C I0 5 ] 
from running back, by a catch that plays iq 
and lays hold of the ratchet o o. 
By this means the hollow cylinder upon which 
the cord winds, and raifes the weight, is put in 
adlion and difcharged therefrom inftantaneoully, 
while the wheel is in motion : for without fome 
contrivance of this kind, it would not be eafy 
to make this fort of experiments with any to- 
lerable degree of exadtnefs. 
The ufe of the apparatus now defcribed will be 
rendered more intelligible, by giving a general idea 
of what I had in view j but as I lhall be obliged to 
make ufe of a term which has heretofore been the 
caufe of deputation, I think it neceffary to affign the 
lenfe in which I would be uuderftood to ufe it 3 and 
in which I apprehend it is ufed by practical Mecba- 
nicks. 
The word Power, as ufed in pra&ical mechanicks, 
I apprehend to lignify the exertion of ftrength, gra- 
vitation, impulfe, or preffure, fo as to produce mo- 
tion : and by means of ffrength, gravitation, im- 
pulfe, or preffure, compounded with motion, to be 
capable of producing an effedt : and that no effect is' 
properly mechanical, but what requires fuch a kind 
of power to produce it. 
The railing of a weight, relative to the height to 
which it can be raifed in a given time, is the moff 
proper meafure of power j or, in other words, if the 
weight raifed is multiplied by the height to which 
it can be raifed in a given time, the produdt is the 
meafure of the power raifing it 5 and conlequently, 
all thofe powers are equal, whofe products, made by 
Vol. LL P fuch 
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