X THE STARRY HEAVENS 383 



tional case, but a height of 100,000 miles is 

 not unusual, and the velocity frequently 

 reaches 100 miles in a second. 



The proverbial spots on the Sun in many 

 respects resemble the appearances which would 

 be presented if a comparatively dark central 

 mass was here and there exposed by apertures 

 through the more brilliant outer gases, but 

 their true nature is still a matter of discus- 

 sion. 



During total eclipses it is seen that the 

 Sun is surrounded by a " corona," or aureola of 

 light, consisting of radiant filaments, beams, 

 and sheets of light, which radiate in all direc- 

 tions, and the true nature of which is still 

 doubtful. 



Another stupendous problem connected 

 with the Sun is the fact that, as geology 

 teaches us, it has given off nearly the same 

 quantity of light and heat for millions of 

 years. How has this come to pass ? Certainly 

 not by any process of burning such as we are 

 familiar with. Indeed, if the heat of the Sun 

 were due to combustion it would be burnt up 

 in 6000 years. It has been suggested that 



