32 FOURTH LETTER ON GLACIERS. [1842. 



lated weight of snow above and behind. Now, neither of these 

 things happen ; the glacier moves on day and night, or from 

 day to day, with a continuous regulated motion, which, I feel 

 certain, could not take place were the sliding theory true. 



But if possible, still stronger, as well as more multiplied, 

 objections are to be found to the theory of dilatation, and I 

 trust I shall not be accused of levity in thus, as it were, in a 

 few lines, dismissing a theory which has so much primd facie 

 plausibility to recommend it, and which has been maintained 

 with so much ingenuity by men such as Scheuchzer, De Char- 

 pentier, and Agassiz. It is essential to the aim of this letter, 

 that I state briefly the grounds of the conclusions at which I 

 have arrived, whilst it is equally essential that my observations 

 should be confined within small compass. In another place I 

 shall give them all the development that may be requisite. 



Summarily, then (1.) The motion of the glacier, in its 

 several parts, does not appear to follow the law which the 

 dilatation theory would require. It has been shewn (Ed. Rev., 

 April 1842, p. 77) that the motion ought to vanish near the origin 

 of the glacier, and increase* continually towards its lower 

 extremity. I have found the motion of the higher part of the 

 Mer de Glace to differ sometimes very little from that several 

 leagues farther down ; whilst in the middle, owing to the 

 expansion of the glacier in breadth, its march was slower than 

 in either of the other parts. (2.) Whilst I admit that the 

 glacier is, during summer, infiltrated with water in all or most 

 of its thickness (a point on which I had last year great doubts), 

 I feel quite confident that, during some months of the year 

 during which the glacier is in most rapid motion, no congelation 

 take* place in the mass of the ice beyond a depth of a very 

 few inches, much less during the cold of each night, and least 

 of all, at all times, as appears to be now the opinion held upon 

 the subject. Whilst I say that I am confident of this, I will 

 state one proof. Less than ten days since I traversed the Mer 

 de Glace up to the higher part of the Glacier de Lechaud, 

 whilst it was covered with snow to a depth of six inches at 



