ASTRONOMY. 191 



seven or eight days before and after the passage 

 of the Earth through its plane. 



I. This is what happens with ordinary telescopes ; 

 but with the forty foot reflector of Dr HERSCHEL, 

 the ring does not cease to be visible. The Doc- 

 tor saw the satellites along the margin of the ring, 

 like bright beads threaded on a string. 



198. There is a third cause of the disappear- 

 ance of the ring, viz. the Earth being placed on 

 the side of the ring that is turned from the Sun. 



The ring may on these accounts disappear twice in 

 the same year. 



LA LANDE, 3357. Opuscula of BOSCOVICH, torn. v. 

 Also SEJOUR, Anneau de Saturne. 



199- The ring is divided into two by a dark 

 line going all round concentric with the outer 

 and inner circles. 



a. This was first observed by CASSINI, Mem. Acad. 

 des Sciences, 1715. SHORT, with his twelve foot 

 reflector, observed the same ; as Dr HERSCHEL 

 has also done. 



b. To Dr HERSCHEL, and some other observers, it 

 has appeared that there are more of these lines 

 than one. 



It 



