Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/75

Rh

For thee forces acting equally (with repect to the quantities of the bodies to be moved), and in the direction of parallel lines, will (by Law 2.) move all the bodies equally (as to velocity), and therefore will never produce any change in the poitions or motions of the bodies among themelves.

Hitherto I have laid down uch principles as have been received by mathematicians, and are confirmed by abundance of experiment. By the firt two Laws and the firt two Corollaries, Galileo dicovered that the decent of bodies oberved the duplicate ratio of the time, and that the motion of projectiles was in the curve of a parabola; experience agreeing with both, unles o far as thee motions are a little retarded by the reitance of the air. When a body is falling, the uniform force of its gravity acting equally, imprees, in equal particles of time, equal forces upon that body, and therefore generates equal velocities; and in the whole time imprees a whole force, and generates a whole velocity proportional to the time. And the paces decribed in Rh