I should not omit the shallow
troughs which I have called "meridian holes," from the accuracy with
which they register the position of the sun. Here and there on the
glacier there are patches of loose materials, dust, sand, pebbles, or
gravel, accumulated by diminutive water-rills, and small enough to
become heated during the day. They will, of course, be warmed first on
their eastern side, then, still more powerfully, on their southern side,
and in the afternoon with less force again on their western side, while
the northern side will remain comparatively cool. Thus around more than
half of their circumference they melt the ice in a semicircle, and the
glacier is covered with little crescent-shaped troughs of this
description, with a steep wall on one side and a shallow one on the
other, and a little heap of loose materials in the bottom. They are the
sundials of the glacier, recording the hour by the advance of the sun's
rays upon them.

In recapitulating the results of my glacial experience, even in so
condensed a form as that in which I intend to present them here, I shall
be obliged to enter somewhat into personal narration, though at the risk
of repeating what has been already told by the companions of my
excursions, some of whom wrote out in a more popular form the incidents
of our daily life which could not be fitly introduced into my own record
of scientific research. When I first began my investigations upon the
glaciers, now more than twenty-five years ago, scarcely any measurements
of their size or their motion had been made. One of my principal
objects, therefore, was to ascertain the thickness of the mass of ice,
generally supposed to be from eighty to a hundred feet, and even less.
The first year I took with me a hundred feet of iron rods, (no easy
matter, where it had to be transported to the upper part of a glacier on
men's backs,) thinking to bore the glacier through and through. As well
might I have tried to sound the ocean with a ten-fathom line. The
following year I took two hundred feet of rods with me, and again I was
foiled. Eventually I succeeded in carrying up a thousand feet of line,
and satisfied myself, after many attempts, that this was about the
average thickness of the glacier of the Aar, on which I was working. I
mention these failures, because they give some idea of the
discouragements and difficulties which meet the investigator in any new
field of research; and the student must remem