METEOROLOGY. 317 



intercourse. If the Earth were deprived of an atmosphere, as 

 we suppose our moon to be, it would present itself to our 

 imagination as a soundless desert. 



The relative quantities of the substances composing the 

 strata of air accessible to us have since the beginning of the 

 nineteenth century, become the object of investigations, in 

 which Gay-Lussac and myself have taken an active part ; it 

 is, however, only very recently that the admirable labours of 

 Dumas and Boussingault have by new and more accurate 

 methods, brought the chemical analysis of the atmosphere to 

 a high degree of perfection. According to this analysis, a 

 volume of dry air contains 20 -8 of oxygen and 79 '2 of nitrogen, 

 besides from two to five thousandth parts of carbonic acid 

 gas, a still smaller quantity of carburetted hydrogen gas,* 

 and, according to the important experiments of Saussure and 

 Liebig, traces of ammoniacal vapours,f from which plants 

 derive their nitrogenous contents. Some observations of Lewy 

 render it probable that the quantity of oxygen varies percep- 

 tibly, although but slightly over the sea, and in the interior 

 of continents, according to local conditions, or to the seasons 

 of the year. We may easily conceive that changes in the 

 oxygen held in solution in the sea, produced by microscopic 

 animal organisms, may be attended by alterations in the 

 strata of air in immediate contact with it.J The air which 

 Martins collected at Faulhorn at an elevation of 8767 feet, 

 contained as much oxygen as the air at Paris. 



The admixture of carbonate of ammonia in the atmosphere, 



* Boussingault, Recherches SILT la composition de I' Atmosphere, in 

 the Annales de Chimie et de Physique, t. Ivii. 1834, pp. 171-173 ; and 

 Ixxi. 1839, p. 116. According to Boussingault andLewy, the propor- 

 tion of carbonic acid in the atmosphere at Audilly, at a distance, there- 

 fore, from the exhalations of a city, varied only between 0*00028 and 

 G'00031 in volume. 



t Liebig, in his important work, entitled, Die organische Chemie in 

 ihrer Anwendung auf Agricultur und Physiologic, 1840, s. 62-72. On 

 the influence of atmospheric electricity in the production of nitrate of 

 ammonia, which coming into contact with carbonate of lime, is changed 

 into carbonate of ammonia, see Boussingault's Economie rurale const- 

 deree dans ses rapports avec la Chimie et la Meteorologie, 1844, t. it 

 pp. 247, 267, and t. i. p. 84. 



J Lewy, in the Comptes rendus del 1 A cad. des Sciences, t. xvii. pt. 2, 

 pp. 235-248. 



Dumas, in the Annales de Chimie, Ze Serie, t. iii. 1841,' p. 257. 



