PARIS. Academy of Sciences, September 22.—M. Bouquet de la Grye in the chair.—The president announced to the Academy the loss it had sustained by the death of M. Damour.—The extension of, Fermat's principle on the economy of time to the orelative movement of light in a transparent homogeneous body subject to a rapid translation, by M. J. Boussinesq. It is shown that the principle of least time as enunciated by Fermat applies to the case of a body subjected to a rapid translatory motion. Polarisation is also unaffected.—The enclosures in the andesites from Mont Pelee, by M. A. Lacroix. The enclosures contain a greenish or yellowish-grey rock of a microlitic character; the mineralogical composition is always the same qualitatively, but the proportion of the elements varies considerably. The most complete type contains plagioclases, hypersthene, augite, titanomagnetite, hornblende and olivine. These enclosures are not fragments of solid rock torn off from the depths of the volcano, there being abundant evidence that they have been formed in place. They greatly resemble certain nodules of hypersthene-andesite from the last eruption of Santorin.—Spectral researches on the rotation of the planet Uranus, by M. H. Deslandres. The first researches on the rotation of the planets have been made by simply measuring the movement of certain well-defined points; if the image, is uniform and without detail, this method fails. On account of the small apparent diameter and feeble lustre of Neptune and Uranus, their time of rotation has hitherto remained undetermined. A new mode of attacking this problem is by applying the Doppler-Fizeau principle. This was first applied successfully to the Sun in 1889, to Jupiter and Saturn in 1895, and to Venus in 1900. The same method in a modified form has now been applied to Uranus, with the result that it is very probable that this planet turns in a retrograde sense, like its satellites. To obtain more definite measurements, further researches must be carried out in observatories nearer the equator, with more powerful instruments and in a very calm atmosphere, and for a period of twenty-one years. Encouraging results have also been obtained by the application of the same method to the planet Neptune.—On the combinations of silicon with cobalt, and on a new silicide of this metal, by M. P. Lebeau. When cobalt is heated in the presence of an excess of fused silicon, or when a mixture of silicide of copper, cobalt and silicon is submitted to the temperature of the electric furnace, a well-crystallised cobalt silicide of the composition Si2Co is formed, the physical properties and chemical reactions of which are given in detail. Cobalt thus forms three definite crystalline compounds with silicon, having the form ilae SiCo2, SiCo and Si2Co, these compounds forming a series in all respects comparable with the silicides of iron.—On the calorific power of coal, by M. Goutal. By an examination of 600 specimens of coal of different kinds, the calorific value (P) is found to be given, with an approximation of 1 per cent., by the formula P = 82 C + aV, in which C is the percentage of ash-free coke, V the volatile matter, and a a coefficient, a curve for the determination of which is given in the paper. The error may amount to 2 per cent, of the calorific value in the case of anthracite and some lignites.—On the existence of stable yeast forms in some moulds, by M. G. Odin.—On a modification produced in Scopolia carnolica following its grafting on the tomato, by M. Lucien Daniel.