The colour of the sky had gradually assumed a deeper tint of blue as we ascended: its present colour was dark indigo, approaching nearly to black. There was something awful in this appearance, so different from any we had ever witnessed. There was nothing to which we could compare it, except to the sun shining at midnight. During some of the first attempts that were made to ascend Mont Blanc, this appearance produced so strong an effect on the minds of the guides, who imagined that Heaven was frowning on their undertaking, that they refused to proceed. The portion of atmosphere above us was entirely free from the vapours which the lower strata always contain, and was truly the 'pure empyreal,' seldom seen by mortal eyes. We had all our life beheld the sun through a mist, but we now saw him, face to face, in all his splendour. The guides asserted that the stars can be seen, in full day, by a person placed in the shade. It being near noon, and the sun almost over our heads, we could not find shadow to enable us to make the experiment. The air on the top of Mont Blanc is of but little more than half the density of that at the surface of the ocean. According to the observations of Saussure, the height of the barometer on the summit, was sixteen and a half inches, while that of a corresponding one at Geneva, was twenty-eight inches. In consequence of this rarity of the air, a pistol, heavily charged, which we fired several times, made scarcely more noise than the crack of a postillion's whip.