THE PHOTOSPHERE AND SUN-SPOTS. 537 



of studying the superficial details as indices of the real nature of the 

 structure, we are naturally led to inquire whether the surface before 

 us is a solid like one of our continents, or a fluid like our seas, or a 

 vapor like our clouds. We know, at the outset, from abundant evi- 

 dence, that the temperature of the sun, whatever it may be, is far 



