Nutation, 34. O. Olbers's hypothesis, 241. Old style, 80. Ophiuchus (constellation), 347. new star in, 362. Opposition, 91, 136. Orion, 341. nebula in, 378. the trapezium of, 356. P. Pallas, the planet, 241. Parabola, the, 49. Parallax, 37. Pegasus (constellation), 343, 346. triple star in, 356. Perigee, 44. Perihelion, 47. Perseids (meteors), 311. Perseus (constellation), 346. cluster in, 353. Phobos, satellite of Mars, 239. Pico, a lunar mountain, 127. Pisces, or the Fishes, 350. Piscis Australis, or the Southern Fish, 350. Planets, 39. inferior, 130. periods of, 132. phases of, 132. inner group of, 221. intra-Mercurial, 230. minor, 223. outer group of, 222, 244. superior, 134. motion of, 134. periods of, 137. phases of, 137. three groups of, 221. Pleiades, the, 328, 342, 351. Pointers, the, 330. Polar distance, 16. Pole Star, the, 7, 330, 365. Poles, celestial, 7, 9. Pollux, star in Gemini, 340, 370. Præsepe, or the Beehive, 350. Precession of equinoxes, 31, 85. Prime vertical, the, 12. Proctor's theory of the stellar universe, 398. Procyon, star in Canis Minor, 340. Ptolemaic system, the, 41. Q. Quadrature, 91, 137. R. Radiant point (meteors), 310. Radius vector, 47. Refraction, 35. Regulus, star in Leo, 334, 370. Rhea, moon of Saturn, 259. Rigel, star in Orion, 340, 370. Right ascension, 16. S. Sagittarius, or the Archer, 347. Saturn, apparent size of, 256. distance of, 256. orbit of, 255. periods of, 256. physical constitution of, 257. ring of, 261. changes in, 268. constitution of, 269. phases of, 263. rotation of, 258. satellites of, 259. volume of, 256. Scorpio, or the Scorpion, 347. cluster in, 355. Seasons, the, 64. Sirius, the Dog-Star, 340, 342, 365, 370, 371. Solar system, the, 41. Solstices, 29, 59, 60. Sound, effect of motion on, 168. Spectra, bright-lined, 158. comparison of, 154. continuous, 158. displacement of lines in, 171. of comets, 318. reversed, 161. sun-spot, 193. types of stellar, 371. Spectroscope, the, 152. diffraction, 157. direct-vision, 155. dispersion, 152. Spectrum analysis, 159. solar, 164. Sphere, defined, 3. the celestial, 5. rotation of, 7. Spring-tides, 72. Stars, circumpolar, 7. clusters of, 328, 350. color of, 357. constellations of, 325. constitution of, 371. distance of, 364. double, 355. drift of, 368. four sets of, 10. magnitude of, 322. motion of, in line of sight, 369. multiple, 356. names of, 325. nebulous, 373. new, 361. number of, 323. parallax of, 364. proper motion of, 365. secular displacement of, 366. temporary, 361. variable, 358.