348 rnYSiCAL GEOGRArnY of the sea, and its meteorology. 



the south pole — the antarctic winter — is annually a week longer 

 (§ 066) than the arctic. Tims, during the period of 10,500 ;years, 

 the antarctic regions will experience 142 3'ears of night, or 

 winter, in the aggregate, more than the arctic. Therefore it is 

 manifest, say the caiaclysmaiists, that though the two hemispheres 

 do receive annually the same amount of solar heat, yet the 

 amount dispensed by radiation is very much greater on one side 

 of the equator than the other. The total effect of the alternate 

 cooling down on each side of the equator causes an accumulation 

 of ice at the pole — when the nights are longest — sufficient, say 

 they, to disturb the centre of gravity of the earth, causing it to 

 iake up its position on the icy side of the equator. As the ice 

 accumulates, so is the water drawn over from the opposite 

 hemisphere. Such, brie% stated, is the theory which has found 

 very ingenious and able advocates in the persons of MM. Julien* 

 and Adhemar.'l' 



64G. Are the climates of the earth clianging ? — This theory is 

 alluded to here, not for the purpose of discussion, but for the 

 purpose of directing attention to certain parts of this work 

 in connection with it, as Chapters VII. and XXI., for example, 

 and of remarking upon the stability of terrestrial climates. 

 Though the temperate regions be cooler in the southern than in 

 the northern hemisphere, it does not appear certain that the 

 climates of the earth are now changing. Observations upon the 

 subject, however, are lacking. The question is one of wide- 

 spread and exceeding interest ; and it may be asked if w^e have 

 not in the strength of the trade-winds a gauge, or in their 

 barometric weight an index, or in the equatorial calm belt a 

 thermometer — each one of the most delicate construction and 

 sensitive character — which would, within the compass of human 

 life, afford unerring indications of a change of climates, if any 

 such change were going on? If the temperature of the S.E. 

 trade-winds, or the barometric pressure upon the X.E. (§ 641), 

 were to be diminished, the S.E. trades would force this calm belt 

 still farther to the north, and we might have a regular rainy 

 season in what is now the great desert of Sahara ; for where this 



* Courants et Revolutions de rAtmosphere et de la IMcr, comprenaut une 

 Tht'orie nouvello sur les Deluges Periodiques. Par Felix Jidieu, Lieutenant de 

 Vaisscau, etc. Paris, 1860. 



t Ee'volutions de la Mer. De'luges Periodiques. Par /. Adhemar. Paris, 

 1860. 



