446 PHYSICAL GEOGRAPHY OF THE SEA, AXD ITS METEOROLOGY. 



face of the antarctic circle is not only land, but that its coasts 

 How the tempera- are probablj biglilands ; that in its topographical 

 SiTed b^'^crosJacf features it presents all the conditions that are re- 

 mountains. ° qnired for the rapid condensation of the vapour with 

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

 valleys beyond mild climates may be expected. The aqueous 

 vapour 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 vapour 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 pui'poses. 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 vapour ; 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 vapom*. 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 vapour at the 

 temperatm-e of 40°. In order to arrive at the place of polar 

 calms, it has to cross a mountain range, we wiU suppose, the sum- 

 mits of which are pushed high up into the regions of perpetual 

 snow. As this air, with its moisture, rises, it expands, cools, and 

 liberates the latent heat of its vapom% which the ah' receives in the 

 sensible form. Now suppose the expansion due the height of the 

 mountain-top to be sufficient to lower the temperature of dry air 

 to — 50 , but, on account of the latent heat which is hberated from 

 the vapour of the moist air, the temperatm*e of the air that has 

 ascended, instead of falling as it crosses the mountain to —50°, as 

 dry air would do, falls, iu consequence of the condensation of its 

 vapour, no lower than —30°. Thus, in the case supposed, heat 

 enough has been set free to raise the temperatm^e of the newly- 

 arrived air 20°. Consequently, when this au', which, at the tempera- 

 tm-e of 40°, came from the sea loaded with vapour, passes the moun- 

 tam, it loses vapour, but receives heat ; descendiog into the valleys 

 beyond, it is again compressed by the weight of the barometric 

 column, which, let us assume, is the same in the valley as at the 

 sea level on the other side of the mountain. The temperature of 



