Societies and Academies

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    PARIS. Academy of Sciences, Sept. 19.—M. Duchartre in the chair.—On the white rainbow, by M. Mascart. This phenomenon, usually known under the name of Ulloa's circle, is explained, not on the untenable assumption of water vesicles, but of very minute drops as constituting the mist upon which it is seen. The diminution of the diameter of the drops causes a displacement of the first maximum of the interference fringes which produce the supernumerary arcs. The relative intensities of the various colours retain equal values long enough to make the rainbow appear achromatic, with perhaps a slight red coloration along the outside. The radius of such a circle has been known as small as 33° 30'.—Observations of the new planet Wolf (1892, Sept. 13), and of the planet Borrelly-Wolf (Eri-gone?), made at the observatory of Paris (west equatorial), by M. Bigourdan.—On a recurring series of pentagons inscribed to the same general curve of the third order, by M. Paul Serret.—On the production of the spark of the Hertz oscillator in a liquid dielectric instead of air, by MM. Sarasin and De la Rive. The two balls of 3 or 4 cm. in diameter, between which the Ruhmkorff discharge takes place in the Hertz oscillator, were plunged into an insulating fluid. This was, in the first place, olive oil, contained in a cylindrical vessel, 20 cm. in diameter, pierced laterally to admit the end branches of the oscillator. Sparks I cm. long were obtained, giving a characteristic sound, louder than that of a discharge through air. The effect on the resonator is notably increased by the arrangement, most brilliant sparks being produced. The interferences of the electric force by reflection from a plane metallic surface give the same results as in air. During the discharge, the oil is carbonized and loses its transparency, but without affecting the intensity. Similar experiments were made with essence of terebenthine and petroleum, but the oil proved the safest and most advantageous medium.—The action of bromine in presence of aluminium bromide on the cyclic chain carbon compounds, by M. W. Markovnikoff. It has been shown that a small quantity of bromide or chloride of aluminium added to the bromine produces a vivid reaction with the carbon compounds of the aromatic series, usually resulting in substitution-products of a crystalline form. Further experiments show the generality of the reaction for all the hydrocarbons of the series CnH2n which were examined. It has been studied chiefly as regards the naphthene (hexacarbon) series, and may be expressed by the general equation-

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    Societies and Academies. Nature 46, 532 (1892) doi:10.1038/046532a0

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