Reflections on the Communication of Motion by Impact and GravityBy the RevIsaac Milner, MAFellow of Queen's College, CambridgeCommunicated by Anthony Shepherd, DDFRSand Plumian Professor at Cambridge . ities are underftood; inthis, their velocities reduced to the fame direction. How-*ever, no material ill confequence can poffibly arife fromfuch a notion of action and re-acSlion, as long as the quef-tion is fuppofed to concern only elaftic bodies: but realmifchief is done, and the debate ceafes to be verbal^whenever the law of the equality of a6lion and re-a(5tionis faid to take place in the co
Reflections on the Communication of Motion by Impact and GravityBy the RevIsaac Milner, MAFellow of Queen's College, CambridgeCommunicated by Anthony Shepherd, DDFRSand Plumian Professor at Cambridge . ities are underftood; inthis, their velocities reduced to the fame direction. How-*ever, no material ill confequence can poffibly arife fromfuch a notion of action and re-acSlion, as long as the quef-tion is fuppofed to concern only elaftic bodies: but realmifchief is done, and the debate ceafes to be verbal^whenever the law of the equality of a6lion and re-a(5tionis faid to take place in the coUifions of all forts ofbodies. CASE THE SECOND. But the truth of thefe remarks^and the neceffity of attending to the precife ufe of terms,,will appear in a ftill ftronger light, if we conlider the fo-lution of a problem given us by j. Bernoulli^^^. Suppofe that two equal and fpherical bodies, a and b,.ftruck at once in the direaion CD perpendicular to theline joining the centers of a and b with a velocity repre-fented by a. Let the quantity of matter in c be called:^, and the quantity of matter in a or b, j^: let the velo-. f4^ Difcouxs fur le mouYcment. ^ city Motion by ImpaSI and Gravity^ 357. city of c after the ftroke be reprefented by a?, and that ofA or B in the dire6tion ac or cb by y^ and fuppofep: q:: rad.: cofin, lcd. Then, becanfe ma the quantity of motion before the ftroke is equal to ;;^A;+^y^, the quantity of motion after the ftroke, and ma^ is equal tomx^¥%ny^ becaufe the quantity of force is not altered by the coUifion; he eafily findsx^^T^l^/^-- ^^^y = Hpqma .*^ • f m-^iqn There is no problem which deferves to be more con-iidered than this by a perfon defirous of having a clear Z z 2 idea 358 Mr. MiLNER on theKCommunkaiion of idea of the grounds of that contention which has iub-filled fo many years. We here fee Bernoulli taking itfor granted, that the quantity of force in elaftic bodies isno ways aj5€<5led by their mutual acStions, whether dire<ffcor
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