NEBULÆ AND CLUSTERS OF STARS, 324. Distinction, 324. Large number visible, 324. Varieties of form and grouping, 325. Distribution in R.A., 326. Early observations, 326. Variable Nebulæ, 327. Nebulous Stars, 330. The Magellanic Clouds, 331. Double Nebulæ, 332. Real dimensions of Nebulæ and Clusters, 332. Round Nebulæ and Clusters, 332. Description of Nebulæ and Clusters, 333. Great Nebula in Andromeda, 334. —— —— in Orion, 334. Planetary Nebulæ, 334. Spiral Nebula, 335. Crab Nebula in Taurus, 336. Dumb-bell Nebula, 337. Ring Nebula in Lyra, 337. Elliptical Nebulæ, 338. Globular Clusters, 338. Further observations, 339. Discovery of new Nebulæ, 341. New Nebulæ discovered at Bristol, 342. List of Clusters of Stars, 343. —— of globular Clusters, 344. —— of Nebulæ, 345. Nebulous Stars, 330. Neison, Lunar observations, 128, 129. NEPTUNE, Discovery of, 221. Observations in 1795, 222. Period &c., 223. Observations, 223. Supposed ring, 223. The satellite, 223. New or temporary Stars, 312. Newton, 128. Newton, Sir Isaac, Experiments on Colours, 9. ——, His reflecting-telescope, 11. ——, On mountainous sites for telescopes, 347. Noble, Occultation of Jupiter, 186. ——, Occultation of Saturn, 210. —— on observations of Mercury and Venus, 348. Nomenclature of Comets, 246. —— of Lunar formations, 123. —— of Mars, 158. —— of Meteor-systems, 271. Number of Comets visible, Large, 228. —— of Nebulæ and Star-clusters, 324. —— of Planetoids, 167. —— of Stars, 293. Observations of Neptune, 223. —— required of the Sun, 97. —— —— of the Moon, 116. —— —— of Mercury, 143. —— —— of Venus, 152. —— —— of Mars, 162. —— —— of Jupiter, 183. —— —— of Saturn, 205. —— —— of Uranus, 219. —— —— of Comets, 243. —— —— of Meteors, 279. —— —— of Stars, 320. —— —— of Nebulæ, 339. ——, Solar, 88. Observatories, 64. Observer’s aims, 42. Observing, Open-air, 75. Observing-seats, 53. Occultations of Jupiter, 185. —— of Jupiter’s satellites, 189, 190. —— of Mars, 166. —— of Mercury, 144. —— of Regulus by Venus, 154. —— of Saturn, 209. —— of Star by Jupiter, 193. —— of Venus, 153. —— of Vesta, 169. Olbers discovers Pallas and Vesta, 167. ——, His Comet of 1815, 235, 241. ——, Observer of Comets, 250. Open-air observing, 75. Opera-glass, 61. Orbits of Comets, Differences in, 230. Orion, Great Nebula in, 334. ——, The constellation, 289. Orionids, 275. Orionis β, 307. —— θ, 318. —— σ, 318. Outbursts of Faculæ, 108. Palisa, Discoverer of Planetoids, 167. Palitzch, Discoverer of Halley’s Comet, 236. Pallas, 168. Parabola, 230. Past and future work, 84. Periodical Comets, 234. —— ——, Grouping of, 241. Periodicity of Jupiter’s markings, 184. —— of Sun-spots, 100.