OF THE .MECHANICAL POWERS. 



77 



H will balance 6 times 48, or 288 pounds hung to the 

 line on the axle : and hence the power or advantage oi\, 

 this machine will be as 288 to 1. That is to say, a 

 man, who by his natural strength could lift a hundred 

 weight, will be able to raise 288 hundred, or 14 *$ ton 

 weight by this engine. 



But the following engine is still more powerful, on 

 account of its having the addition of four pulleys : and 

 in it we may look upon all the mechanical powers as 

 combined together, even if we take in the balance. For A 

 as the axis D of the bar A B 

 is in its middle at C, it is plain 

 that if equal weights are sus- 

 pended upon any two pins equi- 

 distant from the axis C, they 

 will counterpoise each other, 

 It becomes a lever by hanging 

 a small weight P upon the pin 

 n, and a weight as much heavier 

 upon either of the pins b, c, d, e, 

 or/, as is in proportion to the 

 pins being so much nearer the 

 axis. The wheel and axle FG 

 is evident ; so is the screw E 

 which takes in the inclined 

 plane, and with it the half 

 wedge. Part of a cord goes 

 round the axle, the rest under 

 the lower pulleys K, m, over the 

 upper pulleys L, n, and then it 



is tied to a hook at m in the lower or moveable block, 

 on which hangs the weight W. 



In this machine, if the wheel Phas 30 teeth, it will be 

 turned once round in thirty revolutions of the bar A B, 

 which is fixed on the axis D of the screw E : if the 

 length of the bar is equal to twice the diameter of the 

 wheel, the pins a and n at the ends of the bar will move 



LECT 

 ill. 



