270 THE OCEAN. [Book X- 



the siiccessive lines of equilibrium (Proposition 

 XXy.), and would revolve all surrounding bodies 

 with a force inversely as the cube of the distance from 

 the earth (Proposition IV.) ; 



Therefore, unless overwhelmed by the action of 

 revolving forces acting from other centres of rotation, 

 that of the earth would revolve the universe with the 

 earth's rotation. 



Corollary. — Therefore the revolving force of the 

 earth's gravitation is constantly endeavouring to re- 

 volve the sun in the opposite direction to that in 

 which the earth actually is revolved round the sun ; ^ 

 but because the sun's revolving force is greater than 

 that of the earth, therefore the earth is revolved 

 round the sun. So also the sun revolves all the 

 planets, because there is no greater force sufficiently 

 near to overwhelm its action. 



The solar system extends as far as its revolving 

 force is greater than that proceeding from any other 

 centre of rotation, and within which all bodies, being 

 under its dominion, are revolved with it as planets. 



The planetary systems extend to the limits within 

 which any one of their revolving forces is greater 

 than that of any of the other planets. Within those 

 limits it revolves surrounding planets, whilst it and 

 they are together revolved by the greater force of 

 the sun's rotation. 



' See the Chapter on the Secular Acceleration of the Moon's 

 Motion in Thr. Kew Principles of Natural Philosophi/. 



