198 THE HUMAN MOTOR 



net yield R is extremely useful. A distinction can then be made 

 between various subjects according to their degree of ability, 

 that is, their social utility, f 1 ) 



The idea of yield ceases to be applicable if the forms of mus- 

 cular activity are of the static order, and if the subject fatigues 

 himself without producing any mechanical work in the strict sense 

 of the word. In true muscular work great resistances have to be 

 displaced, and the work is evaluated in kilogrammetres according 

 to the yield. 



Ernest Solvay : Formules d'Energttique, p. 9 ; Bruxellea, 1906. 



