226 On Machines in General. 



fact be the case, when we wish to employ them \\\ the most 

 advantageous manner possible. 



LI. Let us therefore designate bv Q, the momentum of 

 activity consumed bv the sohciting forces in a given time?, 

 and by q, the momentum of activity exercised at the same 

 time bv the rcsislin? forces: this being done, whatever be 

 the movement of the machine, we shall always have, by 

 the filth cornllarv, O t= q; in such a manner, for example, 

 that if each F of the soliciting forces be constant, its velo- 

 city V uniform, and the angle Z formed by the directions 

 of F ai^d V alwavs null, we shall have at the end of the time 

 t s ¥\* t =^ q; and if all the soliciting forces are reduced to 

 a single one, we shall consequently have F V ^ = gr (XXXIf 

 and XXXill), 



LI I. Wc may in general regard the moiiientum of ac- 

 tivity 7, cxerc'.sed by the resisting forces, as the effect pro- 

 duced by the soliciting forces:- for instance, when it is re- 

 quisite to raise a weight P to a given height H, it is very 

 easy to regard the effect produced by the moving force as 

 being in a compound ratio of the weight, and the height to 

 which we have to raise it ; so that P H is what we then na- 

 turally tmderstand by the effect produced. Now, on the other 

 hand, this quantity P H is precisely what we have called the 

 momentum of activity exercised by the resisting force P ; 

 therefore this momentum of activity, or q, is what we na- 

 turally understand in this case by the effect produced. 



Now, in the other cases, it is evident that q is always a 

 quantity analogous to that just mentioned : this is the reason 

 why 1 shall frequently, in the course of my subsequent ob- 

 servations, call this quantity q the effect produced : thus, by 

 the terms efff-ct produced, I shall mean the moitientum of 

 activity exercised by the resisting forces; in such a manner 

 that, in virtue of the equation O = q, we may establish as a 

 general rule, that the effect produced in a g'nicr:. time ly any 

 systcvi of rnoi'ivg foixp.s, is cqzuil to the yvninciituTn. of activity 

 ronaumcd at the same time by all these forces. 



LI 1 1. We see by the equation F V t = q, found in the 

 f)iK;eeding article, that it is of no use to be acquainted with 



the 



