THE LEVER. 



45 



of weight. This rule will be better understood after con- 

 sidering its application to the different simple machines. 



The simplest of all machines is the lever. It consists of 

 a rod or bar, one end resting upon a prop or fulcrum^ F 

 (fig. 41), near which is the weight, W, moved by the 

 liand at P. The stone may weigh 1000 pounds; yet, if it 

 is ten times as near the fulcrum as the man's hand is, a 

 force of 100 pounds will lift it ; but it will be moved only 

 a tenth part as high as the hand has been moved, as shown 



Fis:41. 



Lexer of the second Und. 



by the dotted lines. By placing the stone still nearer the 

 fulcrum, still less will be the power required to raise it, 

 but then the distance elevated would be also still less. By 

 sufficiently increasing the disproportion between the two 

 parts of the lever, the strength of a child merely might 

 be made to move more than many horses could draw. 



These performances of the lever often excite astonisli- 

 ment at what appears to be out of the common course of 

 things ; yet, when examined by the principles of mechan- 

 ics, instead of appearing matters of astonishment, they are 

 found to be only the natural and necessary results of the 

 laws of force. In the case of the lever just described, it is 

 often incorrectly supposed that the power itself sustains 

 the weight. But this is not the case ; nearly the whole 

 of it rests upon the fulcrum. We often see proofs of this 

 error in common practice, where fulcrums or props entirely" 

 insufficient to uphold the enormous weight to be raised 

 are attempted to be used. If the weight, for instance, be 

 ten times as near the fulcrum as to the power, then nine- 

 tenths of the weight rests upon the fulcrum, and the re- 



