450 



ANIMAL MECHANICS. 



From the preceding data, we may calculate the maximum 

 velocity which the muscles employed as in the experiments 

 are capable of giving to the hand. For, since the work done 

 on the arm is a maximum when iv = o, we find from equa- 

 tion (115) the maximum range of an infinitely small weight 



, m P- 11 s -? = 29 | feet 

 ? 39 



Now, it is well known that the velocity of projection 

 corresponding to the maximum range on a horizontal plane is 



V= Vgi, (122) 



from which we find 



V = 30.9 feet per second, 



showing that the muscles in question can produce on the hand 

 a velocity nearly equal to that of a body which has fallen for 

 one second. 



Law III. The Law of Fatigue. — The third Law of Mus- 

 cular Action states that the total work done multiplied by the 

 rate of work is constant ; — and as soon as this product attains its 

 constant value, fatigue sets in, and the muscles become in- 

 capable of giving out more work, until they have been allowed 

 to rest. Hence, the Third Law may be appropriately termed 

 the Laiv of Fatigue. 



First Illustration of Law of Fatigue. — I shall take my first 

 proof of this Law from Mr. Jevons' experiments.* Mr. Je- 

 vons raised and lowered various weights by a pulley and cord 

 through the convenient range of the arm, continuing the 

 motion with unrelaxed rapidity until the power of the muscles 

 was entirely exhausted. From these experiments, he found 

 the following results : — 



* Nature, 30th June, 1870, p. 159. 



