( 71 ) 



CHAPTER IX. 



MFXHANISM OF DRAUGHT. 



Draught in the collar or breast-harness is, as explained by M. 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 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. 2)Zi 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. But it is impossible to fix its exact direction ; as we cannot deter- 

 mine 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. 70, 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. 



