On scanning the place carefully, however, the value of the observation appeared to me to outweigh the amount of danger. I therefore took my axe, placed a stake and an auger against my breast, buttoned my coat upon them, and cut an oblique staircase up the wall of ice, until I reached a height of forty feet from the bottom. Here the position of the stake being determined by Mr. Hirst, who was at the theodolite, I pierced the ice with the auger, drove in the stake, and descended without injury. During the whole operation however my guide growled audibly.
On the following morning we commenced the ascent of Mont Blanc, a narrative of which is given in Part I. We calculated on an absence of three days, and estimated that the stakes which had just been fixed would be ready for measurement on our return; but we did not reach Chamouni until the afternoon of Friday, the 14th. Heavy clouds settled, during our descent, upon the summits behind us, and a thunder-peal from the Aiguilles soon heralded a fall of rain, which continued without intermission till the afternoon of the 16th, when the atmosphere cleared, and showed the mountains clothed to their girdles with snow. The Montanvert was thickly covered, and on our way to it we met the servants in charge of the cattle, which had been driven below the snow-line to obtain food.
THROUGH GLOOM TO THE TACUL.
On Monday morning, the 17th, a dense fog filled the valley of the Mer de Glace. I watched it anxiously. The stakes which we had set at the Tacul had been often in my thoughts, and I wished to make some effort to save the labour and peril incurred in setting them from being lost. I therefore set out, in one of the clear intervals, accompanied by my friend and Simond, determined to measure the motion of the stakes, if possible, or to fix them more firmly, if they still stood. As we passed, however, from l'Angle to the glacier, the fog became so dense and blinding that we halted. At my request Mr. Hirst returned to the Montanvert; and Simond, leaving the theodolite in the shelter of a rock, accompanied me through the obscurity to the Tacul. We found the topmost stake still stuck by its point in the ice; but the two others had disappeared, and we afterwards discovered their fragments in a snow-buttress, which reared itself against the base of the precipice. They had been hit by the falling stones, and crushed to pieces. Having thus learned the worst, we descended to the Montanvert amid drenching rain.
DESCENT OF BOULDERS.
On the morning of the 18th there was no cloud to be seen anywhere, and the sunlight glistened brightly on the surface of the ice. We ascended to the Tacul. The spontaneous falling of the stones appeared more frequent this morning than I had ever seen it. The sun shone with unmitigated power upon the ice, producing copious liquefaction. The rustle of falling débris was incessant, and at frequent intervals the boulders leaped down the precipice, and rattled with startling energy amid the rocks at its base. I sent Simond to the top to remove the looser stones; he soon appeared, and urged the moraine-shingle in showers down the precipice, upon a bevelled slope of which some blocks long continued to rest. They were out of the reach of the guide's bâton, and he sought to dislodge them by sending other stones down upon them. Some of them soon gave way, drawing a train of smaller shingle after them; others required to be hit many times before they yielded, and others refused to be dislodged at all. I then cut my way up the precipice in the manner already described, fixed the stake, and descended as speedily as possible. We afterwards fixed the bottom stake, and on the 20th the displacements of all three were measured.[C] The spaces passed over by the respective stakes in 24 hours were found to be as follows:—
| Inches. | |
| Top stake | 6.00 |
| Middle stake | 4.50 |
| Bottom stake | 2.56 |
MOTION OF STAKES.
The height of the precipice was 140.8 feet, but it sloped off at its upper portion. The height of the middle stake above the ground was 35 feet, and of the bottom one 4 feet. It is therefore proved by these measurements that the bottom of the ice-wall at the Tacul moves with less than half the velocity of the top; while the displacement of the intermediate stake shows how the velocity gradually increases from the bottom upwards.