The aim has been to show that artificial light has become intricately interwoven with human activities and that it has been a powerful influence upon the progress of civilization. The subject is too extensive to be treated in detail in a single volume, but an effort has been made to present a discussion fairly complete in scope. It is hoped that the reader will gain a greater appreciation of artificial light as an economic factor, as an artistic medium, and as a mighty influence upon the safety, efficiency, health, happiness, and general progress of mankind. M. LUCKIESH. ACKNOWLEDGMENTS It is a pleasant duty to acknowledge the cooeperation of various companies in obtaining the photographs which illustrate this book. With the exception of Plates 2 and 7, which are reproduced from the excellent works of Benesch and Allegemane respectively, the illustrations of early lighting devices are taken from an historical collection in the possession of the National Lamp Works of the General Electric Co. To this company the author is indebted for Plates 1, 3, 4, 5, 6, 9, 11, 15, 18b, 20, 21, 29; to Dr. McFarlan Moore for Plate 10; to Macbeth Evans Glass Co. for Plate 12; to the Corps of Engineers, U. S. Army, for Plate 13; to Lynn Works of G. E. Co. for Plates 14, 16; to Edison Lamp Works of G. E. Co. for Plates 17, 24; to Cooper Hewitt Co. for Plate 18a; to R. U. V. Co. for Plate 19; to New York Edison Co. for Plates 22, 26, 30; to W. D'A. Ryan and the Schenectady Works of G. E. Co. for Plates 23, 25, 31; to National X-Ray Reflector Co. for Plate 28. Besides the companies and the individuals particularly involved in the foregoing, the author is glad to acknowledge his appreciation of the assistance of others during the preparation of this volume. CONTENTS CHAPTER PAGE I LIGHT AND PROGRESS 3 II THE ART OF MAKING FIRE 15 III PRIMITIVE LIGHT-SOURCES 24 IV THE CEREMONIAL USE OF LIGHT 38 V OIL-LAMPS OF THE NINETEENTH CENTURY 51 VI EARLY GAS-LIGHTING 63 VII THE SCIENCE OF LIGHT-PRODUCTION 80 VIII MODERN GAS-LIGHTING 97 IX THE ELECTRIC ARCS 111 X THE ELECTRIC INCANDESCENT FILAMENT LAMPS 127 XI THE LIGHT OF THE FUTURE 143 XII LIGHTING THE STREETS 152 XIII LIGHTHOUSES 163 XIV ARTIFICIAL LIGHT IN WARFARE 178 XV SIGNALING 194 XVI THE COST OF LIGHT 208 XVII LIGHT AND SAFETY 225 XVIII THE COST OF LIVING 238 XIX ARTIFICIAL LIGHT AND CHEMISTRY 256