188 OUTLINES OF'NATURAL PHILOSOPHY. 



29' 42"; the third, 22' 28"; and the fourth, 

 9' 39". 



192. The planets Saturn and Uranus Iiave al- 

 so satellites ; the former seven, and the latter 

 six ; which, with the Moon, make eighteen se- 

 condary planets in the solar system. 



. The fourth of the satellites of Saturn was the first 

 discovered j it was seen by HUYGENS in 1655. 

 The first, second, third, and fifth, were discovered 

 by CASSINJ, between the years 1671 and 1684-. 

 Other two satellites, which we improperly call the 

 sixth and seventh, though they are nearer to Sa- 

 turn than any of the rest, were discovered by Dr 

 HERSCHEL in 1789. 



193. The connection between the periodic 

 times and the mean distances of the satellites of 

 Saturn, is the same as in the satellites of Jupi- 

 ter, and in the primary planets. 



a. The fifth satellite disappears regularly for about 

 one-half of the time of its revolution round Sa- 

 turn ; and hence NEWTON concluded, that its re- 

 volution on its axis is of the same duration with 

 its revolution round Saturn. Princip. Math. lib. 

 in. prop. 17. 



194. The 



