362 Prof. BischofF oti the Temperature of 



that, in the winter, no more ice is melted away from the lower 

 end of the glacier. And this was no more than was to be ex- 

 pected, as the freezing temperature to which the soil beneath 

 the lower end of the glacier is exposed in winter, must neces- 

 sarily cool it down to the freezing point, or still lower. These 

 observations also prove, that even at the depth of four feet, the 

 earth was reduced to the freezing point, so that at a less depth 

 the temperature must certainly have been below 32°. But 

 from this it by no means follows, that the temperature of the 

 soil under the glacier, at a distance from its lower extremity, 

 where it is not exposed to the immediate influence of the frost, 

 is reduced to so low a degree. We must, therefore, still allow 

 of the possibility of the melting away of the glacier from under- 

 neath, at the expense of the internal heat of the earth in those 

 places. In this case, however, the water cannot effect its escape 

 from under the glacier, because so soon as it approaches the 

 lower extremity, it must freeze, and form such a dam of ice as 

 to prevent all possibility of escape. 



If it is as certain that some glaciers yield water in the winter, 

 as that others give none, there seems scarcely any other mode 

 of accounting for this difference, than by supposing the melting 

 of the under surface of the glacier in the latter case only to l)e 

 effected at the expense of the internal heat of the earth, and in 

 the former by the additional assistance of springs, by means of 

 which the water, even during the winter, acquires a temperature 

 higher, though perhaps but by a few tenths of a degree, than 

 the freezing point, which renders the uninterrupted efflux 

 possible. 



But where do the waters remain which in winter cease to 

 flow from under the glaciers ? Ebel* relates, that, in winter, 

 nothing is to be seen of the caverns in the ice at the lower end 

 of the glaciers : they are covered with snow and ice, but in the 

 spring and summer the swollen streams break through the ice, 

 and form caverns of 100 feet in height, and from 50 to 80 feet 

 broad, the shape and size of which are variable. 



This swelling of the water might, indeed, be attributed to the 



• Partiii. p. 120. 



