375-378] The Outer Atmosphere 315 



Constitution of the Outer Atmosphere. 



377. Throughout the whole of the outer atmosphere the law of distribu- 

 tion is that expressed by equation (753). We can now carry out calculations 

 similar to those of 369, but having reference to the outer atmosphere'. 



We shall not carry these calculations to a height above the earth's surface 

 so great that the rotational term becomes of any importance. We can 

 therefore replace equation (753) by the simpler equation 



i/ a = Ae~- h **. 



At a height z above the surface of the planet, the value of ^ a is 



a + z 

 so that the equation becomes 



v a = Ae VaW ; 



and (jv) , the value of v a at the lower boundary of the outer atmosphere, is 

 given by 



since we may neglect the thickness of the inner (convective) atmosphere in 

 comparison with the earth's radius. 



The elimination of A leads to 



-2Aw a 0(-4^) />7K7\ 



Va \ V a)o 6 \ + 2/ ('57). 



Also at the inner surface the proportion in which the different con- 

 stituents occur is the same as throughout the inner atmosphere, and there- 

 fore the same as at the earth's surface. 



378. The following table gives the constitutioiTof the atmosphere at the 

 earth's surface : 



Hydrogen* less than 1 in 100,000 



Helium f 1 to 2 1,000,000 



Neonf 1 to 2 100,000 



Argon* , 0-93 to 0'95 100 



Krypton 1 20,000,000 



Xenon 1 170,000,000 



Oxygen 21'00 100 



Nitrogen 78'06 100 



Traces of Carbon dioxide and Ammonia are also present in the atmo- 

 sphere. 



* Dewar, I.e. ante. t Travers, Study of Gases, pp. 113, 116. 



J Moissan, Comptes Rendus, cxxxvu. p. 600. 

 W. Ramsay, Royal Soc. Proc. LXXI. p. 421. 



