PHYSICS AND NATURAL HISTORY OF GENEVA. 241 



have tended constantly to confirm the theory which he had given of 

 the aurora boreal is. 



Besides the communications just mentioned, M. De la Rive submitted 

 to the society the remarkable improvements introduced by M. Leon 

 Foucault, in the construction of curved plated mirrors designed for 

 telescopes, and the labors of M. Hoffman, of London, in regard to the 

 vegetable parchment which for some years has been manufactured in 

 England with great success. 



The last-mentioned communication already touches rather on chem- 

 istry than physics, and in effect there remains only, to terminate this 

 first part of our report, an account of two important memoirs on 

 chemical subjects presented by their authors to the Society. The 

 first, by MM. Deville and Troost, is directed to the determination 

 of the densities of vapors at very high temperatures, its authors hav- 

 ing successively employed, as the source of heat, the vapor of sulphur, 

 which boils at 450°, and that of cadmium, which boils at 850°. They 

 hope to be able to make use of that of zinc, which boils at about 1200°. 

 Among the results obtained, we will distinguish that relating to sulphur, 

 which gives 2.2 for the density of the vapor of that substance at a 

 very high temperature, contrary to determinations generally received, 

 whiph pointed to too high a number and one not in accordance, as has 

 been now shown, with the theoretic value. The researches of MM. 

 Deville and Troost are in general favorable to the opinion that at a 

 very elevated temperature, the elements of compound bodies are dis- 

 sociated, ceasing thus to exist in a state of combination. 



The second communication alluded to is that by M. Pyrame Morin, 

 on the presence of iodine in the mineral waters of Saxony, in Valais. 

 The author had, in 1853, already indicated that this principle is pre- 

 sent in the fountain only in an intermittent way — a result which, 

 though confirmed by other chemists, had been contested by M. Ossian 

 Henry, of Paris. M. Morin has resumed his investigation by employ- 

 ing still more sensible reactives than at first; and new experiments 

 have been made on sixty-one bottles of the water drawn at different 

 times and under different circumstances. He has succeeded in estab- 

 lishing with certainty that the quantities of iodine are very variable, 

 and that between 0.2257 grains and five millionths, all intermediate 

 quantities are met with. These variations take place at intervals of 

 time sometimes very distant, sometimes very close; so that several 

 oscillations may be observed in the course of a day, which proves 

 that the presence of iodine is really intermittent. Sulph-hydricacid, 

 whether free or combined, was not detected in the water by M. Morin, 

 contrary to the assertion of M. Henry. Bromine and ehloriue exist 

 in minute quantity; the latter very constantly, the former only when 

 there is iodine. It would seem highly probable that this water of 

 Saxony proceeds from two sources, having their origin, the one in a 

 certain rock, and the other, from which is derived the iodine, in the 

 Cargneule. 



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