We remained an hour and a quarter on the summit, part of which time was spent in useless regrets at not having waited to provide ourselves with instruments, as we were now so admirably situated to make with them a series of interesting experiments. Those which had suggested themselves, were principally concerning the absorption and radiation of caloric, and on the degree of cold produced by the evaporation of æther and other liquids. We found the descent more easy and much less fatiguing, though perhaps more dangerous than the ascent, on account of the greater risk of slipping. We passed under the place where the avalanche threatened us, with even more caution and more rapidity than before, as we found that a small piece had actually fallen, and covered our path since we had passed by. We arrived in about an hour at the 'Grand Plateau,' where we stopped to refresh ourselves, and gratify our returning appetites. We found the guide whom we had left, quite relieved. Here the sun, reflected from the walls of snow which surrounded us on three sides, poured down upon us with the most burning heat that I ever experienced from its rays, while our feet, cold from being immersed in the snow, prevented perspiration, and thus increased its power. Wherever its rays could penetrate, as between the cap and neckcloth, or even to the hands, it resembled the application of a heated iron. We were compelled, in addition to the assistance of our veils, to keep our eyes half closed, and even then the light was too powerful for them.