JUPITER, SATURN 175 



him. The results he arrived at were very near the 

 reality. 



Time of rotation of Jupiter on his axis l 



Herschel. 



H. M. s. 



9 55 49 

 Time of revolution in its orbit of 



D. H. M. D. H. M. S. 



First satellite . .. . 1 18 26'6 1 18 27 34 



Second satellite . \ . 31817'9 3131342 



Third satellite .... 7 3 59 '6 7 34233 



Fourth satellite . . . 16 18 5'1 16 16 32 11 



If the white spots on the belts were connected with 

 drifting masses in Jupiter's atmosphere, they would 

 drift as well as rotate. Herschel was aware of this, 

 and, since his day, the amount of drift has been 

 estimated at 270 miles an hour in the same direction 

 as the rotation. In other words, they would take 

 42 days to go round the planet from this cause 

 alone. Herschel was also persuaded that the four 

 satellites revolve on their axes in the same period as 

 they revolve round Jupiter, resembling in this respect 

 our moon. Laplace was disposed to accept this 

 conclusion. 2 



For more than a century and a half the planet 

 Saturn had been the object and, it may be said, the 

 despair of every astronomer's curiosity, mainly in 

 consequence of the ring which the telescope had 

 shown it to possess, and the singular shapes the 

 ring was found to assume. Five moons were also 

 discovered to be circling round the planet, and 



1 The great red spot gives 9 h. 55 m. 34 s. 



2 System of the World, Bk. I. chs. viii. vii. 



