94 HISTORY OF ASTRONOMY. 



to the principles of mechanics, increased, until the cen- 

 trifugal force arising from the rotation became equal to 

 the attraction of the central mass for the exterior zone, 

 when this zone necessarily became detached from the 

 central mass. As the central mass continued to contract 

 in its dimensions, and its velocity of rotation continued to 

 increase, the centrifugal force again became equal to the 

 attraction of the central mass for the exterior zone, and a 

 second zone was detached. Thus, a number of zones of 

 nebulous matter were successively detached ? until, by 

 condensation, the central mass became of comparatively 

 small dimensions and great density. 



The zones thus successively detached would form con- 

 centric rings of vapor, all revolving in the same direction 

 round the sun. If the particles of each ring continued to 

 condense without separating from each other, they would 

 ultimately form a liquid or a solid ring. But generally 

 each ring of vapor would break up into separate masses, 

 revolving about the sun with velocities slightly differing 

 from each other. These masses would assume a spheroidal 

 form ; that this, they would form planets in the state of 

 vapor. But if one of these masses was large enough to 

 attract each of the others in succession to itself, the ring 

 of vapor would be converted into a single spheroidal 

 mass of vapor, and we should have a single planet of 

 great mass for each zone of vapor detached. But if no 

 one of these masses had a preponderating size, they would 

 all continue to revolve about the sun in independent 

 orbits, and would form a zone of little planets, such 



