Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/339

 it is manifet that by its own force it will never change its axis, or the inclination of it. Let now this globe be impelled obliquely by a new impule in the ame part of its uperficies as before; and ince the effect of an impule is not at all changed by its coming ooner or later, it is manifet at thee two impules ucceively impreed will produce the ame motion, as if they were impreed at the ame time; that is, the ame motion as if the globe had been impelled by a imple force compounded of them both (by cor. 2. of the laws) that is a imple motion about an axis of a given inclination. And the cae is the ame if the econd impule were made upon any other place of the æquator of the firt motion; and alo if the firt impule were made upon any place in the equator of the motion which would be generated by the econd impule alone; and therefore alo when both impules are made in any places whatoever; for thee impules will generate the ame circular motion, as if they were impreed together and at once in the place of the interections of the equators of thoe motions, which would be generated by each of them eparately. Therefore a homogeneous and perfect globe will not retain everal ditinct motions, but will unite all thoe that are irnpreed on it, and reduce them into one; revolving, as far as in it lies, always with a imple and uniform motion about one ingle given axis with an inclination perpetually invariable. And the inclination of the axis, or the velocity of the rotation will not be changed by centripetal force. For if the globe be uppoed to be divided into two hemipheres, by any plane whatoever paing