CLIMATE AND CARBONIC ACID. 243 



In considering the climatic conditions which gave to the coast of 

 southern New England the aspect of Greenland at the present time, 

 thought naturally turned to the antithetic phase when Greenland pos- 

 sessed the climate of Florida. And seemingly linked with these were 

 other climatic variations, such as the great humidity of the Coal 

 Measure period and the great aridity of epochs when salt and gypsum 

 deposits accumulated; while the cause of that redness, which in several 

 continents is characteristic of strata of certain geologic ages, might be 

 traced to world-wide atmospheric conditions. The problem was thus 

 greatly broadened in the scope of related phenomena, and the demands 

 to be met by an adequate hypothesis became correspondingly complex. 



The investigation upon which the hypothesis under review rests 

 considers the physics and chemistry of the atmosphere in relation to 

 temperature, the physics and chemistry of the ocean, the interaction of 

 the ocean and the air, and those events of geologic history which as 

 cause or effect may be related to the constitution of the atmosphere. It 

 is not here proposed to review critically the several articles in which 

 Professor Chamberlin and his associates have presented the results of 

 profound researches. Suffice it to endeavor clearly to present an out- 

 line of their reasoning and conclusions. 



The constitution of the atmosphere has long been known, and in a 

 general way is stated for dry air as 21 parts of oxygen and 79 parts of 

 nitrogen by volume. Argon, a newly discovered component, was for- 

 merly measured as nitrogen, and frequently there are impurities, 

 though in small amount. There are 3 to 4 parts of carbonic acid in 

 10,000, and under natural conditions moisture is present in greater or 

 less proportion. It is with these last, the carbonic acid and moisture, 

 that the student of climatic changes has to deal chiefly. 



The functions of carbonic acid and moisture in the atmosphere are 

 threefold. They both absorb radiant heat in an unusual degree. By 

 thus raising the temperature of the air, they both increase its capacity 

 for moisture. And they both are chemically active. 



Radiant light and heat penetrate the atmosphere to reach the solid 

 earth, and are in part radiated back through the air into space. As 

 the air is transparent toward light, so is it also toward heat, allowing 

 both forms of energy to pass with moderate absorption. A photog- 

 rapher who compares the exposure of his plate at a considerable altitude 

 with that near sea level roughly measures the relative strength of light 

 at the two places and finds it less beneath the greater depth of atmos- 

 phere. The direct heat of the sun's rays is correspondingly less by the 

 sea. The energy which the heated earth radiates back toward space is 

 in part also absorbed by the air, which is thus warmed by the passage 

 of rays to and from the earth. 



In this absorption the mass of nitrogen and oxygen has but an 



