Abstract
PARIS.
Academy of Sciences, August 21.—M. Lœwy in the chair.—On the equations of motion of a solid body moving in an indefinite liquid, by M. C. Maltézos.—On the alternations of colours presented by gratings, by M. Georges Meslin. If the achromatic fringes previously obtained by the author by means of a grating are observed more and more closely to the latter, they become more and more delicate, and certain colours begin to appear. The black fringes remain dark, but of two consecutive bright fringes the one appears violet and the other yellow; the same phenomena occurs along the whole field, which is covered with these two alternate colours. On moving the microscope slowly forward, a great variety of colours is observed, but the most usual are a mauve-violet associated with yellow, green combined with pink, or blue accompanied by white. The two colours in juxtaposition are thus nearly complementary, and during this displacement the same appearances recur several times, becoming more complex as the distance diminishes. The black fringes become very fine, the interval between two of them closes up, whilst the adjoining interval opens out and splits into coloured bands with a blue, pink, or yellow axis. In every case the phenomenon retains its periodic character. M. Meslin has succeeded in obtaining some very instructive photographs of these fringes.—On two new diseases of the mulberry, by MM. G. Boyer and F. Lambert. One of these diseases is caused by a bacterium, the other by a fungus. The disease caused by the Bacterium mori, chiefly affects young nursery mulberries, and arrests the development of their branches. It is manifested by dark brown patches at some points on the under side of the leaves and on the branches. Artificial patches in the parenchyma and in the veins of the leaves have been produced by inoculation. The bacterium when isolated and cultivated on artificial solid media, gives hemispherical colonies passing from white to yellow. The fungus disease is the more common of the two. The buds and leaves wither and dry up. The disease proceeds from the twigs to the branches and the trunk, and finally attacks the roots. The grey colour assumed by the wcod is caused by the mycelium of a parasitic fungus not yet completely isolated. The mycelium is varicose, septiferous, and ramified. Its colour passes from white to a pale yellow, and finally to brown.—On the geogeny and stratigraphy of the coal basins of Central France, by M. A. Julien.—The Cambrian of the Herault, by MM. de Rouville, Delage, and Miguel. The authors have recognised three groups in the Herault Cambrian which they provisionally name Anteparadoxidian, Paradoxidian, and Postparadoxidian, corresponding to the Longmynd, Menevian, and Tremadoc groups respectively. In the third group, corresponding to the Tremadoc slates and Lingula flags, tracts of Lingulæ have been found. An important fact concerning the stratigraphy of the country has been discovered in certain inversions extending over great lengths, unaccompanied by any indication of violent dislocation or rupture.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies. Nature 48, 432 (1893). https://doi.org/10.1038/048432a0
Issue Date:
DOI: https://doi.org/10.1038/048432a0