Societies and Academies

    Abstract

    LONDON. Royal Society, June 16.—Prof. C. S. Sherrington, president, in the chair.—H. B. Dixon, Dr. C. Campbell, and Dr. A. Parker: The velocity of sound in gases at high temperatures, and the ratio of the specific heats.—Prof. J. R. Partington: The ratio of the specific heats of air and of carbon dioxide. The ratio of the specific heats, γ=C-p/C-r has been determined by the method of adiabatic expansion for the gases air and carbon dioxide. The gas was contained in a 120-litre vessel, and the temperature change immediately after expansion followed by a platinum thermometer, with compensating leads of wire 0.001 mm. diameter, the resistance of which was observed by an Einthoven string galvanometer of o-oi seconds period. The fundamental temperature measurements were made by a mercury thermometer. The results were calculated by the characteristic equation of D. Berthelot, so that deviations from the ideal gaseous state were allowed for. The final results, accurate to 1 part in 1000, are: γ for air at 17° C.=1.4034; γ for carbon dioxide at 17° C.= 1.3022, whence c-p for air at 17° C. =0.2387 cal. and c-p for carbon dioxide at 17° C.= 0.1996 cal. All the values refer to atmospheric pressure.—Dr. A. B. Wood and Dr. F. B. Young: (1) “Light-body” hydrophones and the directional properties of microphones. A light prolate ellipsoid possesses directional properties by virtue of its shape. Quantitative results obtained agree with calculated values supplied by Prof. Lamb. Owing to the pronounced intrinsic directional properties of the microphone, a spherical “light-body” hydrophone is practically equal in directional efficiency to one of ellipsoidal form. “Light-body” hydrophones are of value as experimental exploring instruments. (2) The acoustic disturbances produced by small bodies in plane waves transmitted through water, with special reference to the single-plate direction finder. Sound distribution was explored round a number of discs immersed at a distance from a small submerged source of sound. By means of a pair of miniature hydrophones-one bi-directional, the other non-directional-it was possible to chart (1) direction of oscillation of the water particles; (2) relative amplitude of the movements; and (3) relative amplitudes of the pressure oscillations. The charts obtained fall broadly info two classes, according as the discs are solid or contain air-filled cavities, very minute air-filled spaces giving marked effects. The behaviour of a typical baffle-plate is investigated, but no satisfactory theory of the baffle is offered.—M. A. Giblett: Some problems connected with evaporation from large expanses of water. The problems of distribution and amount of water-vapour present are considered for a current of air of uniform speed moving over a water-surface of uniform temperature. Near the surface is a thin layer of air, through which water-vapour diffuses slowly by molecular processes, but above this is a rapid transition to a turbulent regime, where diffusion becomes much more rapid. At and near the water-surface the problem is treated as one of eddy diffusion. Formulæ are obtained for humidity at any point of the air-current, and for rate of evaporation from stretches of water extending any distance downwind. The distribution of water-vapour is obtained for some typical cases, and an estimate made of the rate of evaporation from long stretches of water under various conditions of wind, water-surface, temperature, and turbulence. The effects which each of these elements exerts, when varied within their natural range, are examined. The results emphasise the control exercised by atmospheric turbulence over evaporation from large areas.—F. C. Toy: The photographic efficiency of heterogeneous light. Two possible laws of action are discussed:— (1) All radiations composing the heterogeneous beam may act simultaneously but independently; and (2) all radiations may act simultaneously but not independently. The possibility of testing the laws depends on the form of law connecting the probability of a single grain of the photographic emulsion being made developable with the intensity of the exciting light. The form of this law proved experimentally! by Slade and Higson is considered, and a result is deduced which can be tested bv experiment. From the evidence obtained it is concluded that over the spectral range used in the experiments (λ4350 to λ4000) radiations of different frequencies act simply as a total amount even when a difference in quality exists.

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    Societies and Academies. Nature 107, 541–543 (1921). https://doi.org/10.1038/107541b0

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