LABOURS RELATIVE TO THE SOLAR SYSTEM. 289 



LABOURS RELATIVE TO THE SOLAR SYSTEM. 



Hcrsclicl occupied himself very much with the sun, 

 but only relative to its physical constitution. The ob- 

 M-rvations that the illustrious astronomer made on this 

 subject, the consequences that he deduced from them, 

 equal the most ingenious discoveries for which the scien- 

 ces are indebted to him. 



In his important memoir in 1795, the great astronomer 

 declares himself convinced that the substance by the in- 

 termediation of which the sun shines, cannot be either a 

 liquid, or an elastic fluid. It must be analogous to our 

 clouds, and float in the transparent atmosphere of that 

 body. The sun has, according to him, two atmospheres, 

 endowed with motions quite independent of each other. 

 An elastic fluid of an unknown nature is being con- 

 stantly formed on the dark surface of the sun, and rising 

 up on account of its specific lightness, it forms the pores 

 in the stratum of reflecting clouds ; then, combining with 

 other gases, it produces the wrinkles in the region of 

 luminous clouds. When the ascending currents are 

 powerful, they give rise to the nuclei, to the penumbrce, 

 to the faculcB. If this explanation of the formation of 

 solar spots is well founded, we must expect to find that 

 the sun does not constantly emit similar quantities of 

 light and heat. Recent observations have verified this 

 conclusion. But large nuclei, large penumbras, wrinkles, 

 facula3, do they indicate an abundant luminous and calo- 

 rific emission, as Herschel thought ; that would be the 

 result of his hypothesis on the existence of very active 

 ascending currents, but direct experience seems to con- 

 tradict it. 



The following is the way in which a learned man, 



13 



