ASTRONOMY. 189 



194. The six satellites of Uranus have their 

 orbits nearly in one plane, at right angles to 

 the plane of the orbit of the planet. 



a. These satellites were discovered by Dr HER- 

 SCHEL, in 1807 and 1808. 



I. The plane in which these satellites move, passes 

 twice in the year through the Sun ; and at those 

 times there may be eclipses, but they cannot be 

 seen unless Uranus be near his opposition. 



Eclipses of the satellites of Uranus were visible in 

 1799, and they will be visible again in 1818. 



Ring of Saturn. 



195. Saturn is surrounded by a circular ring, 

 concentric with himself, which, being seen 

 obliquely, is of an oval or elliptic form, and 

 shines with the same light as the planet. 



a. If we suppose the radius of Saturn, at his mean dis- 

 tance, to subtend an angle of 9", the interior dia- 

 meter of the ring, supposing it circular, will be 

 15", and the exterior 21", leaving a void of 6" be- 

 tween the planet and the ring, and the same quan- 

 tity for the breath of the ring. Stars have been 



observed 



