THE ENVIRONMENT 57 



may, it is at least automatic, and must repeat 

 itself in other similar circumstances. 



There is, moreover, direct evidence in sup- 

 port of the above conclusions. Spectro- 

 scopic investigation has proved the presence 

 of water vapor in the atmospheres of Mars, 

 Venus, Jupiter, and Saturn, and nobody has 

 suggested what the snowcaps of Mars may be 

 unless they are real snow (hoarfrost) or, im- 

 probably, carbonic acid. Lowell and Arrhe- 

 nius agree in considering them snowcaps. 1 



In the earth's atmosphere carbonic acid has 

 been very largely converted into oxygen and 

 vegetable matter, which later has been turned 

 into enormous quantities of coal. It is, in 

 fact, possible, in accordance with the sugges- 

 tion of Koene, that all the oxygen of the 

 atmosphere has been thus formed from car- 

 bon dioxide, and that therefore coal, peat, and 

 other similar substances within the earth are 

 chemically equivalent to the oxygen now free. 



If a typical atmosphere must contain water 

 and carbon dioxide, its evolution must ob- 

 viously be in part conditioned by the presence 

 of these substances. Hence terrestrial meteor- 

 ology, no less than terrestrial geology, must be 

 in greater or less degree a special case of a 



1 Arrhenius, " Kosmisclie Physik," p. 173 ; Lowell, " Mars 

 as the Abode of Life," p. 81. 



