172 HEAT OF THE WATERS, 



depth downwards to nine hundred and fifty feet an 

 unvarying temperature of 6 0, 6 0. (43 0, 9 F.) pre- 

 vails. In Lake Constance a constant tempera- 

 ture of 4°-5 C. (40°-l F.) was found at the deepest 

 part ; in the Lake of Lucerne 4°'9 C. (40°'82 F.) ; 

 in that of Neufchatel 5°'C (41° F.), and so on. 

 These slight excesses above 4° have been attributed, 

 and most likely with correctness, to the heat of the 

 bottom. In southern countries, whose temperature, 

 even in the winter months, never falls for any length 

 of time so low as 4° C, the lakes must in general 

 keep up, in their depths, a temperature nearly the 

 same as, but a little higher than, the lowest annual 

 temperature of the locality. The Mediterranean 

 Sea, which by reason of its slight communication 

 with the ocean may almost be considered as a great 

 lake, has, at the depth of from 1000 to 3000 feet, 

 a temperature of 12°'6 C. (54°*7 F.) Its mean 

 temperature at the surface reaches 17° or 20° C. 

 (62°-6 or 68° F.) 



In the great oceans the temperature has been 

 examined at many points, at some to depths as 

 great as 6000 feet. It appears that in general it 

 diminishes with the increase of the depth, at first 

 quickly, then more slowly, and at last almost im- 

 perceptibly; and it is especially remarkable that 

 even near the equator, where the temperature at 

 the surface of the sea never falls below 25° C. 

 (77° F.) it was found at the depth of 3000 feet 



