_S_ Doradus, 182, 269, 270 St John, C. E., 343, 344 Salinity of oceans, 151 Sampson, R. A., 17, 308 Satellites, atmospheres on, 196 birth of (Laplace), 231 birth of (Tidal Theory), 241, 243, 246 discovery of, 23 Saturn, 16, 17, 18, 19, 32, 45 birth of, 240, 242, 243 rings of, 226, 231, 246, 247, 250 rotation of, 225 satellites of, 23, 196, 240, 241 ff., 250 temperature of, 21 Schrödinger, E., 305 Schwarzschild, K., 308 Seares, F. H., 26, 163, 281, 282 Sedimentation, 151 Shapley, H., 26, 59, 63, 65, 213, 216, 223, 247 Shooting-stars, nature of, 176, 247 origin of, 238, 247 swarms of, 247, 248, 251 Sirius, 36, 48, 259, 278, 279, 280, 316 system of, 265 Sirius _B_, 48, 262, 280, 292 Soddy, F., 111 Solar spectrum, 51, 105, 125, 256 Solar system, arrangement of, Bode’s law, 19 arrangement of (Copernican), 3, 5, 6, 27, 32 arrangement of (Ptolemaic), 2, 4, 6, 8, 31 atmospheres in, 194 ff., 343, 344, 347 orbits in, 45, 46, 224 ff., 238 origin of, 230 ff. Sound, 96, 198 Spectra, stellar, 50, 125, 130 and Plate VIII (p. 51). _See also_ Displacements Spectral types, 51 relation to stellar weights, 164 relation to surface-temperatures, 257 Spectroscope, 50 Spectroscopic binaries, 52 orbits of, 171, 172 origin of, 169, 222, 223 Spectroscopic parallaxes, 62, 303 Spectroscopic velocities, 50 Spectroscopy, 105 Spectrum, 50 of sun, 50, 105, 125, 256 Spherical nebulae, 207, 218, 219 Spiral nebulae, 30, 236 arms of, 236 Stability of stellar structures, 295, 296, 300 ff. Stars, ages of, 84, 155, 167, 173, 174, 186 arrangement of, 24, 65 birth of, 209 density of, 263 ff., 273, 282, 292 diameters of, 260 ff., 277, 278, 321 distances of, 31, 35, 37 evolution of, 313 ff. internal constitution of, 285 ff. internal temperatures of, 286 liquid, 222, 296 ff., 298, 301, 310 luminosity of, 49, 179, 180, 269 motions of, 36, 50, 66 ff., 164, 212, 213 number of, 68, 69, 88 spectra of, 51, 125, 130 and Plate VIII (p. 51). _See also_ Displacements stability of, 295, 296, 300 ff. surface-temperatures of, 254, 257, 263 ff., 270, 271 variable, 55 ff., 223 weights of, 46, 48, 49, 164, 179, 268, 280 ff. Star-streaming, 212, 214 Statistical methods in astronomy, 212, 213 Stellar, _see_ Stars Struve, Otto, 223 Struve, W., 33 Sun, age of, 181, 184 candle-power of, 55 distance from earth, 34, 227, 346 future of, 348, 350 internal constitution of, 286, 290 internal temperature of, 286, 288 loss of weight of, 178, 227, 346 past history of, 180 position in galactic system, 26, 66 radiation of, 55, 175, 189, 190 rotation of, 168, 205, 245