182 



THE HUMAN MOTOR 



Langsdorf ( l ) obtained : 



v = 0-757 m. ; F = 13-30 ; hence Fv = 10 kilogrammetres. 



Euler's first formula, which 

 is represented graphically by 

 a parabola (fig. 136) is there- 

 fore sufficiently correct, but 

 the time should be introduced 

 into these relations if they are 

 to have a practical significa- 

 tion. Calling the factors of 

 the daily maximum work 

 F x , v v t similar formulae are 

 obtained to that of Mas- 

 check (*) : 



and that of Gerstner ( 3 ) : 



- M 



;^s 



"V. 



These formulae are unsatisfactory. The German engineers ( 4 ) 

 stated that, for 8 hours of work per day, the normal effort of a 

 man represents a third of his weight, 20 to 25 kilogrammes. It 

 will be seen that this is not often the case, .and that calculation 

 cannot replace experiment. 



125. (ii) The Energetic Point of View. The idea of fatigue had, 

 in Coulomb's mind, the value that we attribute to the idea of 

 energy. " The whole question," he wrote, " resolves itself into 

 how to find the combination with each other of the different 

 degrees of pressure, speed and time, so that a man, with equal 

 fatigue, can produce the greatest amount of work." But fatigue 

 is not a precise thing, and is difficult to define. Fatigue occurs 

 in walking, for example, from the first kilogrammetre accom- 

 plished, because each unit of work has an effect, often negligible, 

 but still real, on the organism. At the limit at which the human 

 forces are incapable of further exertion, fatigue is more a patho- 

 logical than a physiological state, and the degrees of fatigue, 

 prior. to that state, are not susceptible of precise measurement 

 ( 146), sensation not having physical dimensions. 



It is therefore desirable to substitute for a sensation, fatigue, 

 the direct estimation of possible work. This is often difficult, 

 all the more so as the work of the muscles is greater than that of 



( 1 ) Quoted by Rhiilmann (Allg. Maschienenlehre vol. i., p. 268, note). 



( 2 ) Quoted by Simms (Proc. Instit. of Civil Eng., vol. ii., p. 112. 



( 3 ) Quoted by Simms (loc. cit.) and Gerstner's Mecanique. 



( 4 ) Weisbach, Lehrbuck d. Ingen. und Maschienen-Mechanik. 



