S92 Prof. BischofF on the Temperature of 



bottom of the lake. This case cannot of course occur in the 

 hake of Constance^ mentioned above by way of example. 



When the rocks which compose the bottoms of lakes, in which 

 the temperature at the bottom is 38°. 75, are very much fissured, 

 water of this temperatui'e will escape from them. If such 

 water reappear as springs at a lower level, the springs will have 

 a temperature nearly equal to 38^75. Thus I found the above 

 mentioned springs (chap, iv.) on the Spital Matte, which pro- 

 bably proceed from lakes situated above, to have a temperature 

 between 37°.6 and 40''. 



If the temperature of the air over a lake never fall so low as 

 that degree at which water possesses its maximum of density, no 

 layers of water can possibly be met with in the depths having so 

 low a temperature as that. For the lowest temperature of the 

 air in the cold season is the minimum of the lowest temperature 

 of the water in the depths. From this it follows, that in the 

 plains of the torrid zone, or in low valleys, where the mean 

 temperature is between 77°.90 and 80°.60, the bottoms of lakes 

 can never be below 69°80 to 71°.60. * 



In the sea, the cooling of the water at the bottom must pro- 

 ceed further, for the greatest density of sea-water is far below 

 38°. 7. Marcet"!* has shewn that sea-water continues to contract 

 and to increase in weight until it freezes to a solid body ; since 

 which a series of experiments have been made by Erman jun., \ 

 by which he found that salt-water of a specific gravity of 1.027 

 has no maximum of density, so long as it remains liquid, and 

 even when ice is formed in it, the remaining liquid part conti- 

 nues to increase very considerably in density. But this property 

 must also belong to the water of the sea, which, according to 

 Gay Lussac,§ from an average of fifteen experiments, possesses 

 a specific gravity of 1.0286 at a temperature of 46°. 4. If, then, 

 as Erman jun. asserts, sea-water offers no anomaly in its con- 

 traction between -|-8° and 25°.2, it is possible that in northern 

 latitudes water may be met with in great depths in the sea of 25°.2. 



* Von Humboldt Reiae etc. iii. 133. 



t In the paper read before the Royal Society of London, alluded to above, 



X PoggeudorfF's Annal. vol. xii. p. 463. 



^ Annal. de Clilmie ct de Phys. vols. vi. and vii. 18 1?- 



