523 



THE SATELLITES OF SATUEN. 



The five satellites of Saturn which have been known 

 longest were discovered between the years 1655 and 1684 

 (Titan, the sixth according to distance, by Huygens; and four 

 by Cassini, viz. Japetus, the outermost of all, Rliea, Tetliys, 

 and Dionc). These were followed by the discovery, by 

 William Herschel, in 1789, of two, Mimas and Encc- 

 ladus, situated nearest to the planet. Finally, the seventh 

 satellite, Hyperion, the last but one according to distance, 

 was discovered almost simultaneously by Bond, at Cambridge 

 (U.S.), and by Lassell at Liverpool, in September, 1848. 

 The relative magnitudes and relations of distances in this 

 partial system have been already treated of. (Cosmos, vol. i. 

 p. 81, vol. iv. pp. 426-445). The periods of revolution and the 

 mean distances, the latter expressed in fractional parts of 

 the equatorial radius of the primary, are, according to the 

 observations instituted by Sir John Herschel, at the Cape of 

 Good Hope, 86 between 1835 and 1837, the following : 



86 Sir John Herschel, Results of Astron. Observations at 

 the Cape of Good Hope, pp. 414-430 ; the same, in the Out- 

 lines o/Astr. p. 650, and upon the law of distances, 550, 



