388 Searles V. Wood, Jun. — The Climate Controversy. 



cussion, and therefore demands the most examination. More than 

 thirty-five years ago, M. Adhemar advanced a theory that the 

 Noachian deluge was the last of a series of deluges which had 

 occurred during past ages from the melting of snow and ice accumu- 

 lated at that pole which lay in the hemisphere where the aphelion, 

 or point of greatest recession of the earth from the sun, occurred 

 during winter. It has long been known that, owing to the pheno- 

 menon called the precession of the equinoxes, the aphelion and 

 perihelion points are transferred from the summer to the winter 

 seasons, and vice versa, every 10,500 years or thereabouts;^ so that 

 for this period the sun is at its greatest distance from the earth 

 during the winter season of one hemisphere and the summer 

 season of the other ; while for the next 10,500 years these condi- 

 tions are reversed. M. Adhemar contended that the effect of this 

 would be, that during the occurrence of the aphelion near the winter 

 solstice of either hemisphere, the polar ice of that hemisphere would 

 be constantly augmenting ; and that as the perihelion point returned 

 to the winter season of such hemisphere, this accumulated ice would 

 be dissolved, and great volumes of water be liberated. In 1866 

 Mr. Croll revived this theory, in so far as it assumed to account for 

 changes in climate, and added to it the effect which would be pro- 

 duced by the varying excentricity of the earth's orbit, in either 

 increasing or diminishing this refrigerating power of the aphelion ; 

 according as by increased excentricity the aphelion was removed 

 further from the sun, or by diminished excentricity was brought 

 nearer to it. 



Many objections have been offered to this theory. One was that, 

 whether the excentricity be great or small, an equal quantity of heat 

 is received by the earth during every revolution round the sun ; the 

 augmented distance of the aphelion being balanced by the diminished 

 distance of the perihelion during increased excentricity, and vice 

 versa; so that the augmented heat of the 10,500 summer seasons, 

 due to the occurrence in them of the perihelion, would balance the 

 refrigerating effect of the occurrence during the same number of 

 years of the aphelion in the winter season, and melt all the extra 

 quantity of ice that the increased winter cold had produced ; the 

 result being merely that the difference of temperature between 

 winter and summer would be greater or less, according to the 

 position of the aphelion and the degree of excentricity. 



It seems, however, that this is not precisely true ; but that the 

 quantity of heat received by the earth from the sun in every revo- 

 lution round it varies inversely as the minor axis of the orbit ; 

 which would make the quantity of heat received greatest when the 

 excentricity was greatest, and vice versa ; thus diminishing any effect 

 produced by an increase of excentricity in augmenting the cold of 

 mid-winter in that hemisphere in which the aphelion occurred at 

 this season. 



It is also admitted that whatever be the variation thus arising 



1 It appears that this period of 10,500 years is subject to large variations ; hut it 

 is conveuient to speak of it as of that duration. 



