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at the same period 20° at the priory of Chamou- 

 ni, and 40° at the top of Mont-Blanc. This last 

 mountain is 540 toises higher than the volcano 

 of Teneriffe ; and if, notwithstanding this differ- 

 ence, the sky is seen there of a less deep blue, 

 we must attribute this phenomenon to the dry- 

 ness of the African air, and the proximity of the 

 torrid zone. 



We collected air on the brink of the crater? 

 which we meant to analyse on our voyage to 

 America. The phial remained so well corked, 

 that, on opening it ten days after, the water 

 rushed in with impetuosity. Several experi- 

 ments, made by means of nitrous gas in the 

 narrow tube of Fontana's eudiometer, seemed to 

 prove, that the air of the crater contained 0*09 

 less oxygen than the air of the sea ; but I have 

 little confidence in this result obtained by means 

 which we now consider as very inexact. The 

 crater of the Peak has so little depth, and the 

 air is renewed with so much facility, it is scarce- 

 ly probable, that the quantity of azot is greater 

 there than on the coasts. We knew also, from 

 the experiments of Messrs. Gay-Lussac and 

 Theodore de Saussure, that in the highest as 

 well as in the lowest regions of the atmosphere, 

 the air equally contains 0*21 of oxygen * 



* During the stay Messrs. Gay-Lussac and myself made 

 at the hospice of Mount Cenis, in March, 1805, we collected 

 air in the midst of a strongly electrified cloud. This air, 



