ANIMAL MECHANICS. 



451 



Mr. J evons Experiments (lifting Weights with Pulley). 



"Weight 

 lifted. 



No. of 



times 

 lifted. 



Useful 

 "Work. 



56 lbs. 



5-7 



319.2 



42 „ 



11. 9 



499.8 



28 „ 



23.0 



644.O 



21 „ 



37-6 



789.6 



H >, 



III.O 



I554.0 



From the manner in which these experiments were made, 

 it is easy to see that the weight of the arm does not enter 

 into the result. Let 



w = weight raised ; 



n = number of times it is raised, carried to point of 



fatigue of muscles ; 

 h = height through which weight is raised ; 

 t = time occupied by a single lift. 



Hence we have 



Total work done = whn 9 

 wh 

 T' 



Rate of work 



The rate of work is found by dividing the work done in a 

 given time by the time itself. Hence we find by the Law of 

 Fatigue 



w 2 h 2 n 



— — = constant ; 

 or, since h and t are constant, 



w 2 n = A. ' 



(■23) 



(124) 



If we write 



? = w, 

 v - n i 

 2 g2 



