1-72 
MOVING FORCE, 
1 
I 
(Cases of d Ifi- 
t*u!iy ill the 
Ooclriijcs cf 
)i.oviug loite. 
2. " We have seen before, in our observations upon the 
effects of undershot wheels, that the general ratio of the power 
to the effect, when greatest, was 3 : 1 j the effect, therefore, 
of overshot wheels, under the same chrcumstances of quantity and 
faU, is at a medium double that of undershot ; and as a conse- 
quence thereof, that non-elastic bodies, when acting by their 
impulse or collision, communicate only q part of their original 
power-, the other part being spent in changing their figure in 
consequence of the stroke*.” 
It was chiefly in this last consideration, that he found the 
prevailing theory to be defective 5 for, according to that theory, 
as it is applied in explaining the collision of bodies, there can 
be no force spent in producing change of flgure ; and it is very 
remarkable, that no succeeding writer has, as far as I can learn, 
paid any attention to this circumstance. 
However much Mr, Smeaton’s valuable observations may 
have been disregarded by authors, they have not been lost to, 
practical men. Before the publication of the paper which I 
have been endeavouring to defend, several mills had been con- 
structed under Mr. Smeaton’s direction, in which his chief ob- 
ject was to apply the water so that less of its force should be 
expended in producing a change of figure, and consequently 
more of its force be communicated to the wheel. Altbougli 
he had obtained by his experiments results which w'ere “ more 
than double of what is assigned by the theory,” yet by com- 
paring the effective with the real head, he found that nearly 
half the power was, in many instances, spent in producing a 
change of figure in the water, before it reached the wheel 5 
and still finding (as stated above In the second observation) 
that more than half of what remained of the power was spent 
in the same way by the manner in which it acted upon the 
wheel ; he determined to apply the water in all cases, so that 
it should act more by its weight, and less by its impulse j and 
the advantage gained by that improved construction was found 
to be fully equal to his expectations. It was afterwards so ge- 
i 
I 
I 
! 
• Phil. Transi 1759, p. 130. 
1 
nerally 
I 
