of Man, or Economic Coefficient of the Human Machine. 361 



gas, gave a figure (34,428 calories) almost identical with that found by 

 Favre and Silbermann (34,462). 



After having used that instrument towards the estimation of the 

 heat given out in a state of rest,* it appeared to us of interest to apply 

 it to the determination of the heat emitted under exercise, so as to 

 obtain finally a figure for the mechanical energy of the human machine, 

 or, as termed by Verdet in his book on the * Mechanical Theory of 

 Heat/f the economic coefficient of the human machine. 



In 1861 Helmholtz, making use of Edward Smith's experiments on 

 the treadmill, calculated by an ingenious mode of argument what 

 ought to be the value of this coefficient. He reasoned in the following 

 way | : A man in a state of repose emits exactly, in one hour, the 

 amount of heat that would be required theoretically to raise his body 

 uphill to a height of 522 m., which he looks upon as a fair rate of 

 climbing in one hour j but, in order to accomplish this work, he would 

 expire five times as much C0 2 as in the state of repose, and, therefore, 

 produce five times as much heat, consequently the relation is 1 : 5, and 

 therefore the economic coefficient would be 1/5. 



Following this mode of argument, it will be readily seen that the 

 supposed subject of this experiment, taking as an average weight 65 

 kilos., would have to emit in the state of rest 80*2 cals. per hour, 

 because, on multiplying 80'2 by 423 (the mechanical equivalent of 

 heat), the result would give 33,925 kilo.-metres ; on the other hand, a 

 man weighing 65 kilos, while raising his body by 522 m., would effect 

 an amount of work = 33,930 kilo.-metres. Therefore the heat emitted 

 in a state of rest in one hour would be exactly the same as the 

 theoretical heat necessary to raise the body 522 m. ; but as (according 

 to Helmholtz) Edward Smith says it is necessary to give out five 

 times more C0 2 than when at rest, to do that work, the coefficient will 

 be 1/5. 



This argument can be criticised as follows : 



1. Most authors give a little over 100 cals. per hour as the mean 

 amount of heat emitted by a person in a state of repose, while, from 

 ninety-two experiments on three different persons, we found from 

 79-056 cals. to 137-636 cals. with a mean of 102-260 cals., these figures 

 being very far from 80*2, which are required to fit the present theory. 



2. An ascent of 522 m. (1712 feet) in an hour is more than anybody 

 can do going uphill ; such exercise might perhaps be kept up for a 

 minute or two, but the average height a man can ascend is usually put 

 down at 1000 feet per hour (perhaps 1200 feet). It is difficult to say 

 what amount of air a man would breathe during such exercise, but it 



* ' Koy. Soc. Proc,,' vol. 63, p. 242. 

 t 'Verdet,' vol. 2, p. 250. 



" On the Application of the Law of the Conservation of Force to Organic 

 Nature." Helmholtz. ' Proceedings of the Koyal Institution,' vol. 3, p. 355, 1862. 



2 F 2 



