4.8 Sir Is a ac Newton’s BookI.

For this rule is never deviated from, that though the degreeof elafticity determines how much more than half its veloci-ty the body firft in motion (hall lofe; yet in every cafe thelofs in the motion of this body fhall be transferred to the other,that other body always receiving by the ftroke as much mo-tion, as is taken from the fir ft.

30. T h 1 s is the cafe of a body ftriking dire&ly againft anequal body at reft, and the reafoning here ufed is fully con-firmed by experience. There are many other cafes of bodiesimpinging againft one another: but the mention of thefefhall be referved to the next chapter, where we intend to bemore particular and diffufive in the proof of thefe laws of mo-tion, than we have been here.

Chap. II.

Farther proofs of the Laws of Motion.

H AVING in the preceding chapter deduced the threelaws of motion, delivered by our great philofopher,from the moft obvious obfervations, that fuggeft them to us;I now intend to give more particular proofs of them, by re-counting fome of the difeoveries which have been made inphilofophy before Sir I s a a c Newton. For as they wereall collected by reafoning upon thofe laws; fo the conformityof thefe difeoveries to experience makes them fo many proofsof the truth of the principles, from which they were derived.

1 . Let