486 ON THE STRUCTURE OF GLACIER ICE 



in the interior of the glacier a proper displacement independently of 

 the movement of the whole." — P. 167. 



(5) "The same flattening of the bubbles is found at a greater 

 depth. While engaged in my boring experiments, I observed atten- 

 tively the fragments of ice brought up to the surface by the borer. I 

 found in them almost flat bubbles, perfectly similar to those of the 

 fragment figured above, at all depths from 10 to 65 metres. I 

 observed, besides, that in the fragments which proceeded from a great 

 depth, all the bubbles without exception were strongly flattened, 

 whilst at less depths there were some less compressed and even 

 altogether round, as at the surface. 



" It follows, hence, that a strong pressure is exercised in the 

 interior of the glacier." — P. 167. 



(6) " I ought also to mention a singular property of these air- 

 bubbles, which at first was very surprising, but afterwards admitted 

 of very satisfactory explanation. When a fragment containing air- 

 bubbles is exposed to the action of the sun, the bubbles insensibly 

 enlarge. Soon, in proportion as they enlarge, a transparent drop 

 .shows itself on some point of the bubble. This drop in enlarging 

 contributes its share to the enlargement of the cavity, and as it 

 progresses it predominates over the air-bubble. The latter then 

 swims in the midst of a zone of water, and incessantly tends to reach 

 the most elevated point, at least if the flatness of the cavity does not 

 hinder it." — Pp. 167, 168. 



(7) In a note appended to this passage, M. Agassiz speaks of the 

 irregularity of the walls of some of the bubbles, and adds, " The same 

 effect has been produced upon the bubbles of the fragment fig. 10. 

 There also all the bubbles have enlarged by diathermanicity, and a 

 little drop has developed in the middle of each. But as the cavities 

 are very small, the drops do not yet move freely in their cavity." 



It will be observed that in Nos. i, 4> 5, 6, M. Agassiz confounds 

 together the water-chambers and the air-bubbles under the common 

 term of " bubbles," and he affirms (6) that the presence of water in 

 the " air-bubbles " is the effect of exposure to the sun's rays, and of 

 the different diathermanicity of air and ice.i A careful analysis of 

 M. Agassiz's facts, however, is very instructive. In the first place, I 

 recognise in his fig. 10, pi. 6, a fair, though rough and sketchy, repre- 

 sentation of the general arrangement and form of the water-chambers 

 with their contained air-bubbles The chambers are as usual flattened, 

 but the artist has rightly represented their contained air-bubbles as 



1 The Messrs. Schlagintweit (Untersuchungen, p. I?) adopt Prof. Agassiz's \-iews on this 

 point, and with him regard the presence of water as a local and partial phenomenon. 



