Moving Force. 129 
Mr. Smeaton, at the commencement of the 
description of his experiments on water-wheels, 
says—‘ The word power, as used in practical 
mechanics, I apprehend to signify the exertion 
of strength, gravitation, impulse, or pressure, 
so as to produce motion.’”’* And near the end 
of his “ Experimental Examination,’ we have 
the following conclusion :— 
“ It therefore directly follows, conformably 
to what has been deduced from the experi- 
- ments, that the mechanic power that must of 
necessity be employed in giving different de- 
grees of velocity to the same body, must be as 
the square of that velocity.” And in the next 
page he observes, “It seems, therefore, that 
without taking in the collateral circumstances 
both of time and space, the terms quantity of 
motion, momentum, and force of bodies in 
motion, are absolutely indefinite; and that 
they cannot be so easily, distinctly, and funda- 
_ mentally compared, as by having recourse to 
the common measure, viz. mechanic power.” + 
M. De Prony, however, gives a different 
conclusion, as follows: “ I] y a eu des disputes 
trés vives parmi les mathématiciens pour sayoir 
si on devoit faire la force d’un corps en mouve- 
ment proportionelle a la vitesse ou au quarré 
* Philos. Trans. 1795, p. 105. 4 Ibid, 1776, p. 473. 
] 
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