PROGRESS OF MODERN ASTRONOMY 



continue to revolve around this body, since their cen- 

 trifugal force was balanced by their weight. But this 

 equilibrium not arising in regard to the atmospheric 

 molecules parallel to the solar equator, the latter, on 

 account of their weight, approached the atmosphere 

 as they condensed, and did not cease to belong to it 

 until by this motion they came upon the equator. 



" Let us consider now the zones of vapor successively 

 left behind. These zones ought, according to appear- 

 ance, by the condensation and mutual attraction of 

 their molecules, to form various concentric rings of 

 vapor revolving around the sun. The mutual gravita- 

 tional friction of each ring would accelerate some and 

 retard others, until they had all acquired the same 

 angular velocity. Thus the actual velocity of the 

 molecules most removed from the sun would be the 

 greatest. The following cause would also operate to 

 bring about this difference of speed. The molecules 

 farthest from the sun, and which by the effects of 

 cooling and condensation approached one another to 

 form the outer part of the ring, would have always 

 described areas proportional to the time since the 

 central force by which they were controlled has been 

 constantly directed towards this body. But this con- 

 stancy of areas necessitates an increase of veloc- 

 ity proportional to the distance. It is thus seen 

 that the same cause would diminish the velocity 

 of the molecules which form the inner part of the 

 ring. 



" If all the molecules of the ring of vapor continued 

 to condense without disuniting, they would at length 

 form a ring either solid or fluid. But this formation 



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