436 



ON DRAUGHT. 



the country, the portion of drauo^ht immediately caused by the state of the 

 roads was ten times as f^reat as on a good turnpike road, and about fifteen 

 times as great as that which arose from friction at the axles. It would be 

 hopeless to attempt to remedy this by increasing the size of the wheel : the 

 experiment was made with wheels of the ordinary size. To double their 

 diameter would evidently be attended, in practice, with insurmountable 

 difficulties ; and yet, even if this were effected, it would barely reduce the 

 total amonnt of the draught by one-fourth ; but the form of the wheel 

 may materially influence the state of the road, we shall, therefore, proceed 

 to consider the various forms employed. 



Some years ago, when the principal turnpike roads of the kingdom were 

 at many parts, at particular seasons of the year, in little better condition 

 than that on which the last experiment was tried, various attempts were 

 made to reduce the resistance, by using narrow wheels. These attempts, 

 and the laws which it was found necessary to enact to prevent the entire 

 destruction of the roads, led, at last, to curious results, having gradually 

 caused the introduction of the worst-formed wheel which could probably 

 be invented, either as regards increasing the draught or the destruction of 

 the roads. 



To understand these alterations clearly, we must describe the principal 

 features of the wheel now in use. 



The general construction of it presents a striking instance of strength 

 arising from the judicious union of substances of very different qualities — 

 wood and iron. 



A strong circular frame of wood, composed of different segments, called 

 felloes, is bound together by a hoop, or several hoops of iron, called tires, 

 which thus, at the same time that it gives great strength, protects the outer 

 surface from wear. 



The nave, a circular block of wood, is sustained in the centre of this 

 frame by the spokes, which, instead of being in the plane of the felloes, 

 form a cone : this is called the dishing of the wheel. The object of it is to 

 give stiffness, to resist lateral shocks, as when the wheel slips sideways, 

 into a rut or hole. A reference to a comparative view of the wheel, with 

 and without dishing, will more clearly explain our meaning. Fig. 28, is a 

 wheel with the spokes all in one place ; Jig. 29, a wheel with a consider- 

 able degree of dishing. 



Fiff. 28. 



Fig. 29. 



Here it is evident that a small pressure on the nave in fig. 29, would have 

 a tendency to push it through, and would meet with but little resistance. 



