THE EXTERNAL ENVIRONMENT 



241 



In a storm the pressure of air reaches 95 kilogrammes, suffi- 

 cient to overturn an adult man, if he did not bend, so as to reduce 

 his surface and thus offer a smaller resistance^ 1 ) 



The speed of the wind ( 2 ) is measured by means of the anemo- 

 meter, which will be described later (Technique, 200). 



176. The influence of the speed of air currents, at a given tem- 

 perature, has been studied by Jules Lefevre ( 3 ) after d'Arsonval's 

 methods. He placed his subject in his physiological calorimeter 

 (see Technics, 250) in a draught of air of known mass and speed ; 

 he noted the temperatures of the air at entry and exit. Let M 

 be the total mass of the air which has circulated in / minutes 

 and been raised to a temperature of 6. By multiplying this 

 excess of temperature 6 by the specific heat of air, 0-237 ( 104) 

 the number oi calories absorbed by the air, that is to say, elim- 

 inated by the subject are obtained. This is, per hour : 



^ 

 Q = 



0-237 X X M 



X 60 calories. 



Here is a table of some results obtained with an adult : 



(*) This inclination to the horizontal constitutes the angle of attack a. 

 The resistance R will therefore be expressed as : 



R = K X S X V* x sin a. 



it diminishes in consequence with the value of the angle a, but only uP 

 to a = 30 (G. Eiffel). 



( 2 ) One can equally well say : "force" of the winds, substituting pressure 

 for speed. 



( 8 ) Jules Lefevre, Bio Inerg Clique (loc. cit., pp. 103, 405, 426). Consult 

 also d'Arsonval (Arch, de PhysioL, 1894, p. 360). 



