108 



THE AMERICAN NATURALIST [Vol. XLVII 



question. But as the temperature falls in the cooling of 

 a sun or planet the affinities of carbon and hydrogen for 

 oxygen increase so that carbonic acid and water must 

 normally result. For oxygen is almost certainly present 

 in the sun, it is found in meteorites, and the vast store of 

 it in the earth's atmosphere and crust (roughly one half 

 of their total mass) justify the belief that it is every- 

 where one of the commonest of elements. Hence an 

 atmosphere containing water and carbonic acid appears 

 to be a normal envelope of a new crust upon a cooling 

 body. Even were not these substances at first present in 

 such an atmosphere, volcanos must soon belch them forth 

 in enormous quantities, to relieve the pressure which in- 

 evitable chemical processes set up. 



In short just as living things permit themselves to be 

 simplified into mechanisms which are complex, regulated, 

 and provided with a metabolism the environment may be 

 reduced to water and carbonic acid. These are simplifica- 

 tions counselled solely by expediency. Neither logical 

 process is necessary, each involves a disregard for many 

 circumstances which might be of weight in the present 

 inquiry. But in the end there stands out a perfectly simple 

 problem which is undoubtedly soluble. That problem 

 may be stated as follows : In what degree are the physical, 

 chemical, and general meteorological characteristics of 

 water and carbon dioxide, the primary constituents of 

 the environment and of the compounds of carbon, hydro- 

 gen and oxygen favorable to a mechanism which must be 

 physically, chemically, and physiologically complex, which 

 must be itself well regulated in a stable environment, 

 and which must carry on an active exchange of matter 

 and energy with that environment. 



The first step in seeking a solution must be to review 

 the data of physics and chemistry which describe the 

 properties of water and carbonic acid, having due regard 

 to their meteorological significance. Such data of the 

 highest accuracy exist in great profusion, for almost 

 every conceivable property of these substances has been 



