Observation^ on Glaciers, 339 



I expect to accomplish during the remainder of the season, I 

 will state them shortly. 



You will recollect that, in my lectures on glaciers delivered 

 last December and January, and afterwards in an article 

 written by me in the Edinburgh Review, 1 insisted on the 

 importance of considering the mechanism of glaciers as a ques- 

 tion of pure physics, and of obtaining precise and quantitative 

 measures as the only basis of accurate induction. I pointed 

 out, also, the several experiments of a critical kind which 

 might be made ; such, for instance, as the determination of the 

 motion of the ice at different points of its length, in order to 

 distinguish between the theories of De Saussure and De Char- 

 pentier ; for, if the glacier merely slides, the velocity of all its 

 points ought (in the simplest case) to be the same ; if the gla- 

 cier swells in all its mass, the velocity of the inferior part 

 ought to be greatest. Of course, I do not now advert to the 

 many causes which might accidentally invert this law, and 

 which would require to be fully taken into account ; still less 

 do I mean to say that any thing I have now to state can be 

 considered as critically decisive between rival theories ; but 

 my experiments certainly do shew that the kind of precision 

 which I desired to see introduced into reasonings about this 

 subject, is practically attainable, even in a far higher degree 

 than I expected. 



For example : — The motion of glaciers by the measurement 

 of the distance of blocks upon its surface from a fixed point, 

 from one year to another, has marked indubitably the annual 

 progress of the ice. I do not know that any one has at- 

 tempted to perform the measurement in a manner which could 

 lead to any certain conclusion respecting the motion of the 

 ice at one season compared with another, or from month to 

 month ; still less has any one been able to state, ivith precision, 

 whether the glacier moves by starts and irregularly (as we 

 should certainly expect on the sliding theory), or uniformly 

 and evenly ; and if so, whether it moves only at one part of 

 the twenty-four hours, and stands still during the remainder 

 (as we should expect on the dilatation theory, as commonly 

 expounded). Now, I have already been able — 



\st. To shew and measure the glacier motion not only from 



