When the thermometers were suspended in the water, Rosset asked how long they must stay there.  I rashly answered, a quarter of an hour; on which he demanded indignantly whether I supposed he meant to stay in that cold for a quarter of an hour.  He had now the candle in his own possession, and I was propped on a stone and an alpenstock in the lake, so he turned to go, vowing that he would leave me alone in the dark if I did not come out at once.  There was no help for it, as the thermometer would have been of no use without a candle, and a step in the dark is not pleasant when all around is water, so I slowly drew up the thermometer and read 33 deg.  F. In making final arrangements for departure, I let it lie in the water for a few seconds longer, and it fell to 321/2 deg.; but Rosset would not stay a moment longer, and I was obliged to be content with that result.  He made himself very easy about the matter, and said we must call it zero; and in the evening I heard him telling the maire that the greatest of the wonders he had missed, by his patriotic care for his neck, was a lake of water which did not freeze, though its temperature was zero (centigrade).

Among the stones at the bottom of this water, I saw here and there patches of a furry sort of ice.  I have often watched the freezing of a rapid Scotch stream, where, in the swifter parts, the ice forms first at the bottom and gradually creeps up the larger stones till it appears on the surface, and becomes a nucleus, round which pieces of floating ice collect; and the substance in the glaciere-lake had exactly the same appearance as the Scotch ground-ice.  But it could not be the same thing in reality, for, as far as I understand the phenomenon of ground-ice, some disturbed motion of the water is necessary, to drive down below the surface the cold particles of water, which become ice the moment they strike upon any solid substance shaped like fractured stone;[75] the specific gravity of freezing water being so much less than that of water at a somewhat higher temperature, that without some disturbing cause it would not sink to the bottom.[76] So that it seems probable that the ice at the bottom of the lake was the remains of a solid mass, of which the greater part had been converted into water by some warm influence or other.  We noticed that a little water trickled down among the stones which formed the slope of descent into the lowest gallery, so that perhaps the lake was a collection of water from all parts of the various ramifications of the fissure.  Whence came the icy wind, it is impossible to say, without further exploration.  It was satisfactory to me to find that the ‘cold current’ of the Genevese savans was thus associated with water, and not with ice, in the only cave in which I had detected its presence to any appreciable extent, the currents of the Glaciere of Monthezy being of a totally different description.