Theories and Experiments 309 



A discussion took place in regard to the influence of atmospheric 

 pressure on human life. 



MM. Antoine d'Abbadie, Maunoir, de Charencey, and de Puydt took 

 part in it. The last mentioned for two years travelled through the 

 valleys of the Andes, in Ecuador and Bolivia, living at altitudes of 

 4800 meters, always keeping his health and vigor. M. l'abbe Durand 

 confirmed this statement, according to M. Stuebel, who made an ascent 

 of Chimborazo two years ago. (P. 552.) 



We can see by the account of Stuebel's ascent which we have 

 given into what an exaggeration M. l'abbe Durand has fallen. But 

 without discussing this for the moment, it is interesting to repro- 

 duce at greater length the arguments presented by M. Virlet 

 d'Aoust and his learned colleagues, according to an authorized 

 journal, the Explorateur: 149 



M. Virlet d'Aoust, on the occasion of the lamentable disaster to 

 the Zenith, which cost the lives of two young scientists, MM. Croce- 

 Spinelli and Sivel, recalled the circumstances of his ascent of Popoca- 

 tepetl, in April 1853, with the purpose of emphasizing the considerable 

 differences which exist between ascents of mountains and vertical bal- 

 loon ascensions in the atmosphere. 



When one rises in the air by means of a balloon, says M. Virlet 

 d'Aoust, he finds himself successively plunged in layers of air, if not 

 of different compositions, at least of different densities, in which, how- 

 ever, the carbonic acid must diminish in proportion because of its 

 greater specific weight. This kind of ascension, moreover, is made too 

 rapidly for the organs of human life to have time to undergo sufficient 

 changes to make the successive differences in atmospheric pressure 

 endurable. 



When one scales a mountain on foot, the layers of air have exactly 

 the same composition as on the plain, for these layers, though becom- 

 ing thinner, rise in currents from below up to the highest summits. 

 The result is that any experiment which has for its sole purpose the 

 determination of differences in the composition of the air at different 

 heights should be carried out vertically in a balloon and not in a 

 mountain ascent. 



The ascent of Popocatepetl (the smoking mountain) by M. Virlet 

 d'Aoust involved numerous companions, and was, so to speak, an 

 international expedition. The United States, England, Mexico, Ger- 

 many, Belgium, Switzerland, Italy, and France were represented. 



Although the plain and the city of Mexico have an elevation of 

 about 2300 meters above sea level, life there is very comfortable; public 

 health is perfect and free from any endemic disease. The travellers 

 halted at the foot of the cone at an elevation of more than 4000 

 meters; they had reached this spot on horseback without the least 

 inconvenience and without feeling the slightest effect of the rarefac- 

 tion of the air. The difficult part was the ascent of the cone, a regular 

 sugar loaf, which had to be climbed on foot. That requires four hours 

 of very difficult walking, although the descent is made in less than a 

 half-hour. Neither M. Virlet dAoust nor his companions experienced 



