THE PLANETS. 101 



NEPTUNE : Galle, at Berlin, September 23, 1846. 



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

 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, Au- 

 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, which form a peculiar and very extended group, 

 forming, as it were, a ring of 132 millions of geographical 

 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 tenth 

 magnitudes. It is now more easy to distinguish between 



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

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

 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~satellite of 

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

 and did not announce it until March 5, 1656) Sy sterna Saturnium, 1659, 

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

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

 table view of the open ring on December 17, 1657 (Systema Saturnium, 

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

 ena until the year 165.9. (Galileo had thought that he saw, on each 

 side of the planet, only two projecting circular disks.) 



