236 Experimental Philosophy. [Lecture 16. 



To this kind of lever may be reduced several 

 sorts of instruments, such as scissars, pincers, 

 snuffers, which are made of two levers acting 

 contrary to one another, their prop or centre of 

 motion being the pin which keeps them together. 



The second kind of lever has the weight to be 

 raised between the prop and the power. Thus, 

 in raising the water-plugs in the streets of Lon- 

 don, you will see the workman put his iron crow 

 through the hole of the plug till he rests the fur- 

 ther extremity of it on the ground, and making 

 that his prop, he raises the lever or crow, and 

 draws out the plug. In this lever, as in the for- 

 mer, the longer the arm of the power is, or the 

 greater the distance of the workman from the 

 weight, the more is his natural force assisted by 

 the machine. To estimate this, if A B (fig. 96.) 

 is a lever on which the weight W of six ounces 

 hangs at the distance of one inch from the prop 

 G, and a power P equal to the weight of one 

 ounce hangs at the end B, six inches from the 

 prop, by the cord CD going over the fixed pulley 

 E, the power will just support the weight ; and 

 a small addition to the power will raise the weight 

 one inch for every six inches that the power 

 descends. 



This lever shows the reason why two men car- 

 rying a burden upon a stick between them, bear 

 unequal shares of the burden in the inverse pro- 

 portion of their distances from it. For it is well 

 known, that the nearer any of them is to the 



