What We Learn from the Sun 



more of the sun's heat would be retained than 

 at the poles, where the atmosphere is shallowest. 

 Thus that excess of heat at the solar equator 

 which is necessary to complete the analogy be- 

 tween the sun-spots and terrestrial cyclones 

 seems satisfactorily established. 



It must be remarked, however, that this reason- 

 ing, so far as the excess of heat at the sun's 

 equator is concerned, only removes the difficulty 

 a step. If there were indeed an increased depth 

 of atmosphere over the sun's equator sufficient 

 to retain the requisite excess of heat, then the 

 amount of heat we receive from the sun's, equa- 

 torial regions ought to be appreciably less than 

 the amount emitted from the remaining portions 

 of the solar surface. This is not found to be the 

 case, so that, either there is no such excess of 

 absorption, or else the solar equator gives out 

 more heat, in other words, is essentially hotter, 

 than the rest of the sun. But this is just the 

 peculiarity of which we want the interpreta- 

 tion. 



It may be taken for granted, however, that 

 there is an analogy between the sun-spots and 

 terrestrial cyclonic storms, though as yet we 

 are not very well able to understand its nature. 



We come next to one of the most interesting 

 discoveries ever made respecting the sun the 

 discovery that the spots increase and diminish 

 in frequency in a periodic manner. We owe 

 this discovery to the laborious and systematic 

 observations made by Herr Schwabe, of Dessau. 



