TRANSACTIONS OP THE SECTIONS. 67 



The force of gravaty, if left free to act, would distribute the air in equal quanti- 

 ties and alike about both poles, and make the bai-ometric pressiu-e nearly the same 

 for all latitudes. There must, therefore, be some force exerted upon the air, or in 

 the air of these vmknown Austral reg^ions, which counteracts gravity to that enor- 

 mous extent, and prevents such equal distribution. 



What the natm-e of this force may be is matter of conjecture, but we think it 

 may sm-ely be traced to heat. " What !" I almost hear you say, "heat enough in 

 pei-petual development about the South Pole to exert a ceaseless lifting force of 

 130 lbs. upon every square foot of surface within an area of 8,000,000 square miles ? " 



Be not startled ; but freeing yom' mind from all bias, give me, I pray you, your 

 attention while I endeavom* to show that in this theory of a constant play of heat 

 about the South Pole there is nothiug either very startling or paradoxical. 



Under the equatorial cloud ring, the mean barometric pressm-e is 20 lbs. less to 

 the square foot than it is in the calm belt of Cancer. This fact is familiar to sea- 

 men, and well known to meteorologists. To this diminished pressure we owe the 

 trade-winds, as Captain Sir James Ross and others have already remarked. More 

 than this : in the centre of the cyclone the atmosphere is so attenuated, that ita 

 pressure is sometimes diminished below the mean pressure of the place by more 

 than 200 lbs. to the square foot. 



To what, if not chiefly to heat, shall we attribute this ? But whence comes the 

 heat at such times and places ? Clearly, it is not direct heat impressed upon the air 

 then and there by the rays of the sun. 



The equatorial cloud ring overhangs a region of constant precipitation, and the 

 low barometer in the vortex of a tornado is always attended by deluges of rain. 

 Here then we have a condition that accompanies the place of low barometer, both 

 in the calm belt and the vortex. During this heavy precipitation that takes place 

 in the centre of the storm, immense volimies of heat, that is always latent in aqueous 

 vapom", are set free among the clouds ; it warms and expands and drives off the 

 upper ail'. Thus, that below is made to rush in at the surface, either, as the case 

 may be, with the constancy of the gentle ti-ades, or the violence of the hurricane, 

 according to the extent and manner of the rarefaction. Moreover, the vapour before 

 it is formed into rain, being lighter than the air, also assists to diive it away, so 

 that the barometer would stand higher under air that is dry, than under air that is 

 damp, even were there no vapour condensed. Now then sm-vey, if you please, on 

 a chart or globe, the Austral regions on the solar side of 40° S., and tell me what 

 do you see ? Why, all the way around, between that parallel and the Antarctic 

 Circle, you see an almost uninterrupted expanse of water. Indeed, with the ex- 

 ception of Patagonia, and a few comparatively small islands here and there and far 

 between, we have nothing but one continuous evaporating surface. Throughout this 

 entire expanse the prevailing vriuds are from the northward and westward. These 

 are the " brave west winds" of the southern hemisphere. They are strong winds ; 

 they suck up fi-om the sea moisture as they go ; they waft immense clouds of it over 

 into the unexplored regions that encu-cle the pole. This vapom- is to the winds what 

 fuel is to the steamer ; the latent heat contained in it being developed, is at once 

 the source of power in the aii", and the means of locomotion for the blast. Thus 

 loaded, these winds impinge, with their vapour and its latent heat, upon the icy 

 banier or upon the mountains there, where it is condensed, and its heat set free to 

 become sensible heat. Thus the severity of the Antarctic winter is mitigated by 

 heat that is rendered latent by the processes of evaporation in wann latitudes, and 

 conveyed to the south by invisible couriers through the air. This heat being thus 

 conveyed and liberated, waims and expands, and causes the polar air to ascend, as 

 the same kind of heat causes the aii* in the centre of the cyclone to ascend and flow 

 off, creating, like a huge stack to some inmiense furnace, a di-aught and innish of air 

 on the surface, from the distance of miles around. This di-aught into the Antarctic 

 unknown, extends from the South Pole all around to the distance of 8000 miles 

 towards the Equator. 



About the North Pole we have no such expanse of water, no such wafting of 

 vapour, no such low barometer, no such inrush of " brave west vsdnds," and conse- 

 quently no such mildness of climate. 



Behold all the rivers of Arctic America, Em'ope, and Asia ! The rains that feed 

 them are but occasional and gentle showers in comparison with those for which 



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