Bodies affebfed by Fridiiort, x 8q 
r i , \ r j -f. rx r , n + rx 
**-■ x »r + ■ xnr , conlequently — : i :: is i nr 
(from what is proved above) m x CB : a x CA ; therefore 
a x CA x r s + a x CA x rx ~ m x CB x rx, hence rx = * 
— ^e radius of the circle which rolling down 
the inclined plane LM, and carrying the body with it, will 
give the true ratio of its progreffive to its rotatory motion, 
and confequently that point of the circle which coincides with 
any given point of the body will, as the circle revolves upon 
the line LM, defcribe the fame curve as the correfponding 
point of the body; but as the nature of the curve defcribed by 
any point of a circle revolving upon a flraight line is already/ 
very well known, it ieems unneceuary to give the invefligatioiv 
By a method of reafoning, not very different, may the nature 
of the curve, which is defcribed by any point of a body moving 
upon an horizontal plane, and affected by fribtion, be detexminedf 
