Societies and Academies

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PARIS. Academy of Sciences, September 17.—M. Des Cloizcaux in the chair.—Complement to the theory of overfalls stretching right across the bed of a water-course (weirs, mill-races, and the like), by M. J. Boussinesq. In supplement to the theory worked out in the Comptes rendus of July 4, October 10 and 24, 1887, the author here deals with the discharge as influenced by the velocities of the currents at the overfall.—On M. Lévy's recent communication on the subject of Betti's theorem, by M. E. Cesaro. This theorem, which plays an essential part in Betti's “Teoria dell' Elasticita,” is practically that of Green, which is capable of such manifold applications, and which M. Lévy has shown to admit of so many interesting corollaries in graphostatics. In the present paper M. Cesaro confines himself to proving that the formula of Laplace, giving the velocity of sound in rectilinear elastic mediums, is itself a consequence of Betti's fruitful theorem.—Compressibility of the gases, by M. E. H. Amagat.—On the chlorides of gallium, and on the value of the elements of the aluminium group, by MM. Nilsson and Otto Pettersson. Here are studied the two different chlorides Ga2Cl6 (or GaCl3) and GaCl2, as determined by M. Lecoq de Boisbaudran, the discoverer of gallium. The combinations are also given that are formed with chlorine by the elements of the third group of the natural system, whose chlorides have so far been studied. It is pointed out that aluminium and gallium displace three atoms, indium two, and thallium one of hydrogen of the hydrochloric gas. In this group, with the increase of the atomic weight the elements show an evident tendency to form several combinations with chlorine.—On ferrous chloride and the chlorides of chromium, by MM. Nilsson and Otto Pettersson. The preparation and properties are described of ferrous chloride, and of the two known chromium chlorides—the trichloride, CrCl3, and the bichloride, CrCl2.—Papers were communicated by M. René Chevrel on the great sympathetic nervous system of bony fishes; by M. Alexandre Vitzou on the incomplete intercrossing of the nerve-fibres in the optic chiasma of the dog; and by MM. Raphaël Dubois and Léo Vignon on the physiological action of para- and metaphenylene-diamine.