• Aaron, 43
• Accidents: 8;
  • street-lighting in relation to, 225 et seq.;
  • percentage (table) of, due to improper lighting, 231
• Acetylene: 62;
  • light-yield of, 106, 107, 170, 187, 191
• Actinic rays: effect of, upon human organism, 275
• Africa, public lighting in ancient, 31
• Agni, god of fire, 40
• Air-pump, 130
• Air-raids, 225
• Alaska, 18, 29
• Alchemy, 20
• Aleutians, 18
• Alexandria, 43, 163
• Allylene, 106
• Aluminum, 108, 179, 180
• Amiens, Treaty of, 69
• Amylene, 106
• Aniline dyes, 106
• Animal: distinction between, and human being, 3; 15;
  • production of light, 24 et seq.;
  • sources of light, 30, 31;
  • oils, 51
• Antimony, 294
• Antioch, 153
• Arago, 114, 196
• Archbishop of Canterbury, 49
• Archimedes, 19
• Arc: lamps, 69, 89;
  • electric, 111 et seq.;
  • distinction between spark and, 112;
  • Davy's notes on electric, 113;
  • formation of, 115, 116;
  • Staite and enclosed, 117, 118;
  • principle of enclosed, 118, 119;
  • types of, 120;
  • flame-, 121, 122;
  • luminous, 122;
  • electric, 127;
  • luminous efficiency of electric (table), 124; 160 et seq.;
  • -lamp in lighthouses, 168 et seq.;
  • magnetite-, 187; 261
• Ardois system of signaling, 199
• Argand, Ami: 52;
  • inaugurates new era in artificial lighting, 53, 54; 63, 70, 76, 77, 78, 97, 167, 196
• Argon, 137
• Aristophanes, "The Clouds," 19
• Art Museums, 9, 13, 322, 323
• Asbestos, 170
• Asia: public lighting in ancient, 31, 39
• Automobiles, 238

• Babylon, 39
• Bacteria: effect of artificial light upon, 272 et seq.; 281, 282
• Bailey, Prof. L. H., 250
• Baltimore, 98
• Bamboo: carbon filaments, 169
• Bartholdi, 302, 303
• Beacons. See Lighthouses.
• Beck, 186
• Beecher, 72
• Beeswax, 35, 51
• Benzene, 106
• Bible, cited on importance of artificial light, 42-44
• "Bluebird, The," Maeterlinck, 9
• Blue-prints, 261
• Bollman, 98
• Bolton, von, 132, 133
• Bombs, illuminating, 182 et seq.
• Boston Light, 164, 165, 166, 177
• Bowditch, production of regenerative lamp by, 78, 79
• Boy Scouts, 17
• Bremer, 120
• Bristol University, 252
• Brush, 68, 159
• Building, 8
• Bunsen, 81, 85, 89, 148, 149
• Bureau of Mines: cited on open flames, 234; 236
• Burning-glasses, 19, 20.
  • See also Lenses.
• Butylene, 106
• Byzantium, 34

• Cæsar, 163
• Canada, 254
• Candle-hour, defined, 215
• Candles: progress and, 7; 25, 28, 29, 30, 33;
  • religious uses of, 34, 35;
  • as a modern light-source, 36, 37;
  • ceremonial uses of, 38 et seq.; 44, 48, 57, 82, 97, 222, 299, 304
• Calcium, 107, 108
• Carbolic acid, 106
• Carbon: 53, 80, 81;
  • physical characteristics of, 80, 81; 90, 104, 105, 128, 129, 144, 170
• Carbon filament: 127 et seq.;
  • preparation of, 129, 130, 131;
  • luminous efficiency of, 131, 132;
  • lamps, 161;
  • lamps in greenhouses, 250 et seq.
• Carbons, formation of, 115, 116
• Carbureted hydrogen, 75
• Carcel, invention of clockwork lamp by, 54, 55
• Cat-gut, 130
• Ceria, 85, 101
• Charleston, S. C., 185
• Charcoal: 113;
  • uses of, for electrodes, 115
• Chartered Gas Light and Coke Co., London, 74
• Chemistry: artificial light and, 256-268
• Chicago, 62, 304, 305
• Chimneys, 54, 60, 62
• China, 19, 31, 32
• Chlorate of potash, 22
• Christ, 33, 46, 47
• Christians, "children of light," 42
• Christmas trees, 43, 304
• Chromium, 294
• Church of England, 49
• Cities: economy of artificial lighting in congested, 13
• Civilization: effect of artificial light upon, 4 et seq.;
  • fire and, 15
• Clark, Parker and, 139
• Clayton, Dr.: invention of portable gas-light by, 64;
  • quoted, 64, 65;
  • experiments of, with coal-gas, 67
• Claude, 147
• Cleaves, Dr., quoted, 276, 277
• Clegg, Samuel: 74;
  • gas-lighting accomplishments of, 75, 76
• Cleveland, 159
• "Clouds, The," Aristophanes, 19
• Coal: 32;
  • as a light-source, 55;
  • supply, 223; 228
• Coal-gas: 63 et seq.;
  • public lighting by, developed, 70 et seq.;
  • analytical production of, 103, 104;
  • yield of, retort (table), 105;
  • analysis of, 106
• Coal-mines, 234 et seq.
• Cobalt, 294
• Coke, 68, 105
• Cologne, 157, 158
• Colomb, Philip, 197
• Color: 9;
  • relation of artificial light to, 284 et seq.
• Colza, 31, 52, 167
• Combustion, 82 et seq.
• Commerce, 8, 97
• Constantine, 42
• Copper, 262, 295
• Cornwall, 63
• Cotton: 101;
  • carbon filaments, 129, 130
• Cromartie, 78
• Crookes, 90, 146
• Crosley, Samuel, improvement of gas-meter by, 76
• Crusies, 32

• Daguerre, 258
• Dancing, 346
• Davy, Sir Humphrey: 33, 68, 73;
  • first use by, of charcoal for sparking points, 112;
  • notes of, on electric arc, 113; 114
• Daylight, artificial, 12: 284 et seq.;
  • application of, 287
• Daylighting, 12-14
• Dollond, 195
• Doty, 61, 167
• Drake, Col. E. L., discovery of oil in Pennsylvania by, 56
• Drummond, Thomas: 171, 185, 196;
  • quoted on signaling, 197
• Dudgeon, Miss, 251, 252
• Dyes, 256, 265

• East Indies, 29
• Eddystone Light, 166, 167
• Edison: and problem of electric incandescent filament lamps, 128 et seq.; 129;
  • quoted on birth of incandescent lamp, 130
• Edward I, 274
• Edward VI, 49
• Efficiency, effect of artificial light upon, 14
• Eggs: relation of artificial light to production of, 247, 248
• Egypt: 31;
  • sacredness of light in ancient, 39; 153, 195
• Electric filament: 81, 127 et seq.:
  • approximate value of, lamps (table), 138
• Electric pile: construction of, 111; 127
• Electricity: 13, 22;
  • as a light-source, 57;
  • for home-lighting, 62, 84; 87, 89;
  • ignition of gas by, 102;
  • lighting by, 109 et seq.
• Electromagnetic waves, 68, 86, 87
• Electromagnets, 114, 116
• Electrodes, 113, 114, 115 et seq.;
  • life of, 122
• Elizabeth, Queen, 274
• England: 32;
  • petroleum discovered in, 56;
  • gas-lighting in, 63 et seq.; 166, 251, 274
• Erbia, 85
• Esquimaux: 18;
  • use of artificial light by, 31
• Ethylene, 106

• Factories: 13;
  • artificial light in, 239 et seq.
• Faraday, 113
• Filaments, carbon, 129 et seq.
• Finsen: 273, 274, 275;
  • on stimulating action of artificial light, 277; 279, 280
• Fire: importance of, to man, 5 et seq.;
  • man's dependence upon, 15;
  • mythical origin of, 16;
  • making, 17 et seq.;
  • production of, in the stone age, 18;
  • in early civilization, 19;
  • ancient worship of, 29, 299
• Fireflies: 24, 81, 96, 148, 149, 150
• "First Men in the Moon, The," H. G. Wells, cited, 148
• Fish: artificial light as bait for, 249
• Flame-arcs, 120, 121, 122, 187
• Flames: 86, 88, 89;
  • open, 233, 234 et seq.
• Flint, 33
• Fool's gold, 18
• Fort Wagner, 185
• France: lamps in, 55;
  • early gas-light in, 72
• Franchot, invention of moderator lamps by, 55
• Frankland, 77
• Franklin, Benjamin: 165;
  • quoted, 210-212; 213
• Fresnel, 167, 196
• Friction, 16, 17

• Gas: 13, 22;
  • discovery of coal, 32, 33;
  • early uses of, as light-source, 63 et seq.;
  • installment of, pipes in England, 63, 64;
  • Shirley's report on Natural, 66, 67;
  • first public display of, lighting, 69;
  • cost of, lighting, 71;
  • first attempt at industrial, lighting, 72;
  • first English, company, 74;
  • first, explosion, 75;
  • house, lighting, 76, 77; 80, 82;
  • spectrum of, 90;
  • modern, lighting industry, 97 et seq.;
  • origin of lighting by, 98;
  • first, works in America, 98;
  • growth of, consumption in United States, 99;
  • electrical ignition applied to, lighting, 102;
  • pressure, 102, 103;
  • water, 105;
  • carbons in, 106;
  • production of Pintsch, 109, 110;
  • salts applied to, flames, 120; 157;
  • Census Bureau figures on cost of, plants, 221, 222; 224, 341
• Gas-burners: 63, 64, 77;
  • candle-power of pioneer (table), 79;
  • improvements in, 84
• Gas-mantle: 61, 81;
  • influence of, 99;
  • characteristics of, 100 et seq.; 187
• Gas-meter, Clegg's, 76
• Gasolene: lamps, 55; 57
• Gassiot, 114
• Gauss, 196
• Geissler, 146
• General Electric Company, 132, 135, 136
• Germany: development of lamps in, 56;
  • early gas-lighting in, 72
• Glass, 195, 290 et seq.
• Glowers, 139
• Glow-worms, 24
• Glycerides, 52
• Gold, 293
• Gout, 275
• Gramme dynamo, 117
• Grass: 18;
  • carbon filaments, 129
• Greece: 39;
  • sacred lamps in ancient, 41; 42
• Greenhouses, carbon-filament lamps in, 250 et seq.

• Hall of Fame, 134
• Happiness, effect of artificial light upon, 14
• Hayden and Steinmetz, 253
• Health, artificial light in relation to, 269-283
• Helium, 89
• Hemig, 155
• Hemp, 21
• Henry, William, 75
• Herodotus, 56
• Hertz, 68
• Hertzian waves, 271
• Hewitt, Cooper, produces mercury-arcs, 124, 125
• Home: artificial light in relation to, 6;
  • lighting, 325 et seq.
• Hindu: light in, ceremonials, 40
• Hudson-Fulton Celebration, 306
• Huygens, 195
• Hydrocarbons, 82
• Hydrogen, 81

• Illiteracy, artificial light and, 9
• Invention, 7, 97
• Iowa, 238
• Iridium, 129
• Iron, 18, 262, 294
• Iron pyrites, 18
• Italy, 249

• Jablochkov: electric candle of, 117
• Jamaica, 19
• Jandus, 118, 122
• Japan: 19;
  • use of oil in, 30; 281
• Jerusalem, 43
• Jews: artificial light among, 40
• Journal, Paris, quoted, 210-212

• Kerosene: 57;
  • weight of, lumens, 60; 62, 187, 233
• Kitson, platinum-gauze mantle applied by, 61

• Laboratories: achievements of, 137
• Lamps: 16, 25;
  • Roman, 30; 31;
  • invention of safety, 33;
  • ancient funereal, 39;
  • sacred, of antiquity, 41;
  • ceremonial, 44;
  • scientific development of oil, 51 et seq.;
  • Holliday, 55;
  • Carcel, 54, 55;
  • Franchot's moderator, 55;
  • gasolene, 55;
  • development of, in Germany, 56;
  • air pressure, 61;
  • supremacy of oil, ends, 62;
  • Bowditch's, 77, 78; 80, 97;
  • mercury-arc, 126;
  • electric incandescent filament, 127 et seq.;
  • gem, 132;
  • tungsten, 133 et seq.;
  • luminous efficiency (table) of incandescent filament, 141; 299;
  • in home, 328-333
• Lange, 167
• Lard-oil, 51
• Lavoisier, 195
• Lead, 262, 294
• Le Bon, 72
• "Legend of Montrose, The," Scott, cited on primitive lighting, 27
• Leigh, Edmund, quoted, 226
• Lenses, 20, 171 et seq.
• Libanius, quoted, 153, 154
• Liberty, Statue of, 301, 302, 303
• Libraries, 9
• Light: relation of artificial, to progress, 3 et seq.;
  • as a civilizing agency, 3-14;
  • primitive man and artificial, 4;
  • Milton, quoted on importance of, 5;
  • artificial, and science, 7;
  • artificial, and industrial development, 8;
  • Maeterlinck's tribute to, 9;
  • Lincoln's debt to artificial, 9;
  • symbolism of, 9, 10;
  • therapy, 10;
  • in war, 11;
  • adaptations of, 12; 13;
  • mythical origin of artificial, 16;
  • earliest source of, 16;
  • production of, in stone age, 18;
  • matches as source of, 21;
  • animals as, sources, 24, 25;
  • primitive sources of, 24-37;
  • evolution of artificial, sources, 24-37;
  • development, 28 et seq.;
  • early outdoor use of artificial, 28;
  • Roman uses of artificial, 30;
  • beginning of scientific, 33, 34;
  • candles as modern, source, 36, 37;
  • symbolism and religious uses of, 38 et seq.;
  • Bible cited on artificial, 42-44;
  • in relation to worship, 43, 45, 46;
  • Argand's contribution to, 53, 54;
  • coal as, source, 55;
  • early uses of gas as, source, 63 et seq.;
  • as a public utility, 70;
  • first installation of industrial gas, 72;
  • science of, production, 80 et seq.;
  • causes of, radiation, 80, 81; 83;
  • lime, 84; electric, 89 et seq.;
  • principle of, production, 90, 91;
  • sources, 93;
  • various gas-burners', supply, 95;
  • relative efficiency of, sources, 95, 96;
  • in the home, 97;
  • influence of, upon science, invention, and commerce, 97 et seq.;
  • yield of acetylene, 106, 107;
  • electric, 109;
  • influence of gas upon development of artificial, 110;
  • development of artificial, 111 et seq.;
  • efforts to improve color of mercury-arc, 125;
  • electric-incandescent-filament, 127 et seq.;
  • effect of tungsten, upon, 133 et seq.;
  • of the future, 143-152;
  • in warfare, 178-193;
  • signaling, 194-207;
  • cost of, 208-224;
  • and safety, 225 et seq.;
  • improper use of, 229, 230;
  • comparison of daylight and artificial, 240;
  • reducing action of, 258;
  • bactericidal action of, 272 et seq.;
  • modifying, 284 et seq.;
  • spectacular uses of, 298-309;
  • expressiveness of, 310-324;
  • utility of modern, 325-340;
  • evolution of the art of applying, 341-356;
  • mobile, 347, 348, 349, 350;
  • psychological effect of, 351 et seq.;
  • as an accompaniment to music, 352-354
• Light-buoys, 10, 169
• Lighthouses: 10, 163-177;
  • optical apparatus of, 172 et seq.
• Light-ships, 10, 169
• Lighting-systems: comparison of, 12-14
• Lime, 84, 107, 108, 294
• Lincoln, Abraham, 9
• Linen, 18
• Link-buoys, 28
• Lithopone, 265, 266
• Liverpool, 167
• Living: comparison of, standards, 238 et seq.
• London, 152, 154, 155, 156, 157, 202
• London Gas Light and Coke Company, 74
• Lucigen, 61
• Lumen-hour: defined, 215
• Lumens: 60, 94, 215
• Lutheran Church, 49
• Lyceum Theatre, London, 73

• Maeterlinck, Maurice, 9
• Magazines, 8
• Magdsick, H. H., 303
• Magnesia: 84;
  • Nernst's application of, 138
• Magnesium, 179, 180
• Magnetite arc, 187
• Man: distinction between, and animal, 3;
  • artificial light and early, 4;
  • light-sources of primitive, 25
• Manganese, 262, 268, 294
• Mangin, 188
• Mann, 129
• Mantles, 95
• Manufacturing, 8
• Marconi, 68
• Marks, 118
• Matches: as light-sources, 21; 22, 82
• Maxwell, 68
• Mazda lamps, 289, 339
• Mecca, 40
• Mediterranean Sea, 163
• Mercury-arc: Way's, 124; 125, 126;
  • quartz, 125, 126;
  • attempts to improve color of, light, 125
• Middle Ages, 46, 47, 274
• Milton, quoted, 5
• Mirror, 19
• Mohammedans, 40
• Moore, Dr. McFarlan, 146, 147
• Morality, effect of light upon, 9
• Morse code: application of, to light-signaling, 198, 199
• Moses, 195
• Moving-pictures, 9, 260, 261
• Munich, 72
• Murdock, William: installment of gas-pipes by, 63; 68, 69, 70;
  • quoted on industrial use of artificial, 71; 72, 73, 74, 76, 78, 217, 309
• Museums: 13;
  • utilization of artificial light by, 322, 323
• Music: light as an accompaniment to, 352-354
• Mythology, 16

• Nantes, 85
• Napoleon, 111
• Napthalene, 106
• National Heat and Light Co., 72, 74
• Natural gas, 99
• Navesink Light, 206
• Nernst, 138, 139
• Newspapers, 8
• Newton, Sir Isaac: 7;
  • quoted on discovery of visible spectrum, 87; 88
• New York, 98, 165, 166, 206, 302, 304
• Niagara Falls, 108, 306
• Nickel, 262
• Nielson, 77
• Niepce, 258
• Niter, 21
• Nitrogen, 137
• Norfolk, 169

• Obesity, 275
• Offices, 13
• Oil: as a light-source, 29 et seq.;
  • development of, lamps, 51 et seq.; 155;
  • in lighthouse, 165 et seq.; 222, 224, 299
• O'Leary, Mrs., and her lamp, 62
• Olive-oil, 51, 52, 167
• Orkney Islands, 29, 177
• Osmium, 133
• Oxygen: relative consumption of, by oil-lamps, 58, 59; 262
• Ozone, 262

• Painting, 342, 343, 347, 348, 349
• Pall Mall, 74
• Panama-Pacific Exposition: 304;
  • artificial lighting of, 306, 307, 308, 309
• Paper: 18;
  • carbon filaments, 129, 130
• Paraffin, 35, 57
• Parker and Clark, 139
• Paris: experimental gas-lighting in, 83, 84;
  • Volta in, 111; 154, 185, 210, 212, 213
• Peckham, John, 195
• Pennsylvania: discovery of oil in, 56
• Periodic Law, 145
• Petroleum: 35, 51, 55;
  • discovery of, 56;
  • constitution of crude, 57; 58, 214
• Pharos, 163
• Philadelphia, 98, 99, 157
• Phillips and Lee, 70, 72
• "Philosophical Transactions of the Royal Society of London," 33;
  • quoted on industrial lighting, 63;
  • Shirley's report on natural gas in, 66, 67;
  • quoted, 87
• Phœnicians, 34, 39
• Phosphorus, 21
• Photo-micrography, 12
• Photography: 126;
  • early experiments in, 258;
  • development of, 259; 291, 292
• Picric acid, 106
• Pigments, 265
• Pintsch: production of, gas, 109, 110, 170
• Pitch, 106
• Plant-growth: artificial light and, 11, 249 et seq.
• Platinum, 85, 128, 129, 262
• Plumbago, 113, 130
• Plymouth, 166
• Poetry, 346
• Police, 162
• Potash, chlorate of, 22
• Priestley, Professor, quoted, 252
• Printing, 8
• Progress: influence of fire upon, 15 et seq.
• Prometheus, 16, 41
• Propylene, 106
• Ptolemy II, 163

• Quartz: 18, 19;
  • mercury-arcs, 125;
  • uses of, 126;
  • in skin diseases, 278, 279

• Radiators, energy, 88 et seq.
• Radium, 150
• Railway Signal Association, 205
• Railways: light-signaling applied to, 205
• Ramie fiber, 101
• Rane, 250, 251
• Rare-earth oxides: 85;
  • properties of, 88, 99
• Recreation, 9
• Redruth, 63
• Reformation: ceremonial uses of light during the, 48, 49
• Rheumatism, 275
• Robins, Benjamin, 201
• Rome, 30, 32, 34, 39, 41, 42, 44
• Röntgen, 270, 280.
  • See also X-ray.
• Royal Society of London: 33, 63, 66, 67, 70, 73;
  • and first gas explosion, 75, 111, 112
• Rumford, 167
• Rushlights, 28, 33
• Russia, 281
• Ryan, W. D'A., 306

• Safety: artificial light in relation to, 14, 225 et seq.
• Salts: chemical, 88, 89;
  • metallic, 120;
  • silver, 257, 258
• Sandy Hook Light, 165, 166
• San Francisco, 304, 306-309
• Savages, 3, 15, 17
• Sawyer, 129
• Scheele, K. W., 133;
  • quoted, 257, 258
• Schools, 9
• Science: light and, 6, 7; 97;
  • systematized, 268
• Scotland: 26, 31, 32, 48;
  • oil industry in, 56
• Scott, Sir Walter, cited, 27, 98
• Sculpture: artificial light in relation to, 184
• Search-lights, 11, 169
• Section of Plant Protection, 225, 226
• Selenium, 267, 293
• Semaphore, 199
• Shells: illuminating, 179 et seq.
• Shirley, Thomas: quoted on natural gas, 66, 67
• Siemens, 78
• Signaling, 194-207
• Silicon: filament, 140
• Silk: artificial, 101;
  • carbon-filaments, 129
• Simpson, R. E., 227, 231
• Silver, 258, 293
• Skin diseases: treatment of, 278, 279, 280
• Skylights, 13
• Sleep, 8
• Smallpox, 274, 275
• Smeaton, 166
• Soho, 69, 72
• South Africa, 129
• Sparks: 33, 125
• Spectrum: visible, 86;
  • Newton quoted on, 87;
  • of elements, 89;
  • of gases, 90; 120, 121;
  • mercury, 124-126
• Sperm, 31, 51, 52, 167
• Spermaceti, 35, 51
• Splinter-holders, 27, 28
• Stage: and artificial light, 319 et seq.; 343
• Staite, 117, 118
• Stearine, 35, 52
• Stearn, 129
• Steel, 18, 33
• Steinmetz, Hayden and, 253
• Sterilization: quartz-mercury-arc and, 280, 281, 282
• Stevenson, Robert Louis, quoted, 177
• Stores, 13
• St. Paul, 43
• St. Paul's Cathedral, 300
• Street-lighting: development of, 152-162
• Sugar, 22
• Sulphide of iron, 18
• Sulphur, 18, 21, 179, 180, 294
• Sulphuric acid, 21, 22
• Sun, 8, 16, 19, 20
• Swan, 129
• Syracuse, 19
• Syria, 153

• Tallow, 34, 35, 51, 52
• Tantalum: 132;
  • filament lamps, 133
• Tar, 68, 106
• Telegraphy, 195
• Telephony, 194
• Textiles, 256
• Thames, 169
• Theaters, 9, 319 et seq.
• Thoria, 85
• Tin, 262
• Tinder-boxes, 18, 19, 22
• Travelers Insurance Company, 227
• Trees, 26
• Troy, 42
• Tuberculosis, 273
• Tungsten lamp, 161 et seq., 187, 261, 290, 303
• Typhus, 273

• Ultra-violet rays: 126, 150;
  • in photographic electricity, 267, 268; 270, 272, 294
• United States: petroleum in, 57;
  • gas-consumption in, 99; 164, 165, 166
• United States Geological Survey, cited on sale of gas, 222
• United States Military Intelligence, 225, 226

• Vacuum tubes, 81, 286
• Venetians, 195
• Ventilation, 13
• Verne, Jules, 143
• Vestal Virgins, 42
• Volcanoes, 166
• Volta, 111, 112, 127
• Voltaic pile: construction of, 111, 127
• Von Bolton. See Bolton.

• War: and artificial light, 11, 178-193
• Washington, 305
• Water: sterilization of, by artificial light, 280 et seq.
• Watson, Dr. Richard, 67, 68
• Watt, 94
• Waves: electro-magnetic, 68, 86, 125 et seq.
• Wax, 34, 46, 51
• Way: mercury-arc produced by, 124
• Wells, 61
• Wells, H. G., cited, 148
• Welsbach, Auer von: 61;
  • invention of mantle by, 99, 100, 133
• Wenham, 78
• West Indies, 25
• Whale-oil, 31
• Wicks, 35, 36, 53, 54, 58, 59
• Winsor, 72, 73.
  • See also Winzler.
• Winzler. See Winsor.
• Wolfram. See Tungsten.
• Wood, 26, 27, 28
• Woolworth Building, 302, 303
• Wounds: treatment of, by artificial light, 10

• X-ray: production of, tubes during War, 131; 137, 150, 270, 280

• Young, James: discovers petroleum, 56
• Yttria, 85

• Zeitung, Cologne: 157;
  • extract from, on street-lighting, 158
• Zinc, 125, 130, 267
• Zirconia, 84, 85