Sir I s a A c Newton’s Book I.

54

thus found, the motion of each body after the ftroke is de-termined, as before.

10. In the next place, fuppofe the bodies A and B wereboth moving the fame way, but A with a fwifter motion, foas to overtake B, and ftrike againft it. The effect of the per-cuftion or ftroke, when the bodies are not elaftic, is difcover-ed by finding the common motion, which the two bodieswould, have after the ftroke, if B were at reft, and A were toadvance againft it with a velocity equal to the excefs of theprefent velocity of A above the velocity of B ; and by ad-ding to this common velocity thus found the velocity of B.

II* If the bodies are elaftic, the effect of the elafticity isto be united with this other, as in the former cafes.

11. When the bodies are perfectly elaftic, the rule ofH uygens a in this cafe is to prolong CD (fig. 7. ) and totake in it thus prolonged C E in the lame proportion to E D,as the greater velocity of A bears to the lefter velocity of B ;after which F G being taken equal to F E, the velocities of thetwo bodies after the ftroke will be determined, as in the twopreceding cafes.

13, T hus I have given the fum of what has been writ-ten concerning the effects of percuftion, when two bodiesfreely in motion ftrike dire&ly againft each other; and the■refults here fet down, as the confequence of our realbning

* In the place above-cited.

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