5S2 PRACTICE OF AGRICULTURE. Pai^t III. 



most freely, and with the least exertion of draught, when the load lies evenly upon the 

 wheels on either side. In proportion as the weight is thrown on one side, or the other, 

 the resistance is increased ; especially on a road which is liable to impression. Hence, an 

 inconveniency of a highly convex road in the face of a steep ; and hence the utility of 

 breaks in long ascents. 



3417. It is evident that every jmrt of a road should he equally and duly convex ; should 

 be equally safe and easy for carriages of every description, otherwise it becomes more 

 partially worn ; the more level parts only are used, the steeper being in a degree useless. 

 Hence, a road of even and due convexity is not only easy and safe, but may be formed 

 of a narrower width, than one whose steep sides are neither easy nor safe to be travelled, 

 and whose crown only is in use. On measuring different passages of roads which ap- 

 peared to lie in the most desirable form. Marshal found that their convexity, or the 

 elevation of the crown or middle of the road above the base line, in roads of twenty feet 

 in width, was about ten inches ; namely, one inch in every foot on either side. And he 

 is of opinion that this result may be taken as a general guide in forming roads, this 

 middle degree of convexity being liable to be altered, according to the width of the road, 

 the nature of the materials, and the other circumstances. 



3418. A whole barrel or convex road cannot easily be kept up in a narrow site, as in 

 the case of narrow lanes. If raised, it presently wears into a middle track and two 

 wheel-ruts, with foul drains on either side of them, and becomes, in wet weather, a dirty 

 trough, which is unfit for either carriages or horses, and in which a foot passenger has 

 not where to set his foot. But if such a lane be thrown into a shelving form, resembling 

 half a barrelled or convex road, a greater width of travelable road for carriages and 

 horses will be obtained ; ruts will not be so liable to be formed ; the whole of the water 

 of rains will be thrown to one side, while the other will afford a comfortable walking 

 path, at all seasons. It is to be remarked, that when water in a wet season is apt to ocze 

 out of the banks on the upper side of the lane, a narrow channel is to be cut, to prevent 

 its overflowing the road ; or, in forming the bed of the road, the inclination may in 

 some cases be reversed, so as to throw the drain on that side of the lane from whence the 

 spring water issues : thus the same drain will serve for the spring and the rain-waters. 



3419. Semi-convex roads are applicable not only to narrow lanes, but to the sides of hills, 

 where the road, as it generally ought, is conducted sidelong (not directly) up the slope. 

 By this form of the road, the whole of the water which falls upon it will be got rid of 

 without inconveniency or expense. And the bed of the road for this purpose may be 

 made narrower than for a full convex road, a circumstance which in some cases may be- 

 come a saving'of much expense. The upper side of a road in this form being nearly 

 level, and firm to the foot of the steep, would be chosen by ascending carriages, while the 

 lower side would acquire a looseness of surface, and be used by laden carriages going 

 downward ; and while a raised footpath on the lower margin would be a secure guard, 

 and a relief to the apprehensions of timorous travellers. 



3420. The convexity of a road, according to Edgeworth, need be no more than what will 

 .prevent it from being worn hollow, before it can be conveniently repaired ; and he very 

 judiciously assigns as a reason, that no lateral inclination of the ground, consistent with 

 the safety of carriages, would empty a rut of three inches deep. So far from this being 

 the case, whoever attends to the fact will find, that even down a moderate slope, where 

 any dirt remains upon the road, the water will be obstructed. Even if there are no ruts 

 on a road, the mud and sludge will not run down aslope even of two degrees, which is 

 the utmost inclination that should be permitted on a mail coach road. 



3421. The degree of convexity prefe^rred by Benjamin and John Farey, is twelve inches 

 in a road fifty-five feet wide ; but to attain this shape when the road is worn down in first 

 forming, there should be a rise in the centre of sixteen or eighteen inches. 



3422. The degree of convexity preferred by Walker is just a sufficient rise towards the 

 middle, to incline the water towards the sides ; and in place of making the whole width 

 the section of one curve, to form it by two straight lines, forming inclined planes, and 

 joined by a curve towards the middle. I have seen, he says, " ridges formed in what I 

 thought well- farmed land, much after what I would recommend for the form of a road. 

 The object of forming the land into ridges, raised a little in the middle, is the same as 

 that of raising the middle of a road to prevent the water from settling upon it ; and what 

 is sufficient for the ploughed land, is certainly enough for a road. If the road is of good 

 stone, four to five inches rise in ten feet is sufficient; gravel and other inferior material, 

 will allow a little more. This shape not only assists the water to pass from the centre 

 towards the sides, but greatly contributes to the drying of the road, by allowing the action 

 of the sun and air to produce a great degree of evaporation. Surveyors ought to use a 

 level in giving roads a proper shape, in order that the surface may be of one uniform cur- 

 vature, without the smallest deviation, in any one spot, from the prescribed line of the 

 cross section." 



