48 Sir Isaac Newton’s Book I.

For this rule is never deviated from, that though the degreeof elasticity determines how much more than half its veloci-ty the body first in motion shall lose; yet in every cafe theloss in the motion of this body shall be transferred to the other,that other body always receiving by the stroke as much mo-tion, as is taken from the first.

30. T h 1 s is the cafe of a body striking directly against anequal body at rest, and the reasoning here used is fully con-firmed by experience. There are many other cafes of bodiesimpinging against one another: but the mention of theseshall be reserved to the next chapter, where we intend to bemore particular and diffusive in the proof of these 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 philosopher,from the most obvious observations, that suggest them to us;I now intend to give more particular proofs of them, by re-counting some of the discoveries which have been made inphilosophy before Sir I s a a c Newton. For as they wereall collected by reasoning upon those laws; so the conformityof these discoveries to experience makes them so many proofs•of the truth of the principles, from which they were derived.

a. Let