242 DRAUGHT AND HAEXESS. 



or point of traction, the trace itself being also hori- 

 zontal. This principle, although mathematically cor- 

 rect, requires certain limitations in practice, some of 

 which have been already alluded to. Let us now take 

 a horse of sixteen hands high ; the point of attachment 

 of the trace to the hames could with this sized animal 

 be scarcely brought nearer to the ground than 44 inches, 

 and with a horizontal trace this Avould involve a fore- 

 wheel of 7 feet 4 inches in diameter, something quite 

 out of the question for carriages, the highest wheel 

 used for field-guns being 5 feet in diameter. It is, 

 therefore, quite impossible to carry out this principle 

 to its fullest extent even with the horizontal trace, 

 which we will admit to be the most favourable for 

 traction on a perfect level and smooth surface, and 'put- 

 ting this slanting direction of the horses shoulder for 

 the present out of the question. 



But we have already pointed out that when the car- 

 riage leaves the level and gets on to an inclined plane, 

 the horizontal trace becomes parallel to the road, and 

 is no longer at right angles with the perpendicular pass- 

 ing through the nave of the wheel, and we shall now 

 proceed to show what happens when the wheel meets 

 an obstacle such as a stone, or gets into a rut, the road 

 being otherwise level. Fig. 22 shows two circles, a 

 smaller and a greater one, representing two wheels of 

 unequal size touching the ground at the point A, and 

 each just in contact with two obstacles N is' of precisely 

 equal height. In order to enable each wheel to sur- 

 mount the obstacle before it, a certain amount of power 

 must be applied to the axles and 0', and this will 

 act respectively onHhe bent levers M A' and 0' M' A', 

 and in both cases will be most advantageously applied 



