and Butterfield one on "Acetylene." A recent book in French by V. Trudelle treats "Lumiere Electrique et ses differentes Applications au Theatre." Many books treat of photometry, power-plants, etc., but these are omitted because they deal with phases of light which have not been discussed in the present volume. "Light Energy," by Cleaves, is a large volume devoted to light-therapy, germicidal action of radiant energy, etc. References to individual articles will often be found in the various indexes of publications. THE END INDEX Aaron, 43 Accidents: 8; street-lighting in relation to, 225 _et seq._; percentage (table) of, due to improper lighting, 231 Acetylene: 62; light-yield of, 106, 107, 170, 187, 191 Actinic rays: effect of, upon human organism, 275 Africa, public lighting in ancient, 31 Agni, god of fire, 40 Air-pump, 130 Air-raids, 225 Alaska, 18, 29 Alchemy, 20 Aleutians, 18 Alexandria, 43, 163 Allylene, 106 Aluminum, 108, 179, 180 Amiens, Treaty of, 69 Amylene, 106 Aniline dyes, 106 Animal: distinction between, and human being, 3; 15; production of light, 24 _et seq._; sources of light, 30, 31; oils, 51 Antimony, 294 Antioch, 153 Arago, 114, 196 Archbishop of Canterbury, 49 Archimedes, 19 Arc: lamps, 69, 89; electric, 111 _et seq._; distinction between spark and, 112; Davy's notes on electric, 113; formation of, 115, 116; Staite and enclosed, 117, 118; principle of enclosed, 118, 119; types of, 120; flame-, 121, 122; luminous, 122; electric, 127; luminous efficiency of electric (table), 124; 160 _et seq._; -lamp in lighthouses, 168 _et seq._; magnetite-, 187; 261 Ardois system of signaling, 199 Argand, Ami: 52; inaugurates new era in artificial lighting, 53, 54; 63, 70, 76, 77, 78, 97, 167, 196 Argon, 137 Aristophanes, "The Clouds," 19 Art Museums, 9, 13, 322, 323 Asbestos, 170 Asia: public lighting in ancient, 31, 39 Automobiles, 238 Babylon, 39 Bacteria: effect of artificial light upon, 272 _et seq._; 281, 282 Bailey, Prof. L. H., 250 Baltimore, 98 Bamboo: carbon filaments, 169 Bartholdi, 302, 303 Beacons. _See_ Lighthouses. Beck, 186 Beecher, 72 Beeswax, 35, 51 Benzene, 106 Bible, cited on importance of artificial light, 42-44 "Bluebird, The," Maeterlinck, 9 Blue-prints, 261 Bollman, 98 Bolton, von, 132, 133 Bombs, illuminating, 182 _et seq._ Boston Light, 164, 165, 166, 177 Bowditch, production of regenerative lamp by, 78, 79 Boy Scouts, 17 Bremer, 120 Bristol University, 252 Brush, 68, 159 Building, 8 Bunsen, 81, 85, 89, 148, 149 Bureau of Mines: cited on open flames, 234; 236 Burning-glasses, 19, 20. _See also_ Lenses. Butylene, 106 Byzantium, 34 Caesar, 163 Canada, 254 Candle-hour, defined, 215 Candles: progress and, 7; 25, 28, 29, 30, 33; religious uses of, 34, 35; as a modern light-source, 36, 37; ceremonial uses of, 38 _et seq._; 44, 48, 57, 82, 97, 222, 299, 304 Calcium, 107, 108 Carbolic acid, 106