THE HORSE AS A MOTOR 



Practically, we are concerned with the recovery in the 

 shape of useful work of the largest possible percentage 

 of heat units supplied to any motor, and on this basis, 

 at least, the horse and the machine may be brought into 

 direct comparison. 



THE MECHANISM OF THE HORSE 



The animal mechanism is composed of (1) bones, which 

 constitute a connected system of levers, with automatically 

 lubricated joints; (2) muscles attached in pairs to these levers 

 so as to resemble a series of independent motors capable of 

 producing an alternating or reciprocating movement, like that 

 of an engine piston; (3) organs of digestion, respiration and 

 excretion for supply ing fuel and removing waste, perhaps analo- 

 gous to the automatic mechanical stoker and 

 ash conveyor; (4) a brain and nervous system 

 for regulating the action of the muscle motors, 

 much as a battleship is governed by electric signals 

 to and from the conning-tower; (5) a covering 

 of skin and hair, like a dust-proof crank case, 

 protecting all working parts from outside in- 

 fluences, and conserving and radiating heat. 



The muscles, with which we are most con- 

 cerned, are made up of bundles of fibers. Un- 

 der the stimulus that come from the nervous 

 system, these fibers have the power of contracting, 

 but only through a short distance. For this rea- 

 son they must work on the short ends of the bony 

 levers in order to move them rapidly through 

 space. In the human biceps, as measured by 

 Professor King, the ratio of the long and short Muscling of a 

 lever arms is as great as 6 to 1, hence to lift a 

 weight of 50 pounds the muscle must exert a pull of 300 pounds 

 on the shot end of the lever. Unlike the human body, 

 which is best adapted to lifting and carrying weights, the 



