212 TRANSFORMATION AND EQUIVALENCE OF FORCES. 



once existed in a diffused state, we have, in the gravitation 

 of its parts, a force adequate to produce the motions now 

 going on. 



Masses of precipitated nebulous matter, moving towards 

 their common centre of gravity through the resisting me- 

 dium from which they were precipitated, will inevitably 

 cause a general rotation, increasing in rapidity as the concen- 

 tration progresses. So far as the evidence carries us, we per- 

 ceive some quantitative relation between the motions so gen- 

 erated and the gravitative forces expended in generating 

 them. The planets formed from that matter which has trav- 

 elled the shortest distance towards the common centre of 

 gravity, have the smallest velocities. Doubtless this is ex- 

 plicable on the teleological hypothesis; since it is a condition 

 to equilibrium. But without insisting that this is beside the 

 question, it will suffice to point out that the like cannot be 

 said of the planetary rotations. Xo such final cause can be 

 assigned for the rapid axial movement of Jupiter and 

 Saturn, or the slow axial movement of Mercury. If, 

 however, in pursuance of the doctrine of transformation, 

 we look for the antecedents of these gyrations which all 

 planets exhibit, the nebular hypothesis furnishes us with 

 antecedents which bear manifest quantitative relations to 

 the motions displayed. For the planets that turn on their 

 axes with extreme rapidity, are those having great masses 

 and large orbits — those, that is, of which the once diffused 

 elements moved to their centres of gravity through immense 

 spaces, and so acquired high velocities. While, conversely, 

 the planets which rotate with the smallest velocities, are 

 those formed out of the smallest nebulous rings — a relation 

 still better shown by satellites. 



" But what," it may be asked, " has in such case become 

 of all that motion which brought about the aggregation of 

 this diffused matter into solid bodies? " The answer is that 

 it has been radiated in the form of heat and light ; and this 

 answer the evidence, so far as it goes, confirms. Geologists 



