SOJOURN OF mi ON THE GLACIER. 319 



snow than that of the Aar ; and though the 

 magnificent ice-cave, so well known to trav- 

 elers for its azure tints, was inaccessible, they 

 could look into the vault and see that the 

 habitual bed of the torrent was dry. The 

 journey was accomplished in a week without 

 any untoward accident. 



In the summer of 1841 Agassiz made a 

 longer Alpine sojourn than ever before. The 

 special objects of the season's work were the 

 internal structure of these vast moving fields 

 of ice, the essential conditions of their origin 

 and continued existence, the action of water 

 within them as influencing their movement, 

 and their own agency in direct contact with 

 the beds and walls of the valleys they occu- 

 pied. The fact of their former extension and 

 their present oscillations might be considered 

 as established. It remained to explain these 

 facts with reference to the conditions prevail- 

 ing within the mass itself. In short, the in- 

 vestigation was passing from the domain of 

 geology to that of physics. Agassiz, who was 

 as he often said of himself no physicist, was 

 the more anxious to have the cooperation of 

 the ablest men in that department, and to 

 share with them such facilities for observation 

 and such results as he had thus far accumu- 



