SECT, xxvi.] EFFECTS OF THE OCEAN. 293 



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 modi- 

 fied by the sea. Besides, the ocean acts more uniformly on 

 the atmosphere than the diversified surface of the solid mass 

 does, both by the equality of its curvature and its homo- 

 geneity. In opaque substances 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 transparent 

 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 of all these circumstances, the ocean is not 

 subject to such variations of heat as the land ; and, by impart- 

 ing its temperature to the winds, it diminishes the rigour of 

 climate on the coasts and in the islands, which are never 

 subject to such extremes of heat and cold as are experienced 

 in the interior of continents, though they are liable to fogs 

 and rain from the evaporation of the adjacent seas. On 

 each side of the equator to the 48th degree of latitude, the 

 surface of the ocean is in general warmer than the air above 

 it. The mean of the difference of the temperature at noon 

 and midnight is about 1'37, the greatest deviation never 

 exceeding from 0< 36 to 2 0< 16, which is much cooler than 

 the air over the land. 



