NATURAL PHILOSOPHY. 155 



NATURAL ICE CAVES. 



In a number of the Bibliotheque Universelle de Geneve, Prof. Shuny 

 has printed a memoir on these remarkable grottoes. The glacier La 

 Baunie, near Besancon, seems to have been the first to attract the 

 attention of philosophers, which appears to be not only a great con- 

 servator, but also a great producer of ice. In 1727, when the camp 

 was at the Saone, the Due de Levi had the ice taken from the cave in 

 a great many carts; yet, in 1743, the cave was re-supplied with ice, 

 which covered the floors and walls, and was suspended as stalactites 

 from the roof. As the mean temperature of the soil where the grotto 

 exists is several degrees above the freezing point, a change must take 

 place between the interior and the exterior, in which, for a time, the 

 heat taken off must exceed that received. M. Shuny gives the theo- 

 ries of Prevost, Pictet, and others, and then, in a second part of his 

 memoir, gives an account of his own excursions and investigations, 

 especially in the glaciers of Jura, in 1857-61. He gives the follow- 

 ing as the causes of the formation of ice : During the winter the heavy 

 cold external air falls through the holes of the grotto, displaces the 

 less cold air, and freezes the waier in the grotto. In the warm sea- 

 son, the heavy <?old air cannot be displaced, and transmits heat feebly, 

 while the radiation of the walls and roof, and the heat of the soil, mc4t 

 only a small quantity of ice, which, absorbs much heat when passing 

 to the liquid state. In addition, the branches of the trees which over- 

 shadow the openings of the cave, the exposure to the north, the vege- 

 tation which covers the soil, the incessant evaporation of the surface, 

 attenuate as much as possible the effects of the solar heat, and main- 

 tain the cold of the upper part of the grotto. In January last M. 

 Joret, with two companions, visited the ice cave of the Vergy, in the 

 Alps. They passed the night at the Convent of the Chatreuse, in 

 the middle of a long valley, a situation of severe beauty. Thence 

 they descended by a steep road, a quarter of a league long, to the vil- 

 lage Pralong du Reposoir, where they halted. The mountaineers 

 affirmed that nothing could be found in the " grand cave " but water 

 and vapor, but had not been there to see. The entry to the grotto 

 was found to be free. The snow had slid down towards the bottom 

 of the valley, where it formed a thick layer. Beautiful stalactites hung 

 from the roof; perfect silence reigned ; very dry ice appeared every- 

 where in the form of columns, slabs, inclined planes, etc. There was 

 no water or snow anywhere, and the atmosphere was very still and 

 cold. 



THE PRODUCTION OF MIST AND HAIL. 



The production of mist is the subject of a note by the veteran Dr. 

 John Davy, in the Edinburgh Philosophical Journal. The cause 

 usually assigned for mist is the access of cold air and its admixture 

 with warmer air, saturated or nearly so with moisture, strikingly ex- 

 emplified in our autumnal and winter fogs, when the water, owing to 

 the heat absorbed during summer, is of higher temperature than the 

 inflowing air. Dr. Davy, however, refers to another cause, not so 

 much noticed, viz., a mild moist air coming in contact with a colder 

 air, equally humid, resting on cold surfaces, whether of land or water, 



