Mechanical Conditions of the Plow. 



195 



figure at f g, are to be understood as extending forward to the 

 shoulders of the horses. Between the evener and the whiffle 

 trees the compensating apparatus is placed, as seen in the figure, 

 consisting of three levers, usually constructed of iron. Two of 

 these, h i and h 2', are levers of the first order, but with unequal 

 arms; the fulcrum, ^, being fixed at one-third of the entire length 



Fiff. JOS. 



from the outward end of each. The arms of these levers are, 

 therefore, in the proportion of two to one, and the entire length 

 of each between the points of attachment is twenty-seven inches. 

 A connecting lever, I, of equal arms, and twenty inches in length, 

 is jointed to the longer arms, ii^ of the former, by means of the 

 d()ul)le short links, m n. The two levers, li i, h i, are hooked by 

 means of their shackles at k to the evener, b. From the mechan- 

 ical arrangement of these levers, if the whole resistance at a be 

 taken at 600 pounds, k and h will each require an exertion of 300 

 pounds to overcome the resistance. But these two forces fall to 

 be subdivided in the proportion of the arms of the levers h i; 

 two-thirds of each, or 200 pounds, being allotted to the arms, h, 

 and the remaining one-third, 100 pounds, to the arms, 2, which 

 brings the system to an equilibrium. The two forces, i 2, being 

 conjoined by means of the connecting levers m n, their union 

 produces a force of 200 pounds, thus equalizing the three ultimate 

 forces, h I h, to 200 pounds each, and these three combined are 

 equal to the whole resistance, a; and the three horses that are 

 yoked to the whiffle trees, c d e, are subjected to equal exertion, 



