MECHANIC POWERS. 49 



is more easily applied, and many other advantages 

 obtained. In all machines, simple as well as com- 

 pound, what is gained in power is lost in time. Sup- 

 pose that a man, by a fixed pulley, raise a beam to 

 the top of a house in two minutes, it is clear that 

 he will be able to raise six beams in twelve minutes ; 

 but by means of a tackle, with three lower pulleys, 

 he will raise the six beams at once with the same 

 ease as he before raised one; but then he will be 

 six times as long about it, that is, twelve minutes : 

 thus the work is performed in the same time 

 whether the mechanical power be used or not. 

 But the convenience gained by the power is very 

 great; for if the six beam's be joined in one, they 

 may be raised by the tackle, though it would be 

 impossible to move them by the unassisted strength 

 of one man. 



Consequently, if by any power you are able to 

 raise a pound with a given velocity, it will be im- 

 possible, by the help of any machine, to raise two 

 pounds with the same velocity; yet, by the assist- 

 ance of a machine, you may raise two pounds with 

 half that velocity, or even one thousand with the 

 thousandth part of that velocity; but still there is 

 no greater quantity of motion produced, when a 

 thousand pounds are moved, than when one pound 

 is moved; the thousand pounds moving propor- 

 tionally slower. 



No real gain of force is, therefore, obtained by 

 mechanical contrivances: on the contrary, from 

 friction, and other causes, force is always lost; but 

 by machines we are able to give a more convenient 

 direction to the moving power, and to apply its 

 action at some distance from the body to be moved, 

 which is a circumstance of infinite importance. By 

 machines, also, we can so modify the energy of the 



vol. i. e 



