PROGRESSION OF GLACIERS. 
271 
duced, aiid exhibit these relations to one another. 
It may he, moreover, that, when the glacier is at 
a temperature below 32°, its motion produces ex- 
tensive fissuration throughout the mass. 
Now that water pervades this network of fis- 
sures in the glacier to a depth not yet ascer- 
tained, my experiments upon the glacier of the 
Aar have abundantly proved ; and that the fis- 
sures themselves exist at a depth of two hundred 
and fifty feet I also know, from actual observa- 
tion. All this can, of course, take place, even 
if the internal temperature of the glacier never 
should fall below 32° Fahrenheit ; and it has ac- 
tually been assumed that the temperature within 
the glacier does not fall below this point, and 
that, therefore, no phenomena, dependent upon 
a greater degree of cold, can take place beyond a 
very superficial depth, to which the cold outside 
may be supposed to penetrate. I have, however, 
observed facts which seem to me irreconcilable 
with this assumption. In the first place, a ther- 
mometrograpli indicating — 2 Centigrade (about 
28° Fahrenheit) at a depth of a little over two 
metres, that is, about six feet and a half, has 
been recovered from the interior of the glacier of 
the Aar, while all my attempts to thaw out other 
instruments placed in the ice at a greater depth 
utterly failed, owing to the circumstance, that, 
after being left for some time in the glacier, they 
