MOVING FORCE. 
175 
of the effects to be, in all cases, in proportion ro the product of Cases of difli- 
tlie pressure multiplied by the space through which it acts, jocVrhies of 
whatever nuy be the time or the manner of its acting, he con- moving force, 
siders tiiai product to be the principle capable of the most gene- 
ral applic..tion. and consequently adopts it as the proper mea- 
lure of inechanical force. 
With regard to the proper economy of time, I have always 
understood, that Mr, Smeaton was fully sensible of its value, 
and most exemplary in his punctual attention to it, in all its 
various bearings. We can form no notion of velocity, without 
taking time as an element of it. As far as it relates, however, 
to mechanical power, time would come under his consideration 
chiefly in the following manner. If, for example, the object 
before him was to apply, to the best advantage, a given stream 
of water in producing a mechanical eti'ect, he would first ascer- 
tain the quantity of water passing in any given lime, and the 
iieight of its fall. He would next inform himself whether 
the effect to be produced .should be continuous or intermitting 
in its duration. If continuous, he would construct his machine 
such dimensions as to receive and apply the power of the 
I itream unifor.mly and constantly from hour to hour, and from 
Hay to day. But if it were required to produce an intermitting 
tjffect, he would construct his machine of larger dimensions, 
aa order to avail himself of the quantity of water whicli might 
xie reserved during the time tliat no effect was required to be 
5 iroduced ; ami he would take care to 3rrang<? and [»roporlion 
.. he whole, so that no more people than necessary should be 
;;mployed in attending it. In the latter c.ase, the machine 
►vould be said to be more powerful than in the former : but 
hie word power, when used in that sense, has no reference to 
le measure of the effect when compared with the fotx:e by 
•hich it is produced. The machine, without the moving 
><irce, has no power; and when we speak of the greater or 
Kss power of a machine, we only mean to s.ay, that we make 
Xie of a larger or smaller instrument to convey the moving 
> rce. If we have to Jet off the water from a reservoir, we 
i.aow that it will be emptied in Jess time through a largo aper- 
ture 
