HERSCHEL THE DISCOVERER. 19 



waxed and waned in size, the north polar cap 

 shrinking during the summer of the northern 

 hemisphere, increasing in winter, and vice versa 

 in the southern hemisphere. He regarded the 

 caps as masses of snow and ice deposited from 

 "a considerable, though moderate, atmosphere," 

 a theory now generally accepted. Herschel gave 

 an immense impetus to the study of Mars. He 

 carefully examined the planet's surface, and the 

 dark markings were regarded by him as oceans. 



During Herschel's lifetime the four small 

 planets, Ceres, Pallas, Juno, and Vesta, were 

 discovered by Piazzi, Olbers, and Harding. The 

 great astronomer was much interested in these 

 small worlds. He commenced a search through 

 the Zodiacal constellations for new planets, but 

 failed. He was of opinion that many minor 

 planets would be discovered. Accepting Gibers' 

 theory of the disruption of a primitive planet, 

 Herschel calculated that Mercury might be 

 broken up into 35,000 globes equal to Pallas. 

 Meanwhile Herschel named the four new planets 

 "Asteroids," owing to their minute size. He 

 estimated the diameter of Ceres at 162 miles 

 and Pallas at 147 miles, but Professor Barnard's 

 measures have shown them to be larger. 



In connection with the discovery of the 

 Asteroids, Herschel showed a very fine spirit. 



