Part 49

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.

Sun, atmosphere of, 149. brightness of, 151. chemical constitution of, 164. chromosphere of, 149, 196. corona of, 149, 196, 204. distance of, 142. faculæ of, 177. heat radiated by, 150. inclination of axis of, 187. mass of, 140. motion of, among the stars, 26. at surface of, 168. in atmosphere of, 172. secular, 366. photosphere of, 149, 175. prominences of, 149, 197. rotation of, 186. spectrum of, 164, 171. temperature of, 149. volume of, 140. winds on, 174.

Sun-spots, 179. and magnetism, 190. birth and decay of, 185. cause of, 194. cyclonic motion in, 182. distribution of, 188. duration of, 181. groups of, 181. periodicity of, 189. proper motion of, 187. size of, 181. spectrum of, 193.

Taurus, or the Bull, 342. quadruple star in, 356.

Telescope, Cassegrainian, 23. equatorial, 19. front-view, 22. Gregorian, 23. Herschelian, 22. Lord Rosse's, 25. Melbourne, 25. Newall, 20. Newtonian, 22. Paris, 26. reflecting, 21. Washington, 20. Vienna, 20.

Telespectroscope, the, 155.

Telluric lines of spectrum, 165.

Tethys, moon of Saturn, 259.

Tides, 67.

Time, clock, 78. sun, 78.

Titan, moon of Saturn, 259, 261.

Toucan, star cluster in, 354, 389.

Transit instrument, 17.

Transits of Venus, 145.

Triesneker, lunar formation, 123.

Tropics, 61.

Twilight, 62.

Tycho Brahe's star, 361. system, 44.

Tycho, a lunar crater, 129.

Universe, structure of the stellar, 396.

Uranus, discovery of, 271. name of, 270. orbit of, 269. satellites of, 271.

Ursa Major, or the Great Bear, 330. nebula in, 386.