[Footnote 27: London's _Magazine of Natural History_, Vol. vii., pp. 644-5. The note was illustrated by engravings from two sketches by the author of the Aiguille de Servoz and of the Aiguille Dru, and by a diagram explanatory of its last sentence but one.--ED.] [Footnote 28: "A small neat copy of a sketch carefully taken on the spot," which, according to the editor of the magazine, accompanied this communication, was not, however, published. See the magazine.--ED.] [Footnote 29: Loudon's _Magazine of Natural History_, Vol. ix., No. 65, pp. 488-90.--ED.] [Footnote 30: The question here discussed was originally asked in the magazine (Vol. ix., pp. 379-80) by Mr. W. Perceval Hunter with reference to the condition of Bodiam Castle, in Sussex.--ED.] OBSERVATIONS ON THE CAUSES WHICH OCCASION THE VARIATION OF TEMPERATURE BETWEEN SPRING AND RIVER WATER.--BY J. R.[31] 274. The difference in temperature between river and spring water, which gives rise to the query of your correspondent Indigena (p. 491),[32] may be the result of many causes, the principal of which is, however, without doubt, the interior heat of the earth. It is a well known fact, that this heat increases in a considerable ratio as we descend, making a difference of several degrees between the temperature of the earth at its surface and at depths of 500 or 600 feet; raising, of course, the temperature of all springs which have their source at even moderate depths, and entirely securing them from the effects of frost, which, it is well known, cannot penetrate the earth to a greater depth than 3 or 4 ft. 275. Many instances might be given of the strong effect of this interior heat. The glaciers of the Alps, for instance, frequently cover an extent of three or four square leagues, with a mass of ice 400, 500, or even 600 feet deep, thus entirely preventing the access of exterior heat to the soil; yet the radiation of heat from the ground itself is so powerful as to dissolve the ice very rapidly, and to occasion streams of no inconsiderable size beneath the ice, whose temperature, in summer, is, I believe, as far as can be ascertained, not many degrees below that of streams exposed to the air; and the radiation of heat from the water of these streams forms vaults under the ice, which are frequently 40 ft. or 50 ft. above the water; and which are formed, as a glance will show, not by the force of the stream, which would only tear itself a broken cave sufficient for its passage, but by the heat which radiates from it, and gives the arch its immense height, and beautifully regular form.