494 ON THE STRUCTURE OF GLACIER ICE 



never penetrate. They are larger than the httle fissures which have 

 just been mentioned, and far less numerous, particularly in the regions 

 in which the latter abound. Their distribution is not uniform in the 

 interior of the compact ice," p. 154 ; but (M. Agassiz goes on to 

 explain) they are arranged in bands and zones, which, becoming more 

 completely infiltrated with water than the intermediate ice, appear 

 blue and transparent, and are the blue veins. 



(9) " The quantity of bubbles with which the white ice is filled, is 

 the reason why the fissures are more slowly propagated in it ; the air, 

 by its elasticity, being unfavourable to the formation of fissures (I'air 

 ■qui est de sa nature elastique ne favorisant aucunement le crevasse- 

 ment). By degrees, however, and in proportion as the infiltration 

 perpetuates itself the rigidity increases, and the fissures multiply in 

 proportion. Every bubble that a fissure meets in its course loses its 

 aeriform contents. It becomes transparent, and the opacity of the 

 mass is so far diminished. The consequence of this multiplication 

 •of fissures is continually to diminish the number of bubbles, and by 

 this means to render the ice more and more transparent and blue. 



" It will be evident to any one who has followed the progress of 

 modern physics, that this phaenomenon is due solely to the diather- 

 manicity of ice. The air first and then the water becomes heated 

 through the ice. However minute may be the degree of heat which 

 is thus transmitted to them, it is enough to melt a part of the ice 

 which surrounds them, and thereby to increase the cavity in which 

 they are imprisoned. I do not think, however, that any very great 

 importance should be ascribed to this phjenomenon ; and the fact that 

 it is produced only when the ice is exposed directly to the rays of the 

 sun, is in my eyes an indication that it exercises no notable influence 

 ■on the mechanism of glaciers." — P. 157. 



(10) " When the ice has acquired a certain degree of transparency, 

 and the network of capillary fissures is fully established in it, water and 

 air penetrate into the fissures with great facility. One may assure 

 oneself of this in many ways, among others by the following experi- 

 ment, which I have repeated many times. Let a cube of ice of a 

 few decimetres on the side be detached from the bottom of a crevasse, 

 in that part of the glacier where the ice is most transparent, and 

 placed upon a rock. At first, a few fissures will appear on the surface, 

 then these fissures will be gradually propagated into the interior, and 

 the network becoming more and more complex, will by degrees reach 

 the base. If then, the block of ice be turned upside down, and water 

 be poured upon it, all the fissures will disappear from above down- 

 •wards, in the same order as they were formed. The block will remain 



