45 ® Mr. smeaton on Mechanic Power . 
I refolved to try a fet of experiments from whence it 
might be inferred, what proportion or quantity of me- 
chanical power is expended in giving the fame body dif- 
ferent degrees of velocity. This fcheme was put in exe- 
cution in the year 1 7 5 9, and the experiments were then 
fhewn to feveral friends, particularly my very worthy and 
ingenious friend Mr. william russell. 
In my experimental inquiry concerning the powers 
of water and wind before referred to, I have, p. 105. 
part 1. defined what I meant by power, as applied to 
practical mechanics, that is, what 1 now call mechanical 
power; which, in terms fynonymous to thole there ufed, 
may be faid to be meafured by multiplying the weight 
of the body into the perpendicular height from which it 
can defcend ; thus the fame weight, defending from a 
double height, is capable of producing a double me- 
chanical effedl, and is therefore a double mechanical 
power. A double weight defending from the fame 
height is alio a double power, becaufe it likewife is capa- 
ble of producing a double effedt ; and a given body, de- 
fending through a given perpendicular height, is the 
fame power as a double body defending through half 
that perpendicular; for, by the intervention of proper 
levers, they will counter-balance one another, conforma- 
bly to the known laws of mechanics, which have never 
been controverted. It mull, however, be always un- 
-derltood, that the defending body, when a<fting as a 
meafure of power, is fuppofed to defcend (lowly, like the 
weight of a clock or a jack; for, if quickly defending, 
3 ^ 
