26 THE ATMOSPHERE. II. 



descending current of air produces a lower proportion, while an 

 ascending wind gives a higher proportion of oxygen." Diffe- 

 rences of '18% (by weight) were observed on two consecutive 

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

 gives 23-20% as the mean proportion of oxygen by weight, 

 while 23.1% by weight is the amount he estimates as the 

 average in London air. 



In 1886 a series of daily analyses of air were made simulta- 

 neously at Dresden, Bonn (Germany), Cleveland (U.S.A.), 

 Para (Brazil), and Tromsoe (Norway), from April 1st to May 

 16th. The mean values for the amount of oxygen were : 



Para ... ... 20*92 %, by volume 



Bonn ... ... 20-92 ,, 



Cleveland ... ... 20'93 ,, 



Dresden ... ... 20-93 ,, 



Tromsoe ... ... 20-95 ,, 



The maximum was 21'0 at Tromsoe and the minimum 20'86 

 at Para. The mean percentage of oxygen of the whole series 

 was 20-93.1 



Argon was discovered in 1894 by Lord Kayleigh and Prof. 

 Eamsay. The experiments which led to its discovery were 

 the determinations of the densities of gases, in which it was 

 noticed that nitrogen prepared by 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 anjon by the dis- 

 coverers. 



Argon is a gas possessed apparently of no chemical proper- 



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

 attains a maximum at about 40 kilometres (about 2o miles), that ;it a height <>f about 

 GO kilometres (37 miles) the oxygen and hydrogen are in the proportion 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 the meteorite through the outermost layers of our atmosphere, which, 

 according to the table, consists of almost pure hydrogen? It may be mentioned that 

 hydrogen is, according to Gautier (Compt. Rend., 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 % 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.</., granite, at a temperature of about 280 or 300 

 (Compt. Rend., 1900, 647). In a later paper, however, doubt is expressed as to the 

 hydrogen being actually derived from the granite. 



: Leduc, (Jomp. Rend., 1898, 413. t Ilempel, Her., _'0, 1864. 



