474 MR. p. W. HARMER ON THE [^^^g- ^QOTj 



atmos])lieric disturbance in the Atlantic, and a distribution of 

 climatic zones even more irregular than that of the present day. 



Dr. Ekholm, however, while applying the carbon-dioxide theory 

 to the climatal variations of the Glacial Period, believes that those 

 of post-Glacial times (some instances of which he mentions) were 

 due to secular changes in the obliquity of the ecliptic. He calculates 

 that at the periods when, owing to this cause, the summers of the 

 IN'orthern Hemisphere were warmer, one series of which occurred 

 about 9100 years ago, the amount of heat received directly from the 

 sun at the JSTorth Pole during the months of May, June, and July, 

 was from 4-1° to 4-4° Cent. ( = 7-4"' to 7-9° Fahr.) greater than at 

 present, while about 28,300 years ago, when the summers were 

 colder, it was from 6-3° to 7-1°*' Cent. ( = 11-3° to 134° Fahr.) less ; 

 the difference in each case during the winter months, when the sun 

 is there below the horizon, being of course zero. He further believes 

 that it was during one of these warmer periods, occurring about 

 48,000 years ago, that the final melting of the great ice-sheets took 

 place.^ 



The great centres of ice-accumulation do not seem to have been 

 at the North Pole, however, but very much farther south : one of the 

 most important of them, that of Labrador, being situated in about 

 lat. 55° N., while the edge of the American ice-sheet, at the time 

 of its maximum extension, is believed to have travelled 17 degrees 

 farther southward. Generally the phenomena with which the 

 glacialist has to deal did not take place in the extreme north. The 

 excess of heat received from the sun in summer at lat. 55° IS"., 

 during the warmer periods, was not nearly so great as at the Pole 

 itself, and the winters having been colder, no material annual increase 

 of temperature could then have taken place. ^ 



Both at the time when the obliquity was greatest and when it 

 was least, the total difference in the amount of heat received from 

 the sun in Labrador during the year was inappreciable, 0*54° Fahr. 

 in the one case, and — 0-54° in the other. When we remember 

 that the summer-temperature of that region may be raised more 

 than 30° Fahr., and its winter-temperature as much as 60° in the 

 course of a few days, by a change of wind (see pp. 438 & 448), 

 it will be seen how much more influence a permanent alteration 

 in the prevalent character of the atmospheric circulation might have 

 exerted on the melting of the American ice-sheet than the astronomical 

 cause now suggested. 



^ It seems to rae improbable that the close of the Glacial Period took place at 

 so remote a date. 



^ Dr. Ekhoim's figures .showing the increase or diminution of heat received 

 from the sun at lat. 55° N., as compared with that of the present era, are as 



f jllows : — 



9100 years ago . 2F, WO years ago. 



Cent. Fahr. Cent. Fahr 



May +l-7°=+a-0B° -2-4°=-4-3l° 



June +l-9<'=+:3-420 -3-0°=~5 40° 



July +l-7°=+3-06° -2-&°=-5-04o 



Pummer months : Apl. to Sept. +!<''= +2-.34« -2-G«'=-3-60° 



Winter months : Oct. to March. -10°=-r8to +r7*>=+3-06° 



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