94 Dr Forry on the Climate of the United States. 



We thus perceive at once the principal cause of the rise 

 of the isothermal line on the western coast of continents in 

 extra-tropical latitudes ; for there is thus swept from the 

 ocean, Avhich never sinks below the freezing point, a humid 

 atmosphere, which, in its passage over the land, has a con- 

 stant tendency to establish an equilibrium of temperature, 

 and as its vapour is gradually condensed, it also evolves its 

 latent heat. As lai'ge bodies of water never become so cold 

 in winter, or so warm in summer, as the earth, the winds that 

 sweep from them have a constant tendency to maintain an 

 equilibrium of temperature. Land winds, on the contrary, 

 must necessarily bear with them the greater or less de- 

 gree of cold induced by congelation, while, in summer, they 

 will convey the accumulated heat absorbed by the earth ; 

 and thus is produced, in a great measure, those extremes of 

 the seasons which characterise extra-tropical latitudes on 

 the eastern coast.-; of continents. 



The difference of temperature on the eastern and westei-n 

 coast of continents is still further inci-eased by local causes. 

 Europe is separated from the polar circle by an ocean, while 

 eastern America stretches northward at least to the 82'' of 

 latitude. The former, intersected by seas, which temper the 

 climate, moderating alike the excess of heat and cold, may 

 be considered a mere prolongation of the old world ; while 

 the northern lauds of the latter, elevated from three thou- 

 sand to five thousand feet, become a great reservoir of ice 

 and snow, Avhich diminishes the temperature of adjoining 

 regions. " America," says Mr Phillips, " with little north 

 tropical and wide polar land, gives us a case of extreme re- 

 frigeration from the pole towards the equator ; Africa and 

 the west of Europe compose a surface of wide and hot noi'th 

 tropical land, with free channels to a polar sea." Hence 

 Lapland, under the 72", experiences a less rigorous climate 

 than Greenland under the 60th parallel. On the other hand, 

 between the 40th parallel and the equator, the influence of 

 land, if not very elevated, produces effects diametrically 

 opposite ; for the surface of the earth absorbs a large quan- 

 tity of caloi'ic, which is diffused by a radiation into the 

 atmosphere. Thus Africa, as Malte-Bruu observes, " like 



