Book II. ROADS OF VARIOUS ENGINEERS- 593 



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 ooze 

 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 whence the 

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



3674. Semi-convex roads are applicable not only to narrow lanes, but to the sides of lulls, 

 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 inconvenience 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 

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

 a relief to the apprehensions of timorous travellers. 



3675. 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 a slope even of two degrees, which is 

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



3676. The degree of convexity preferred by Benjamin and John Farey is one of 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. 



3677. The convexity preferred by Telford is no more than is just sufficient to permit the 

 water to pass from the centre towards the sides of the road ; the declivity may increase 

 towards the sides, and the general section form a very flat ellipsis, so that the side 

 should (upon a road of about thirty feet in width) be nine inches below the surface 

 in the middle. 



3678. The degree of convexity proposed by Clarke, a young Irish road-surveyor, is still 

 less than that of Telford. Were it not absolutely necessary, he says, to let the rain-water 

 run off quickly, the best shape for a road would be a flat surface, and, therefore, the 

 nearer we can approach to that form the better ; for, if the road is much elevated in the 

 centre, wheel carriages will all run in the middle, and, of course, very soon wear that part 

 into deep ruts ; and if they arc then forced to go upon the sides, almost the whole weight 

 will press upon the lower wheel, which will, of course, sink deeper, and occasion a dis- 

 tressing resistance to the shoulder of the horse at that side: therefore, as before observed, 

 the flatter a road can be made, consistently with a moderate fall for the rain-water to 

 escape, the more convenient and durable it will be ; for a road should be as hard and as 

 smooth as possible. An idea of a perfect road may be formed from a frozen canal, where 

 flatness, smoothness, and hardness, are combined : in imitation of such a surface railways 

 were invented, and fully illustrate the principles assumed. Roads cannot be made so as 

 fully to attain those perfections: but we should always have them in our view; for the 

 nearer we approach to such a standard, the less will be the friction, and the greater the 

 facility of draught. On a site of sixty-three feet he forms a metalled road of thirty-four 

 feet, with a rise of nine inches in the middle; a six-feet path at one side; and a ditch and 

 bank at each side, occupying ten feet six inches, (fg. 546.) 



| _ 5<I6 



! ! 



_ _42 



3679. The degree of convexity preferred by Walker is just a sufficient rise towards the 



middle, to incline the water to 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 bv a curve towards the middle. " I have seen," he says, " ridges formed in what I 



. Qq 



