ON DRAUGHT. 553 



more nearly to the true cylinder, in proportion as the roads 

 approach nearer to perfection in point of hardness and flat- 

 ness. When the roads are good, a very little dishing will be 

 sufficient, and a slight inclination of the wheel from the vertical 

 will make it correspond with the barrel or curve of the road, 

 which is now generally very trifling. 



Next to the form, the breadth of the wheel is the point requir- 

 ing most consideration : it is one, however, which depends entirely 

 upon the state of the road. 



We have seen, that the displacement or crushing of the materials 

 forming the upper surface of the road is one of the principal causes 

 of resistance. If the whole mass of the road were formed of a 

 yielding substance, into which the wheel would sink to a depth 

 exactly proportionate to the weight bearing upon it, it is probable 

 that great breadth would be advantageous, so that the wheel 

 might form a roller, tending to consolidate the materials rather than cause any 

 permanent displacement ; but, in the improved state of modern roads, it may 

 safely be considered that such is never the case. 



A road, as we have before stated, always consists of a hard bottom, covered 

 with a stratum, more or less thick, of soft, yielding material. A wheel, even 

 moderately loaded, will force its way through, and form a rut in this upper 

 coating. The resistance will be nearly proportionate to the breadth of this rut ; 

 the depth of it will not increase in the ratio of the pressure. In considering, 

 then, simply, the case of a single wheel or a pah" of wheels forming two distinct 

 ruts, it is evident that it should form as narrow a rut as possible, but that it 

 should not in any degree crush or derange the core or hard basis of the road. 

 When a rut is thus formed, a small track or portion of the road is for a time 

 rendered clean and hard, and consequently capable of bearing a greater load than 

 before, and with less injury. It is, then, highly important in a four-wheel 

 carriage that the hind wheels should follow exactly hi the track of the front 

 wheels. If rollers were necessary for the road, as if, for instance, it was merely 

 a bed of clay, then indeed, but only in such a case, might it be judicious to cause 

 the wheels to run in different tracks, as has been proposed, and was at one time 

 carried into effect under the encouragement of an act of Parliament. Such 

 wheels were called straddlers : they might have been necessary tools for the 

 preservation of such roads as then existed, but the increased draught soon taught 

 the public to evade the law which encouraged them. 



Mr. Deacon, one of the principal carriers in England, in an excellent practical 

 work on wheel-carriages, published in 1810, describing these wheels, says, " If 

 the axle of a six-inch wheel is of that length to cause the hind wheels to make 

 tracks five inches outside the tracks of the fore-wheels, and nine-inch wheels 

 seven inches outside, they are then called straddlers, and are allowed to carry a 

 greater weight than if not so. The original intent of these was most excellent ; 

 but the effect has been defeated by the carrier or other person not only making 

 the bed or axle contrary to what was intended, but also by carrying with them 

 a false collar, with a joint therein, to put on and take off at pleasure ; so that 

 they have no great difficulty in making the wheels fctraddlers a little before they 

 come to a weighing-machine, and making them not so when they have passed 

 the same." 



On modern roads such an arrangement would hardly be beneficial, even to 

 the road itself, and would nearly double the amount of draught. 



Too great care and precaution cannot be taken to insure the wheels running 

 in the same track. Let it be remembered that, on a good road, the forming the 

 rut is the cause of three-fourths, and oftener five -sixths, of the whole resistance. 



