YIELD OF THE HUMAN MACHINE 



189 



specified whether the question involved was of motor or resistant 

 work. As a rule, only the former is considered, but it is 

 known that the latter produces a smaller expenditure. A man 

 mounting a staircase makes a larger expenditure of energy than 

 that necessary for descending the stairs, but the descent is more 

 or less restrained by the muscles, which fact modifies, within wide 

 limits, the corresponding value of the expenditure. Therefore, 

 the yield of a resistant work is not a correct statement, since the 

 motor does not perform the work ; it acts against the accelera- 

 tion of Gravity in the manner of a brake. As for the muscular 

 work, it is obvious that its value is less in this case than in the 

 other where Gravity has to be overcome and the expenditure is 

 less in about the same proportion. Therefore R is taken as the 

 yield, both of motor and resistance work.f 1 ) 



133. Examples of Yield. (a) The Use of an Experimental 

 Bicycle Dynamometer.- The following results were obtained by 

 some American observers with a robust student, weighing 76 

 kilogrammes and from 20 to 23 years old. His static expenditure 

 D s was 2,397 Calories in the calorimetic chamber at 20 (see 104). 

 By causing him to perform work to the amount of 200,000 to 

 250,000 kilogrammetres the following results were obtained, the 

 average being given at the foot of each column : - 



The average value of R is 20-5% ; that of r is 11-82%. 



The duration of the experiment was eight hours, except in the 

 last trial, which lasted sixteen hours. The net yield appears 

 to be practically constant, but it rose in certain cases, ( 3 ) 



(!) Jules Amar (Comptes Rendus Sciences, June, 1911, p. 161 |J). 



() Atwater and Benedict (Bulletin, No. 136, p.,51, 66, 97, 184, 307, 1903). 



( 3 j Atwater and Benedict (Ibid., p. 59). 



