PRINCIPLES OF DRAUGHT. 117 



SECTION IV. 



PRINCIPLES OF DRAUGHT. 



An examination of the nature or laws of friction en- 

 ables us to ascertain the best line of draught for teams 

 when attached to wagons and carriages. If there were 

 no friction whatever upon the road, the best direction 

 for the traces would be parallel to the road, that is, on a 

 level with the wagon ; but as there is always some fric- 

 tion, the line of draught should be a Uttle rising, so as 

 to tend to lessen the pressure of the wheels on the road. 

 Now this upward direction of the draught should al- 

 ways he exactly of such a slope, that if the same slope 

 were given to the road, the wagon would just descend 

 by its iveight. The more rough or muddy the road is, 

 the steeper should be this line of draught or direction 

 of the traces.* On a good common road it would be 

 much less, and on a plank road but slightly varied 

 from a hori2ontal direction. On a rail-road the line 

 should be about level. On good sleighing, some of the 

 strength of the team is commonly lost by too steep a 

 Une of draught. 



The reason of this rule may be understood by the 

 following explanation: Let the ob- 

 struction, a, in the annexed figure 

 {Fig. 91), represent the friction the 

 wheel constantly meets with in roll- 

 ing over a common road. To over- 

 come this friction, the wheel must 



* Provided the wheels are not made smaller for this purpose, in- 

 creasing their resistance. 



