382 A Short History of Astronomy [CH. xin. 



Mars rotates, so that to the Martians it must rise in the 

 west and set in the east. Lastly, Jupiter's system received 

 an addition after nearly three centuries by Professor Barnard's 

 discovery at the Lick Observatory (September gth, 1892) of 







\ 



\ \ "-/ ')' /" ?'" i 



. ' 



\ \ v -- -' / / 



\ '*----' / / ; 



N s ' 



^*. .**' 



' / 



\ 



\ 



\ / 



X \ +*''' 



* -** 



**-... .** 



FIG. 93. Jupiter and its satellites. 



an extremely faint fifth satellite, a good deal nearer to Jupiter 

 than the nearest of Galilei's satellites (chapter vi., 121). 



296. The surfaces of the various planets and satellites 

 have been watched with the utmost care by an army of 

 observers, but the observations have to a large extent 

 remained without satisfactory interpretation, and little is 

 known of the structure or physical condition of the bodies 

 concerned. 



Astronomers are naturally most familiar with the surface 



