TIIK IlAMA MAN o\ I III. I \KM. 



837 



The force pxerted by the horse in traction consists of pushing. The term 

 " pulling," although customary, is incorrect, inasmuch a^ ;i hor9e can only 

 pull when he is attached to a load by the tail. The force is obtained b\ 

 the propulsion <>f his own weight, the forward movement being due to 

 the contraction or expansion of the muscles attached to the various bones. 

 These bones form a system of levers, acted upon by the muscles. Propulsion 

 can only take place when one extremity of the lever is fixed while the other 

 is movable. This is tie' case with the horse. The fixed point is the foot, 

 which is against the ground, while the movable point is the surface of the 

 shoulder carrying the collar, [n practice it is found that this force can be 

 • xerted most efficiently when the traces are attached to the liames just above 

 the point of the shoulder (Fig. 1), provided, of course, that the proper line 

 of draught between this point and the load is maintained. 



The weight of the horse, which is very important when considering his 

 power, becomes effective only when the body is thrown forward beyond the 

 centre of gravity. In the horse this lies about the seventh rib, in the middle 

 of the girth. It is evident that the heavier the shoulders, neck, and head of 

 the horse, the greater is the force which he can exert. 



This is appreciated and taken advantage of by draymen,' who load their 

 drays " heavy on " — that is, in such a way that a portion of the weight is 

 thrown on to the horse's back. This increases the weight which can be 

 thrown into the collar ; but in loading in this way, care must be taken that 

 the horse is not overweighted. A considerable strain is thrown upon the 

 front feet, which rapidly causes fatigue, and may lead to injury. The weight 

 thrown on to the horse should not be more than can be fairly comfortably 

 lifted by raising the point of the shafts. 



In light vehicles no weight should be thrown on to the back, especially on 

 slippery roads, as the horse is more likely to stumble. 



The weight can only be exerted efficiently against the collar when the line 

 of draught is riant. The feet act as a fulcrum, and the system of bones, 

 embracing the legs, haunch, spinal 

 column, &c, acts as the lever. The 

 weight is most effective when it acts 

 downwards on this lever against the 

 fulcrum. If the horse were attached 

 to the load in such a manner that 

 the line of draught lay above his 

 back, the effect would be to lift him 

 from his feet, and consequently 

 render Ids weight ineffective. This 

 occurs when a dray is loaded so 

 " light on " that the shafts are lifted, 

 and are only prevented from l-ising 

 into the air by the belly-band. 

 This takes a part of the horse's 

 ■weight off the fulcrum (the feet), and renders it useless. 



By lowering the line of draught to the horizontal, greater effectiveness 

 ■would be secured, but the horse would still be unable to exert his full 

 power. 



The actual efficient angle of the correct line of draught varies according 

 to the height of the horse, and also his length, but generally it should form 

 an angle of about 20 desfrees with a horizontal line taken through the 



Fig. 4. — An incorrect method of attaching leading 

 chains to those of the rear horse. 



