"At this place I had an opportunity of measuring the height of the snow which had fallen during the preceding winter, and which was distinguished by its superior whiteness from that of the former year. I found it to be five feet. The snow of each particular year appeared as a separate stratum; that which was more than a twelve month old, was perfect ice, while that of the last winter was fast approaching to a similar state. At length, after a difficult ascent, which lay among precipices, and during which we were often obliged to employ the hatchet in making a footing for our feet, we reached, and reposed ourselves upon, a narrow flat, which is the last of three from the foot of the small mountain, and which, according to M. de Saussure, is but 150 fathoms below the level of the summit. Upon this platform I found a beautiful dead butterfly, the only appearance which, from the time I entered on on the snow, I had seen of any animal. The pernicious effects of the thinness of the air were now evident on us all; a desire, of sleep, almost irresistible, came on; my spirits had left me: sometimes indifferent to the event, I wished to lie down; at others, I blamed myself for the expedition; and, though just at the summit, had thoughts of turning back, without accomplishing my purpose. Of my guides, many were in a worse situation; for, exhausted by excessive vomiting, they seemed to have lost all strength, both of mind and body.

"But shame at length came to our relief. I drank the last pint of water that was left, and found myself amazingly re-freshed, and invigorated for renewed toil. Yet the pain in my knees had increased so much, that at the end of every twenty or thirty paces I was obliged to rest till its sharpness was abated. My lungs with difficulty performed their office, and my heart was affected with violent palpitation. At last, however, but with a sort of apathy which scarcely admitted the sense of joy, we reached the summit of this mountain; when six of our guides, and with them my servant, threw themselves on their faces, and were immediately asleep. I envied them their repose, but my anxiety to obtain a good observation for the latitude subdued my wishes for indulgence. The time of my arrival was half an hour after ten, so that the hours which elapsed from our departure from Chamouni, were only twenty-seven and a half, ten of which we had passed in the hut. The summit of the hill is formed of snow, which spreads into a sort of plain, which is much wider from east to west than from north to south, and in its greatest width is perhaps thirty yards. The snow is every where hard, and in many places is covered with a sheet of ice.

"When the spectator begins to look around him from this elevated height, a confused impression of immensity is the first effect produced upon his mind ; but the blue colour of the canopy above him, deep almost to blackness, soon arrests his attention. He next surveys the mountains, many of which, from the clearness of the air, are to his eye within a stone's throw from him; and even those of Lombardy (one of which appears of an altitude but little inferior to that of Mont Blanc) seem to approach his neighbourhood; while those on the other side of the vale of Chamouni, glittering with the sunbeams, are to the view directly below his feet, and affect his head with giddiness. On the other hand, all objects, of which the distance is great, and the level low, are hid from his eye by the blue vapour which intervenes, and through which I could not discern the Lake of Geneva, (at the height of 15,700 English feet, which, according to M. de Saussure, was the level on which I stood,) though even the Mediterranean Sea must have been within the line of vision. The air was still, and the day so remarkably fine, that I could not discover in any part of the heavens the appearance of a single cloud.

"As the time of the sun passing the meridian now approached, 1 prepared to take my observation. I had with me an admirable Hadley's sextant, and an artificial horizon, and I corrected the mean refraction of the sun's rays. Thus I was enabled to ascertain with accuracy, that the latitude of the summit of Mont Blanc is 45° 49' 59" north.

"I now proceeded to such other observations as the few instruments which I had brought permitted me to make. At twelve o'clock the mercury in the thermometer stood at 38° in the shade; at Chamouni, at the same hour, it stood, when in the shade, at 78°. I tried the effect of a burning-glass on paper, and on a piece of wood, which I had brought with me for the purpose, and found (contrary, I believe, to the generally received opinion,) that its power was much greater than in the lower regions of the air. Having continued two hours on the summit of the mountain, I began my descent at half an hour after twelve. I found that, short as my absence had been, many new rents were opened, and that several of those which I had passed in my ascent were considerably wider. In less than six hours we arrived at the hut in which we had slept the evening before, and should have proceeded much further down the mountain, had we not been afraid of passing the Glacier de la Cote at the close of the day, when the snow, from the effect of the sunbeams, was extremely rotten. Our evening's repast being finished, I was soon asleep; but in a few hours I was awakened with a tormenting pain in my face and eyes. My face was one continued blister, and my eyes I was unable to open; nor was I without apprehensions of losing my sight for ever, till my guides told me, that if I had condescended to have taken their advice, of wearing, as they did, a mask of black crape, the accident would not have befallen me, but that a few days would perfectly restore the use of my eyes. After I had bathed them with warm water for half an hour, I found, to my great satisfaction, that 1 could open them a little; on which I determined upon an instant departure, that I might cross the Glacier de la Cote before the sun was sufficiently high for its beams to be strongly reflected from the snow. But, unluckily, the sun was already above the horizon; so that the pain of forcing open my eyes in the bright sunshine, in order to avoid the chasms and other hazards of my way, rendered my return more irksome than my ascent. Fortunately, one of the guides, soon after I had passed the glacier, picked up in the snow a pair of green spectacles, which M. Bourret had lost, and which gave me wonderful relief.

"At eleven o'clock of August 10, after an absence of fifty-two hours, of which twenty were passed in the hut, 1 returned again to the village of Chamouni. From the want of instruments, (the scale of the barometer I had being graduated no lower than twenty inches, which was not sufficiently extended,) the observations I made were but few, yet the effects which the air in the heights I visited produced on the human body, may not perhaps be considered as altogether uninteresting; nor will the proof I made of the power of the lens on the summit of Mont Blanc, if confirmed by future experiments, be regarded as of no account in the theories of light and heat. At any rate, the having determined the latitude of Mont Blanc may assist in some particulars the observations of such persons as shall visit it in future; and the knowledge which my journey has afforded, in addition to that which is furnished by M. de Saussure, may facilitate the ascent of those who, with proper instruments, may wish to make on that elevated level, experiments in natural philosophy."