TEMPEHATUEE OF GLACIEItS. 165 



Few of these rivulets entirely cease flowing in 

 the winter. Their temperature, whenever it has 

 been examined, has been found above 0° Cent. 

 (32° F.), but seldom higher than 1° C. (33°-8 

 F.) If we connect with tins fact the constant 

 though slow action of the heat of the ground, the 

 springs which probably come up in many places 

 under the glaciers, and the penetration of the 

 external air under the cracked ice-mass, we find 

 causes enough to account for the continual melt- 

 ing of the ice at the bottom of the glacier. Agas- 

 siz has shown too, by immediate experiment, that 

 the interior of the glacier-mass has invariably the 

 temperature of melting ice. For this purpose he 

 had a hole bored by degrees down to a depth of 

 two hundred feet. Only at the surface, and at the 

 depth of a few feet, can it be found that there is any 

 fall of the temperature below the freezing point, 

 due to nocturnal radiation. This lowering of the 

 temperature cannot, even in winter, go much 

 farther, because at this season all the glaciers are 

 covered with a thick layer of snow. 



The whole mass of the glacier rests on the 

 bottom of the valley, and presses by reason of its 

 weight against the unevennesses on the general 

 slope of the ground While now the parts of the 

 ice, which rest on the ground, are gradually 

 melting away, the load pressing from above effects 

 an onward movement down the valley. 



