Chap. XXL] THE HEAVENS. 281 



farther than its primary from the central force : be- 

 cause there is then a conjoint action of the revolving 

 forces, as shown in Proposition XXXVI. , Section 4, 

 concerning; the revolvino; action of the sun and earth 

 upon the moon. 



If the two motions of rotation were in opposite 

 directions, then the conjoint action on the non-rotat- 

 ing body would occur when the latter was nearer 

 than its primary to the central force, making the 

 distortion of the ellipse the reverse of that resulting 

 from the foregoing conditions. 



6. As reoj'ards the action of the central force on 

 the bodies in Section 3, supposing it to revolve in 

 the same plane as they ; then, if they be equidistant 

 from the centre they would simply be swept round 

 in the same orbit. 



But, if the action of any extraneous force (such 

 as a force causing an ellipticity of their orbit) prevent 

 them from being equidistant, then, in their efforts at 

 mutual revolution, the one nearer the common centre 

 will be more retarded than the one more remote, and 

 therefore the latter will have a motion onwards in its 

 orbit round the former which will at the same time 

 have a faster motion than it roiuid the common 

 centre. 



Thus, whilst carried round the central force, they 

 would be revolved about each other by the alternate 

 preponderance of their revolving action. 



