ESTIMATING THE POWER OF LEVERS. 



Fig. 48. 



-6- 



69 



as much greater than the other as four is to tliree, 

 then the weaker horse should be attached to the arm 

 of the whipple-tree made as much longer than the oth- 

 er arm as four is to three. 



In all the preceding estimates, the influence of the 

 weight of the lever has not been taken into consider- 

 ation. In a lever of the first kind, if the thickness of 

 the two arms he so adjusted that it will remain bal- 

 anced on the fulcrum, its weight will have no other 

 effect than to increase the pressure on the fulcrum ; 

 but if it be of equal size throughout, its longer arm, 

 being the heaviest, will add to its power. The amount 

 thus added will be equal to the excess in the weight 

 of this arm, applied so far along as the centre of grav- 

 ity of tliis excess. If, for example, a piece of scantling 

 Fig. 49. twelve feet long, 



a b, Fig. 49, be 

 used as a lever to 

 lift the corner of 

 a building, then 

 the two portions, a c, c d, will mutually balance each 

 other. If these be each a foot m length, the weight of 

 ten feet will be left to bear down the lever. The cen- 



