184 



ACTION OF A HORSE IN DRAUGHT 



CH. X 



the horizontal force will be equal to about 1 1 1 

 pounds, since the joints about which the body moves 

 may be considered as being about 36 inches from 



Fig. 79. 



the ground, and 36 is to 4 as 1000 is to 1 1 1, so that 

 a moderate inclination is sufficient to produce a con- 

 siderable effect of draught. * 



* This proportion is determined by what is known in mechanics as 



the parallelogram of forces. The weight 

 at I), supported by a rigid strut, DB, will 

 tend to move in a circle of which B is the 

 centre, unless prevented by a resistance 

 acting in the line DC, and its effect will 

 be represented in direction and amount by 

 the lines DB and DC, DA representing the 

 weight. 



The pressure on the ground acting in 

 the direction DB is greater than the weight 

 itself, and it would appear, therefore, that 

 some force is in this way made out of nothing, but it must be remem- 

 bered that mechanical work is the result of pressure multiplied by the 



Fig. 80. 



