AND THEORY OF THE HEAVENS. 1 23 



ascended from the surface of that planet as vapours, 

 have kept revolving freely in circles at the height of 

 their distance in virtue of the momentum which they 

 derived from its axial rotation and still carry on, the 

 particles have not equal periodic revolutions at all their 

 distances from the centre. On the contrary, they are 

 related to each other as the square roots of the cubes 

 of their distances, if they continue revolving according 

 to the laws of the central forces. Now, according to 

 this hypothesis the time in which the particles of the 

 inner rim perform their revolution is about ten hours, 

 and the time of the revolution of the particles in the 

 outer rim, according to correct calculation, is fifteen 

 hours ; and therefore when the lowest parts have revolved 

 thrice the most distant have done so only twice. But 

 however small we may reckon the resistance which the 

 particles offer to each other from their great dispersion 

 in the plane of the ring, it is probable that the lagging 

 behind of the more distant particles at each of their 

 revolutions gradually retards and keeps back the more 

 rapidly moving lower particles ; and, on the other hand, 

 these particles must impress on those above them a 

 portion of their motion so as to make them revolve 

 more rapidly. Now if this reciprocal action were not 

 finally interrupted, it would go on till such time as the 

 particles of the ring both the nearer and the more 

 distant were brought to revolve in the same time, in 

 which, state they would be at rest with respect to each 

 other, and through the revolution they would exert no effect 

 upon each other. But such a condition, if the motion 

 of the ring came to it, would entirely destroy the ring; 

 because if we take the middle of the plane of the ring 



