482 ENGINEERING ON THE FARM 



all in a straight line. If the holes for the singletree pins 

 are set some distance back of the draft pin, the rear horse 

 will be pulling more than his share of the load, since the 

 length of the two evener arms will not be balanced when 

 the evener is inclined to the line of draft. The length of the 

 evener arm is the distance, at right angles to the line of draft, 

 from the draft pinhole to the singletree pin. This inequality 

 increases as the draft pinhole increases in distance in front 

 or back of a line connecting the singletree pinholes. Con- 

 sequently, when the holes in the evener are constructed in 

 this manner, the animal that hangs back must do more 

 than his share of the work. This may be demonstrated in 

 a laboratory by a board cut to represent an evener and 

 balanced at the center on a nail, weights being used to repre- 

 sent the pull of the horses. The fact that one horse in the 

 team travels ahead of the other is not an indication that 

 he is doing more than his share of the work. The lead 

 horse may have learned that by keeping in the lead he is 

 doing less work than if he travels abreast of his mate. 



An evener should be selected which has holes as nearly in 

 line as it is practical to place them. By the use of iron 

 plates and rivets to reinforce the wood, it is possible to 

 arrange the holes so near in line that the load will be uniform 

 on each horse, even though one is considerably ahead of 

 the other. The efficiency of the team may be increased 

 considerably if the evener is given proper attention and 

 is so adjusted that each horse is working in accordance 

 with his physical ability. Eveners should be as light as 

 is consistent with strength. Tests made with commercial 

 eveners indicate that wood eveners, properly made, are 

 stronger than metal eveners of the same weight. 



MECHANICAL MOTIVE POWER 



Steam engines. The development of a portable steam 

 engine, followed by the traction engine, made power avail- 

 able for sawing, grinding, threshing, and other stationary 



