440 



Farm Mechanics. 



541. Direction of the Line of Draft. In drawing a load 

 over a plane surface which remains unchanged during the 

 movement the least draft is required \\hen the line of draft 

 is maintained parallel with the road as shown at A. B., 

 Fig. 212, where the apparatus may be used to clearly dem- 

 onstrate this principle. It will be seen that as the spring 

 balance is moved up upon its arc the line of draft is such 

 that it tends partly to lift the load off the road and so 

 much that if it were pnrhcd around until the direction 



FIG. 212. Apparatus for demonstrating the influence of the direciiuu ui 

 "the line of draft on the draft of wnjrons. 



became vertical the whole weight of the load would come 

 upon the spring balance. Then, too, if the line of draft 

 is carried below a parallel to the road-bed the draft must 

 increase because then it is partly downward upon the bed, 

 tending to practically increase the weight of the load by 

 the lost portion of the force of traction, for it is clear that 

 were the scales carried downward until the draft became 

 vertical to the road the whole effect would be lost in pro- 

 ducing pressure. 



In the movement of cars by the locomotive ovQr the 



