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MECHANISM OF DRAUGHT. 



Draught in the collar or breast-harness is, as explained by Colin, an act 

 of pushing, and not one of pulling. The only kind of draught I have ever 

 heard of, which could be put under the latter heading, is that of making a 

 horse draw by attaching the weight to his tail, like what farmers in some 

 countries used to do long ago, when they wanted to plough ! 



Propulsion in draught, like in other forms of locomotion, is effected by 

 placing a series of levers, bent on one another, between a fixed point and a 

 movable one. In locomotion of the body itself, the series of levers are those 

 only of the limbs. The movable point, in the hmd limb, is the portion of 

 the pelvis against which the head of the thigh bone rests ; and in the fore 

 extremity, the lower end of the humerus. In harness, on the contrary, 

 the series of levers is that between the spot against which the foot rests and 

 the centre of pressure on the inner surface of the collar, which, in this case, 

 is the movable point. 



In Fig. 42, the line A B represents the direction of the propelling force 

 given by the hind leg which is on the ground ; and E B, that by the fore 

 limb : B being the assumed centre of pressure. The resultant of these two 

 forces must pass somewhere between the points A and E, and through the 

 point B. It is, however, impossible to fix its exact direction ; as we cannot 

 determine the respective amounts of these two forces, and as the proportion 

 they bear to each other continually varies. If two hind feet, as in Fig. 92, 

 were engaged in pushing against the collar at the same time, the direction of 

 their resultant would naturally pass between them and between the two points 

 occupied by the respective centres of pressure on each side of the collar. 

 From a practical point of view, we may assume that this centre of pressure, 

 on each side, is on a level with that portion of the harness to which each 

 respective trace is attached. This would place it somewhere between the 

 middle and lower third of the bearing surface of the collar. 



The force applied to the collar by the animal is obtained in two different 

 ways : first, by the weight of the animal, and second, hj 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. 46), the anterior 

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

 on the ground. It is evident that the further 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 m propulsion. This forward translation of 



