ON THE RESISTANCE OF ROAD VEHICLES TO TRACTION. 



329 



He then goes on to consider the uniformity of draught, deducing a 

 formula 



P = W cos a (tan R + tan A — ) + W sin a 



2r 



for the draught upon an acclivity in -which a is the angle of ascent and R 

 the angle of friction of rolling corresponding to any description of surface. 

 Comparing this last equation -with that for the draught upon a level 

 road — 



P = W (tan R + tan A ~) nearly— 



he concludes by drawing up the following table of uniform draught : — 



Table of Unifonn Dratight. 



Description of Surface 



Kate of Inclination 



Ordinary broken stone surface 

 Cloiie firm stone paving 



„ timber paving 



,, ,, trackway 



,, cut stone trackway . 



„ iron tramway 



„ „ railway 



Level 

 1 in 48iL 

 1 in 4l| 

 1 in 31^ 

 1 in3li 

 1 in 29i 

 1 in 28i 



VII. The Work of M. Charic-Marsaines. 



M. Charic-Marsaines, inspector of roads and bridges, being struck by 

 the instinctive preference of the farmers in the department Du Nord for 

 paved road, undertook a series of experiments in order to compare paved 

 and macadam roads, as to durability, cost of maintenance, and the maxi- 

 mum load capable of being supported. 



Below are the results of his experiments : — 



The results of Charie-Marsaines' researches are as follows : — ■ 



(i.) The wear on the harness is less on paved than on. macadam roads. 



(ii.) The wear and tear on the vehicles is greater. 



(iii.) The lasting power of the horse is much less on macadam roads. 

 A harness lasts six years on paved roads and five on macadam. A vehicle 

 lasts seven years on paved roads and nine on macadam. 



These results difiier very little from those given by Schwilgue in his 

 experiments performed in 1832 on the roads between Paris and Havre. 



