Book II. 



PRESERVATION AND REPAIR OF ROADS. 



605 



of the gate-keeper and those passing through. After this light had remained between 

 two and three years, it was taken down, as being too brilliant and as having frightened 

 some horses ; but it might surely have been softened, so as to be retained. Where 

 there are two gates, as in various examples, a lamp post is very properly placed between 

 them, which thus answers all the purposes of the cupola and triple lamp at Edgeware. 



Sect. VI. Preservation and Repair of Roads. 



3727. The preservation of a road depends in a great measure on the description of ma- 

 chines and animals which pass over it, and on keeping it dry and free from dust and mud. 

 The repair of a road should commence immediately after it is finished, and consists in 

 obliterating ruts the moment they appear, filling up any hollows, breaking any loose 

 stones, and correcting any other defect. After cleaning and this sort of repair have gone 

 on hand in hand for a longer or shorter period, according to the nature of the materials 

 and traffic on the road, a thorough repair or surface-renewal, by a coating of metal of 

 three or more inches in thickness over the whole of the road, may be required. 



3728. To preserve a road, by improving the wheel carriages which pass over it, all agree 

 that the wheels should be made broader than they usually are, and cylindrical ; that 

 carts with two horses abreast are less injurious than such as are drawn by two horses in 

 a line ; and that it would be an advantage to have the axletrees of different lengths. 



3729. Edgeu-orth, upon a careful examination, concludes that the system of rolling 

 roads by very broad wheels should be abandoned ; and that such a breadth only should be 

 insisted upon, and such restrictions made as to loading, as will prevent the materials of 

 the road from being ground to powder, or from being cut into ruts. With this view the 

 wheels of carriages of burthen should have felloes six inches broad, and no more than one 

 ton should be carried upon each wheel. 



3730. Farey is of opinion, that six-inch cylindrical wheels, or under, are the most 

 practicable and useful, provided the projecting nails are most rigidly prohibited, which 

 can never be done but by a penalty per nail upon the wheelers who put in those nails, 

 and upon the drivers of the carriages who use such roughly-nailed wheels. 



3731. Telford thinks that no waggon or cart wheel ought to be of less breadth than 

 four inches, and that in general no carriage ought to be allowed to carry more than at 

 the rate of one ton per wheel : " when it exceeds that weight," he says, " the best 

 materials for road-making must be deranged and ground to pieces." 



3732. Paterson is a warm advocate for broad wheels. " If the wheels were used 

 double the breadth that they are at present," he says, " they would act as rollers upon 

 the materials, binding them together ; and consequently the surface would remain always 

 smooth and free from ruts, and the waste or decay would, of course, be exceedingly 

 little." All broad wheels, however, should be constructed differently from those that are in 



563 f"^\ common use (fig. 563. a). Those in common use, 

 whether broad or narrow, are generally dished (as it 

 is called) on the outside, and the ends of the axle- 

 tree bent a little downwards. This causes the 

 wheels to run wider above than below ; and the 

 reason, I believe, for adopting this plan was to 

 allow people to increase the breadth of their car- 

 riages, and yet the wheels to run in the same track. 

 Upon this plan, the edges of the wheel, to run flat 

 upon the road, must be of a conical shape, the outer edge being of a less diameter than 

 the inner one. Any bad effect arising from this is, indeed, very little felt from the 

 narrow wheels ; but as they increase in breadth, the evil increases in the same proportion. 

 " A conical wheel," says Edgeworth, " if moved forwards by the axletree, must partly 

 roll and partly slide on the ground, for the smaller circumference could not advance in 

 one revolution as far as the larger. Suppose," says he, " the larger revolution sixteen 

 feet, and the smaller thirteen feet, the outer part must slide three feet, while the carriage 

 advances sixteen, i. e. it must slide nearly one fifth of the space through which the car- 

 riage advances, — thus, if loaded with ten tons, the horses would have two tons to drag, 

 as if that part of the weight were placed on a sledge." The same thing has been ably 

 and beautifully demonstrated by Gumming (Essay on the Principles of Wheels and Wheel 

 Carriages, &c), and is very easily illustrated : take, for instance, the frvstrum of a cone, 

 or a sugar loaf from which you have broken off a little bit at the point ; then set this a 

 rolling upon a table, and instead of going straight forwards it will describe a circle ; and 

 if you will put a pin or axletree right through the centre of it, and upon that axle cause 

 it to move straight forwards, the smaller diameter must slide instead of rolling. It is 

 evident, therefore, that the rims of the wheels ought to be of a cylindrical form (b). 

 Edgeworth states, in relation to this, that, from the testimony given to the committee 

 of parliament, cylindrical wheels and straight axletrees have been unequivocally pre- 

 ferred by every person of science and judgment. 



