A HISTORY OF SCIENCE 



turning one upon the other, such as those double stars 

 of which we already know the respective movements. 



" But how did the solar atmosphere determine the 

 movements of the rotation and revolution of the plan- 

 ets and satellites ? If these bodies had penetrated very 

 deeply into this atmosphere, its resistance would have 

 caused them to fall into the sun. We can therefore 

 conjecture that the planets were formed at their suc- 

 cessive limits by the condensation of a zone of vapors 

 which the sun, on cooling, left behind, in the plane of 

 his equator. 



"Let us recall the results which we have given in 

 a preceding chapter. The atmosphere of the sun could 

 not have extended indefinitely. Its limit was the point 

 where the centrifugal force due to its movement of 

 rotation balanced its weight. But in proportion as 

 the cooling contracted the atmosphere, and those mole- 

 cules which were near to them condensed upon the 

 surface of the body, the movement of the rotation in- 

 creased ; for, on account of the Law of Areas, the sum 

 of the areas described by the vector of each molecule 

 of the sun and its atmosphere and projected in the 

 plane of the equator being always the same, the rota- 

 tion should increase when these molecules approach the 

 centre of the sun. The centrifugal force due to this 

 movement becoming thus larger, the point where the 

 weight is equal to it is nearer the sun. Supposing, 

 then, as it is natural to admit, that the atmosphere 

 extended at some period to its very limits, it should, 

 on cooling, leave molecules behind at this limit and 

 at limits successively occasioned by the increased ro- 

 tation of the sun. The abandoned molecules would 



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