278 THE OCEAN. [Book X. 



Neptune to that in which the moon is revolved round 

 the earth, from which it is to be inferred that Neptune 

 rotates in that direction. 



Therefore the acceleration caused by the disturb- 

 ing; force occurs when the satellite is inside the 

 normal line of its orbit, and retardation when it is 

 outside, so that, though the path described backwards 

 and forwards across the normal line of the orbit will 

 be similar to that described by the moon, the relative 

 velocities of the motion at different distances from 

 the sun will be reversed. 



And, besides this, the action of the retardation of 

 the moon's motion tending to bring it nearer to both 

 of the centres of rotation, might be accomphshed 

 without any increase in the inclination of the planes 

 of rotation. 



But the acceleration of Neptune's satellite causing 

 an increase of distance from both centres of rotation, 

 could not be accomplished, whilst Neptune remained 

 at the same distance from the sun, without throwing 

 the satellite out of the plane in which I^eptune and 

 the sun rotate. 



