On the 5th we were engaged for some time in an important measurement at the Tacul. We afterwards ascended towards the _seracs_, and determined the inclinations of the Glacier du Geant downwards. Dense cloud-masses gathered round the points of the Aiguilles, and the thunder bellowed at intervals from the summit of Mont Blanc. As we descended the Mer de Glace the valley in front of us was filled with a cloud of pitchy darkness. Suddenly from side to side this field of gloom was riven by a bar of lightning of intolerable splendour; it was followed by a peal of commensurate grandeur, the echoes of which leaped from cliff to cliff long after the first sound had died away. The discharge seemed to unlock the clouds above us, for they showered their liquid spheres down upon us with a momentum like that of swan-shot: all the way home we were battered by this pellet-like rain. On the 6th the rain continued with scarcely any pause; on the 7th I was engaged all day upon the Glacier du Geant; on the morning of the 8th heavy hail had fallen there, the stones being perfect spheres; the rounded rain-drops had solidified during their descent without sensible change of form. When this hail was squeezed together, it exactly resembled a mass of oolitic limestone which I had picked up in 1853 near Blankenburg in the Hartz. Mr. Hirst and myself were engaged together this day taking the inclinations: he struck his theodolite at the Angle, and went home accompanied by Simond, and the evening being extremely serene, I pursued my way down the centre of the glacier towards the Echelets. The crevasses as I advanced became more deep and frequent, the ridges of ice between them becoming gradually narrower. They were very fine, their downward faces being clear cut, perfectly vertical, and in many cases beautifully veined. Vast plates of ice moreover often stood out midway between the walls of the chasms, as if cloven from the glacier and afterwards set on edge. The place was certainly one calculated to test the skill and nerve of an iceman; and as the day drooped, and the shadow in the valley deepened, a feeling approaching to awe took possession of me. My route was an exaggerated zigzag; right and left amid the chasms wherever a hope of progress opened; and here I made the experience which I have often repeated since, and laid to heart as regards intellectual work also, that enormous difficulties may be overcome when they are attacked in earnest. Sometimes I found myself so hedged in by fissures that escape seemed absolutely impossible; but close and resolute examination so often revealed a means of exit, that I felt in all its force the brave verity of the remark of Mirabeau, that the word "impossible" is a mere blockhead of a word. It finally became necessary to reach the shore, but I found this a work of extreme difficulty. At length, however, it became pretty evident that, if I could cross a certain crevasse, my retreat would be secured.