[Footnote 214: The English edition of Bischof affords here a proof of the danger of frequent changes from one scale to another. Bischof in the first instance rendered Boussingault into degrees Réaumur, and this was in turn reduced to degrees Fahrenheit; the result being that the authorised English edition of his book gives 2°·25 F. for 127·5 feet, which does not come within 10 feet of Boussingault's statement.] [Footnote 215: M. Thury calculates a decrease of 1° C. for every 174 mètres between Geneva and S. Bernard, which is less than the decrease given in the text. He arrives at this conclusion by correcting the mean temperature of Geneva from 8°·9 C., the observed mean of eighteen years, to 9°·9 C., in consequence of supposed local causes, which unduly depress the temperature of Geneva. With the mean 8°·9 C. a result nearly in accordance with that of the text is obtained.] [Footnote 216: Professor Phillips found, in the course of his investigations in the Monk Wearmouth mines, some hundreds of yards below the sea, that when a new face of rock was exposed, its temperature was considerably higher than that of the gallery or shaft in which it lay. In some cases the difference amounted to 9 and 10 degrees. The rock soon cooled down to an agreement with the surrounding temperature.] * * * * * APPENDIX. M. Thury's observations during his winter visit to the Glacière of S. Georges are so curious and valuable, that I give the principal results of them here. It will be remembered that this glacière consists of a roomy cave, 110 feet long and 60 feet high, with two orifices in the higher part of the roof, one of which is kept covered with the trunks of trees to shut out the direct radiation of the sun. A little thought suggested to M. Thury that the cold in the cave in mid-winter would most probably be greater than the external cold of the day, and less than that of the night; so that there should be a time in the later evening when a column of colder and heavier air would begin, to descend through the hole in the roof. To test the correctness of this supposition, he took up his abode in the cavern for the evening of the 10th January, 1858, with a lighted candle. The flame burned steadily for some time; but at 7.16 P.M. it began to flicker, and soon inclined downwards through an angle of about 45°; and when M. Thury placed himself under the principal opening, the flame was forced into an almost horizontal position. At 8 P.M. the current of air had all but disappeared. This violent and temporary disturbance of equilibrium was a matter of much surprise to M. Thury; for he had naturally expected a quiet current downwards, continuing through the greater part of the night.