534 



ON DRAUGHT. 



be so applied_ as greatly to impede an engine of considerable power, or 

 even to stop it altogether. The power of an engine is limited, and resist- 

 ance must always be proportioned to it ; and there is a proportion beyond 

 which it is useless to go, and less than which would not absorb the whole 

 force. 



An animal is but a beautiful piece of machinery, and although perfect 

 in its construction, and wonderfully accommodating in its movements, it 

 still, like the engine, has a limited poAver, and has its peculiar modes of 

 action, its strong and its feeble parts ; and we must well consider its struc- 

 ture, to be able to apply the resistance in that degree, and in that manner, 

 which shall enable it to produce the greatest effect. The consideration of 

 the comparative effects of 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 

 is 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 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 over- 

 come. 



If the legs are inflexible, the body, acting by its gi^avity, 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 



