ciation, 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

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 Insu