754 T^^^^ Journal of Forestry. 



Wherever this is possible the gradient of a road should not exceed 

 1 in 40. As tlie gradient increases, the cost of maintenance also 

 becomes greater. The brakes, slides, or skidpans put on in descending 

 slopes cause great abrasion of the surface ; and the efforts of the horses 

 to obtain a firm footing where the ascent is steep cause a considerable 

 excavation of the surface at every step. 



Experiments by Mr. Mitchell show that wlien a cubic yard of stone 

 is broken into road-metal of about Sy inches, and laid on to a thickness 

 of six inches, it contains about 11 cubic feet of interspaces. And as a 

 well rolled road-covering contains only from 20 to 30 per cent, of such 

 interspace, and must therefore consist of from 70 to 80 per cent, of 

 solid stone, the great advantage of the latter in point of solidity is at 

 once apparent. The diminution of bulk by efficient steam-rolli g 

 reduces the interspaces one-half. 



Moderately wide roads are much more durable than very narrow 

 ones, where every vehicle has to follow in the same track ; and as their 

 surface is so much drier the draught upon them is proportionally 

 decreased. In our northern latitudes it is very essential to have the 

 hedge on the south side of the road as low as possible, in order to 

 insure the full benefit of the sun's rays. 



A series of experiments by JNI. Dupuit, upon macadamized roads 

 only, enabled him to arrive at the following conclusions : — 



1. The resistance to traction is directly proportioned to the load. 



2. It is independent of the width of tyre. 



8. It is inversely to the square root of the diameter of the wheel. 



4. It is independent of the speed. 



Experiments made in the north of France, where powerful Flemish 

 horses are used, show that the average daily work of such horses is to 

 draw 25 tons over one mile of macadamized road. At the same time it 

 was proved that the work performed per hour in winter upon paved 

 roads was greater than that done in summer upon the macadamized. 

 Statistics collected at the same time proved that horses in regular work 

 lasted a much shorter time upon the macadamized roads than upon the 

 pavement. Waggons wore out in the proportion of 7 years to 9, and 

 harness as 5 to C years. 



Trivial as these details may appear, when we consider the total 

 amount of money invested in horses, harness, and carriages of various 

 kinds throughout the country, the subject of road-making, and the 

 importance of securing the smallest possible amount of wear and tear, 

 demand greater attention than has hitherto been bestowed upon them. 



In country places no available data are at hand, upon which to base 

 reliable calculations. But it has been computed that within a circle 

 of 4^ miles from Charing-cross about £4,000,000 sterling is invested 

 in horses, carriages of all kinds, and harness. This estimate does 



