Cqap. XXL] THE HEAVENS. 277 



the changing of the conjoint action of the disturbing 

 force, reduce the velocity ; and then the reduction 

 of the astral force allows the moon to fall inwards 

 towards the sun : and this falling towards the sun 

 continues as the motion is retarded by the opposing 

 action of the earth's force when the moon passes in- 

 side the earth's orbit, until the increase of the sun's 

 revolving force and the changing of the earth's action 

 from direct to less and less complete opposition cause 

 a gradual acceleration of the motion, and a conse- 

 quent increase of the astral force, which again draws 

 it outwards from the sun. 



Thus, in consequence of the action of an ex- 

 traneous force alternately accelerating and retarding 

 the moon's motion in its orbit rojmd the sun, the 

 alternate increase and decrease of the retarding force 

 of astral gravitation carries the moon alternately 

 inside and outside the normal line of its orbit. 



PROPOSITION XXXVII. 



Problem. — To apply Propositions XXXIV. and 

 XXXV. to the motion of the satelHtes of Neptune 

 round the sun. 



In respect to the sun's rotation the satellites 

 of Neptune revolve in the opposite direction round 



