Observations on Glaciers. 341 



spending a few days on a glacier, determine at any particular 

 season the amount of its motion at all the essential points, 

 within the limits which any glacier theory can require. 



Chamouni, \Oth Aiujust 1842. 



My Dear Sir, — Since I last wrote to you on the 4th July 

 from Courmayeur, I have examined, in detail, the two princi- 

 pal glaciers of the AUee Blanche ; and having re-crossed the 

 Alps from Courmayeur by the Col du Geant, where I had the 

 satisfaction of still finding the remains of Saussure's Cabane of 

 1788, I have pursued for a fortnight my experiments on the 

 motion of the Mer de Glace. Being composed, as you know, 

 of several tributaries which are in some degree independent, 

 and presenting also a considerable variety of surface, this 

 glacier seems as proper as any for detailed experiments, such 

 as those which I am attempting. Being about to quit this 

 place on a tour to Monte-Rosa and the glaciers east of the 

 Great St Bernard, I wish to explain to you now in what re- 

 spect my observations differ from those formerly undertaken 

 on the glaciers, and to mention a few results, which, of course, 

 being as yet only partial, ought not to be considered as alto- 

 gether decisive of the truth or falsehood of any theory; still 

 I believe it will be admitted that the facts established in my 

 last (and which farther experience has confirmed), militate 

 strongly against some of the received opinions as to the cause 

 of glacier motion. 



You are aware, that, in my lectures on glaciers in December 

 and January last, and in an article in the Edinburgh Review 

 for April, I insisted, and so far as I know it was for the first 

 time, on the importance of considering the glacier theory as a 

 branch of mechanical physics, by which I mean that the cause 

 of movement should be ascertained inductively from the ob- 

 served motion, carefully and numerically ascertained at differ- 

 ent points. It is because authors have considered the problem 

 as too simple a one to require a systematic analysis, that we 

 find little or nothing done in this respect ; and it may be affirm- 

 ed, without any disrespect to the ingenious persons who have 

 assigned probable causes for the movement of these masses of 

 ice, that their solutions have been, like the astronomical theories 



