22 A CENTURY'S PROGRESS IN ASTRONOMY. 



round the planet in about 22 hours. These 

 two satellites were not seen by any astronomers 

 except Herschel ; and after his death they could 

 not be observed. His son, however, rediscovered 

 them. 



The eighth satellite, Japetus, was shown by 

 Herschel to rotate on its axis in a period equal 

 to that of its revolution, and his observations 

 were confirmed by modern observers. " I can- 

 not," Herschel said, "help reflecting with some 

 pleasure on the discovery of an analogy which 

 shows that a certain uniform plan is carried 

 on among the secondaries of our Solar System ; 

 and we may conjecture that probably most of 

 the satellites are governed by the same law." 

 In April 1805 Herschel observed the globe of 

 Saturn to present not a spherical but a "square- 

 shouldered" aspect. It was for long believed 

 that this was an optical illusion ; but Proctor 

 and others have shown that it is quite possible 

 for storms in Saturn's atmosphere to cause the 

 planet's apparent distortion in shape. 



Herschel paid much attention to the planet 

 Uranus, which he discovered on March 13, 1781. 

 The discovery of Uranus, which was mentioned 

 in a previous chapter, was in a sense the most 

 striking of Herschel's achievements. Uranus was 

 the first planet discovered within the memory 



