d cut on a level with the surface of the
glacier, in the summer of 1840, was found, on my return in the summer of
1841, to project seven feet, and in the beginning of September it showed
ten feet above the surface. Before leaving the glacier, in September,
1841, I planted six stakes at a certain distance from each other in a
straight line across the upper part of the glacier, taking care to have
the position of all the stakes determined with reference to certain
fixed points on the rocky walls of the valley. When I returned, the
following year, all the stakes had advanced considerably, and the
straight line had changed to a crescent, the central rods having moved
forward much faster than those nearer the sides, so that not only was
the advance of the glacier clearly demonstrated, but also the fact that
its middle portion moved faster than its margins. This furnished the
first accurate data on record concerning the average movement of the
glacier during the greater part of one year. In 1842 I caused a
trigonometric survey of the whole glacier of the Aar to be made, and
several lines across its whole width were staked and determined with
reference to the sides of the valley;[B] for a number of successive
years the survey was repeated, and furnished the numerous data
concerning the motion of the glacier which I have published. I shall
probably never have an opportunity of repeating these experiments, and
examining anew the condition of the glacier of the Aar; but as all the
measurements were taken with reference to certain fixed points recorded
upon the map mentioned in the note, it would be easy to renew them over
the same locality, and to make a direct comparison with my first results
after an interval of a quarter of a century. Such a comparison would be
very valuable to science, as showing any change in the condition of the
glacier, its rate of motion, etc., since the time my survey was made.

These observations not only determined the fact of the motion of the
glacier itself, as well as the inequality of its motion in different
parts, but explained also a variety of phenomena indirectly connected
with it. Among these were the position and direction of the crevasses,
those gaping fissures of unknown depths, sometimes a mile or more in
length, and often measuring several hundred feet in width, the terror,
not only of the ordinary traveller, but of the most experienced
mountaineers. There is a variety of such crevasses up