50 



MECHANICS. 



Fii?. 48. 



If equidistant between tbem, each will sustain a like por- 

 tion. If the load be twice as near to one as to the other, 

 the shorter end will receive double the weight of the 

 longer. For the same reason, when three horses are 



worked abreast, the two 

 horses placed together 

 should have only half 

 the length of arm of the 

 main whiffle-tree as the 

 single horse, fig. 48. 

 The farmer who has a 

 team of two horses un- 

 like in strength, may 

 thus easily know how to 

 adjust the arms of the 

 whiffle'-tree so as to correspond with the strength of each. 

 If, for instance, one of the horses possesses a strength as 

 much greater than the other as four is to three, then the 

 weaker horse should be attached to the arm of the whiffle- 

 tree made as much longer than the other arm as four is 

 to three. 



In all the preceding estimates, the influence of the 

 weight of the lever has not been taken into consideration. 

 In a lever of the first kind, if the thickness of the two 

 arms be so adjusted that it will remain balanced on the 

 fulcrum, its weight 



Fi"- 49. 



will have no other 

 effect than to in- 

 crease the pressure 

 on the fulcrum ; but 

 if it be of equal 

 size throughout, its longer arm, being the heavier, 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 gravity of this excess. If, for ex- 

 ample, a piece of scantling twelve feet long, a h, fig. 49, 



