On Machines in General.^ -' '85 



by a current of air, or water, See. We give in general the 

 name of power to the eHort exerted by ihe agent, e. e, to 

 that pressure or tension hy which it acts upon- the body to 

 which it is appUed ; and we compare these different- efforts 

 without regarding the agents which proddce them, because 

 the nature of the agents cannot change the forces which 

 they are obliged to exercise in order to fulfil the different 

 objects for which machines are destined : the machine itseJf, 

 i. e. the system of fixed pointSj obstacles, rods, levers, 

 and other intermediate bodies, which serve to transmit these 

 different efforts from one agent to another; the machine, 

 itself, I say, is considered as a body stripped of its Inertness : 

 its proper mass (when it is necessary to have regard to it, 

 whether on account of the movement which it absorbs, or 

 on account of its gravity or of other motive forces witli 

 ■which it may be animated,) is regarded as a foreign power 

 applied to the system; in a word, a machine properly so 

 called, is an assemblage of immaterial obstacles, and of 

 moveable particles incapable of reaction, or deprived of in- 

 ertness, i. e. (XXIX.) a system of bodies the densities of 

 which are infinite or nothina;. To this system we imao-ine 

 that different external agents, in the number of which we 

 comprehend the mass of the machine, are applied, and trans- 

 mit their reciprocal action by the intermedium of this machine. 

 It is the pressure or other effort exercised by each ao;ent upon 

 this intermediate body, which we call force or power j and 

 the relation which exists between these different forces, 

 forms the subject of the inquiry, which has for its object ihe 

 theory of machines properly so called. Now, it is in this 

 point of view that we proceed to treat of equilibrium and 

 of movement ; but a force taken in this sense is not the less a 

 quantity of movement lost by the agent which exercises it, 

 whatever this agent may be in other respects, whether it acts 

 upon the machine by drawing it by a cord or by pushing 

 it by a rod ; the tension of this cord, or the pressure of this 



I. e. the resistance which it opposes to this change, or its vh ineriicc; whence 

 it is easy to conclude, that the tu inertia: "fany body n the result qf its actual 

 mutemtnt, and of a movement eqwl and dirictly opposed to that which it should 

 Jiai'e Ihf instant after wc^ds. 



C 2 rod. 



