Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/300



Of the motions of bodies tending to each other with centripetal forces.

I have hitherto been treatin of the attractions of bodies towards an immoveable centre; tho' very probably there is no uch thing existent in nature. For attractions are made towards bodies; and the actions of the bodies attracted and attracting, are always reciprocal and equal by law 3. that if there are two bodies neither the attracted nor the attracting body is truly at ret, but both (by cor. 4. of the laws of motion) being as it were mutually attracted, revolve about a common centre of gravity. And if there be more bodies, which are either attracted by one ingle one which is attracted by them again, or which, all of them, attract each other mutually; thee bodies will be o moved among themelves, as that their common centre of gravity will either be at ret, or move uniformly forward in a right line. I hall therefore at preent go on to treat of the motion of bodies mutually attracting each other; conidering the centripetal forces as attractions; though perhaps in a phyical trictnes they may more truly be called