BLANC, MONT, a lofty mountain in France, and 'the highest of the Pennine Alps, is situated in the duchy of Faucigny, formerly a part of the king of Sardinia's dominions, but now subject to the Empe ror of France. It receives its name from the im mense mantle of snow, with which its summit and sides are covered, and which is estimated to extend not less than 12,000 perpendicular feet, without the least appearance of rock to interrupt its glaring whiteness. • When viewed from the Col de Balme and the vale of Chamouni, its summit seems to be of a roundish form, its surface smooth and covered with snow, its whole appearance uniting beauty with grandeur, and its towering head rising majestically above the sur rounding mountains ; but, when seen from the valley of Aost, its sides are less completely covered with snow, its aspect more rugged and dark, and the pros pect which it presents partakes more of the wild and 'terrific. ' It rises imperceptibly from amidst the nu irregular mountains, which bound the vale of Chamouni, then terminates rather abruptly in a point or top called de Goute, orDrime do Goute. Beyond this height, with a considerable hollow be tween, it forms another mount, called by some Little 'Mont Blanc, or more properly 7'he Middle Dome. From this station it gradually sinks again into a con cave surface, in the midst of which is a small pyramid of ice ; and then reaches its highest point of eleva tion, which is in the shape of a compressed hemi sphere, and is called from its form La Bosse du Dro vtedaire. Upon a nearer inspection, the summit of this gigantic mountain is found to be a very narrow ridge, lying nearly in a horizontalre direction, resem bling the roof of a house ; and at its west end parti cularly, scarcely sufficiently broad to admit of two persons walking abreast. The snow, which covers the top, is encrusted with ice, of a firm consistence, but penetrable by a staff; and beneath this icy sur face, especially on the declivities of the summit, is discovered a soft dusty snow without any cohesion.
The highest rocks of Mont Blanc are formed of strata- of granite, running parallel to one another, and nearly in a vertical direction. Those on the east side are mixed with steatites ; those on the south with schcerl and lapis cornetts ; and some of them, about 150 yards below the summit, have the appearance of having been shive-ed with lightning.
Mont Blanc is unquestionably the highest moun tain in Europe ; and there is no reason to think, that it is surpassed by any in Africa or Asia. According to the calculations of Dc Luc, its height above the level of the sea is 2391+ French toises, or 15,304 English feet ; according to Sir George Shuck burgh, 15,662 feet and according to other observa tions, 15,680 feet, or nearly three English miles above the level of the sea.
At the elevation of 11,392 feet above the sea, M. De Saussure observed the silene acaulis, or moss tampion in flower ; still higher, on the most elevated rocks, he found the lichen sulpliztreus and lichen rupestris of Hoffman ; and, on the summit, he noti ced two butterflies on the wing, which he supposed to have been driven thither by the wind. On the top of Mont Blanc, on the third day of August, Reau mur's thermometer stood, in the shade, at 2.below the freezing point, or 27 of Fahrenheit ; while, at the same time, at Geneva, it was found at 22.G or 82 of Fahrenheit, which gives a difference of nearly 25 de grees of Reaumur, or 15 of Fahrenheit, between the temperature of the atmosphere at both places. Dc Luc's barometer fell to 16.0' while it stood at Geneva at 27.21P", a difference of 11.2, with a -small fraction. By experiments with the hygrometer, the air was found to contain six times less humidity than that of Geneva; and to this extreme dryness of the atmosphere, the burning thirst, which Saussure and his companions experienced in the extraordinary elevation, is supposed to have been owing. While 15 or 16 minutes are sufficient to boil water at Geneva, and 14 or 15 at the sea side, it requires half an hour on the top of this mountain. By experiments with the electrometer, the electricity of the air was found to be positive, and the balls diverged only three lines; and by experiments with lime water, and the caustic alkali, atmospheric acid, or fixed air, was detected in the atmosphere. Owing to the extreme rarefaction of the air, sounds were remarkably feeble, and the re port of a pistol discharged on the summit, did not ex ceed that of a small Chinese cracker in a room. From the same cause, respiration becomes diffi cult at so immense an altitude ; and it was found, that the pulses of three persons, which beat at Chamouni, in a state of repose, 49, GO, and 72, were increased, on the summit of Mont Blanc, to 98, 112, and 100.