104 A CENTURY'S PROGRESS IN ASTRONOMY. 



George Philip Bond (1826-1865), director of the 

 Harvard Observatory, found from experiments 

 that Jupiter seemed to give out more light than 

 it received, but he did not dare to suggest that 

 Jupiter was self-luminous, considering that the 

 inherent light might result from Jovian auroras. 



In 1865 Zollner showed that the rapid motions 

 of the cloud-belts on both Jupiter and Saturn 

 indicated a high internal temperature. At the 

 distance of Jupiter sun-heat is only one twenty- 

 seventh as great as on the Earth, and would be 

 quite incapable of forming clouds many times 

 denser than those on the Earth. In 1871 

 Zollner drew attention to the equatorial accel- 

 eration of Jupiter, analogous to the same phe- 

 nomenon on the Sun. In 1870 these opinions of 

 Zollner' s were adopted and supported by Proctor 

 in his ' Other Worlds than Ours.' In his subse- 

 quent volumes Proctor did much to popularise 

 the idea, which is now accepted all over the 

 astronomical world. 



During the century many valuable observations 

 on Jupiter were made by numerous observers, 

 among them Airy, Madler, Webb, Schmidt, and 

 others. Much time was devoted to the accurate 

 determination of the rotation period, which was 

 fixed at 9 hours 55 minutes 3 6 '5 6 seconds by 

 Denning in observations from 1880 to 1903. No 



