474 Mr. smeaton on Mechanic Power. 
time, produce two fuch effedts, or twice that effedt. A 
mechanical power, therefore, properly fpeaking, is mea- 
fured by the whole of its mechanical effedt produced, 
whether that effedt is produced in a greater or a leffer 
time; thus, having trealured up 1000 tuns of water, 
which I can let out upon the over-fhot wheel of a mill, 
.and defcending through a perpendicular of 20 feet, this 
power applied to proper mechanic inftruments, will pro- 
duce a certain effedt, that is, it will grind a certain quan- 
tity of corn ; and that, at a certain rate of expending it, 
it will grind this corn in an hour. But fuppofe the mill 
equally adapted to produce a proportionable effedt, by 
the application of a greater impullive power as with a 
lefs, then, if I let out the water twice as faft upon the 
wheel, it will grind the corn twice as fait, and both the 
water will be expended and the corn ground in half an 
hour. Here the fame mechanical effedt is produced; 
viz. the grinding a given quantity of corn, by the fame 
mechanical power, viz. 1000 tuns of water defcending 
through a given perpendicular of 20 feet, and yet this 
effedt is in one cafe produced in half the time of the 
other. What time, therefore, has to do in the bufinels 
is this : let the rate of doing the bufinefs, or producing 
the effedt, be what it will, if this rate is uniform, when I 
have found by experiment what is done in a given time, 
then, proceeding at the fame rate, twice the effedt will be 
produced in twice the time, on fuppofition that I have a 
fupply of mechanic power to go on with. Thus 1000 
tuns of water, defcending through 20 feet of perpen- 
dicular, 
