Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/273

 intead of the planes upon which thoe bodies roll or slide, and which are therefore tangent plane; to the bodies, I hall ue planes parallel to them, in which the centres of the bodies move, and by that motion decribe orbits. And by the ame method I afterward determine the motions of bodies performed in curve uperficies.