THE PLANETS. 101 



NufiuxE : Galle, at Berlin, September £3, 184G. 



The first satellite of Neptune : W. Lassell, at Starfield, iieai 



Liverpool, November, 1846 ; Bond, at Cambridge (U, S.). 

 Hebe^ : Hencke, at Dresden, July 1, 1847. 

 Iris=^ : Hind, in London, August 13, 1847. 

 Flora=* : Hind, in London, October 18, 1847. 

 Metis^ : Graham, at Markree Castle, April 25, 1848. 

 The seventh satellite of Saturn (Hyperion) : Bond, at Cam 



bridge (U. S.), September, 16-19 ; Lassell, at Liverpool, 



September 19-20, 1848. 

 Hygeia^ : De Gasparis, at Naples, April 12, 1849. 

 Parthenope^ : De Gasparis, at Naples, May 11, 1850. 

 The second satellite of Neptune : Lassell, at Liverpool, Aii' 



gust 14, 1850. 

 Victoria^ : Hind, in London, September 13, 1850. 

 Egeria^ : De Gasparis, at Naples, November 2, 1860. 

 Irene^ : Hind, in London, May 19, 1851 ; and De Gasparis, 



at Naples, May 23, 1851. 



In this chronological summary=^ the principal planets are 

 distinguished from the secondary planets or satellites by a dif- 

 ferent type. Some bodies are included in the class of princi- 

 pal planets, v^^hich form a peculiar and very extended group, 

 .forming, as it were, a ring of 132 millions of geographicaj 

 miles, situated between Mars. and Jupiter, and are generally 

 called small planets, as well as telescopic planets, co-planets, 

 asteroids, or planetoids. Of these, four were discovered in the 

 first seven years of this century, and ten during the last six 

 years ; which latter circumstance is to be attributed less to 

 the perfection of the telescopes, than the industry and dex- 

 terity of the investigators, and especially the improved charts 

 enlarged by additions of fixed stars of the ninth and tentli 

 magnitudes. It is now more easy to distinguish between 



* In tlie history of the discoveries, it is necessary to distinguish be- 

 tween the epoch at which the discovery was made, and the time of ita 

 first announcement. In consequence of a neglect of this distinction, 

 dissimilar and erroneous dates have been introduced into astronomical 

 manuals. So, for example, Huygens discovered the sixth sateJite of 

 Saturn (Titan) on March 25, 1655 {Hiiy genii Opera varia, 1724, p. 523), 

 and did not announce it until March 5, 165G) Systema Satiirnium, 1659, 

 p. 2). Huygens, who devoted himself uninterruptedly from March, 

 1655, to the study of Saturn, had already obtained the full and indubi 

 table vie\V of the open ring on December 17, 1657 (Systema SjturHtm/i, 

 p. 21), but did not publish his scientific explanation of all the phenom 

 ena until the year 1659. (Galileo had thought that he saw, on each 

 oide of the planet, mly two projecting circular disks.) 



