98 Mr. J. Stevenson on the Chemical and 



by volume, which is not far from the results obtained by 

 chemical analysis. 



Prof. Arrhenius has made an elaborate investigation of the 

 subject by a special method, the results of which he gave in 

 a paper published in the Philosophical Magazine for April 

 1896, p. 297. From conclusions drawn from the data ob- 

 tained by means of his experiments, he calculated the extent 

 to which the carbonic acid in the atmosphere would have to 

 vary in order to bring about the temperature of the Tertiary 

 and the Ice Ages respectively. He found that the tempe- 

 rature in the Arctic regions would rise about 8° or 9° 0. 

 if the carbonic acid were increased to 2*5 or 3 times its 

 present value ; and that in order to get the temperature of 

 the Ice Age between the 40th and 50th parallels of latitude 

 the carbonic acid in the air should sink to 0'6 2-* 5 of its 

 present value (lowering the temperature by 4° or 5° C). 



Assuming that these results are reliable, the question arises 

 as to whether it is possible or probable that the amount of 

 carbonic acid in the atmosphere may have varied to the 

 above extent ; that is, whether it may at one period have been 

 two or three times as much as at present, and at another 

 period only about half of the present quantity. 



If we suppose that the amount of carbonic acid annually 

 restored to the atmosphere by the oxidation in various ways 

 of organic remains amounts to 99*9 per cent, of the amount 

 annually removed by the growth of vegetation and the 

 weathering of rocks, it is evident that 0*1 per cent, of the 

 amount would have to be added from subterraneous sources 

 to maintain the balance ; or, following the estimate above 

 given regarding the growth of vegetation, there would be 

 annually required 46*9 x 10 6 tons of carbonic acid of telluric 

 origin. Now if we suppose this to be increased through any 

 cause by 50 per cent, of itself, or 23*4 x 10 6 tons, there would 

 be a net addition of 23*4 x 10 6 tons per annum to the carbonic 

 acid of the atmosphere ; and if we suppose this addition or 

 extra quantity to be continued steadily for many years, in 

 141,000 years the total carbonic acid of the atmosphere would 

 be 5*5 x 10 12 tons, or 2-J times its present amount, and in 

 188,000 years it would be 6'6 X 10 12 tons, or 3 times its 

 present amount. Similarly, if the amount of subterranean 

 carbonic acid should fall off by the above quantity, causing a 

 deficiency of 23*4 x 10 6 tons per annum, and if this deficiency 

 should continue for a long term of years, then in 47,000 years 

 the amount of atmospheric carbonic acid would be reduced to 

 1*1 x 10 12 tons, or one-half of its present value. 



The above figures are probably well within the limits 





