Theories and Experiments 213 



the Alps, which makes one ill, and that of the Cordilleras, "where 

 one feels no effect": 



I have noted that these symptoms can be avoided by walking . . . 

 a means of renewing the air in the lungs and maintaining their activity. 



I know that it would be difficult, not to say impossible, to live a 

 long time on Mont Blanc . . . 



From all these circumstances we must conclude that the air which 

 we breathe on the high Alps is much rarer than that of the Cordilleras 

 at the same height, because the latter are beneath the equator, and for 

 that very reason they are more impregnated with heavy and dense 

 vapors. (Vol. II, p. 98.) 



If this idea seems very strange to us today, what shall we say 

 about that of d'Arcet,- ■"■ who first denies mountain sickness (he had 

 ascended only the peak of Midi) and then asks himself whether 

 the air of lofty regions is really rarer than that of the plains! 



As to the difficulty in breathing which it has been thought was 

 sometimes felt on lofty mountains, and which we have never experi- 

 enced, I think that it may come from the oppression which one feels 

 when, heated and weary with the ascent, he reaches a very open and 

 very lofty summit. There, he is suddenly struck by a cold and keen 

 air . . . 



No matter how tired one is, when one reaches the top of a lofty 

 mountain, he is promptly refreshed; he feels nimbler, lighter; the face 

 is pale and the flesh less ruddy. In a word, what one feels then has 

 nothing in common with, or rather it is the opposite of, the effects pro- 

 duced upon living beings by an air which is too expanded and too rare. 

 (P. 123.) 



He next discusses the observations of Bouguer and La Conda- 

 mine, and says in conclusion: 



I urge physicists who have the opportunity to attempt new experi- 

 ments, if it is possible, to ascertain whether at certain heights the air 

 really becomes rare and expands to such a degree that animals cannot 

 ascend there without suffocating as they do in a vacuum; whether this 

 more or less great density is the only cause of the rising and the varia- 

 tions of the mercury in the barometer. 



De Saussure,- 4 in the first volume of his great work, after tell- 

 ing of his sufferings from mountain sickness during his ascent of 

 Buet, tries to find the reason for them. It is strange that he alludes 

 to the real explanation, although only to oppose it, which the 

 recent discoveries of Priestley and Lavoisier permitted him to 

 glimpse: 



559. — We cannot attribute the exhaustion of muscular strength to 

 fatigue alone, as M. Bouguer thought. A fatigued man, on the plain 

 or on mountains of moderate height, is rarely so exhausted that he 



