i!2G Account of an Aerostatic Voyage, 



At the same time a measure of very pure oxvgen gas- re- 

 quired -2'04: measures of hydrogen gas ; and as this result 

 dificrt'd only 0-01 from that found by experiments made ort 

 a very large scale, and with a great deal of care, on the 

 composition of water, it appears that great confidence may 

 be placed in our results. They prove, then, that atmo- 

 spheric air, and air taken at the height of G636'5 metres, 

 are exactly the same, and that they contain each 0'2149 of 

 oxygen. In analysing the last air by bydro-sulphuret of 

 potash, we found 0-2163 of oxygen. I cannot present the 

 result of the comparative experiment made on atmospheric 

 air, because we were not able to collect it ; but the propor- 

 tion of oxygen I have indicated is still a little greater than 

 that given by the combustion of hydrogen gas, and it is 

 comprehended between the limits of the variations which 

 have been found for the composition of the atmosphere at 

 the surface of the earth, and which have not prevented us 

 from considerino; it as constant. 



The identity of the analyses of the two airs made by hy- 

 drogen gas proves directly, that the air I brought back con- 

 tained none of the latter gas. I, however, still ascertained 

 in it, by burning with the two airs, a quantity of hydro- 

 gen gas, smaller than that which would have been neces- 

 sary to absorb the whole of the oxygen gas j for I saw that 

 the residuums of the combustion of the two airs with hy- 

 drogen gas were exactly the same. 



Saussure junior found also, by making use of nitrous gas, 

 that air collected on the Col-du-Geant contained, within a 

 hundredth part, as much oxygen as that of the plain ; and 

 his father confirmed the presence of the carbonic acid on 

 the summit of Mont Blanc. Besides, the experiments of 

 Messrs. Cavendish, Macartney, Berthollet, and Davy, have 

 coutiruied the identity o'^f the composition of the atmosphere 

 over all the surface of the earth. We may therefore con- 

 clude, in general, that the constitution of the atmosphere 

 is the same from the surface of the earth to the greatest 

 heights to which it is possible to attain. 



Such are the two principal results of my last voyage. 

 M. Riot and myself confirmed the fact we observed in re- 

 gard to the sensible permanence of the intensity of the mag- 

 netic force as one recedes from the surface of tlie earth ; and 

 I think, also, I have proved that the proportions af oxygen 

 and azote, which constitute the atmosphere, do not sensibly 

 vary in very extensive limits. There still remain a great 

 many things to be cleared up in regard to the atmosphere, 

 and we wish the facts we have collected mav prove suffi- 

 etently interesting to the Institutt to iuduce it 10 make us 

 continue oar experiments. Table 



