296 ' . On Machines in General. 



first case would be employed entirely in conquering the 

 weight of the body, is here divided into two, the first of 

 which continues to make an equilibrium in the weight, and 

 the other produces the movement. VVe therefore cannot aug- 

 ment one of these efforts except at the expense of the other ; 

 and this is the reason why the effect of machines in motion 

 is ;ilway< so limited that it can never surpass the momentum 

 of activity exercised by the agent which produces it. 



It is, without doubt, for want of paying sufficient atten- 

 tion to these different effects of one and the same machine, 

 considered sometimes in a state of repose and sometimes in 

 movement, that some persolis not unacquainted with sound 

 theory frequently abandon themselves to the most chimerical 

 ideas, while we see simple workmen turning to advantage, 

 as it were by instinct, the real properties of machines, and 

 judging very accurately of their effects. Archimedes only 

 wanted a lever and a fixed point, in order to move the globe 

 of the earth ; how did it happen then, it may be said, that 

 so great a man as Archimedes could not, even when fur- 

 nished with the best machine in the world, raise a weight of 

 one hundred pounds in one hour to a small given height ? 

 It is because the effect of a machine at rest and of one in 

 movement are two very different things, and somewhat he- 

 terogeneous : in the first case it is requisite to destroy and 

 to hinder the movement ; in the second, the object is to pro- 

 duce it and to keep it up ; now it is clear that this last case 

 requires more consideration than the first : viz. the real ve- 

 locity of each point of the system ; — but we shall better per- 

 ceive the reason of this difference by the following remark. 



Any given fixed points or obstacles are forces purely 

 passive, which may absorb a movement however great it may 

 be, but which can never produce one, let it be never so small, 

 in a body at rest : now it is very improperly that in the case 

 of equilibrium we say of a small power, that it destroys a 

 great one : it is not by the small power that the great one is 

 destroyed; it is by the resistance of the fixed points: the 

 small power in reality destroys but a small part of the great, 

 and the obstacles do the rest. If Archimedes had possessed 

 what he wished for, it would not have been he who would 



have 



