Motion of stars, 310 planetary, 253 of sun, 274 of aether, 80 and work, 95 modes of, 92, 122, 163 first law of, 15, 16, 239 second law of, 19, 244 third law of, 20, 251 Multiple stars, 308 Natural philosophy, 4 Nebulae and aether, 313 structure of, 314 spiral, 322 annular, 320 elliptical, 320 planetary, 321 spectrum of, 314 irregular, 319 Nebular hypothesis, 317 Nebulous stars, 311 Neptune, 68 discovery of, 25 mass of, 235 orbital velocity of, 251, 265 distance from sun, 242 a magnet, 196 Newton's coloured rings, 107 _Optics_,72, 98, 122 letter to Bentley, 2, 96 Rules of Philosophy, 3 _Principia_, 3, 7, 38 emission theory, 123 law of gravitation, 24 atoms, 44 on aether, 98 Nichols and Hull, 32, 153 Ocean, 81, 90 Operations, cycle of, 114 _Optics_, Newton's, 2, 122 Orbital motions of planets, 266 Orbit of earth, 33 of Venus, 33 Orbits of satellites, 34 of planets, 33-4, 266 moon, 267 stars, 310 sun, 270 Origin of sun's heat, 95 Orion, 79, 307, 314, 319 Oxygen, 40, 44, 60, 93 Parallelogram of forces, 15 Pendulum, 88 Periodic times, 37 Perpetual motion, 93, 220 _Phil. Mag._, 58, 67, 71, 73, 74, 80 _Phil. Trans._, 58, 62, 64, 75 Philosophy, Rules of, 3 Phobos, 38 Physical lines of force, 203-6 Pitch of Sound, 105, 120, 139 Plane of ecliptic, 277-9 Planetoids, 31 Planets, minor, 31 origin of, 240 orbits of, 33, 266 electrified bodies, 177 masses of, 242 relative distances of, 242 orbital velocities of, 251 periodic times of, 251 Platinum, 48 Pleiades, 79 Polarization, 176 Potential energy, 87 Potential, electric, 170 magnetic, 194 Pouillet, M., 109 Poynting, 91 Pressure, aetherial, 181 Preston, Prof., 283 Prevost, theory of exchanges, 105 Primitive impulse, 9, 10, 12, 319 _Principia_, Newton's, 3, 7, 38-9, 122 Properties of matter, 42 Quantity of sun's heat, 109 Query, 18-19 _Optics_, 72, 122 Radiant heat, 109 energy, 115 Radiation, 104 Radius Vector, 26 Rankine, 103 Rays, actinic, 141 dark heat, 140 infra-red, 141 ultra-violet, 140 Rontgen, 341 X, 341 Rectilinear propagation of light, 144 of heat, 111 Reflection, 160 Refraction, 160 Relative motion 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