96 THE OCEAN. [Book III. 



CHAPTER VIIL 



THE MOTIVE EORCE. 



The foregoing chapters of this Book have shown 

 that vis -inertias is a really inherent property in 

 matter, by virtue of which it endeavours to be just 

 what it is and where it is ; and that gravitation is 

 simply an effect of vis-merti^ — this effect of vis- 

 inertiee being brought into existence in consequence 

 of the action of some other force tending to cause a 

 constant change of form and place. 



They have also shown that this motive force acts 

 from, the central parts of the sun, causing the latter 

 to rotate and to revolve the surroundmg planets 

 with it. And that a similar motive force acts from 

 the central parts of the earth, causing it to rotate and 

 to revolve the moon in the same direction. 



Whatever be the source or abstract cause of the 

 force which rotates the earth and the sun as above 

 shown, the term evanescence may appropriately be 

 applied to it in a limited sense, and even a com- 

 prehensive signification of the term may be shown 

 to be not inappropriate. For the tendency of the sole 

 action of gravitation would be to consolidate the 

 universe into one motionless mass ; but if evanescence 



