Animals as Motors. 489 



the strength of the triceps muscle is measured in a similar 

 way it is found to be able to exert a pull of 25 to 30 

 pounds; and as the lengths of the lever arms in this case 

 are in the ratio of 1 to 20 or 1 to 24 the power of the mus- 

 cle must equal 500 to 600 pounds. 



< 

 FIG. 234. Showing the mechanical action of. muscles. 



It is clear from these measurements that the power of 

 the larger muscles in a horse must be very great indeed. 



608. Need of Great Muscular Strength. It is because the 

 rate at which muscles are able to change their length is 

 relatively quite slow and because they are only able to con- 

 tract through short distances, that it is necessary to have 

 them act upon the short ends of levers in order to secure 

 the rapid movements through long distances which ani- 

 mals are obliged to make. The horse as an engine consists 

 of a large number of very powerful motors acting through 

 a system of levers. 



609. Rate at Which a Horse Can Generate Energy. It is 

 recorded in (532) that about the maximum walking draft 

 of a horse is one-half his own weight; pulling with this in- 

 tensity and traveling at the rate of 2.5 miles per hour the 

 ability of a 1,600-pound horse would be 



2.5X 5280 X 800 

 60 X 60 X 550 = 5 i horse power. 



