In describing the surface of the glacier, 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 remember, for his consolation under such disappointments, that his failures are almost as important to the cause of science and to those who follow him in the same road as his successes.  It is much to know what we cannot do in any given direction,—­the first step, indeed, toward the accomplishment of what we can do.