l66 DRAUGHT CH. X 



and at much higher speeds than coaches attain, as 

 on railroads, it varies as follows : — * 



At 5, 10, 15, 20, 30, 40, 50, 60 miles per hour. 

 9. 15 ; 9.6 ; 10. 5 ; 1 1.4 ; 14.6 ; 19.0 ; 24.0 ; 31.5 pds per long ton. 



On hard roads that are rough, the draught in- 

 creases rapidly with the speed, owing to the shocks 

 which absorb part of the power, and on such roads 

 suspension on springs diminishes the draught, at 

 high speeds, by diminishing the shocks. 



Well-laid, firm, stone pavements give from one- 

 half to two-thirds the resistance to rolling that is 

 given by good, broken-stone roads. This difference 

 seems, at first sight, to be too great ; but all the 

 experiments give substantially the same result, and 

 show that a solid, unyielding road is better than an 

 elastic one with ever so smooth a surface ; this is 

 confirmed by the experience of old coaching men, 

 who consider what they call the soundness of a road 

 its most important quality. 



On a smooth surface, with a well-made vehicle, 

 there is no indication that the distance between the 

 axles in any way affects the draught. 



It is a general opinion, however, that placing 

 the axles close together, or making a coach ' short- 

 coupled,' as it is called, makes it run easier. 



No doubt a very long-coupled carriage, like a 



* When it is said that the draught increases with the speed in a 

 certain degree, only the statical draught as indicated by a dyna- 

 mometer, is meant. The amount of actual work expended is repre- 

 sented by this quantity combined with the distance passed over. 



