j ~ 0 Mr. Vikce on the Motion of 
i 
4. Having proved that the retarding force of all hard bodies 
ariting from friction is uniform, the quantity of friction, con- 
fidered as equivalent to a weight without inertia drawbng the 
body on the horizontal plane backwards, or acting contrary to 
the moving force, may be immediately deduced from the fore- 
going experiments. For let M = the moving force exprefied by 
its weight ; F = the friction ; W = the weight of the body 
upon the horizontal plane; S = the fpace through which the 
moving force defcended in the time t exprefled in feconds ; 
r— 16 - feet; then the whole accelerative force (the force of 
gravity being unity^ will be ^ ^ > hence, by the laws of uni- 
formly accelerated motions, ~~xr* a = S, confequently 
F = M — To exemplify this, let us take the cafe of the 
laft experiment, where M^t*, "W— 25I, S=4 r 7 _feet, t — 4 ; 
hence F = 7 - 
32! X 4 & _ 
l6 r ^X ifc 
6.417 ; 
confequently the fridtion was 
to the weight of the rubbing body as 6.4167 to 25.75* -Ann 
the great accuracy of determining the friction by this method is 
manifeft from hence, that if an error of 1 inch had been made 
in the defcent (and experiments carefully made may always de- 
termine the fpace to a much greater exadtiiefs^ it would no*, 
have affedled the conclufion -^-g-s-dth pait of the whole, 
5, We come in the next place to determine, whether fric- 
tion, cater is paribus , varies in proportion to the weight or 
preflu re. Now if the whole quantity of the friction of a body, 
meafured by a weight without inertia equivalent to the fridtion 
drawing the body backwards, increafes in proportion to its 
weight, it is manifeft, that the retardation of the velocity of 
the body ariling from the fridtion will not be altered ; for the 
_ * retardation 
