president's address. 33 



the work of Professor Langley on the determination of tlie 

 variations in the amount of heat received from the full moon 

 when at different altitudes above the horizon and thus shining 

 through varying thicknesses of atmosphere. 



Professor Chamberlin assumes that even in earl}' Palaeozoic 

 times the atmosphere did not materially differ from its present 

 composition, there having always been a conflict between sources 

 of supply and causes of depletion of carbon dioxide. The amount 

 of this constituent in the existing atmosphere varies somewhat in 

 different regions, but may be stated as averaging about 0*03 per 

 cent, by volume. Arrlienius has calculated that a reduction 

 sufficient to bring this down to 0*016 to 0*018 per cent., or the 

 removal of rather more than one half, would suffice to reduce the 

 mean tempeiature by an amount equivalent to 7 to 9° F., which 

 would mean the extension of glacial conditions to within about 

 20° on either side of the equator; while an increase of from 2J 

 to 3 times the present proportion, bringing the carbon dioxide 

 content to 0*075 to 0*090 per cent., would result in an increase 

 of the mean temperature by 14 to 16° F., and give semitropical 

 conditions well within the arctic and antarctic zones. In support 

 of the possibility of such variation in atmospheric carbon dioxide, 

 Arrhenius quotes the opinions of Professor Hogben who has 

 published in a Swedish journal* the result of his studies on the 

 probable sources of supply and causes of depletion of this gas to 

 and from the atmosphere. Hogben considers that the atmosphere 

 is and has always been continuously supplied with carbon dioxide, 

 amongst other gases, from the earth's interior. Such supplies 

 would be quite independent of surface conditions, and would 

 continue even during periods of extreme glaciation. This is the 

 important point on which the whole theory depends. 



That there are large supplies of carbon dioxide available is 

 well known. Examination of numerous volcanic and meta- 

 morphic rocks has shown that they contain, on an average, 

 several times their own volume — at atmospheric pressure — of 



* Svensk Kemisk Tedskrift, 1894, p. 169. 



