76 MECHANISM OF DRAUGHT. 



different ways : first, by the weight of the animal, and second, by the 

 force of propulsion to which I have just alluded. 



The weight of the animal acts on the collar by reason of the centre of 

 gravity being placed in front of the base of support (p. 60), the anterior 

 limit of which is marked by the position of the toe of the fore foot that 

 is on the ground. It is evident that the farther a perpendicular dropped 

 from the centre of gravity falls in front of the base of support, the more 

 effectively will the weight of the body act in propulsion. This forward 

 translation of the centre of gravity with reference to the position of the 

 base of support, is influenced, first, by the degree of slope which the fore 

 leg makes with the ground immediately before it quits it, and before the 

 other fore leg is brought down ; and second, by the lowering of the head 

 and neck. It is manifest that horses with toe-pieces to their fore-shoes 

 can, while retaining their foothold, bring the centre of gravity farther 

 beyond the base of support, by the slope of the fore leg which rests on 

 the ground, than they could do with fiat shoes ; supposing, of course, that 

 the surface of the ground was not abnormally smooth and hard, like 

 wood or asphalte. From the foregoing considerations, and from argu- 

 ments which will be submitted further on, we may draw the following 

 deductions with respect to cart-horses that are required to exert their 

 strength to the utmost. 



I. Bodily weight, especially in the fore-hand, is an advantage in 

 draught ; for the greater it is, the more effective will be the push against 

 the collar caused by the centre of gravity falling beyond the base of 

 support. Agreeably to this fact, the experienced driver of a heavily- 

 laden two-wheeled cart will endeavour to place a fair share of the burden 

 on the animal's back, so that the horse may pull to the best advantage. 

 The experiment of a man winning a single-handed " tug of war," against 

 a stronger man than himself, by carrying another man on his back, 

 is also an instance of this principle. The gain in power from increased 

 weight on the fore-hand is well illustrated by the practice, which I 

 have seen, of the driver of a one-horse cart mounting his animal and 

 getting well forward on its back, when he finds that it is unable to 

 pull its load up a hill. 



Bodily weight is of special use in draught on slippery roads, such as 

 those of wood pavement and asphalte ; because, in such a case, the 

 security of the foothold of a heavy horse would not be so much en- 

 dangered as that of a lighter, though equally strong, animal. Also, 

 the employment of bodily weight on a smooth and level road, would 

 entail less strain and fatigue, than that of muscular propulsion. Hence, 

 improvements in roads have been accompanied by increase in the weight 

 of cart-horses. The question as to the relative proportions of the 

 weight and strength of these animals cannot be decided with accuracy 

 owing to the infinite variety of conditions which would have to be con- 



