334 Professor Forbes’s Ninth Letter on Glaciers. 
169.2 Swiss feet 
177.1 
141.3 
150.1 
133.1 
83.7 
58.3 
This result is very different numerically from that which 
I obtained on the Mer de Glace of Chamouni, but the differ- 
ence is of the kind which might have been expected from 
their great diversity of situation and circumstances. I never 
expected, or pretended to find in the Mer de Glace the same 
peculiarities of velocity as in other glaciers ; on the contrary, 
I endeavoured to shew* what were the local peculiarities as 
to slope, and breadth, which probably produced the law of 
variation of the motion which I observed, slowest in the 
middle, and quickest towards either end, precisely the reverse 
of that observed by M. Agassiz; but I neither depreciate the 
accuracy of his surveyor, nor contend that one cause of mo- 
tion sways the glacier of the Aar, and another that of the 
Montanvert. On the contrary, the difference appears to me 
entirely conformable to the viscous theory; and the glacier 
of the Aar, in this respect, a more instructive example than 
the Mer de Glace of Chamouni. 
I have shewn in one of the passages of my work just cited, 
that the velocities of the different portions of the glacier 
depend, among other things, on their inclination or slope ; 
and hence, I should have inferred, that in a glacier which 
did not slope faster and faster towards its lower end, till it 
becomes almost precipitous, there would be accumulating 
resistance due to the friction of the ice on the bed of a long, 
nearly uniform, gently sloping valley, such as that which 
contains the glacier of the lower Aar, which must magnify 
the tendency which the ice has to be squeezed forwards and 
upwards against the mass immediately in advance of it, 
which produces the frontal «ip of the ribboned structure or 
* Travels in the Alps, p. 145, 371. 
