THE OUTER PLANETS. 107 



elude that native emissions from Jupiter's visible 

 surface are local and fitful, not permanent and 

 general." 



Herschel's idea, that the rotations of the four 

 satellites of Jupiter were coincident with their 

 revolutions, has on the whole been confirmed 

 by recent researches, although in the case of 

 the two near satellites (lo and Europa) W. H. 

 Pickering's observations in 1893 indicated shorter 

 rotation periods. There is much to learn re- 

 garding the geography of the satellites, although 

 in 1891 Schaeberle and Campbell at the Lick 

 Observatory observed belts on the surface of 

 Ganymede, the third satellite analogous to those 

 on Jupiter. Surface-markings on the satellites 

 have also been seen by Barnard at the Lick 

 Observatory, and by Douglass at Flagstaff. 



Since the time of Galileo no addition had been 

 made to the system of satellites revolving round 

 Jupiter. Profound surprise was created, there- 

 fore, by the announcement of the discovery of 

 a fifth satellite by Barnard at the Lick Observ- 

 atory, on September 9, 1892. The satellite, 

 one of the faintest of telescopic objects, was 

 discovered with the great 3 6 -inch telescope, and 

 its existence was soon confirmed by Andrew 

 Anslie Common (1841-1903), with his great 5- 

 foot reflector at Ealing, near London. The new 



