§ 867, 863. THE ANTARCTIC REGIONS, ETC. ^63 



Falkland Islands and their neigliboring shores the cattle fnid pas- 

 turage always in winter. The thermometrical difference of climate 

 at these two places, north and south, may be taken as a sort of 

 index to the relative difference between the arctic and antarctic 

 climates of our planet. 



867. Along the eastern base of the Kocky Mountains the iso- 

 Thermai difference thcrms mouut up* toward thc uorth in consequence 

 antarctic climates, of the hcavy wiutcr prccipitation upon the western 

 slopes of these mountains. The heat which is required to con- 

 vert the water of the Columbia and other rivers into vapor is set 

 free on the mountain range, and the upper Missouri is by this heat 

 kept open for navigation long after the lower and more southern 

 portion of it is frozen up. 



SQS. In the preceding chapter the circumstances have been 

 How the temperature considcrcd which favor the idea that most of the 

 byTroTs^i^g^mouJTt^ uukuowu surfacc of the antarctic circle is not only 

 ^'°'' land, but that its coasts are probably highlands ; 



that in its topographical features it presents all the conditions 

 that are required for the rapid condensation of the vapor with 

 which the impinging air from the sea is loaded, and that in the 

 valleys beyond mild climates may be expected. The aqueous 

 vapor which the air carries along is one of the most powerful 

 modifiers of climates. It is to the winds precisely what coals are 

 to the steam-ship at sea — the source of motive power. The con- 

 densation of vapor is for one what the consumption of fuel is for 

 the other ; only with the winds the same heat may be used over 

 and over again, and for many purposes. By simply sending 

 moist air to the top of snow-capped mountains, condensing its 

 moisture, and bringing it down to the surface again, it is made 

 hot. Though by going up the air be cooled, it is expanded, 

 and receives as sensible heat the latent heat of its vapor ; being 

 brought down to the surface again, and compressed by the whole 

 weight of the barometric column, it is hotter than it was before 

 by the amount of heat received from its vapor. That we may 

 form some idea as to the modifying influences upon climate which 

 might arise from this source, let us imagine the air as it impinges 

 upon the antarctic continent to be charged with vapor at the 

 temperature of 40°. In order to arrive at the place of polar 



* Blodget's Climatology of the United States. 



