THE EXTERNAL ENVIRONMENT 249 



The problem of altitude sickness would not be amongst the 

 preoccupations of science if aviation had not become an arm for 

 national defence and an industry of importance, f 1 ) 



The phenomena which accompany the rapid descent of the 

 aviator are most curious ; and they merit a more careful study 

 now that an aeroplane can rise sometimes to more than 5,000 

 metres. Descending rapidly gives rise to troubles which are 

 expressed by the smarting of the face, etc. (see above). There is 

 a mechanical explanation ot this. First of all, consider the fall 

 of a body animated by an acceleration y ; if this boay supported 

 a weight, the pressure of that weight would be reduced to m 

 ( Y) instead of being mg. Compare this to what takes place 

 in the human body ; the blood is a liquid of which every particle 

 pushes internally with a force mg ', in the accelerated descent 

 of the aviator, this force is reduced to m (g y), and in a great 

 acceleration everything would take place as if our blood had 

 no longer any weight ; there must result from it a peculiar 

 sensation of smarting in the lace where the blooa arrives with 

 an apparently stronger cardiac impulsion, and very probably 

 a sensation of cold in the legs. Of course, if this explanation is 

 correct, it follows that a descent at a constant speed, without 

 acceleration, would do away with the aviator's troubles. 



(*) H. de Grafifrgny, Hygiene Pratique et Physiologie de I'Aviateur et de 

 I' Aeronauts, Preface by Ch. Richet, Paris (Maloine), 1912. 



