ON DRAUGHT. 



571 



but renio\dng at once the prime source of this evil, improving the roads, 

 can remedy this. We are thus naturally led to the third division of our 

 subject, viz. the road, or channel of conveyance. In considering this as a 

 branch'of the subject of draught by animal power, we shall merely point 

 out what are the principal desiderata in the formation of a good road, and 

 what are the evils principally to be avoided. To enter into all the details 

 of their construction, dependent as it is on the different materials to be 

 found in the neighbourhood, their comparative cost, the quality of the 

 ground over which the road is made, and many other points, would be to 

 enter upon a much more extensive field than is at all requii-ed for the 

 proper consideration of the subject of di^aught by animal power. The 

 requisites for a good road are all that we shall indicate. 



Channel of conveyance, in a general point of view, Avould include canals, 

 roads, and railways. Of the first, however, we shall say little ; their 

 construction does not materially affect the amount of draught, and we 

 have already examined the mode of applying the power, and the quantity of 

 effect produced. We shall proceed therefore at once to the question of roads. 



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 plain, 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 excessive, 

 is not nearly so great as that which is caused by the yielding of the sub- 

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

 chist and dirt, which is easily crushed or displaced, is the great desideratum 



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 everything 

 which can tend to form them must be avoided. 



A road should, in its transverse section, be nearly flat. A great cur- 

 vature 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 prac- 

 ticable curvature will effect this ; and if the road is hard and smooth, a 

 very shght 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 fig. 38. The conical 

 wheels still in use, although 

 much inclined at the axle, are 

 never sufficiently so to bring 

 the lower surface of the wheel 

 even, horizontal, and therefore 

 are constantly running upon the 

 edge, as in fig. 39, until they 

 have formed a rut coinciding 

 vvdth their own shape. In a 

 barrelled or curved road, the 



Fig. 38. 



Fig. 39. 



