ON DRAUGHT. 



525 



the exertions of a man and a horse will at once exemplify this, and lead us 

 more clearly to the knowledge of the peculiar qualities or faculties of the horse. 



If a horse be made to carry a heavy weight rapidly up a steep ascent, or if 

 a man be employed to drag slowly a heavy carriage along a rough road, the 

 strength of both will be soon exhausted, and little effect produced ; but if a 

 man be made to carry a weight up a ladder, and if a horse draw a heavy 

 carriage along a road, they will each produce a considerable effect : yet, in the 

 former case, the horse and the man are as strong as in the latter, but their 

 power is not properly applied, and is consequently wasted. 



These different results are easily explained, by considering the mechanical 

 structure of the two bodies, and the mode in which their muscular strength i* 

 exerted. 



The action of pulling is effected in either case by throwing the body forward 

 beyond the feet, which form the fulcrum, and allowing the weight of the body, 

 in its tendency to descend, to act against the resistance applied horizontally, and 

 drag it forward ; as the resistance yields, the feet are carried forward ; and 

 the action renewed, or rather continued. 



Let A (Jig. 1.) be the centre of gravity, or the point in which the whole of 



Fig. I 



Fig. 2 



the weight of the body may be supposed to be accumulated, and B the fulcrum, 

 or point of resistance ; AC the direction of the power to be overcome. 



If the legs are inflexible, the body, acting by its gravity, tends in its descent 

 to describe a circle around the point B, but is opposed by the resistance AC ; 

 and it is demonstrable, by the law of the resolution of forces, that if BD be 

 drawn parallel to AC, the lengths of the lines AD, AB, and DB represent 

 respectively the proportions between the weight of the body, the strain upon 

 the point of support, and the effect produced ; that is, if AD be taken as the 

 measure of the weight of the body, then AB is the measure of the strain upon 

 the legs, and BD or AE the power pulling in the direction of AC. 



Consequently, the effect increases with the weight of the body and the 

 distance which it is thrown beyond the feet, and is limited only by the capa- 

 bility of resistance at B, or the muscular strength of the legs. This is evidently 

 the case in practice ; for even if the body were brought nearly horizontal, when 

 its weight would act to the greatest advantage, still, if the legs are incapable of 

 resisting the strain, they would yield, and no effect be produced. In a man, 

 this muscular strength of the limbs is very great, and he can lift or carry 

 immense weights, and ascend easily, even loaded, a ladder ; but he is not 

 well adapted to the purpose of dragging : as his own weight is small proportion- 

 ably to his strength, and the centre of gravity is low, and by the construction 

 of his body cannot be thrown far beyond the fulcrum at his feet ; consequently, 

 however capable his legs may be of resisting a great strain, AE remains small, 

 and his muscular force is not advantageously brought into action. 



A horse, on the contrary, by the formation of the body, can relieve his 



