90 
MOVING FORCE. 
Casrs of tliffi- 
ciilty ii> the 
doelriiu’s of 
moving force. 
I 
Dr. Wollaston’s opinion is, that “ the conception of a quan- n 
tity dependent on the continuance of a given vis viotrix for a . il 
certain time may have its use, when correctly applied, in certain ■ 
philosophical considerations j but the idea of a quantity result- 
ing from the same force exerted through a determinate space is 
of greater practical utility, as it occurs daily in the usual occu- 
pations of men*.” And he concludes his lecture on the force 
of percussion thus : “ In short, whether we are considering 
the sources of extended exertion, or of accumulated energy, 
whether we compare the accumulated forces themselves by 
their gradual or by their sudden effects, the idea of mechanic 
force in practice is always the same, and is proportional to the 
space through which any moving force is exerted or overcome, 
or to the square of the velocity of a body in which such force I 
is accumulated.” This conclusion coincides nearly with Mr. B 
Smeaton's, but still it remains to be explained how two given || 
quantities of force may^ consistently, be considered as equal to 
each other for philosophical purposes, but unequal for aU prac- 
tical purposes. 
The Edinburgh reviewers of Dr. Wollaston’s lecture adopt adif- 
ferent doctrine. In reference to the first passage quoted above, they 
say, “ Now, with the judgment here given as to the respective 
utiliiy of the two measures of the force of moving bodies, 
we cannot entirely agree, though w-e differ from Dr. Wollaston 
t 
♦ with considerable diffidence ; and the more, that his opinion 
is supported by one of the greatest authorities in practical me- 
chanics. of which this or any other country can boast — the late 
HJr. Smeatonf.” And after some remarks on supposed errors 
of Mr. Smeaton, which I shall have occasion to refer to again, | 
they say, “ To whatever cause, theiefore, the imperfection of 
the theory of the machines moved by water is to be ascribed, 
it is not to any thing that would be corrected by the introduc- 
tion of a measure of force differeiit from that which is com- 
monly in usej.” At the beginning, however, of the same ar- 
• Hiil. Trans. 1806, p. 15. 
t lidiuliiirgh Review, vol. 12, p. l' 2 « 
^ Ibid, p. ISiG. 
tide. 
