16 A CENTURY'S PROGRESS IN ASTRONOMY. 



could not observe them to the north and south 

 of the Sun, thus proving their connection with 

 the spots which are confined to the regions 

 north and south of the equator. " There is all 

 over the Sun a great unevenness," said Herschel, 

 "which has the appearance of a mixture of 

 small points of an unequal light ; but they are 

 evidently a roughness of high and low parts." 



Herschel's solar observations were very valu- 

 able, and did much for our knowledge of the 

 orb of day. His theory of the Sun's constitu- 

 tion a development of the hypothesis put 

 forward by Alexander Wilson (1714-1786), Pro- 

 fessor of Astronomy in Glasgow was, however, 

 very far from the truth. This was almost the 

 only instance in which Herschel was mistaken. 

 He regarded the Sun as a cool, dark globe, 

 " a very eminent, large, and lucid planet, 

 evidently the first, or, in strictness of speaking, 

 the only primary one of our system." In his 

 opinion an extensive atmosphere surrounded the 

 Sun, the upper stratum forming what Schroter 

 named the "photosphere." This atmosphere, 

 estimated as two or three thousand miles in 

 depth, was regarded as giving out light and 

 heat. Below this shining atmosphere there 

 existed, Herschel believed, a region of clouds 

 protecting the globe of the Sun from the 



