The people of the district assured Professor Pleischl that the hotter the summer, the more ice is formed; and that it disappears when the nights become long and the days short.  Dr. Weiss, for six years head of the Gymnasium of Leitmeritz, stated that when one of the holes was emptied of ice in the summer, it filled again in a few days.  The explanation given by the Professor of this phenomenon is, that the blocks of basalt, that being an excellent conductor of heat, pass so much warmth through to their under surfaces—­which form the roof of small chambers filled with a spongy mass of decaying leaves—­that the rapid evaporation thereby caused produces the cold air and the ice.  He omits to explain why there should be anything exceptional in the winter phenomenon of the crevices among the stones.

There are two other places in Bohemia where ice is found in summer.  One is on the Steinberg, in the county of Konaged;[132] it is a small basin, surrounded by trees, where, in the middle of summer, lumps of ice are found under basaltic debris.  This ice is only formed, according to Sommer, in the hottest part of the year.  The other is on the Zinkenstein, one of the highest points of the Vierzehnberg, in the circle of Leitmeritz.  It is described by Sommer[133] as a cleft, five fathoms deep, in the basaltic rock, where ice is found in the hottest seasons.  Professor Pleischl put this assertion to the test by visiting the spot in the end of August, when he found no signs of ice.

Another writer in Poggendorff[134] describes a somewhat similar appearance on the Saalberg.  Here ice is found on the surface from June to the middle of August; and that, too, with a west exposure and in moderate shade.  In July, the ice was so abundant that it could be seen from some distance:  it was half a foot thick, and yielded neither to sun nor rain.  In the middle of August there was no ice on the surface; but when the loose debris was removed, the most beautiful ice appeared, and at a little depth all was frozen as hard as if it had been the depth of winter.[135] The people who work in the neighbourhood declare that the place remains open, and free from ice or snow, in the greatest cold, and that no ice begins to form till the month of June.  When the writer of the account in Poggendorff visited the ice-hole, the peasants were in the habit of carrying large masses of ice down to their houses, through a temperature of 81 deg.  F.

Reich[136] gives a detailed and valuable account of the prevalence of subterranean ice on the Sauberg, a hill which forms one side of a ravine near Ehrenfriedersdorf.  The surface is about 2,000 feet above the sea, and its mean temperature, as determined by many careful observations, about 45 deg.  F. There are several tin-mines in this district, and the extended observations made by the authorities establish the curious fact that the mean temperature is considerably lower beneath than at the surface.  For instance, in the S.