174 
MOVING FORCE. 
Cases of (IffB- which he quoted^ becanse they omitted to take into considera* 
docnines*'of circumstances which render that application inconsistent, 
moving force, as Dr, Milner acknowledges, with the facts. When a stream 
of water strikes a plane opposed to it, a small number only of 
the particles of the water touch the plane, and unless we sup- 
pose these particles to be pressed forward by the water which is 
behind them, the actual pressure exerted against the plane cannot 
be accounted for. But that action of the water is not considered 
in the prevailing theory j and it is omitted even in the corrected 
theory which has been proposed by M. de Borda and Mr. 
Waring ; they appear not to have considered, that when the 
number of planes acted upon are increased, the quantity of 
water acting upon each plane is decreased in the same pro- 
portion ; neither are the number of planes acted on in a given I 
time, ” inversely as the relative velocity,” as stated by Mr. I 
Waring. 
The Edinburgh reviewers object to Mr. Smeaton’s opinions 
upon more general grounds, at pages 126 — 7 — 8 , and con- 
tinuing to reason as if he had understood the consideration of 
the time to be necessarily evcludcd in all estimations of force, 
they truly and eloquently observe, that, “ in most instances, 
time is a very material element in the estimation of an effect, 
or an event of any kind j and is, of all our resources, that 
■which it most behoves us to economize*.” 
Now, I apprehend it is obvious, from the whole of Mr. 
Smeaton’s reasoning on this subject, that he was perfectly aware ' 
that, in most cases of moving force, if the pressure, the time, ■' 
and the ma?iner of its .acting be given, the effects may be ^ 
found. He observed, however, (as in the two first cases) that 
the effects were not always in proportion to the pressure and the •' 
time of its acting. But he found, that if the pressure and the '• 
space through which it acts (or when variable, the fluent of the 
pressure into the space) be given, the effects may always be 
determined without reference to the warmer or the time in 
which they may be produced; and finding the total amount * 
* EdiaUurgh Keview, vol. 12, p. 128. 
of 
