Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/46

whatever differently condenſed. I have no regard in this place to a medium, if any ſuch there is, that freely pervades the interſtices between the parts of bodies. It is this quantity that I mean hereafter everywhere under the name of Body or Maſs. And the ſame is known by the weight of each body, for it is proportional to the weight, as I have found by experiments on pendulums, very accurately made, which shall be ſhewn hereafter.

Definition II.

The Quantity of Motion is the meaſure of the ſame, ariſing from the velocity and quantity of matter conjunctly.

The motion of the whole is the Sum of the motions of all the parts; and therefore in a body double in quantity, with equal velocity, the motion is double; with twice the velocity, it is quadruple.

Definition III.

The Vis Insita, or Innate Force of Matter, is a power of reſiſting, by which every body, as much as in it lies, endeavours to perſevere in its preſent ſtate, whether it be of reſt, or of moving uniformly forwards in a right line.

This force is ever proportional to the body whoſe force it is; and differs nothing from the inactivity of the Maſs, but in our manner of conceiving it. A body, from the inactivity of matter, is not without