The top of Mont Blanc is a ridge of perhaps 150 feet in length, and six or eight in breadth. It is entirely composed of snow, which is probably of immense depth, and is constantly accumulating. We could see no traces of the obelisk, 12 feet in height, which had been set up about ten years before. One of our guides was of the number of those who placed it, and designated to us its position. The highest rock which appears above the snow, is a small one of granite, 600 feet below the summit. We remained but a few minutes immediately on the top, as the wind blew hard and piercingly cold. Descending a few feet on the south side, we were partially sheltered from the wind, and here the sun shone with an excessive brightness, heating every part of the body exposed to his rays; but the least breath of wind, which reached us at intervals, was sufficient to make us shiver with cold. Farenheit's thermometer in the sun, was two degrees below freezing, and five and a half in the shade. It must be considered, however, that we suffered a much greater degree of cold than the thermometer indicated, from the rapid evaporation from the surface of our bodies, of the insensible transpiration occasioned by the dryness and great rarity of the surrounding air. This cause, familiar to physiologists, affected our sensations, and could not influence the thermometer. Most of our guides stretched themselves on the snow in the sun, and yielded to the strong inclination to sleep, which we all felt. Only one or two of them ate: the others, on the contrary, evinced an aversion to all kinds of food. We did not suffer the great thirst which Saussure and his party experienced; This we prevented by drinking vinegar and water, which was very grateful to us, instead of pure water. Our pulses were increased in frequency and fulness, and we had all the symptoms of fever. I occupied myself, notwithstanding the indisposition to action which I felt, in making a few observations, and in stopping and sealing very carefully a bottle which I had filled with the air of the summit, intended for examination on my return.