Michelson and Morley, 7, 67

Milky way, 79, 309, 314

Molecules, 44

Momentum, 20

Moon, 61

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 mot