206 FOURTEENTH LETTER ON GLACIERS. [1847. 



sophical Transactions for 1846,* for the following reason : 

 There has lately appeared in the BibliothZque Universelle de 

 Geribve, a paper by M. Collomb, in which it is maintained, on 

 the authority of the experiments of M. Dollfuss on the Glacier of 

 the Aar, that the velocity of progress of that glacier is the same 

 at all seasons and in all weathers ; and that previous observers 

 who arrived at different conclusions on that glacier were in 

 error. It may be so. The Glacier of Aar is, as I have else- 

 where shewn,f in very peculiar conditions of mechanical con- 

 straint ; but it is important that it should be shewn by the 

 testimony of by far the completest series of observations which 

 has yet been published, and which extends over the entire year, 

 that this independence of the velocity upon external circum- 

 stances is not at least the general rule. 



The passage in M. Collomb's paper, to which I have alluded, 

 may be thus translated : " It results from the examination of 

 the registers of M. Dollfuss, which contain several thousand 

 observations, that the Glacier of the Lower Aar moves with per- 

 fect regularity ; no sudden starts nor pauses ; the movement 

 of any particular point taken on the surface of the glacier, whe- 

 ther in the centre or at the edges, is very slow, uniform, and 

 independent of atmospheric influences. (He goes on to say, 

 that, as it is the fastest in the centre of the glacier, and almost 

 nothing at the edge.) Fine weather or rain, dryness of the air 

 or humidity, cold or heat, day or night, or different seasons, 

 have no influence upon the velocity of any particular point of 

 the surface of the glacier. 



" The observers of previous years believed, on the other 

 hand, that the general march of great glaciers was in intimate 

 connection with the accompanying state of the atmosphere. 

 They believed, for instance, that the movement was retarded in 

 dry and cold weather, and accelerated by moisture and rain. 



* [Already printed at page 125, etc.] 



t Ninth Letter on Glaciers, Ed. Phil. Jour., vol. xxxviii., p. 332. [See above, 

 p. 68.] I may add, that M. Martins gives a similar account of the results of Mr. 

 Dollfuss' experiments in the Comptes Rendus, 26th October 1846. 



