Abstract
PARIS.
Academy of Sciences, November 6.—M. Lœwy in the chair.—On Goubet's joint and its application to marine screw-propellers, by M. H. Resal. This is a mathematical investigation of the action of a joint capable of making the propeller act as supplementary steering gear, and of adapting it to submarine navigation. It is shown to possess several advantages over the similar American Clemens joint.—On a class of differential equations whose general integral is uniform, by M. Emile Picard.—Significance of the variety of organs in the gradation of vegetable species, by M. Ad. Chatin.—On a Nymphæa bed recently found and explored in the Aquitanian of Manosque, by M. G. de Saporta.—On equations of the second order with fixed critical points, and univocal correspondence between two surfaces, by M. Paul Painlevé.—On certain ordinary differential equations, by M. Alfred Guldberg.—On certain families of gauche cubes, by M. Lelieuvre.—On the nature of the reflection of electric waves at the end of a conducting wire, by MM. Kr. Birkeland and Ed. Sarasin.—Observations upon the preceding communication of MM. Birkeland and Sarasin, by M. H. Poincaré. This is an application of Maxwell's theory to the phenomena of propagation of energy into space round the end of a conducting wire along which electric waves are passing. It is shown that the deductions from the theory are in general accord with the facts observed.—On the measurement of coefficients of induction, by M. H. Abraham. The employment of a differential galvanometer in these measurements permits of an accurate determination within 1 per cent., and a reading to within 0˙1 per cent, without much difficulty. The induced currents from a commutator regulated by a stroboscopic method are sent through one circuit of a differential galvanometer, the deflection being compensated by a continuous current derived from the same battery. The commutator is then stopped, and a current equivalent to the induced current is derived from the primary circuit through a resistance r, and sent through the secondary circuit, r being chosen so as to establish equilibrium in the differential galvanometer. Then this actual resistance r may be put equal to the fictitious resistance nM obtaining while induction was going on, and we have M = r/n where M is the coefficient of mutual induction, and n the frequency of the commutator. The resistance r may be constituted by a standard ohm coil. M. Abraham has found by this method that the coefficient of mutual induction is reciprocal in the case of two circuits free from iron, but that this reciprocity is disturbed if they contain iron cores.—On vision of opaque objects by means of diffracted light, by M. Gouy. If an opaque and non-reflecting object is examined by means of a microscope or telescope, the object being placed in the path of a beam of light, the image is formed both by the rays following geometrical paths and by those diffracted by the outlines of the object. If the former are intercepted, the diffracted rays only form the image. This may be done by placing a small screen at the focus of the object-glass inside the telescope, so as to intercept the rays from a very distant source which converge there. The outline of the object is then seen as a thin bright line on a dark background, and with sufficient enlarging power this line is seen to consist of two, very close together, and separated by a very sharp black line. This black interval disappears on intercepting the diffracted rays either inside or outside the geometrical shadow, thus showing that it is due to the interference of these two beams. They possess a difference of phase of half a wave-length, and equal amplitudes. An arrangement such as this may prove useful when the outlines of an object require to be sharply defined.—On a new method of preparing methylamine and on the constitution of hexamethylene-tetramine, by MM. A. Trillat and Fayollat.—On the alkaline methyl-tartrates and ethyl-tartrates, by M. J. Fayollat.—Researches on the homologues of gallanilide; preparation of galloparatoluide, by M. P. Cazeneuve.—Experimental hereditary influences, by MM. Gley and Charrin.—On a phenomenon of inhibition in Cephalopoda; paralytic constriction of chromatophores, by M. C. Phisalix.—On the serial craniological continuity in the genus Lepus, by M. Remy Saint-Loup.—On the genus Polydora Bosc (Leucodore Johnston), by M. F. Mesnil.—The Callibrachion, a new reptile of the Permian of Autun, by MM. M. Boule and Ph. Glangeau.—On the glacial and erratic phenomena in the Cachapoal Valley (Andes of Chili), by M. A. F. Noguès. The phenomena of transport by water and glaciers have contributed to the formation of the erratic system in the valleys of the Chili. Andes. There must have existed lakes or deep terrace ponds. The glaciers must formerly have descended further than they do at present, and at the Cachapoal they are actually retreating now.—An earthquake shock at Grenoble, by M. Kilian. This happened at 4h. 13m. 40s. A.M., Paris time, on November 5, in a direction from N. to S., and was recorded by the seismometer of the Geological Laboratory of the Faculty of Sciences.
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Societies and Academies. Nature 49, 71–72 (1893). https://doi.org/10.1038/049071b0
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DOI: https://doi.org/10.1038/049071b0