Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/74

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For the differences of the motions tending towards the ame parts, and the ums of thoe that tend towards contrary parts, are, at firt (by uppoition), in both caes the ame; and it is from thoe ums and differences that the colliions and impules do arie with which the bodies mutually impinge one upon another. Wherefore (by Law 2.) the effects of thoe colliions will be equal in both caes; and therefore the mutual motions of the bodies among themelves in the one cae will remain equal to the mutual motions of the bodies among themelves in the other. A clear proof of which we have from the experiment of a hip; where all motions happen after the ame manner, whether the hip is at ret, or is carried uniformly forwards in a right line. Rh