Draft of Wagons. 441 



smooth unyielding bed of the steel rail the line of draft 

 is always parallel with the rail. 



542. Line of Draft on Eoad Wagon. The statements of 

 the last paragraph may appear to be contradicted by the 

 general practice of having the traces nearly always slope 

 decidedly backward and downward. The former state- 

 ments, however, are not incorrect, neither is the common 

 practice fundamentally wrong. The apparent contradic- 

 tion grows out of the fact that the road is seldom either 

 smooth or rigid so that the wheels on the average are in 

 effect continually rolling up an inclined plane. 



The principle is clearly shown in Fig. 213 where the 

 wheel is rising over the obstruction which in effect makes 



Km. 213. Apparatus for demonstrating the influence, upon the draft, of 

 the direction of the line of the draft of a wagon when the wheels are 

 passing over an obstruction or cutting into the road or ground. 



an inclined road upon the general road-bed. If now 

 the draft required to bring this load upon the obstruc- 

 tion is measured when the line of draft is parallel with 

 the general road-bed and then the line of draft is made 

 more and more slanting until the direction finally be- 

 comes parallel with the secondary road made by the ob- 



