Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/79

Rh concurr'd with contrary motions, A with twelve parts of motion, and B with ix, then if A receded with 2, B receded with 8; to wit, with a deduction of 14 parts of motion on each ide. For from the motion of A ubducting twelve parts, nothing will remain; but ubducting 2 parts more, a motion will be generated of 2 parts towards the contrary way; and o, from the motion of the body B of 6 parts, ubducting 14 parts, a motion is generated of 8 parts towards the contrary way. But if the bodies were made both to move towards the ame way, A, the wifter, with 14 parts of motion, B, the lower, with 5, and after reflexion A went on with 5, B likewie went on with 14 parts; 9 parts being tranferred from A to B. And o in other caes. By the congres and colliion of bodies, the quantity of motion, collected from the um of the motions directed towards the ame way, or from the difference of thoe that were directed towards contrary ways, was never changed. For the error of an inch or two in meaures may be eaily acribed to the difficulty of executing everything with accuracy. It was not eay to let go the two pendulums o exactly together that the bodies hould impinge one upon the other in the lowermot place AB; nor to mark the places s and k, to which the bodies acended after congres. Nay, and ome errors, too, might have happened from the unequal denity of the parts of the pendulous bodies themelves, and from the irregularity of the texture proceeding from other caues.

But to prevent an objection that may perhaps be alledged againt the rule, for the proof of which this experiment was made, as if this rule did uppoe that the bodies were either abolutely hard, or at leat perfectly elatic; whereas no uch bodies are to be found in Rh