of Temperature between Spring and River Water. 535 



the same, llj ; or, if the centesimal thermometer was used, 

 524 Fahr. ; if Reaumur's, 57| Fahr. 



In another gallery, 564: ft. below the surface, the water and 

 air had likewise the same temperature, 12J°, either 54J or 

 60£ Fahrt. The water at the bottom, 677 ft., was 14°, °57% 

 or 63J Fahr. The ratio in which the heat increases, there- 

 fore, increased as we descend; since a difference of 113 ft., 

 between the depth of the bottom of the shaft and the lowest 

 gallery, makes a greater difference in temperature than the 

 difference of 243 ft. between the lowest and upper gallery. 

 This heat is the more striking, when it is considered that the 

 water is impregnated with salt : indeed, Saussure appears 

 inclined to consider it accidental, perhaps occasioned by the 

 combustion of pyrites, or other causes in the interior of the 

 mountain. {Voyages dans les Alpes, torn. iv. c. 50.) All experi- 

 ments of this kind, indeed, are liable to error, from the fre- 

 quent occurrence of warm springs, and other accidental causes 

 of increase in temperature. The water at the bottom of deep 

 lakes is always found several degrees colder than the atmo- 

 sphere, even when the water at the surface is warmer : but 

 this may be accounted for by the difference in the specific 

 gravity of water at different temperatures ; and, as the heat of 

 the sun and atmosphere in summer is greater than the mean 

 heat of the earth at moderate depths, the water at the bottom, 

 even if it becomes of the same heat with the earth, must be 

 colder than that at the surface, which, from its exposure to 

 the sun, becomes frequently warmer than the air. The same 

 causes affect the temperature of the sea; and the greater 

 saturation of the water below with salt renders it yet more 

 susceptible of cold. Under currents from the poles, and the 

 sinking of the water of low temperature, which results from 

 the melting of the icebergs which float into warmer latitudes, 

 contribute still farther to lower the temperature of the deep 

 sea. If, then, the temperature of the sea at great depths is 

 found not many degrees lower than that at the surface, it 

 would be a striking proof of the effect produced by the heat 

 of the earth : but 1 am not aware of the results of the experi- 

 ments which have been made on this subject. 



We must, then, rest satisfied with the well-ascertained fact, 

 that the temperature of the earth, even at depths of a few 

 feet, never descends, in temperate latitudes, to the freezing 

 point ; and that at the depth of 60 ft. it is always the same ; 

 in winter much higher, in summer considerably lower, than 

 that of the atmosphere. Spring water, then, which has its 

 source at a considerable depth, will, when it first rises, be of 



