The Evolution of the Sciences 



approximately the same duration as the lotation 

 of the equatorial solar zone. It is probable that 

 this coincidence is not fortuitous and that 

 the sun modifies the magnetism of the earth. 



We have thus, from the careful observation 

 of the spots, acquired the certitude that the 

 bright external surface of the sun is fluid, and 

 new reasons for considering that the same is true 

 of the central regions; these conclusions are in 

 complete agieement with the inferences drawn 

 from the mean density and the temperature. 



But there is still much to be learned from an 

 attentive study of the spots; we know neither 

 their nature nor their origin. The question 

 has long remained an open one, for Galileo 

 thought they were clouds floating in the solar 

 atmosphere, and De Lalande took them for 

 mountains, the varying steepness of whose sides 

 produced the phenomenon of the penumbra. 

 Derham saw in them the smoke discharged by 

 the sun's volcanic craters, and many savants 

 have considered them to be scoriae floating on 

 an ocean of fire. But since the observations 

 made in 1774 by Wilson, corroborated by Sir 

 William Herschel, no doubt is permissible 



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