ion of aether and matter, 224-6

Resistance to motion, 17

Resisting medium, 228

Reversible cycle, 116, 118

Rings, vortex, 45

Rival theories, 8

Rivers, 89-90

Roemer, and velocity of light, 148

Rotation of earth, 219
of planets, 219
of sun, 246

Rotatory motion, 93

Rucker, Prof., 59

Rules of Philosophy, 3
first, 3
second, 4
third, 3, 7

Rumford, 98

Running water, 95

Satellites of Mars, 38, 178
Jupiter, 149, 178
Uranus, 254
Neptune, 254

Saturn, 26-7, 68
mass of, 235, 242
orbital velocity of, 251, 265
rotation of, 219
density of, 242
a magnet, 196
satellites of, 178

Schuster, Prof., 8, 218, 311

Sirius, 306, 308-9

Sodium, 43

Solar system, motion of, 257, 271
spectrum, 79, 139
magnetism, 211

Sound, 75
waves, 104, 120

Space, interstellar, 310, 313

Spectroscope, 47, 79

Spectrum analysis, 50, 139

Spiral nebulae, 322

Stars, fixed, 58
number of, 11, 306
binary, 309
distances of, 280
magnitude of, 306, 309
colour of, 79, 308
motion of, 310-11
nebulous, 320
proper motions of, 312
variable, 307
double, 308
clusters of, 314
orbits of, 310
are magnets, 307

Stokes, Sir G., 69, 152, 218

String, 21

Sun, diameter of, 280
constitution of, 79
a magnet, 164, 198-9
mass of, 190
heat of, 109
motions of, 270
orbital velocity of, 35
rotation of, 246
centre of two forces, 186

Tails of comets, 300, 304
straight, 300
curved, 301
multiple, 300

Tait, Prof., 18, 40-1, 88, 247

Telescope, 79

Temperature, 104-5

Terrestrial magnetism, 207-12
gravity, 29

Theory, atomic, 44
rules for making, 3
undulatory, 123
of exchanges, 105

Thermodynamics, first law of, 87, 114
second law of, 116

Thomson, J. J., Prof., 43, 326, 335

Tidal water-power, 88

Tides, 89, 96

Torsion balance, 185

Trade winds, 96, 249

Transformation of energy, 86
of motion, 93

Transverse vibration of light, 130

Tuning-fork, 104

Tympanum, 120

Tyndall on radiation, 104, 106
on light, 71
on Lines of Force, 174
on aether, 77
on atoms, 106
on aether waves, 112

Ultra-violet rays, 140
red rays, 140

Unity of universe, 322-9

Universal gravitation, 24
aether, 58

Universe, 313, 322, 347

Uranus, 68
mass of, 235
density of, 242
orbital velocity of, 265
a magnet, 196

Ursa Major, 307
Minor, 307

Vapour, 49

Variation