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THE MECHANICAL POWERS. 



find the power of the wheel, crank, or capstan by means of 

 the rules given under " The Wheel and the Axle," and de- 

 duct the force thus acquired from the force necessary to drive 

 the screw in raising the weight alone. The remainder is the 

 force required to raise the weight by the combined power 

 of the screw and the lever. 



THE PULLEY. 



"When only one cord or rope is used. 



To find the force necessary to raise a given weight by 

 means of a pulley of a given number of sheaves, &c. 



RULE. Divide the weight to be raised by the number of 

 parts of the rope engaged in supporting the lower or mov- 

 able block. 



