112 A CENTURY'S PROGRESS IN ASTRONOMY. 



which he deduced a rotation period of 10 hours 

 39 minutes, a period considerably longer than 

 that found by Hall. In the same year various 

 spots on Saturn were observed by Denning, who 

 found a period of 10 hours 37 minutes 56*4 

 seconds, and at Barcelona by Jose Comas Sola, 

 now director of the Observatory there, who 

 may be considered Spain's leading astronomer. 

 The result of these observations has been to 

 show that the spots on Saturn have probably 

 a proper motion of their own, apart from the 

 rotation of the planet. As to the spectrum 

 of Saturn, little has been learned. It closely 

 resembles that of Jupiter. In 1867 Janssen, 

 observing from the summit of Mount Etna, 

 found traces of aqueous vapour in the planet's 

 atmosphere. 



In the chapters on Herschel we have seen that 

 he discovered the sixth and seventh satellites 

 of Saturn. The next discovery was made on 

 September 19, 1848, by W. C. Bond, at 

 Harvard, Massachusetts, and independently by 

 William Lassell (1799-1880), at Starfield, near 

 Liverpool. The new satellite received the name 

 of Hyperion, and was found to be situated at 

 a distance of about 946,000 miles from Saturn. 

 Its small size led Sir John Herschel to the 

 idea that it might be an asteroidal satellite. 



