THE GASEOUS POBTIONS OF THE ATMOSPHERE. 



17 



sation, and a local ascending current is created, into which 

 adjoining air and vapour rush from considerable distances, and 

 are carried to the higher regions to have the vapour condensed 

 to a large extent by the cold due to the elevation : the result 

 is a heavy fall of rain. The vapour that went up as an 

 aeriform substance com'^s down as a liquid, leaving the atmo- 

 sphere dry and clear. In just the same way many mountains 

 condense the vapour of the northern hemisphere, leaving the 

 air there comparatively free from it, and ready to acquire the 

 cool temperature which belongs to dry air in the middle and 

 upper regions of northern latitudes. In the southern hemi- 

 sphere, particularly beyond 50*^ of latitude, there are few 

 elevations of land to collect and condense the vapour that is 

 constantly furnished from the immense surface of the southern 

 ocean ; it is therefore slowly but extensively condensed in the 

 open atmosphere, and to a certain extent warms and swells it, 

 leaving the whole atmosphere less heavy than in the north. 

 But though there are only few elevations in the south, as 

 compared with the north, there are some, and they shew 

 the effects of the peculiar state of the atmosphere in this 

 hemisphere. The few elevations that exist there are remark- 

 able for having an abundance of rain, and for the strength and 

 continuance of the winds that blow about them. These 

 striking features are seen in Kerguelen's land, — Van Diemens' 

 land, — New Zealand, — Auckland and Campbell's islands, and 

 generally about such elevated land as exists in the colder 

 latitudes of the hemisphere. But distinguished among them 

 may be particularly noticed the extreme point of South 

 America about Cape Horn. Up the high lands of this part 

 of the world, the saturated air of the southern hemisphere 

 rushes with a fotce and constancy not to be paralleled in any 

 other part. Deluges of rain are almost continuous, and the 

 vortices created by them cause the saturated air to press 

 towards them from a large portion of the southern ocean, 

 reaching almost to New Zealand on the west, and far to the 



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