Beport of the Researches of M. Agamz, 147 



coating of remarkably pure ice. That the precipitation of 

 these watery-vapours is the sole cause of the increase of 

 weight the ice acquires during the night, is clearly proved by 

 this circumstance, that, during the prevalence of cold weather, 

 when the temperature of the day differs but little from that 

 of the night, any pieces of ice which are freely exposed to the 

 air undergo no difference in respect to their weight. The 

 variations, then, which M. Hugi has observed in this matter, 

 are entirely due to the drought or moisture of the atmosphere, 

 and the variations of the temperature. 



Observations upon the Crevasses. — At first sight it appears 

 strange that the crevasses, which of all the phenomena of 

 glaciers are those which have been most frequently described, 

 and have most engaged the attention of travellers and the 

 public, are those concerning which we possess the least accurate 

 information. The crevasses, as every one admits, are the re- 

 sult of an internal tension. But the inquiry still remains. 

 What is the cause of this tension ? and this is the problem 

 which remains to be solved. Repeated observations at differ- 

 ent periods of the year, and under diff'erent atmospheric con- 

 ditions, can alone sufficiently instruct us upon the point, and 

 enable us to decide among the various explanations which 

 have hitherto been proposed. According to our own obser- 

 vations, the probability is, that few crevasses are formed ex- 

 cept during the summer ; an opinion which coincides with 

 that maintained by those mountaineers who are most fami- 

 liar with the changes of the glaciers. During our sojourns in 

 the years 1840 and 1841, we often heard reports, occasioned 

 by the glaciers, during the night; but never actually wit- 

 nessed their formation. The summer of 1842 appeared to 

 have produced a great number ; for not only did we hear 

 many detonations during the night, but on many occasions we 

 saw them open under our eyes. For an account of these ob- 

 servations, see as under.* 



From these observations, it follows that the formation of the 

 crevasses occurs chiefly during those cold nights which succeed 

 to very wet and humid days, — a fact which appears decidedly 

 to support the theory of infiltration. At all events the sudden 



♦ Jameson's Journal, vol. xxxiii., p. 402. 



