450 



ON DRAUGHT. 



^ The inquiry into the best form and construction of wheel carriages has 

 taught us what we might indeed have 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 

 shght 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 developement of his power than otherwise ; that the 

 inconvenience of roughness is obviated ])y 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 

 excessive, 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 

 desideratum in roads. 



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

 requisite, as the ])rominent 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 should, in its transverse section, be uearly 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 cur- 

 vature will effect this ; and if the road is hard and smooth, a very slight 

 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^g-. 38. The conical 

 wheels still in use, although 

 much inclined at the axle, 

 are never sufHciently so to 

 bring the lower surface of 

 the wheel even horizontal, 

 and therefore are constantly 

 running upon the edge, as 

 in Jig. 39, until they have 

 formed a rut, coinciding 

 with their own shape. Iw a 

 barrelled or curved road, the 

 mischief done will, of course, 

 be great in proportion to this curvature. This form is, therefore, mis- 

 chievous 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 featm-e, 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 is necessary to keep a road thus formed in good 

 condition. 



