56 Diferent Kfads [Book I. 



I. The LEVER is of all machines the moft fimple ; 

 it is a bar of iron, of wood, or of any fimilar material, 

 by means of which a fmall force applied to one end, 

 aided by a. fulcrum, or prop, placed at any part be- 

 tween he middle and the other extremity, is capable 

 of overcoming or refitting a greater. 



There are three kinds of levers. A lever of the 

 firft order is where the prop C (Plate I. fig. i.) is 

 placed between the moving power * A and the point 

 of refinance B. Upon this plan are conilrucled ba- 

 lances, fleelyards, and the moft ufual inftruments for 

 weighing, as well as the common inftruments for cut- 

 ting, &c. as fcifiars, pincers, (buffers, &c. ; and feveral 

 large but fimple machines for raifmg weights, draw- 

 ing watrr, and other fimilar purpofes. A lever of the 

 Jccond order is when the refilling force B (fig. 2.) is 

 placed between the power at A and the prop at C. : 

 and a lever of the third order is when the power at A 

 (fig. 3.) is placed between the weight or refiftance B 

 and the prop C. 



Thefe may be confidered as the different kinds of 

 levers, and diey admit of a further diftinc~uon or fub- 

 divifion, according as the point of power and the 

 point of refiftance are rriore or lefs diftant from the 

 prop. For example, in the lever (fig. 4.) if the prop 

 is at a, the power at p, and the refinance at r, ir is 

 called a lever of the firft order with equal arms j if the 

 prop is at b y it is a lever whofe arm of power/), is to 

 that of the refiftance r, as two to one; and if the prop 

 is at c, the arm of power is to that of refiftance as 

 three to one $ and the fame may be applied to the 

 other orders. Thus if the point of power f, in a 



* That which moves the lever, or adls upon it. 



lever 



