380 A Short History of Astronomy [CH. xm. 



light-observations seems to indicate that the total mass of 

 those at present known is many hundred times less than 

 this limit. 



295. Neptune and the minor planets are the only planets 

 which have been discovered during this century, but several 

 satellites have been added to our system. 



Barely a fortnight after the discovery of Neptune (1846) 



\ 

 \ 



JAPETUS 

 / HYPERION 



FIG. 91. Saturn and its system. 



a/satellite was detected by William Lassell (1799-1880) 

 at Liverpool. Like the satellites of Uranus, this revolves 

 round its primary from east to west that is, in the direction 

 contrary to that of all the other known motions of the solar 

 system (certain long-period comets not being counted). 



Two years later (September i6th, 1848) William Cranch 

 Bond (1789-1859) discovered, at the Harvard College 



