. [ 2 -! 
the effedt is a maximum, and the force a current, 
is determined by computation to be four ninths of 
the weight which would caufe the Engine to reft. 
This, then, being fuited only to -an uniform velocity 
both in the lever and obftacle, I would conlider the 
cafe of an uniformly accelerated one in repeated vi- 
brations. The maximum which correfponds to it is 
adapted to the fteam-engine, and of no lefs import- 
ance to be determined than the other. And, no 
doubt, thefe fpeculative inquiries into mechanical fub- 
jedts, were they even barely confidered as our guides 
in experiment, may appear to deferve the attention 
of the Society. But indeed, and I ingenuoully con- 
fefs it, an opportunity to make fome remarks upon 
what I formerly laid before you, concerning the 
proportion of the cylinders, was a further induce- 
ment to the prefent refearch. 
A general expreflion for the time of a ftroke in 
fuch vibratory Engines, will lead us without trouble 
to a computation of their effects. 
A a C 5 D 
m A n 
Let A D be a lever, whofe Brachia are a and 
and fuppofed without weight. Let m be a Power, 
and n a weight. Then a : b :: n : — , the balance 
b n 
for n at A, and m — is the effective force at A, 
which multiplied by the lever a gives m a — nb for 
the efficacioufnefs of that force in the angular ve- 
locity of the Power and weight. Now, by the prin- 
ciples of Mechanics, the Inertia of any bodies re- 
volving 
