150 



ON DRAUGHT. 



The inquiry into the best form and construction of wheel-carria'^os haa 

 taught us what we might have indeed foreseen, that perfection in a road 

 would be a plane, level, hard surface: to have learned this only would not 

 have advanced us much, as such perfection is unattainable; but we have 

 learned also the comparative advantages of these different qualities of 

 hardness, smoothness, and level. We have come to the conclusion that 

 slight alterations of level, which shall vary the exertion required of the 

 animal, without, at any time, causing excessive fatigue, are rather advan- 

 tageous for the full development of his power than otherwise ; that the 

 inconvenience of roughness is obviated by the use of springs, and that 

 even when the ordinary carts and waggons without springs are used, still 

 the resistance arising from mere unevenness of surface, when not exces- 

 sive, is not nearly so great as that which is caused by the yielding of the 

 substance of the road. Hardness, therefore, and consequently the absence 

 of dust and dirt, which is easily crushed or displaced, is the grand deside- 

 ratum in roads. 



To satisfy this condition, however, smoothness is, to a certain degree, 

 requisite, as the prominent parts would be always subject to abrasion and 

 destruction: for the same reason, even if for no other, ruts and every thing 

 which can tend to form them must be avoided. 



A road siiould, in its transverse section, be nearly flat. A great curva 

 ture or barrel, as it is termed, is useless; for the only object can be to 

 drain the water from it: but if there are ruts, or hollow places, no curva- 

 ture will effect this; and if the road is hard and smooth, a very sliglit 

 inclination is sufficient. Indeed, an excess of curvature is not only useless 

 with the present construction of carriages, but facilitates the destruction of 

 the road; for there are few wheels perfectly cylindrical: yet these, when 

 running on a barrelled or curved road, can bear only upon one edge, as in 



jig. 38. The conical wheels 

 still in use, although nmch in- 

 clined at the axle, are never 

 sufficiently so to bring the lower 

 surface of the wheel even hor- 

 izontal, and therefore are con- 

 stantly running upon the edge, 

 as in jig. 39, until they have 

 formed a rut, coinciding with 

 their own shape. In a barelled 

 or curved road, the mischief 

 done will, of course, be great in proportion to this curvature. This form is, 

 therefore, mischievous as well as useless. Six or eight inches' rise in the 

 centre of a road of twenty feet wide is amply sufficient to ensure drainage, 

 if drainage is not effectually prevented by ruts or hollow places, and is a 

 curve to which the position of the wheel may be easily adapted. 



The hardness of the surface, the most important feature, will, of course, 

 principally depend upon the materials used, and the formation of the 

 road, and still more upon the state of repair in which it is kept. It is 

 easy to form a good road when the foundation is already laid by the 

 existence of an old one: levelling the surface, applying a covering of 

 eight or ten inches in thickness of broken stones, having no round or 

 smooth surfaces, the hardest that can be obtained, and securing good 

 drainage at the sides, is all that is required: but constant repair and 

 unremitting attention, however, is necessary to keep a road thus formed 

 in srood condition. 



