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,

Huygens, 364, 372; portrait of, 364

Hydraulic elevator, 18

Hydraulic press, 17

Hydraulic ram, 88, 89
Hydrogen thermometer, 132

Hydrometer, 23

Hydrostatic bellows, 447
Hydrostatic paradox, 14

Hygrometry, 173

Ice, manufactured, 201

Ignition, automobile system of, 198,
199

Images, by convex lenses, 378 ff.;
size of, 381; virtual, 382; by con-
cave lenses, 382; in plane mirrors,
383; in convex mirrors, 384, 386;
in concave mirrors, 384, 387,

Loudness of sound, 326

Machines, general law of, 116, 124,
156; efficiencies of, 147
Magdeburg hemispheres, 33
Magnet, natural, 214; laws of the,
215; poles of the, 215; lifting, 247
Magnetism, 214 ff.; nature of, 220;
theory of, 221; terrestrial, 222;
residual, 301

Magnifying power, of lens, 395; of
telescope, 396; of microscope, 397;
of opera glass, 398

Malleability, 92
Manometric flames, 343
Marconi, 423; portrait of, 316
Mass, unit of, 4; measurement of, 6
Matter, three states of, 55

Maxwell, 436; portrait of, 102
Mechanical advantage, 109
Mechanical equivalent of heat, 153 ff.
Melting points, table of, 164; effect

of pressure on, 166

Meter, standard, 3
Michelson, 357; portrait of, 358
Microphone, 315
Microscope, 397

Mirrors, 383 ff.; convex, 384, 386;
concave, 384, 387; formula for, 388

Mixtures, method of, 159
Molecular constitution of matter, 49
Molecular forces, in solids, 90; in
liquids, 93

Molecular motions, in gases, 49, 50;
in liquids, 53; in solids, 55
Molecular nature of magnetism, 220
Molecular velocities, 52, 129
Moments of force, 111
Momentum defined, 84

Morse, 260; portrait of, 260
Motion, uniformly accelerated, 75;

laws of, 76; perpetual, 156
Motor, Liberty, 191; electric-induc-
tion, 291; street-car, 302. See also
Electric motor

Motor rule, 293
Moving pictures, 386

Newton, law of gravitation, 66; laws
of motion, 83-87; portrait of, 84;
principle of work, 116; corpuscular
theory, 364

Niagara, 157
Nichols, E. F., 417

Nodes, in pipes, 334; in strings, 340
Noise and music, 325
Nonconductors, of heat, 205; of elec-
tricity, 227

North magnetic pole, 222

Ocean currents, 207

Oersted, 246; portrait of, 246
Ohm, 263; portrait of, 268
Ohm's law, 267

Onnes, Kamerlingh, 135, 178
Opera glass, 398
Optical instruments, 390 ff.
Organ pipes, 353, 354

Oscillatory discharge, 422

Overtones, 341; in pipes, 350

Parabolic reflector, 400

Parachute, 44

Power, definition of, 121; horse, 122;
electric, 284

Pressure, in liquids, 13; defined, 13;
transmission of, by liquids, 15; in
air, 27; amount of atmospheric,
29; coefficient of expansion, 133,
136; effect of, on freezing, 166; of
saturated vapor, 170; in primary
and secondary, 311
Projectile, path of, 78
Pulley, 108 ff.; differential, 119
Pump, air, 33, 41; compression, 41;

lift, 42; force, 43

Quality of musical notes, 342
Quebec Bridge, 70

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; α, β, and y,
442 ff.

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

Sleet, formation of, 174
Snow, formation of, 174
Soap films, 95, 402
Solar spectrum, 414, 415
Sonometers, 339

Sound, sources of, 319; nature of,
319; speed of, 320; musical, 325;
intensity of, 326; reflection of,

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,

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

Units, of length, 2; of area, 2; of
volume, 2; of mass, 4; of time, 5;
three fundamental, 5; C. G. S., 6 ;
of force, 57, 86; of work, 106; of
power, 122, 284; of heat, 152; of
magnetic pole, 215; of magnetic
field, 219; of current, 251, 257;
of resistance, 267; of potential,
277; of light, 375, 376

Vacuum, sound in, 320; spark in,

436

Vaporization, heat of, 181, 182
Velocity, of falling body, 75; of
sound, 320; of light, 357

Ventilation, 210, 211
Vibration, forced, 331; of strings,

339; sympathetic, 346 ff.

Vibration numbers, 337
Vision, distance of most distinct,

394; binocular, 398

Visual angle, 394
Volt, 239, 277, 294
Volta, 245; portrait of, 240
Voltmeter, electrostatic, 239; com-
mercial, 265, 266

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