64 



THE ANIMAL AS A MACHINE, 



see that the animal could not travel far with any 

 vehicle if he must carry three men on his back in 

 addition to hauling his load." 



Therefore, to deal justly with our horses, we should 

 not only study cause and effect, but should devise some 

 means by which, automatically, every possible advan- 

 tage could be given to the horse at all times. Other- 

 wise there must be a constant waste of energy, tiring 

 the horse prematurely and increasing the chances of 

 his stumbling and falling." 



These principles are thus illustrated by Mr. Brigg : 



In the accompanying figure, let the horse be har- 

 nessed in the usual manner and driven up hill. 



Suppose that the horse is exerting a force of 36 lbs. 

 through AB in a line from the hame to the centre of 

 the wheel. Let AC represent the vertical depression 

 necessary to hold down the shafts. Since AB and AC 

 are the forces necessary to produce motion, by com- 

 pleting the parallelogram ACDB we find that AD 

 represents the resultant of the forces AC and AB. 

 Thus we determine one arm of the lever, GS^ acting 

 against GT, the other arm. GS is a line drawn at right 

 angles from the resolved angle of force AD. 



If the load had been balanced on the axle, then, 

 regardless of the angle of trace or hame-chain, the 

 angle of draught would be through AB to the centre 

 of the wheel. Then a line at right angles with AB to G 

 would have been the short arm of the lever, which would 

 have enabled the horse to have pulled a much greater 

 load than is possible with the longer arm, GS. But, 



* Mr. Brigg had already devised and applied such a system of self- 

 adjustment of the harness as to secure this effect. 



