i-o Mr. ViTsCE on the Motion of 



4. Having proved that the retarding force of ali hard bodies 

 ariilng ITom fridion is uniform, the quantity of fridion, con- 

 iidered as equivalent to a weight without inertia drawing the 

 body on the horizontal plane backwards, or a<fling contrary to 

 the moving force, may be immediately deduced from the fore- 

 going experiments. For let M = the moving force exprefled by 

 its weight; F = the friction; W = the weight of the body 

 upon the horizontal plane ; S=rthe fpace through which the 

 moving force defcended in ti:ie tim.e / exprefled in feconds ; 

 rrs 1 6^^ feet ; then the whole acceierative force (the force of 



\I — F 



gravity being unity) will be ^j-t"^ ; hence, by the laws of uni- 

 formly accelerated motions, ^^ ^ x r/' _ S, confequently 



F =:M ~ — 2^. To exemplify this, let us take the cafe of the 



laft experiment, where M = 7, W=23i, 8—4/- feet, i — /i/'\ 



hence F= 7 - ^l\\^'u = ^A^1 » confequently the fri<i1ion was 



to the weight of the rubbing body as 6.^i6y to 25.75. And 

 the great accuracy of determining the friction by this method is 

 manifeft from hence, that if an error of i inch had been made 

 in the defcent (and experiments carefully made may always de- 

 termine the fpace to a much greater exaflnefs) it would not 

 have affected the conclufion .^^.^dthpart of the whole. 



5. We come in the next place to determine, whether fric- 

 tion, cateris paribus, varies in proportion to the weight or 

 preffure. Now if the whole quantity of the fridion of a body, 

 meafured by a weight without Inertia equivalent to the fri£lion 

 drawing the body backwards, increafes in proportion to its 

 weight, it is manifefl, that the retardation of the velocity of I 

 the body arifing from the fridion will not be altered; for the 

 7 retardation 



