Gravitation, law of, 66

Gravity, variation of, 58, 67; center
of, 68

Guericke, Otto von, 31, 41; portrait
of, 32

Gun, 354-mm., in action, 73
Gyrocompass, 83, 223

Hail, formation of, 174

Hardness, 92

Harmony, 347

Hay scales, 120

Headlight, automobile, 400
Heat, mechanical equivalent of,
151 ff.; unit of, 152; produced by
friction, 153; produced by colli-
sion, 154; produced by compres-
sion, 154; specific, 158; of fusion,
161; of vaporization, 181; trans-
ference of, 203

Heating, by hot air, 211; by hot
water, 212; by steam, 213
Heating effects of electric currents,
284, 289
Helium, 45, 445
Helmholtz, 345

Henry, Joseph, portrait of, 246
Henry's law, 104

Hertz, 422, 436; portrait of, 102
Heusler alloys, 216
Hiero, 21

Hirn, 154

Imp, bottle, 43

Incandescent lighting, 285
Incidence, angle of, 358
Inclination, 223

Inclined plane, 63, 117
Index of refraction, 371

Induction, magnetic, 216; electro-
static, 228; charging by, 230; of
current, 290

Induction coil, 308
Induction motor, 291
Inertia, 83

Insect on water, 100
Insulators, 227

Intensity, of sound, 326; of illumi-
nation, 374

Interference, of sound, 333; of light,
365

Ions, 235, 249, 273
Iron, electric, 269
Isoclinic lines, 457
Isogonic lines, 223

Jackscrew, 118

Joule, 106, 122, 151 ff.; portrait of, 122

Kelvin, portrait of, 134
Kilogram, the standard, 4
Kilowatt, 122

Kilowatt hour, 285
Kinetic energy, 123, 126
Kirchhoff, 415

Laminated cores, 310

Lamps, incandescent, 285; arc, 286;
Cooper-Hewitt, 288

Lantern, projecting, 391
Leclanché cell, 277

Lenses, 378 ff.; optical center of, 378;
principal axis of, 378; principal
focus of, 378; formula for, 380;
magnifying power of, 395; achro-
matic, 410

Lenz's law, 291
Level of water, 13

Lever, 110 ff.; compound, 120
Leviathan, 135
Leyden jar, 241

Liberty motor, 191

Lignt, speed of, 357; reflection of,
358; diffusion of, 359; refraction
of, 360; nature of, 364; corpuscular
theory of, 364; wave theory of,

R-34, dirigible airship, 44

Radiation, thermal, 208; invisible,

417 ff.; and temperature, 418; and
absorption, 419; electrical, 421
Radioactivity, 441 ff.

Radiometer, 417

Radium, discovery of, 441

Rain, formation of, 174

Rainbow, 411

Ratchet wheel, 146

Rayleigh, portrait of, 358

Rays, infra-red, 417; ultra-violet,
417; cathode, 437; Röntgen, 439;
Becquerel, 442; a, B, and y,
442 ff.

Rectifier, tungar, 314; crystal, 425
Reflection, of sound, 327; of light,
358; angle of, 358; total, 361,
462

Refraction, of light, 360; explana-
tion of, 368; index of, 371
Refrigerator, 163
Regelation, 167
Relay, 260

Resistance, electric, defined, 262;
specific, 262; laws of, 262; unit of,
263; internal, 268; measurement
of, 269

Resistances, table of, 262

Resonance, acoustical, 328 ff.; elec-
trical, 421

Resonators, 331
Resultant, 59
Retentivity, 217
Retinal fatigue, 407

Right-hand rule, 252, 254

Rise of liquids, in exhausted tubes,
27; in capillary tubes, 97
Roller bearings, 146
Römer, 357

Röntgen, 439; portrait of, 446
Ross, 222

Rotor, generator, 257

Rowland, 155; portrait of, 358
Rubens, 408

Rumford, 151, 374

Rutherford, 442; portrait of, 446

Saturation of vapors, 169; magnetic,

222

Scales, musical, 337; diatonic, 338;
even-tempered, 339
Screw, 118

Sea breeze, 207
Searchlight, 400

Secondary cells, 281 ff.

Self-induction, 307

Separator, cream, 85

Series connections, 270, 279

Spectra, 411 ff.; continuous, 412;
bright-line, 413; pure, 414; solar,
414; X-ray, 447

Spectrum, 403; invisible portions of,

417

Spectrum analysis, 413

Speed, of sound, 320; of light, 357;
of light in water, 369; of electric
waves, 423 ff.
Spinthariscope, 443
Starting box, 304
Steam engine, 189 ff.
Steam turbine, 199
Steelyards, 115
Stereoscope, 398

Storage cells, 281, 283
Strings, laws of, 339
Sublimation, 168
Submarine, 23, 44

Sun, energy derived from, 157; spec-
trum of, 414
Surface tension, 95

Sympathetic electrical vibrations, 421
Sympathetic vibrations of sound,
346 ff.

Tank, British, 190

Telegraph, 259 ff.; wireless, 423 ff.
Telephone, 316 ff.; wireless, 427 ff.
Telescope, astronomical, 396; Yerkes,
365, 396, 397

Temperature, measurement of, 128;
absolute, 134; low, 134
Tenacity, 90

Thermometer, Galileo's, 128; mer-
cury, 129; Fahrenheit, 131; gas,
132-134; alcohol, 132, 134; the
dial, 143

Thermos bottle, 209
Thermoscope, 418
Thermostat, 142

Thomson, 438; portrait of, 440
Three-color printing, 408
Torricelli, experiment of, 28
Tower, high-tension, 241
Transformer, 312-314

Transmission, of pressure, 15; elec-
trical, 312; of sound, 321
Transmission, automobile, 196
Transmitter, telephone, 316, 317
Trowbridge, 418

Tungar rectifier, 314

Turbine, water, 149; steam, 199

Watch, balance wheel of, 141; wind-
ing mechanism of, 453

Water, density of, 4; city supply of,
19; maximum density of, 138; ex-
pansion of, on freezing, 166
Water wheels, 148-150
Watt, 122, 284

Watt, James, 122, 189; portrait of,
122

Watt-hour meter, 304

Wave length, defined, 322; formula
for, 323; of yellow light, 367; of
other lights, 403

Wave theory of light, 364
Wave train, 322, 424, 425
Waves, condensational, 323; water,
324; longitudinal and transverse,
325; light, are transverse, 371;
electric, 422; modulated, 427
Weighing by method of substitu-
tion, 6

Welsbach mantle, 442
Weston cell, 277

Wet- and dry-bulb hygrometer, 178
Wheel, and axle, 116; gear, 119;
worm, 119; water, 148-150