( i<B ) XIII. An Account of an Experiment contrived hy G.J. s'Gravefande, r Prof. Math, at Leyden, F. % S: relatingto the Force of moving Bo- &k$,fhewn to the Royal Society , by J # X Defaguliers, LL T>. and F. % S. HAving laft Year (hewn ieveral Perfons in HoU land the Experiment contrived by Mr. Geo, Grab am j to explain theDoQxine relating to the Mo* mentum of Bodies (viz. That the Momentum ox Quantity of Motion in Bodies is always as the Mafs multiplied into the Velocity) which Experiment is made with a flat, pendulous Body, that receives the Addition of a Weight equal to -itfetf at the lower Part of its Vibration, and by the Reception of that equal Quantity of Matter always lofes half its Ve- locity. Dr. Mufchenbroek, ProfeiTor of Mathe* maticks and Aftronomy at Utrecht, communica- ted to me the following Experiment, made in Op- pofition to that which I fhewed,* by Mr. ProfeiTor iGravefande. In this laft a Spring equally bent every time, pulhes forward, unequal Quantities of Matter fucceflively, and in every Experiment the Pro* du& of the Mafs of the Body by the Square of the Velocity is the fame ; and therefore, as the Quantity of Motion muft always be the fame from the fame Caufe (viz. the fame Tenfion of the Spring) it fol* lows, by every Experiment, that it is as the Mafs mui« liplied intothe Square of the Velocity* ( l 44 ) Exp. i.] The pendulous Cylinder is fliot by the Springfrom o Deg. to 7 Deg. meafured upon a Tan- gent Line. Exp. 2.] The Cylinder with a leaden Weight in it that makes its Weight double, is (hot forward to 4 Deg. and 9 Tenths. Exp. 3.] The Cylinder with a Weight in it that made its Weight triple, was (hot forward to 4 Degrees and a little farther. Exp. 4J The Cylinder with a triple Weight of Lead fo as to quadruple the whole Weight, was (hot forward to 3 Deg. and an half. Thefe 4 Experiments at firflt feem agreeable to the new Hypothecs ; for according to the old, the Cylin- der in the xd Experiment ought to have gone but to 3 \ Deg. in the 3d Experiment but to 3 7 Deg. and in the laft but to 2 Deg. . But if we take in the Confederation of Time, all will be reduced to the old Principle. As for Example, let us compare the firft and laft Experiments. . In the firft, the Spring during a certain time a£b upon the Cylinder which is driven forward with the Velocity 8. When the quadrupled Weight is driven forward with the Velocity 4 inftead of 2,, it is be- caufe the fame Spring ads twice as long upon the Cy- linder before it ceafes to impel it - 5 and certainly the fame Caufe a&ing twice as long muft produce a doubk Effed. FINIS.