TRANSACTIONS OF SECTION A. 433 
agree, and even the Rosenlaui Glacier, which a few years ago seemed doomed to 
total annihilation, is recovering and increasing. That the general advance will not 
remain without its exceptions is more than probable from previous experience. He 
is speaking only about the majority of glaciers in the western Alps, for he has 
heard nothing as to the behaviour of the ice in the Engadine or in the Tyrol. 
It was generally said in Chamonix, during this last summer, that the lower end 
of the Glacier des Bossons came forward at the rate of one metre a week. He went 
on Wednesday, July 11, to mark some rocks at the base of the glacier, which was 
then melting rapidly, in order to see whether the downward motion really over- 
balanced the decrease by fusion, The eastern side of the glacier rested against a 
large boulder, while at the western end only loose stones covered the ground in 
front of the ice. He returned on Monday, the 28rd, and noted the following change: 
The eastern end rested still against the same boulder, covering it exactly to the 
same spot as before; and so unchanged did this side appear that one might have 
imagined it was the same ice that formed the end of the glacier. The ice which 
had melted against the rock was replaced by the advancing glacier, but no change 
in the position of the front could be seen. Not so on the western side. Here a 
thick tongue of ice projected from the glacier, and reached over one metre further 
down the valley than the former limit of the glacier. 
Here we have, then, in the middle of summer an actual advance of the glacier, 
which, though not so large as reported, is yet already sufficiently important, and 
will be still more so as the season advances and the melting takes place less 
rapidly. 
The weather during the interval between his two visits had, with the exception 
of two hot days, been rainy and bad, but it was never exceptionally cold. 
He also took some rough sights to see whether the level of the glacier at the 
point where tourists generally cross it is rising or not, but it seemed, if anything, 
to be lower on his second visit than on his first. 
It seemed interesting, on account of this forward motion of the lower end of 
glaciers, to study once more their daily rate of descent. As glaciers flow down the 
valleys, and melt away on their surface and front, they will appear to advance or 
to retreat, according as the gain by daily downward motion overbalances or not 
the loss by melting. It seemed, therefore, probable that the daily motion was 
more rapid now than it had been while the glaciers were retreating, and this 
seemed only a consequence of the fact that the upper ends of the glaciers were 
generally acknowledged to be much higher and bulkier than of late years, The 
author's results do not, as will appear, allow us to draw any very certain inference 
on that point; but the cause of this uncertainty is worth relating. 
He undertook to make a series of measurements on stakes placed along an 
approximately straight line across the Mer de Glace, a little higher up than the 
Montanvert. The theodolite was firmly placed on shore. Measurements were 
taken on the morning and afternoon of July 21, on July 24 and 25. They 
revealed an irregularity of motion which has not, to his knowledge, been 
previously observed. 
To Forbes we owe the first series of accurate measurements, and the following 
quotation will show that his observations pointed to a very regular advance of the 
glacier :! 
‘(5) When we compare the motion of a given point of a glacier any day of 
one year and the same day of another, the probability is that the velocity will 
be exactly the same, if the season be equally hot or cold; hence, surely, a most 
unexpected result, which I first announced in 1842, that a few days’ observation 
of a glacier will enable anyone to compare its mean rate of motion over tts various 
pats and with different glaciers. Thus the motion of a point marked D2 on the 
Mer de Glace was, in 1842 from August 1 to August 9, 163 inches daily; from 
_ August 9 to September 16, 18 inches. Now next year, 1843, one observation gave 
16 inches, and in 1844 one observation in September gave 173 inches. But still 
further (6), the very law of flexure of the ice is the same from year to year; a 
1 Phil. Trans. 1846, p. 177; Theory of Glaciers, p. 149. 
1883. FF 
