ON THE STRUCTURE OF GLACIER ICE 485 



(i) "At its origin, near the N6v6, the compact (or proper glacier 

 ice) contains, like the ice of the Neve, a notable quantity of air. But 

 there is this difference between the two, that in the compact ice the 

 air, instead of being distributed through the whole mass, is united in 

 small perfectly circumscribed bubbles, whilst the interspaces of these 

 bubbles are perfectly transparent, so that without being as diaphanous 

 as ordinary water-ice, the compact ice has not the opacity of Nev6 

 ice. Moreover, it is more compact, and what is especially character- 

 istic, it presents no trace of granular structure : a fragment exposed 

 to the action of heat does not become resolved into grains of Nev6, 

 but breaks up into angular fragments. 



" This difference of structure is accompanied by a greater imper- 

 meability ; water no longer traverses the mass with the same ease and 

 uniformity, but is seen to follow in preference certain angular routes 

 which are the capillary fissures." — P. 151. 



(2) " The means employed by nature to maintain this amount of 

 plasticity and compressibility in glacier ice is the water which circulates 

 throughout the mass, and which, while it lubricates it, contributes to 

 maintain within it a constant temperature during the greater part 

 of the year." — Pp. 152, 153. 



(3) " Superficial fissures which must not be confounded with the 

 capillary fissures. 



" When during a fine summer day one travels over the upper 

 regions of the compact ice (about the region of the Abschwung, on 

 the Aar glacier), a continual crepitation is heard on all sides. It is 

 caused by the bubbles of air which on approaching the surface escape 

 through the ice, where they have been dilated by the effect of 

 diathermanicity, and cause the parietes of the ice to burst when they 

 are no longer sufficiently strong to resist the dilatation of the air." — 



P- 153- 



(4) " The air-bubbles undergo no less curious modifications. In 

 the neighbourhood of the Neve, where they are most numerous, those 

 which one sees at the surface are all spherical or ovoid ; but by 

 degrees they begin to be flattened, and near the end of the glacier 

 there are some which are so flat, that they might be taken for fissures 

 when seen in profile. The drawing, pi. 6, fig. 10, represents a bit of 

 ice detached from the gallery of infiltration. All the bubbles are 

 greatly flattened. But what is most extraordinary is, that, far from 

 being uniform, the flattening is different in each fragment, so that the 

 bubbles, according to the face which they offer, appear either very 

 broad or very thin. I know of no more significant fact than this, 

 since it demonstrates that each fragment of ice is capable of undergoing 



