THE ANTARCTIC REGIONS AND THEIR CLIMATOLOGY. 447 



this air now, instead of being 40°, ^dll be 60°. A powerful modifier 

 of climate is the latent heat of vapour in the air. 



870. At one time, as has been shown in Chap. lY., this heat is 

 Local variations of broiight dowTL fuom the cloud region to scorch the earth ; 

 climate, how caused, g^^ another time it causes the warm air to ascend, and 

 cooling currents to come down from the upper sky. To this cause 

 Dr. Franklin ascribed the cold summer gusts in America that come 

 from the west. To the effect of this vapour and its heat, mth the 

 constant vertical circulation imparted to the atmosphere, we owe those 

 variations of our climates wiuch make any given day of one year 

 to differ from its corresponding day of another. Were it not for 

 those vertical movements, our days would gi'adually grow cooler 

 from midsummer to midwinter ; as the sun recedes in the ecliptic, 

 each day, after he reached a certain degree of south declination, 

 would grow cooler and cooler until his return towards the north 

 again ; so that were it not for this vertical chculation the tempe- 

 rature of the day of the month, hke the rising and the setting 

 of the sun, or the changes of the moon, might be foretold in a 

 calendar. 



871. There is not only reason to suppose that the topogra- 

 Aurora anstraus. phical fcaturcs and thc cHmates of the antarctic re- 

 gions differ greatly fr'om the topographical features and climates 

 of the arctic, but there is reason to suppose a difference in other 

 physical aspects also. The aurora points to these. " On the 

 morning of the second of September last," says Capt. B. P. Howes, 

 in his abstract log of the "Southern Cross," lat. 58° S., long. 

 70° W., " at about half-past one o'clock, the rare phenomenon of 

 the aurora austrahs manifested itseK in a most magnificent man- 

 ner. Our ship was off' Cape Horn in a violent gale, plunging fu- 

 riously into a heavy sea, flooding her decks, and sometimes bm-y- 

 ing her whole bows beneath the waves. The heavens were black 

 as death: not a star was to be seen when the brilliant spectacle 

 first appeared. I cannot describe the »awful grandeur of the 

 scene ; the heavens gradually changed from murky blackness tiU 

 they became like vivid fire, reflecting a lurid, glowing brilliancy 

 over everything. The ocean appeared like a sea of vermihon 

 lashed into fury by the storm ; the waves, dashing furiously over 

 om- sides, ever and anon rushed to leeward in crimson torrents. 

 Our whole ship, sails, spars, and all, seemed to partake of the 

 same ruddy hues. They were as if lighted up by some terrible 

 conflagration. Taking all together, the howling, shiiekiiLg storm, 



