Hot and Thermal Springs. 387 



feet. The same temperature would of course be found at the 

 same depth on the bottom of the lake, if it were entirely filled 

 up with the solid masses which compose our globe. But 680 

 feet is not the greatest depth of the lake, for it measures as 

 much as 950 feet in some parts. Supposing the increase of 

 temperature to proceed in the same proportion as was observed 

 in the neighbouring sounding, a temperature of 68°.34 would 

 be found to prevail at the depth of 950 feet. These thermo- 

 metrical relations, which must be imagined quite independently 

 of the lake, were doubtless interrupted at the moment of the 

 formation of the lake, but yet not entirely destroyed.* We may 

 therefore still be allowed to assume 68°.34 for the temperature 

 of the bottom of the lake, at a depth of 950 feet, although its 

 actual temperature must be the same as that of the water at the 

 same depth, which, according to Saussure, is 47°.T2. We have 

 therefore to distinguish between the actual temperature of the 

 bottom of the lake, and that which it would have, considering 

 only its latitude, its elevation above the sea, and its depth. 

 The difference between them is the thermometrical expression, 

 or as it were a measure, for the heat communicated from the 

 earth to the water, and with it carried to the surface. Thus 

 this thermometrical expression would be for the Luke of Geneva, 

 at a depth of 950 feet, 68^34- — 9°.72=58°.62. The positive 

 quantity of heat which escapes from the bottom of the lake into 

 the water, however, depends on the degree of conductibility of 

 the earthy and rocky strata which lie beneath it. 



In lakes, therefore, relations exist similar to those in the gla- 

 ciers, namely, that there rests upon a certain surface a mass, in 

 the one case of snow and ice, in the other of water, which con- 



• With respect to this, I cannot agree with my friend Professor Sfuncke, 

 who considers that the source of heat at the bottom of the lakes must ah-eady 

 have been exhausted by time. See Gehler's n. VVorterb. as above. Such a 

 supposition could only be admitted, if we could consider the bottoms of lakes 

 to a considerable depth as non-conductors of heat. But for such a supposi- 

 tion there are no grounds. To whatever depth, then, the cooling influence 

 of the water is felt in the earth, from the same depth will the warming in- 

 fluence of the interior of the earth be able to exert itself; that is to say, the 

 water at the bottom of the lakes will receive heat from the interior of the 

 earth. 



VOL. XXITI. \0. XLVI. OCTOBEn 1837. c c 



