Paris: experimental gas-lighting in, 83, 84; Volta in, 111; 154, 185, 210, 212, 213 Peckham, John, 195 Pennsylvania: discovery of oil in, 56 Periodic Law, 145 Petroleum: 35, 51, 55; discovery of, 56; constitution of crude, 57; 58, 214 Pharos, 163 Philadelphia, 98, 99, 157 Phillips and Lee, 70, 72 "Philosophical Transactions of the Royal Society of London," 33; quoted on industrial lighting, 63; Shirley's report on natural gas in, 66, 67; quoted, 87 Phoenicians, 34, 39 Phosphorus, 21 Photo-micrography, 12 Photography: 126; early experiments in, 258; development of, 259; 291, 292 Picric acid, 106 Pigments, 265 Pintsch: production of, gas, 109, 110, 170 Pitch, 106 Plant-growth: artificial light and, 11, 249 _et seq._ Platinum, 85, 128, 129, 262 Plumbago, 113, 130 Plymouth, 166 Poetry, 346 Police, 162 Potash, chlorate of, 22 Priestley, Professor, quoted, 252 Printing, 8 Progress: influence of fire upon, 15 _et seq._ Prometheus, 16, 41 Propylene, 106 Ptolemy II, 163 Quartz: 18, 19; mercury-arcs, 125; uses of, 126; in skin diseases, 278, 279 Radiators, energy, 88 _et seq._ Radium, 150 Railway Signal Association, 205 Railways: light-signaling applied to, 205 Ramie fiber, 101 Rane, 250, 251 Rare-earth oxides: 85; properties of, 88, 99 Recreation, 9 Redruth, 63 Reformation: ceremonial uses of light during the, 48, 49 Rheumatism, 275 Robins, Benjamin, 201 Rome, 30, 32, 34, 39, 41, 42, 44 Roentgen, 270, 280. _See also_ X-ray. Royal Society of London: 33, 63, 66, 67, 70, 73; and first gas explosion, 75, 111, 112 Rumford, 167 Rushlights, 28, 33 Russia, 281 Ryan, W. D'A., 306 Safety: artificial light in relation to, 14, 225 _et seq._ Salts: chemical, 88, 89; metallic, 120; silver, 257, 258 Sandy Hook Light, 165, 166 San Francisco, 304, 306-309 Savages, 3, 15, 17 Sawyer, 129 Scheele, K. W., 133; quoted, 257, 258 Schools, 9 Science: light and, 6, 7; 97; systematized, 268 Scotland: 26, 31, 32, 48; oil industry in, 56 Scott, Sir Walter, cited, 27, 98 Sculpture: artificial light in relation to, 184 Search-lights, 11, 169 Section of Plant Protection, 225, 226 Selenium, 267, 293 Semaphore, 199 Shells: illuminating, 179 _et seq._ Shirley, Thomas: quoted on natural gas, 66, 67 Siemens, 78 Signaling, 194-207 Silicon: filament, 140 Silk: artificial, 101; carbon-filaments, 129 Simpson, R. E., 227, 231 Silver, 258, 293 Skin diseases: treatment of, 278, 279, 280 Skylights, 13 Sleep, 8 Smallpox, 274, 275 Smeaton, 166 Soho, 69, 72 South Africa, 129 Sparks: 33, 125 Spectrum: visible, 86; Newton quoted on, 87; of elements, 89; of gases, 90; 120, 121; mercury, 124-126 Sperm, 31, 51, 52, 167 Spermaceti, 35, 51 Splinter-holders, 27, 28 Stage: and artificial light, 319 _et seq._; 343 Staite, 117, 118 Stearine, 35, 52 Stearn, 129 Steel, 18, 33 Steinmetz, Hayden and, 253 Sterilization: quartz-mercury-arc and, 280, 281, 282