75 



CHAPTER IX. 



MECHANISM OF DRAUGHT. 



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

 of pushing, and not 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 the locomotion of the body, the series of levers 

 are those only of the limbs. The movable point, in the hind 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. 49, the line A B represents the direction of the propelhng 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. 127, 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 



