74 MECHANISM OF DRA UCHT. 



in the body, as compared to his height ; that he should be lower over the 

 croup than he is at the withers ; and that he should not have a horizontal 

 croup. We should not, however, desire his hind quarters to be so drooping 

 as to cause him to be actually " goose-rumped " {see p. 233). 



The ajnount of forward propulsion given by the fore limb varies according 

 to the position of the humerus ; for the more horizontal is this bone, the 

 more effective will be the push. As its degree of slope with the ground is 

 directly affected by that of the shoulder blade, it follows that the shoulders of 

 the cart-horse which has to fully exert the powers of his fore legs in propulsion, 

 should be more upright than sloping. 



It is a well-known mathematical fact that the most advantageous direction 

 for the pull in draught to be, is one which makes an angle with the ground 

 equal to the angle of friction. I may explain that if, for instance, 10° was the 

 greatest slope of ground upon which a body could rest without sliding down, 

 its angle of friction would be equal to 10°. The best direction then of the 

 traces would be at an angle to the ground equal to the angle of friction. In 

 many cases the pull of the traces is not at a sufficient angle to the ground, and 

 the work is consequently performed at a mechanical disadvantage, which might 

 be remedied by the employment of a taller horse than the one used, by having 

 smaller wheels, or by a change in the harnessing anangement. For instance, 

 in such a case, instead of attaching the traces to the hooks on the shafts of a 

 dog-cart, they might be connected, as is sometimes done, to the axletree. 

 In the Indian ccka {see PL 8), the slope of the shafts, which act as traces, 

 appears to have been made with due regard to the angle of friction of this 

 cart with the g;round. 



