II. 



THE ATMOSPHERE 



21 



Comparatively few experiments on the composition of air from 

 great heights have been made, but the general result of what is known 

 is in agreement with theory, which indicates that relatively less of the 

 heavy constituent, oxygen, should be present in such air. 1 In the 

 Alps it has been observed that a descending current of air produces a 

 lower proportion, while an ascending wind gives a higher proportion of 

 oxygen. 2 Differences of O18 per cent (by weight) were observed on 

 two consecutive days at a height of 2060 metres. In Paris the same 

 author gives 2 3 '20 per cent as the mean proportion of oxygen by 

 weight, while 23'1 per cent by weight is the amount he estimates as 

 the average in London air. 



Argon was discovered in 1894 by Lord Eayleigh and Prof. 

 Eamsay. The experiments which led to its discovery were the deter- 

 minations of the densities of gases, in which it was noticed that 

 the residue left after the removal of oxygen and carbon dioxide from 

 atmospheric air, was distinctly heavier than nitrogen prepared from 

 chemical compounds. This fact was eventually traced to the 

 presence, in air, of a hitherto unknown substance, which was named 

 argon by the discoverers. 



1 According to Hinrichs (Compt. Bend., 1900, 131, 442), if each constituent of 

 the air were independent of the others the composition of air at various heights 

 would be as given in the accompanying table. 



From the above table it is seen that the carbon dioxide becomes inappreciably 

 small at a height of 30 kilometres (about 18-6 miles), that the proportion of 

 nitrogen attains a maximum at about 40 kilometres (about 25 miles), that at a 

 height of about 60 kilometres (37 miles) the oxygen and hydrogen are in the pro- 

 portion in which they combine with explosion to form water. Explosion in this 

 highly rarefied atmosphere would be impossible, especially in the presence of so 

 large a quantity of nitrogen. 



Hinrichs asks might not the hydrogen found in meteoric iron be obtained 

 during the passage of a meteorite through the outermost layers of our atmosphere, 

 which, according to the table, consists of almost pure hydrogen ? It may be men- 

 tioned that hydrogen is, according to Gautier (Compt. Bend., 1898, 127, 693), 

 always to be detected in pure air, in proportion varying from 11 to 18 per 100,000, 

 i.e., -01 to -018 per cent by volume. Moreover, he has shown that hydrogen is to 

 be found among the gases evolved by the action of water upon many rocks, e.g., 

 grmite, at a temperature of about 280 or 300 (Compt. Bend., 1900, 647). In a 

 later paper, however, doubt is expressed as to the hydrogen being actually derived 

 from the granite. 



2 Leiuc, Compt. Bend., 1898, 413. 



