ON DRAUGHT. 



549 



Force of Traction required to move the 

 Description of Road. Carriagej independent of the Friction at the Axles. 



Turnpike-road hard, dry, about . . 18 Ibs. 



Ditto dirty .... 



Ditto new gravelled . . 1 



Loose, sandy road . . . . 



So that in the last case, one by no means of rare occurrence in many parts of 

 the country, the portion of draught immediately caused by the state of the 

 road was ten times as great 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 amount 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 plane ; fig. 29, a wheel with a considerable degree of dishing. 



Fig. 28. 



Fig. 29. 



