Index of Subjects 425 
N.Q.C. 5850, Plate X (p. 336) 
„ 5866, Plate XIII (p. 356). 
„ 6720 ( = M 57), Plate IV (p. 27) 
„ 6822, 18, 341 
„ 7009, Plate IV (p. 27) 
,, 7217, Plate XIV (p. 357) 
„ 7479, Plate X (p. 336) 
„ 7662, Plate IV (p. 27) 
Nebulae, elliptical, 18, 332, 334 
,, extra-galactic (great), 18, 29, 331 ff., 
415 
,, extra-galactic, masses of, 352, 353, 
415 
,, irregular, 18, 28, 333 
,, spindle, 18, 333 
,, spiral, 12, 18, 332, 357, 379 
Nebular hypothesis of Laplace, 255, 353, 
396 
Neptune, 4, 5, 408 
o Ceti, Plate VI (p. 49), 63, 392 
Orion, belt of, 24 
,, great nebula in, Plate V (p. 28), 18, 28 
PallaB (asteroid), 4 
Parallax (defined), 6 
,, Cepheid, 10, 18, 25 
,, spectroscopic, 10 
Parsec (defined), 6 
Partial stability, 239, 293 
Pear-shaped configurations of a rotating mass, 
216, 221 
Pearce’s star (H.D. 1337), 57, 92,120,129, 288, 
289 
Period-luminosity law, 11, 12, 385 
Planetary nebulae, 27 
,, systems in space, 409, 416, 420 
Planeteslmal theory, 399 
Planets, 3, 399, 405 ff., 409, 420 
Plaskett’s star (B.D. 6°, 1309), 32, 57, 92, 109, 
120, 129, 185 
Pleiades, 24, 380 
Poincaré’s Theorem (21'+ W = 0), 67 
,, ,, (rotating masses), 279 
Polaris, 41, 53, 313, 382 
Pressure of radiation, 37, 74, 141 
,, „ in liquid stars, 141, 142 
Procyon, 7, 33, 59, 63, 132, 182 
Proxima Centauri, 5, 7, 23, 24, 32, 59 
Pulsations of gaseous stars, 384, 393, 394 
R Scuti, 392 
Radiation, 35 ff. 
,, energy of, per unit volume, 37, 79 
,, partition of energy of, 37 
,, pressure of, 37, 74, 80 
Radiative equilibrium, 79, 80 
„ transfer of energy, 77, 79 
„ viscosity, 270, 277 
Radii of Btars, 47, 60, 419 
Radioactivity, 111, 127, 135 
Resisting medium, effects of, 408, 409 
Roche’s limit, 232, 243 
Rotating stars, 194, 206, 223, 245, 268, 279, 
284, 411 
„ stellar systems, 371 
Rotation of nebulae, 333, 414, 415 
Satellites, the birth of planetary, 399, 406 
Saturn, rings of, 243, 407 
„ system of, 3,4, 7, 243,255,406,407,408 
Secular decrease of mass, 114, 131, 298, 417 
Secular instability, 199, 201 
Slrlometer, 6, 32 
Sirius, 5, 7, 31, 33, 41, Plate VI (p. 49), 58, 59, 
129, 130, 182 
,, companion of (Sirius B), 33, 58, 59, 
74, 132, 182 
Solar constant, 36 
,, spectrum, 49, 51, 53 
,, system, 3, 4, 394 ff. 
„ „ origin of, 395 ff., 400, 416 
Spectra, stellar, 48, 53 
Spectral type,.52, 292 
Spectroscopic parallaxes, 10 
Spiral nebulae, 12, 18, 332, 357 
Stability of motion of stellar systems, 367 
,, ,, stellar structures, 117,144,149,190 
,, ,, rotating stars, 212, 221 
,, ordinary, of a dynamical system, 190, 
198, 214 
„ secular, 199, 201 
,, „ of binary systems, 229, 236 
,, ,, ,, Maclaurin spheroids, 214 
,, ,, ,, Jacobian ellipsoids, 215 
,, ,, ,, pear-shaped configura 
tions, 221 
Star-clouds, 17, 18 
Star-clusters (globular), 12, Plate III (p. 25), 
25, 26, 372, 377 
,, (moving), 24, 26, 372, 375, 379 
„ (open), 26 ' 
Star-streaming, 362, 366, 368 
Stellar distances, 1, 5 
,, luminosities, 30 
,, magnitudes, 30 
,, radiation, 35 
,, radii, 47, 60, 419 
,, spectra, 48, 53 
,, velocities (law of distribution), 302, 361, 
368, 369, 371 
Sun, physical data for, 55 
Surface-brightness of nebulae, 339