196 THE HUMAN MOTOR 



readings of the instrument to obtain the total output of muscular 

 energy, and the real yield ( 61) . Thus Benedict and Carpenter ( l ) 

 corrected their nett results for R by the amount of 6-50% above 

 mentioned. 



Witz ( 2 ) gave a simple method for evaluating the frictional 

 losses in the apparatus. 



In the case of the bicycle dynamometer the machine is run up, 

 unloaded, to the required speed and the motive force, in this case 

 the pressure of the feet on the pedals is then suddenly withdrawn. 

 The machine continues to revolve until it has exhausted the energy 

 imparted to it. Let it make N revolutions in time t before it stops, 

 the initial speed being no revolutions per second. Let K be the 

 moment of inertia of the rotating system. Then the work done 

 in overcoming the internal friction W, is represented by the 

 equation : 



n 



2 



W = -0055K - - kilogrammetres. 



N 

 Where n = . 



If the normal speed is n' revolutions per second, the power 

 absorbed by friction is W X n'. The measured power being W', 



W' 



the organic yield, p = - can be deduced for the whole 



system in movement. 



Example : Let K = 0-28, n = 2, n = 040, n' = 2-05. Then : 



W' = 0-032 kgm. 



W has been measured as 1-93, therefore : 

 1-93 1-93 



P = 



= 0-98. 



1-93+0032 1-963 



The above test was made on the before-mentioned bicycle 

 dynamometer, the speeds being registered electrically ( 321). 

 As a general rule, " coasting " with French bicycles absorbs 

 nearly 5% of the total work. 



140. Summary : Chauveau's Ratio. The most complete 

 experiments on the work done by man under conditions as to load, 

 duration and alimentation give an average net yield of 25%, i.e. 



This is the maximum in the case of the arms. 



(M Benedict and Carpenter (Bulletin, No. 208, p. 39, 1909). 

 () Aim6 Witz (Comptes Rendus Sciences, 3rd Aug., 1908) ; Dernitre 

 Evolution du Moteur & Gaz, p. 225. 



