Abstract
PARIS Academy of Sciences, Sept. 19.—M. Wurtz in the chair.—The president gave a welcome to the foreign members of the International Congress of Electricity who were present, including Clausius, Clifton, Du Bois Reymond, Everett, Förster, Helmholtz, Kirchhoff, Melsens, Spottiswoode, Siemens (William and Werner), Smith, Stas, Thomson, Warren De La Rue, and Wartmann.—The following papers were read:—On the relative resistances that should be given, in dynamo-electric machines, to the active bobbins, the inductor electro-magnets, and the interior circuit, by Sir William Thomson.—On experiments made in 1826 on electric currents by lightning far from the place of observation, and on recent studies of M. René Thury on sounds of telephones during thunderstorms, by M. Colladon. M. Thury stretched a copper wire horizontally between two houses at the height of the roofs, and connected it with the water pipes, and with two telephones. The telephones gave a characteristic sound each time and at the same instant as a flash of lightning was seen, near or far (and even when no thunder was heard). It was like the sound of a Swedish match rubbed on the box. M. Colladon, in 1826, observed deflections in a galvanometer in Paris during a thunderstorm at a distance, while there was no cloud within 30° of the zenith, and M. Peclet describes like inductive effects in his “Traité de Physique” (1832). M. Colladon thinks the sounds will be best heard in the telephone when the air is surcharged with humidity. The telephone affords an easy method of measuring the velocity of transmission of those influences.—Measurement of rotation of the plane of polarisation of light under the magnetic influence of the earth, by M. H. Becquerel. Repeating his experiments under more favourable conditions, he finds that the yellow rays D, traversing horizontally a column of 1 metre of sulphide of carbon at 0°, under the influence of terrestrial magnetism at Paris, and in a direction parallel to the declination needle, undergoes a simple magnetic rotation of 0′·8697 from right to left for an observer supposed to lie with his head towards the magnetic north. In the C.G.S. system of units this leads to the number 1·3l × 10–5 as expressing the magnetic rotation of yellow rays through sulphide of carbon between two points of unit distance in a magnetic field equal to unity. (Mr. Gordon's figures, got by different methods, give 1·24 × 10–5 for sodium light.)—On the passage of projectiles through resistant media, on the flow of solids and the resistance of air to the motion of projectiles, by M. Melsens. He arranged experiments with a view to catching the air carried in front of a projectile. Lead balls (about 0·017m. in diameter) were shot into a hollow cone in a block of iron, the apex being of steel, and having an opening, smaller than the ball, into a gun-barrel communicating with a bell-jar in a reservoir. The gun, the reservoir, and the bell-jar were filled with water, which was prevented escaping through the cone by a light obstacle of paper or thin brass. Detached fragments of the lead entered the gun-barrel, the bulk of the ball stopping the hole of the cone, and appearing pointed, or with an oblong drop. The effects of the penetrating air are indicated in the cracks and rupture of the gun-barrel, the bell-jar, and the bent tube between them. M. Melsens considers the resistance of the air implies factors of which artillery has not taken sufficient account. This resistance is variable throughout the trajectory, in virtue of the mass of the projectile, the form of the mass of adherent air, the velocity, the thrust of the powder-gases, up to a certain distance from the gun, and, lastly, from the very brief moment when the projectile is equally pressed in all directions by air.—On new sulphurised salts produced with sesquisulphide of phosphorus, by M. Lemoine.—On tungstoboric acid and its salts, by M. Klein.—Determination of phosphoric acid by titrated liquors, by M. Perrot.—On some of the scientific researches contained in the manuscripts of Leonardo da Vinci, by M. Ravaisson. He calls attention to a passage recommending, as a method of hearing distant sounds at sea or on land, inserting one end of a tube in the water or in the earth, and putting one's ear to the other. M. Ravaisson is preparing the manuscript B, one of twelve in the Bibliothèque de l'Institut, for publication (to follow MS. A, published in December last).
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Societies and Academies . Nature 24, 551–552 (1881). https://doi.org/10.1038/024551a0
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DOI: https://doi.org/10.1038/024551a0