liesearches on Existing Glaciers, 249" 



guides assured us, that the water disappeared from those cre- 

 vasses which contained it during summer, either by its flowing 

 away or becoming frozen. Let it not be objected, that this is 

 quite natural, and that it is useless to mention it. It fre- 

 quently happens that, in summer, the mean temperature of 

 several consecutive days is some degrees below zero (32° F.), 

 without the water of the crevasses being frozen ; there is only 

 a pellicle of ice formed, which covers it during the night, and 

 disappears during the day. A circumstance which inclines 

 me to believe that the water they contain during the summer 

 freezes rather than runs off, is, that, on the glaciers, we have 

 on several occasions met with circumscribed portions of ice in 

 the form of an ellipse, which had completely the appearance 

 of congealed baignoires. The ice was full of air-bubbles, but 

 its surface was perfectly smooth ; it was extremely hard, and 

 more brittle than usual. The bubbles were pretty uniformly 

 distributed, and were nearly of an equal size, affecting in ge- 

 neral an elongated and pyriform shape ; but we did not re- 

 mark any of those vertical laminae of varied colour, to the 

 study of which M. Agassiz means afterwards to devote parti- 

 cular attention. Subsequently we did not find any example 

 of ice so full of bubbles, except on the last summit of the 

 Jungfrau. It would be extremely difficult, in the present state 

 of our knowledge, to point out the cause of these differences. 

 Up to the present time we have only obtained very imperfect 

 data regarding the modifications to which ordinary ice is sub- 

 jected under the influence of atmospheric agents ; and, as to 

 the modifications which glaciers undergo in the interior of 

 their mass, at different periods of the year, these are as yet 

 entirely unknown. 



" We were scarcely able to recognise our glacier of the 

 Aar, so varied and animated in summer, under the uniform 

 bed of snow. The great medial moraine itself was more or 

 less effaced, and only formed a longitudinal ridge, whose 

 flanks were much less inclined than in summer. We first of 

 all reached the northern flank, and when we had passed over 

 about a third of the glacier, we crossed to the southern flank, 

 at the point where the morabie is considerably swollen. We 

 there saw, to our great satisfaction, that our route improved 



VOL. XXXIII. NO. LXVI.-— OCTOBER 1842. R 



