256 EFFECTS OF THE OCEAN. SKCT. XXVI. 



and continents about the north pole. Icebergs seldom 

 float farther to the south than the Azores ; whereas 

 those that come from the south pole descend as far as 

 the Cape of Good Hope, and occasion a continual ab- 

 sorption of heat in melting. 



The influence of mountain-chains does not wholly 

 depend upon the line of perpetual congelation. They 

 attract and condense the vapors floating in the air, and 

 send them down in torrents of rain. They radiate heat 

 into the atmosphere at a lower elevation, and increase 

 the temperature of the valleys by the reflection of the 

 sun's rays, and by the shelter they afford against pre- 

 vailing winds. But on the contrary, one of the most 

 general and powerful causes of cold arising from the vi- 

 cinity of mountains, is the freezing currents of wind 

 which rush from their lofty peaks along the rapid decliv- 

 ities, chilling the surrounding valleys : such is the cut- 

 ting north wind called the bise in Switzerland. 



Next to elevation, the difference in the radiating and 

 absorbing powers of the sea and land has the greatest 

 influence in disturbing the regular distribution of heat. 

 The extent of the dry land is not above the fourth part 

 of that of the ocean ; so that the general temperature 

 of the atmosphere, regarded as the result of the partial 

 temperatures of the whole surface of the globe, is most 

 powerfully modified by the sea. Besides, the ocean 

 acts more uniformly on the atmosphere than the diver- 

 sified surface of the solid mass does, both by the equality 

 of its curvature and its homogeneity. In opaque sub- 

 stances the accumulation of heat is confined to the 

 stratum nearest the surface. The seas become less 

 heated At their surface than the land, because the solar 

 rays, before being extinguished, penetrate the trans- 

 parent liquid to a greater depth and in greater numbers 

 than in the opaque masses. On the other hand, water 

 has a considerable radiating power, which, together 

 with evaporation, would reduce the surface of the ocean 

 to a very low temperature, if the cold particles did not 

 sink to the bottom on account of their superior density. 

 The seas preserve a considerable portion of the heat 

 they receive in summer, and from their saltness do not 

 freeze so soon as fresh water. So that in consequence 



