Masterpieces of Science 



of the sun where the solar spots make their ap- 

 pearance. 



We know that the cyclone is due to the excess 

 of heat at the earth's equator. It is true that 

 this excess of heat is always in operation, whereas 

 cyclones are not perpetually raging in sub- 

 tropical climates. Ordinarily, therefore, the 

 excess of heat does not cause tornadoes. Certain 

 aerial currents are generated, whose uniform 

 motion suffices, as a rule, to adjust the conditions 

 which the excess of heat at the equator would 

 otherwise tend to disturb. But when through 

 any cause the uniform action of the aerial cur- 

 rents is either interfered with, or is insufficient 

 to maintain equilibrium, then cyclonic or whirl- 

 ing motions are generated in the disturbed at- 

 mosphere, and propagated over a wide area of 

 the earth's surface. 



Now we recognize the reason of the excess of 

 heat at the earth's equator, in the fact that the 

 sun shines more directly upon that part of the 

 earth than on the zones which lie in higher 

 latitudes. Can we find any reason for suspecting 

 that the sun, which is not heated from without 

 as the earth is, should exhibit a similar peculi- 

 arity? Sir John Herschel considered that we 

 can. If the sun has an atmosphere extending 

 to a considerable distance from his surface, then 

 there can be little doubt that, owing to his rota- 

 tion upon his axis, this atmosphere would assume 

 the figure of an oblate spheroid, and would be 

 deepest over the solar equator. Here, then, 

 8 



