My failure, however, taught me to sink the next set of stakes ten or fifteen feet below the surface of the ice, instead of five; and the experiment was attended with happier results. A stake planted eighteen feet deep in the ice, and 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.