Hot and Thermal Springs. 371 



will find a passage. But these currents will take a contrary 

 direction in the winter, and will enter from below, and make 

 their escape above, so long as the temperature of the atmosphere 

 is lower than that of the interior of the glacier. However, 

 these currents, which tend to cool the under surface of the gla- 

 cier, can never be so considerable as those which take place in 

 the summer, for the cold air cannot be warmed within the gla- 

 cier above 32°, so that there can be but a small difference be- 

 tween the density of the atmospiiere and that of the air within. 

 The under surface of the glacier cannot, therefore, suffer any 

 considerable depression of temperature during the winter, so 

 that the hypothesis, that the soil beneath the glaciers remains 

 at about 3S° throughout the whole year remains almost un- 

 shaken. 



It is probable that the piercing cold currents of air, which is- 

 sue from the fissures, when a sudden change takes place in the 

 temperature of the atmosphere, carrying fine grains of ice along 

 with them, and scattering them, far and wide, like fine snow 

 over the country,* take place when the external temperature 

 suddenly sinks below 32°.0, by which the current is found 

 to alter its direction, and to rush from the cavern towards the 

 fissures above. For if the air which issues from the fissures at 

 a temperature of 32°, be impregnated with humidity, when it 

 enters an atmosphere of a temperature below 32°, the water 

 must be frozen, and thus form the grains of ice. And this 

 phenomenon is precisely analogous to one which I observed a 

 short time since at the mouth of a shaft, during a sharp frost, 

 where the warm air, which rose out of the shaft, deposited flakes 

 of snow on the whim, and on the buildings over the shaft. 



It is of importance to the study of the internal heat of the 

 earth, to ascertain whether glaciers in general increase or not. 

 The annual advance of the glaciers during the warm season, 

 which Saussure-f- very simply explained by the under surface be- 



• Ebel, part iii. IIC. Gruner in his " Beschreibung der Eisgebirge des 

 Schweitzerlandes.'' Bern, 17C0, relates an example of this, witnessed by a 

 friend of his, who travelled across a glacier in the middle of July. 



t Voyages, i. p. 453. Esciier in Gilb. Annal. vol. Ixix. p. 113. ITorncr in 

 the Neucsphysikal, Worterbiich, vol. iii. p. 135. Against this opinion see 



vol.. XXIII. NO. XI. VI. OCTOHKK 1837. 13 b 



