Between the base of the circular column and the wall, we found a rare instance of clear jelly-like ice, without any lines external or internal, such as is formed in the open air under very favourable circumstances. The ordinary number of undergraduate May Terms had afforded various opportunities for studying the comparative clearness of different pieces of ice, but certainly no one ever saw a lemon pippin through an inch and a half of that material so clearly as we now saw the white rock through 1-1/2 feet. Mignot, indeed, said 2 feet; but it was his way to make a large estimate of dimensions, and he constantly interrupted my record of measurements by the assertion that I had made them _moins que plus_. We were all disappointed by the actual size of the ice-fall which it had cost us so much time and trouble to descend, the distance from the first step to the last being only 26 feet: as this, however, was given by a string stretched from the one point to the other, and not following the concave surface of the ice, the real distance was something more than this. It was now getting rather late, considering the journey one of us had yet to perform, and we walked quickly away from the glacière, agreeing that it was not improbable that in that part of the Jura there might be many hidden caves containing more or less ice, with no entrance from the world outside, except the fissures which afford a way for the water. The entrance to this cave was so small, that the same physical effect might well be produced by one or two cracks in the rock, such as every one is well acquainted with who has walked on the fissured limestone summits of the lower mountains; and, indeed, Renaud positively affirmed that at the time of his former visit there was not even this entrance to the lower cave, for the ice-stream reached then a higher point of the wall, and completely filled and hid the arch we had discovered. It is very difficult to see how ice can exist in a cave which has no atmospheric communication with the colds of winter, as would apparently be the case with this cave if the one entrance were closed; but where the cracks and small fissures in the rock do provide such communication, there is no reason why we should not imagine all manner of glacial beauties decorating unknown cavities, beyond the general physical law to which all the glacières would seem to be exceptions. Mignot now became communicative as to the amount of ice supplied by his glacière, the lower of the two we had seen; and his statistics were so utterly confused, that I gave him ten centimes and an address, and charged him to write it all down from his account-book, and send it by post. The letter was accordingly written on July 24, and after trying many unsuccessful addresses in various parts of Switzerland, it finally reached England in the middle of September. It tells its own tale sufficiently well, and is therefore given here with all the mistakes of the original.