( 33G ) 



On the Motion of Glaciers. By M. Ch. Martins, in a Letter 

 to Professor Jameson, Editor of the Edinburgh New 



Philosophical Journal. 



O' 



Sir, — In Mr J. D. Forbes' fourteenth letter on glaciers, 

 which appeared in April 1847 in your valuable Journal, I 

 observe, at page 330, the following expression : — " The opi- 

 nion of MM. Dollfus, Martins, and Collomb is, that seasons 

 and weather make no difference whatever on the motions of 

 the glacier of the Aar." On no occasion have I expressed 

 the opinion Mr Forbes here ascribes to me. I have even 

 affirmed the very opposite, in the course of Geology which I 

 had the honour to deliver this winter to the Faculty of 

 Sciences at Paris. On considering what may have led Mr 

 Forbes into this error, I can think of nothing else than an 

 expression in a letter addressed to M. Arago, and inserted 

 in the Comptes E-endus of the meeting of the Academy of 

 Sciences of Paris on the 26th October 1846. At page 824, 

 it is stated: — " From the 18^/^ of August at noon^ till the 2^th 

 at half past six in the evening^ the glacier has advanced 

 1™. 874, or 0"^. 173 in twenty-four hours. This progress has 

 been uniform by day and night, independent of changes in the 

 temperature, of rain or snow ; in a word, of all atmospheric 

 modifications." It will be seen that there is no reference 

 here to the uniform progress of the glacier throughout the 

 course of the year, but only during eleven days of the latter 

 portion of the month of August 1846. 



Allow me, Mr Editor, to make another remark. At the 

 commencement of his thirteenth letter on glaciers, Mr 

 Forbes gives an account of an experiment made by him on 

 the glacier of the Bois, and by M. Dollfus and myself on 

 that of the Grunberg, for the purpose of measuring the rela- 

 tive speed of the surface and the bottom. He asserts the 

 priority of his experiment, and also of its publication in your 

 Journal on the 1st October 1846. I think it due to my fel- 

 low-labourer M. PoUfus, at present in Spain, to mention the 



