THE ANTARCTIC REGIONS AND THEIR CLIMATOLOGY. 441 



seem to serve as cliimneys to the atmosi:>Jiere. The latent heat 

 which is hberated by the vapour they condense has the effect 

 of bringing down the barometer, and of causing, dm^ing the 

 rainy season, an indraught thitherward from many miles at sea. 

 Such is the rarefaction produced by the hberation of this heat, that 

 its effects are, as the pilot charts show, felt and confessed by the 

 winds at the distance out to sea of more than a thousand miles from 

 the Sandwich Islands. Thus the land and the islands give us in 

 the circulation of the atmosphere systems within system. In the 

 Mississippi and aU great rivers, the general movement of the waters, 

 notwithstanding the eddies and the whirlpools, is down stream with 

 the current. So with the atmosphere : its general movements are 

 indicated by observations at sea ; its eddies and whnlpools are 

 created by the mountains, and the islands, and other inequalities 

 which obstruct its flow in the regular channels. The mean read- 

 ing of the barometer when the rainy season in India is at its height 

 is 0.4 inch less than it is in the midst of the dry. 



860. The diagram (Plate XYI.) shows the observations in the 

 Agreement of obser- southcm hemisphere to be so accordant, and the cm-ve 

 vaiions at sea. itself SO regular, that we feel no hesitation about pro- 

 jecting this curve into the unexplored spaces of the south, and assert- 

 ing, with all the boldness consistent with the true spirit of philoso- 

 phical deduction, that, whether the actual barometric pressm-e at 

 the south pole be as low as 28.14 or not, it is nevertheless very 

 much lower in the antarctic than in the arctic regions. 



861. The question now arises. Whence tliis unequal distribu- 

 The question why tiou of atmosphcro betwcen the two hemispheres, 



the barometer should ^ , iitii i*ii/^n i l 



stand lower about the auQ why shouid the mean height 01 the barometer 

 poi?considercd°°'^^^' iH chcumpolar regions be so much less for the 

 austral than for the boreal ? No one, it is submitted, will attempt 

 to account for tliis difference by reason of any displacement of 

 the geometrical centre of the earth with regard to its centre of at- 

 traction, in consequence of the great continental masses of the 

 northern hemisphere ; neither can it be ascribed to any difference 

 in the forces of gravitation arising from the oblateness of our 

 globe ; neither can it be accounted for by the effects of diurnal 

 rotation after the Halleyan theory : that Avould create as low a 

 barometer at one pole as the other. The air, m its motions to the 

 east and in its motions to the west, ls in equipoise between the paral- 

 lels of 35^ and 40° N., 25° and 30° S. There is near each pole 

 and about the equator a place of permanently low barometer. 



