On Machines in General, 295 



things in an absolute manner, but solely place them in 

 the relations in which experience has shown they will be of 

 most advantage: for instance, I shall suppose that a maa 

 attached or eight hours in a day to a winch of one foot ra- 

 dius, . ight make cr.nlinually an effort of 25 tons by making 

 one turn every two seconds, which nearlv amounts to the 

 velocity of three feet per second ; but if we forced this man 

 to go quicker, thinking thereby to hasten the business, we 

 should retard it, because he would not be in a condition to 

 make an cff^ort of 23 tons, or could no longer work at the 

 rate of eight hours a day. IF, on the contrary, we diminish- 

 ed the velocity, the force would augment, but in a less de- 

 gree, and the momentum of activity would also diminish: 

 thus, according to experience, in order that this momentum 

 should be a maximum, we must proportion the machine so 

 as to preserve to the power the velocity of three feet per se- 

 cond, and not let it work more than eight hours a day. 

 It is well known that each kliitl of agent has, in respect of 

 its physical nature or constitution, a maximum analogous to 

 that of which we have spoken, and that this maximum can 

 in general only be found bv experience. 



LVm. This first condition being fulfilled, nothing re- 

 mains to be done, to produce with any given machine the 

 greatest effect possible, but to manage matters so as that tiie 

 wliole quantity O is employed in producing this eficct; 

 for if this be done, wc shall have q = Q; and this is all wc 

 can expect, since O can tiever be less than q. 



Now in order to fulfil this condition, I say, in the first 

 place, that we should avoid every shock or sudden change 

 whatever; for it is easy to apply to all imaginable cases the 

 reasoning which has been laid down (XLVll.) as to ma- 

 chines with weights; whence it follows, that every time there 

 is a shock, there is at the same time a loss of momentum of 

 activity on the part of the soliciting forces; a loss so real 

 that the effect of it is necessarily diminished, as we have 

 shown with respect to machines with weights in the above 

 article : it is therefore with reason that wc have advanced 

 (LI.), that in order to make machines produce the greatest 

 efl'ect possible, they must of nccebsity never change their 



movement. 



