ON DRAUGHT. 563 



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 pair 

 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 de- 

 range 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 in the tract 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 ParUament. 

 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 sis-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 

 origiaal 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 straddlers a httle before they come to a 

 weio-hiuo-- 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 run- 

 ning 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-sisths, of the 

 whole resistance. Narrow wheels, therefore, running in the same track, 

 without doubt offer the least resistance, provided there is surface sufficient 

 to bear the weight, without destruction to the foundation of the road. 



Six inches in breadth of the flat or cyhndrical part, a b, fig. 36, indepen- 

 dent of the rounded edges, will be quite sufficient, in a wheel of ordinary 

 size, to bear a ton without injury to the roads, if in good condition ; and 

 according as the weight upon each wheel is more or less than this, the 

 breadth should be proportionably increased or diminished. 



The most simple innovation upon the original wooden wheel is the cast- 

 iron nave. This we should tliink must be much less liable to wear than 

 the wooden nave, which is hterally honey-combed with the mortices for the 

 spokes ; and a wheel of this sort can be repaired by the most ordinary 

 wheelwright, provided he has one of the castings at hand. 



We should strongly recommend that these naves should be made with a 

 double row of sockets for the spokes, so as to cross the dishing of them in 

 the same manner as those of the H'rought-iron wheels described above; and 



