railway ,signal ,association1 #bje ,railways3 light-signaling applied to1 #bje ,ramie fiber1 #aja ,rane1 #bej1 #bea ,rare-earth oxides3 #he2 properties of1 #hh1 #ii ,recreation1 #i ,redruth1 #fc ,reformation3 ceremonial uses of light during the1 #dh1 #di ,rheumatism1 #bge ,robins1 ,benjamin1 #bja ,rome1 #cj1 #cb1 #cd1 #ci1 #da1 #db1 #dd ,rntgen1 #bgj1 #bhj4 ,see also ,x-ray4 ,royal ,society of ,london3 #cc1 #fc1 #ff1 #fg1 #gj1 #gc2 and first gas explosion1 #ge1 #aaa1 #aab ,rumford1 #afg ,rushlights1 #bh1 #cc ,russia1 #bha ,ryan1 ,w4 ,d',a41 #cjf ,safety3 artificial light in relation to1 #ad1 #bbe et seq4 ,salts3 chemical1 #hh1 #hi2 metallic1 #abj2 silver1 #beg1 #beh ,sandy ,hook ,light1 #afe1 #aff ,san ,francisco1 #cjd1 #cjf-cji ,savages1 #c1 #ae1 #ag ,sawyer1 #abi ,scheele1 ,k4 ,w41 #acc2 quoted1 #beg1 #beh ,schools1 #i ,science3 light and1 #f1 #g2 #ig2 systematized1 #bfh ,scotland3 #bf1 #ca1 #cb1 #dh2 oil industry in1 #ef ,scott1 ,sir ,walter1 cited1 #bg1 #ih ,sculpture3 artificial light in relation to1 #ahd ,search-lights1 #aa1 #afi ,section of ,plant ,protection1 #bbe1 #bbf ,selenium1 #bfg1 #bic ,semaphore1 #aii ,shells3 illuminating1 #agi et seq4 ,shirley1 ,thomas3 quoted on natural gas1 #ff1 #fg ,siemens1 #gh ,signaling1 #aid-bjg ,silicon3 filament1 #adj ,silk3 artificial1 #aja2 carbon-filaments1 #abi ,simpson1 ,r4 ,e41 #bbg1 #bca ,silver1 #beh1 #bic ,skin diseases3 treatment of1 #bgh1 #bgi1 #bhj ,skylights1 #ac ,sleep1 #h ,smallpox1 #bgd1 #bge ,smeaton1 #aff ,soho1 #fi1 #gb ,south ,africa1 #abi ,sparks3 #cc1 #abe ,spectrum3 visible1 #hf2 ,newton quoted on1 #hg2 of elements1 #hi2 of gases1 #ij2 #abj1 #aba2 mercury1 #abd-abf ,sperm1 #ca1 #ea1 #eb1 #afg ,spermaceti1 #ce1 #ea ,splinter-holders1 #bg1 #bh ,stage3 and artificial light1 #cai et seq42 #cdc ,staite1 #aag1 #aah ,stearine1 #ce1 #eb ,stearn1 #abi ,steel1 #ah1 #cc ,steinmetz1 ,hayden and1 #bec ,sterilization3 quartz-mercury-arc and1 #bhj1 #bha1 #bhb ,stevenson1 ,robert ,louis1 quoted1 #agg ,stores1 #ac ,st4 ,paul1 #dc ,st4 ,paul's ,cathedral1 #cjj ,street-lighting3 development of1 #aeb-afb ,sugar1 #bb ,sulphide of iron1 #ah ,sulphur1 #ah1 #ba1 #agi1 #ahj1 #bid ,sulphuric acid1 #ba1 #bb ,sun1 #h1 #af1 #ai1 #bj ,swan1 #abi ,syracuse1 #ai ,syria1 #aec ,tallow1 #cd1 #ce1 #ea1 #eb ,tantalum3 #acb2 filament lamps1 #acc ,tar1 #fh1 #ajf ,telegraphy1 #aie ,telephony1 #aid ,textiles1 #bef ,thames1 #afi ,theaters1 #i1 #cai et seq4 ,thoria1 #he ,tin1 #bfb ,tinder-boxes1 #ah1 #ai1 #bb ,travelers ,insurance ,company1 #bbg ,trees1 #bf ,troy1 #db ,tuberculosis1 #bgc ,tungsten lamp1 #afa et seq41 #ahg1 #bfa1 #bij1 #cjc ,typhus1 #bgc ,ultra-violet rays3 #abf1 #aej2 in photographic electricity1 #bfg1 #bfh2 #bgj1 #bgb1 #bid ,united ,states3 petroleum in1 #eg2 gas-consumption in1 #ii2 #afd1 #afe1 #aff ,united ,states ,geological ,survey1 cited on sale of gas1 #bbb ,united ,states ,military ,intelligence1 #bbe1 #bbf ,vacuum tubes1 #ha1 #bhf ,venetians1 #aie ,ventilation1 #ac ,verne1 ,jules1 #adc ,vestal ,virgins1 #db ,volcanoes1 #aff ,volta1 #aaa1 #aab1 #abg ,voltaic pile3 construction of1 #aaa1 #abg ,von ,bolton4 ,see ,bolton4 ,war3 and artificial light1 #aa1 #agh-aic ,washington1 #cje ,water3 sterilization of1 by artificial light1 #bhj et seq4 ,watson1 ,dr4 ,richard1 #fg1 #fh ,watt1 #id ,waves3 electro-magnetic1 #fh1 #hf1 #abe et seq4 ,wax1 #cd1 #df1 #ea ,way3 mercury-arc produced by1 #abd ,wells1 #fa ,wells1 ,h4 ,g41 cited1 #adh ,welsbach1 ,auer von3 #fa2 invention of mantle by1 #ii1 #ajj1 #acc ,wenham1 #gh ,west ,indies1 #be ,whale-oil1 #ca ,wicks1 #ce1 #cf1 #ec1 #ed1 #eh1 #ei ,winsor1 #gb1 #gc4 ,see also ,winzler4 ,winzler4 ,see ,winsor4 ,wolfram4 ,see ,tungsten4 ,wood1 #bf1 #bg1 #bh ,woolworth ,building1 #cjb1 #cjc ,wounds3 treatment of1 by artificial light1 #aj ,x-ray3 production of1 tubes during ,war1 #aca2 #acg1 #aej1 #bgj1 #bhj ,young1 ,james3 discovers petroleum1 #ef ,yttria1 #he ,zeitung1 ,cologne3 #aeg2 extract from1 on street-lighting1 #aeh ,zinc1 #abe1 #acj1 #bfg ,zirconia1 #hd1 #he ,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 444,applications an ,thatre4 444,applications au ,thatre4 ,,index ,photo-micography ,photo-micrography ,siemans ,siemens