82 TERRESTRIAL ADAPTATIONS. 



coast of Africa, tends to cool the parts nearer the 

 equator. Great as the difference of temperature 

 is in different climates, it would be still greater 

 if there were not this equalizing and moderating 

 power exerted constantly over the whole surface. 

 Without this influence, it is probable that the two 

 polar portions of the earth, which are locked in 

 perpetual ice and snow, and almost destitute of 

 life, would be much increased. 



We find an illustration of this effect of the 

 ocean on temperature, in the peculiarities of the 

 climates of maritime tracts and islands. The 

 climate of such portions of the earth, corrected in 

 some measure by the temperature of the neigh- 

 bouring sea, is more equable than that of places 

 in the same latitudes differently situated. Lon- 

 don is cooler in summer and warmer in winter 

 than Paris. 



2. Water expands by heat and contracts by 

 cold, as has been already said ; and in conse- 

 quence of this property, the coldest portions of 

 the fluid generally occupy the lower parts. The 

 continued progress of cold produces congelation. 

 If, therefore, the law just mentioned had been 

 strictly true, the lower parts of water would have 

 been first frozen ; and being once frozen, hardly 

 any heat applied at the surface could have melted 

 them, for the warm fluid could not have descended 

 through the colder parts. This is so far the case, 

 that in a vessel containing ice at the bottom and 



