THOUGHTS ON NATURAL PHILOSOPHY. IQ 



rotation on its axis. There is no difficulty in con- 

 ceiving how a nebula, quite independently of any 

 internal motion of its parts, shall also have had as 

 a whole a movement of rotation. In fact a little 

 consideration will show from the law of probabilities 

 that it is infinitely probable that such an object 

 should really have some movement of rotation, no 

 matter by what causes the nebula may have originated. 

 As this vast mass cooled it must by the laws of heat 

 have contracted towards the centre, and as it con- 

 tracted it must, according to a well-known law of 

 dynamics, rotate more rapidly. The time would 

 then come when the centrifugal force on the outer 

 parts of the mass would more than counterbalance 

 the attraction of the centre, and thus we would have 

 the outer parts left as a ring. The inner portion 

 will still continue to contract, the same process will 

 be repeated, and thus a second ring will be formed. 

 We have thus grounds for believing that the original 

 nebula will separate into a series of rings all revolving 

 in the same direction with a central nebulous mass 

 in the interior. The materials of each ring would 

 continue to cool and to contract until they passed 

 from the gaseous to the liquid condition. If the 

 consolidation took place with comparative uniformity 

 we might then anticipate the formation of a vast 

 multitude of small planets such as those we actually 

 do find in the region between the orbit of Mars and 

 that of Jupiter. More usually, however, the ring 

 might be expected not to be uniform, and therefore 

 to condense in some parts more rapidly than in 

 others. The effect of such contraction would be to 



