46 MECHAXICS. 



maining tenth only is sustained by the lifting power. 

 The lever only allows the power to expend itself through 

 a longer distance, and thus, by concentrating itself at the 

 weight, to elevate the latter through the shorter distance, 

 according to the rule of virtual velocities already ex- 

 plained. 



The fulcrum may be placed between the weight and the 

 Ei^v. 42. power, as in fig. 42, 



1 /-"^ or the power may be 



Lever of tlie first kind. 



S placed between the 

 fulcrum and the 

 weight, as in fig. 43, 

 the same principle of virtual velocities applying in all cases. 



Where the fulcrum is between the power and the 

 weight, as in fig. 42, it is called a lever of the first kind. 



Where the weight is between the fulcrum and the 

 power, as in fig. 41, it constitutes a lever of the second 

 kind. 



Where the power is between the fulcrum and the 

 weight, as in fig. 43, it is termed a lever of the third 

 kind. 



1. Many examples occur in pi*actice of levers of the first 

 kind. A crow-bar, used to raise stones from the earth, is 

 an instance of this sort : 

 so IS a handspike oi 

 any kind used in the 

 same way. A hammer 

 for drawing a nail 

 operates as a lever of the first kind, the heel being the ful- 

 crum, the nail the weight, and the hand the power ; the 

 distance through which the handle jmsses being several 

 times greater than that of the claws, the force exerted on 

 the nail is increased in like proportion. A pair of scissors 

 consists of two levers, the rivet being the fulcrum ; and in 

 using them, as every one has observed, a greater cutting 

 force is exerted near the rivets than toward the points. 



Leter of the third kind. 



