144 EULOGY OX GAY-LUSSAC. 



the scientific study of the physical constitution of our atmosphere will 

 certainly not fail to take my suggestions into serious consideration. 



The hygrometer of de Saussure gave indications, during the ascension 

 of Gay-Lussac, of an irregular movement, but taking into account, at 

 the same time, the degrees indicated by this instrument and the tem- 

 perature of the strata in which it was observed, our associate found that 

 the amount of humidity contained in the air continued to diminish with 

 extreme rapidity. 



It was already known at the time of this memorable ascension that 

 air in all latitudes, and at a height very slightly above the level of the 

 sea, contained about the same proportions of oxygen and azote. Tbis 

 resulted with proof from the experiments of Cavendish, Macarty, Ber- 

 thollet and Davy. It had also been ascertained by the analyses of The- 

 odore de Saussure, of air brought from the Col du Geant, that at the 

 height of that mountain the air contains the same proportions of oxy. 

 gen as that of the i^lain below. 



The eudiometrical analyses of Gay-Lussac, made with the greatest 

 care, of air collected at a height of 0,G30 meters, established the fact 

 that the air of those high regions was not only composed of oxygen and 

 nitrogen, like that at the surface of the earth, but, moreover, that it did 

 not contain an atom of hydrogen. 



It is not necessary to insist here upon the importance of these results; 

 they showed the 7agueness of the explanations given then by meteorolo- 

 gists of shooting-stars and other atmospheric phenomena. 



The following extract from Gay-Lussac's own narrative gives some 

 clew to a true explanation of the discomfort experienced by the most 

 robust travelers in climbing elevated peaks, such as Mont Blanc : 



'•On reaching the highest point of my ascension, 7,010 meters above 

 the mean level of the sea," said the courageous physicist, "my respira- 

 tion was sensibly affected, but I was far from feeling yet a discomfort 

 sufficient to induce me to descend. My pulse and respiration were very 

 much accelerated ; breathing very rapidly in air of extreme dryness, I 

 ought not to have been surprised that my throat was so dry that it was 

 impossible to swallow bread." 



Let us now pass on to the experiment which was the chief object of 

 the two aerostatic voyages, undertaken under the auspices of the 

 first class of the Institute. The question was, as I have previously 

 said, to assure themselves whether, as announced, the magnetic attrac- 

 tion exerted by the earth on a magnetic needle decreases very rapidly 

 with the height. Gay-Lussac succeeded, in this second ascension, in 

 counting, in a given time, twice as many oscillations as in the first. 

 The results must, therefore, furnish much greater exactness. He found 

 that a needle which at the surface of the earth required 42^2 to make 

 ten oscillations, at a height of 4.808 meters above Paris made the same 

 number of oscillations in only 42^8. The result was 42^5 at 5,631 

 meters, and 4P.7 at G,SS4 meters. These numbers do not give much 



