COMETS AND COMET-SEEKING, 227. Ideas concerning Comets, 227. Appearance of Comets, 228. Large number visible, 228. Nature of apparition, 229. Tenuity, 229. Differences of orbit, 230. Discoveries of Comets, 230. Large Comets, 231. Periodical Comets, 234. Halley’s Comet, 236. Encke’s Comet, 236. Biela’s Comet, 238. Brooks’s double Comet, 239. Brorsen’s Comet, 239. Faye’s Comet, 240. D’Arrest’s Comet, 240. Pons-Winnecke’s Comet, 240. Tuttle’s Comet, 241. Grouping of Periodical Comets, 241. Further Observations required, 243. Nomenclature of Comets, 246. Curiosities of Comets, 248. Naked-eye Comets, 248. Comet-seeking, 249. English weather and Comet-seeking, 251. Aperture and Power required, 252. Annual rate of discovery, 255. Telescopic Comets, 256. Ascertaining positions, 257. Dr. Doberck’s hints, 258. Prizes for Discoveries, 258. Common, His large Reflectors, 15; Their performance, 28. Computation of a Meteor’s real path, 278. Conjunctions, Planetary, 225. Constellation figures, The, 290. Cooke & Sons mount a 24·8-inch refractor, 18; Its barren record, 25. Copernicus, 127. Course of the Milky Way, 296. “Crab” Nebula in Taurus (M. 1), 336. Crape-ring of Saturn, 202. Crucis κ, Cluster at, 318. Curiosities of Comets, 248. Cyclonic action in Sun-spots, 108. Cygnus, Nebulous streams in, 339. Dallmeyer on Dividing power, 293. D’Arrest’s Comet, 240. Dawes’s observations of Jupiter, 173. —— observations of Saturn’s Crape-ring, 202. ——, On Dividing power, 292. —— Solar Eyepiece, 92. Definition in towns, 81. Deimos, Outer Satellite of Mars, 165. Democritus explains the Milky Way, 2. Dennett announces the Red Spot on Jupiter, 173. Denning’s Comet, 243. Denza on the Meteors of Nov. 27, 272. Derham, his list of Nebulæ, 327. Description of Nebulæ and Clusters of Stars, 333. Determination of the Sun’s rotation-period, 104. Detonating Fireballs, 267. Dewing of Mirrors, 62. Diffraction-rings, 293. Dimensions of Nebulæ and Scar-clusters, 332. —— of Sun-spots, 94. Disappearance of Saturn’s ring, 205. Discordant observations of Saturn, 204. Discoveries of Comets, 230. —— of Nebulæ, 341. Discovery of Neptune, 221. —— of Planetoids, 167. —— of Uranus, 215. Distance of the stars, 299. Distinction between Nebulæ and Star-clusters, 324. Distribution of Nebulæ in R.A., 326. Disturbances, Recurrent solar, 110. Dividing power, 292. Divisions in outer ring of Saturn, 201. Doberck, Dr., On the Invention of the Telescope, 5. ——, On Comet-seeking, 258. Dollond patents his Achromatic Telescope, 12. ——, His object-glasses, 16. Donati’s Comet of 1858, 233. Dörfel mountains, 131. Double Comets:— Biela’s, 238. Brooks’s, 239. —— Nebulæ, 332. —— Stars, 300, 302.