The thermometers referred to at p. 17 were placed on Mont Blanc in 1859. I had proposed to the Royal Society some time previously to establish a series of stations between the top and bottom of the mountain, and the council of the society was kind enough to give me its countenance and aid in the undertaking. At Chamouni I had a number of wooden piles shod with iron. The one intended for the summit was twelve feet long and three inches square; the others, each ten feet long, were intended for five stations between the top of the mountain and the bottom of the Glacier de Bossons. Each post was furnished with a small cross-piece, to which a horizontal minimum thermometer might be attached. Six-and-twenty porters were found necessary to carry all the apparatus to the Grands Mulets, whence fourteen of them were immediately sent back. The other twelve, with one exception, reached the summit, whence six of them were sent back. Six therefore remained. In addition to these we had three guides, Auguste Balmat being the principal one; these, with Dr. Frankland and myself, made up eleven persons in all. Though the main object of the expedition was to plant the posts and fix the thermometers, I was very anxious to make some observations on the transparency of the lower strata of the atmosphere to the solar heat-rays. I therefore arranged a series of observations with the AbbÉ Veuillet, of Chamouni; he was to operate in the valley, while I observed at the top. Our instruments were of the same kind; in this way I hoped to determine the influence of the stratum of air interposed between the top and bottom of the mountain upon the solar radiation.

Wishing to commence the observations at daybreak, I had a tent carried to the summit, where I proposed to spend the night. The tent was ten feet in diameter, and into it the whole eleven of us were packed. The north wind blew rather fiercely over the summit, but we dropped down a few yards to leeward, and thus found shelter. Throughout the night we did not suffer at all from cold, though we had no fire, and the adjacent snow was 15° Cent., or 27° Fahr., below the freezing point of water. We were all however indisposed. I was indeed very unwell when I quitted Chamouni; but had I faltered my party would have melted away. I had frequently cast off illness on previous occasions, and hoped to do so now. But in this I was unsuccessful; my illness was more deep-rooted than ordinary, and it augmented during the entire period of the ascent. Towards morning, however, I became stronger, while with some of my companions the reverse was the case. At daybreak the wind increased in force, and as the fine snow was perfectly dry, it was driven over us in clouds. Had no other obstacle existed, this alone would have been sufficient to render the observations on solar radiation impossible. We were therefore obliged to limit ourselves to the principal object of the expedition—the erection of the post for the thermometers. It was sunk six feet in the snow, while the remaining six feet were exposed to the air. A minimum thermometer was screwed firmly on to the cross-piece of the post; a maximum thermometer was screwed on beneath this, and under this again a wet and dry bulb thermometer. Two minimum thermometers were also placed in the snow—one at a depth of six, and the other at a depth of four feet below the surface—these being intended to give some information as to the depth to which the winter cold penetrates. At each of the other stations we placed a minimum thermometer in the ice or snow, and a maximum and a minimum in the air.

The stations were as follows:—The summit, the Corridor, the Grand Plateau, the glacier near the Grands Mulets, and two additional ones between the Grands Mulets and the end of the Glacier de Bossons. We took up some rockets, to see whether the ascensional power, or the combustion, was affected by the rarity of the air. During the night, however, we were enveloped in a dense mist, which defeated our purpose. One rocket was sent up which (though we did not know it) penetrated the mist, and was seen at Chamouni. Lecomte’s experiments on the alleged influence of light and rarefaction in retarding combustion caused me to resolve on making a series of experiments on Mont Blanc. Dr. Frankland was kind enough to undertake their execution. Six candles were chosen at Chamouni, and carefully weighed. All of them were permitted to burn for one hour at the top, and were again weighed when we returned to Chamouni. They were afterwards permitted to burn an hour below. Rejecting one candle, which gave a somewhat anomalous result, we found that the quantity consumed above was, within the limits of error, the same as that consumed at the bottom. This result surprised us all the more, inasmuch as the light of the candles appeared to be much feebler at the top than at the bottom of the mountain.

The explosion of a pistol was sensibly weaker at the top than at a low level. The shortness of the sound was remarkable; but it bore no resemblance to the sound of a cracker, to which in acoustic treatises it is usually compared. It resembled more the sound produced by the expulsion of a cork from a champagne-bottle, but it was much louder. The sunrise from the summit was singularly magnificent. The snow on the shaded flanks of the mountain was of a pure blue, being illuminated solely by the reflected light of the sky; the summit of the mountain, on the contrary, was crimson, being illuminated by transmitted light. The contrast of both was finer than I can describe.

About twenty hours were spent upon the top of Mont Blanc on this occasion. Had I been better satisfied with the conduct of the guides, it would have given me pleasure at the time to dwell upon this out-of-the-way episode in mountain life. But a temper, new to me, and which I thought looked very like mutiny, showed itself on the part of some of my men. Its manifestation was slight, I must say, in most cases, and conspicuous only in one. Regrets and apologies followed, and due allowance ought to be made for the perfectly novel position in which the men found themselves. The awe of entire strangeness is very powerful in some minds; and to my companions the notion of spending a night at the top of Mont Blanc was passing strange. The thing had never been attempted previously, nor has the experiment been repeated since.

As stated at p. 17, I made an attempt during the execrable weather of 1860 to reach the top, but was driven down after a delay of twenty hours at the Grands Mulets. The same weather destroyed the lower stations. In 1861, though the cross still remained at the top, the thermometers exhibited broken columns and were worthless for observation.

I may add, in conclusion, that the lowest temperature at the summit of the Jardin during the winter of 1858 was 21° Cent. below zero. In 1859 I vainly endeavoured to find a thermometer which had been placed in the snow upon the summit of Mont Blanc a year previously.