STRATUM OF UNIFORM TEMPERATURE. 401 



temperature at all depths. At the equator it 

 is colder as we descend until we reach the depth 

 of 7,200 feet, after which the temperature does 

 not alter with the depth. These results, which 

 have been obtained with extreme care, are 

 highly satisfactory, and appear to set at rest 

 the vexed question of ocean temperature. 



It .might be thought that, as it was found 

 that the internal temperature of the earth in- 

 creased on descending into it, the effect of this 

 increase of temperature would be experienced 

 by the deep ocean ; but Sir J. Ross is disposed 

 to believe that the internal heat of the earth 

 exercises little or no influence upon the mean 

 temperature of the ocean. 



Dr. Williams assigns as one cause of the 

 existence of this stratum of uniform tempera- 

 ture, and which, in the two polar regions, 

 appears as a bed of warm water underlying the 

 cold surface, the effect of pressure upon water. 

 He asserts that he has found, by experiment, 

 that water acquires a considerable increase of 

 temperature under great pressure ; an effect 

 apparently due to the extraction of the latent 

 heat of its dissolved gases. 



The temperature of the ocean, it is thus 

 seen, is greatly influenced by its depth. Under 

 ordinary circumstances, it appears that the 

 water close by the shore ^ is colder than that far 



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