Societies and Academies

Abstract

LONDON. Royal Society, February 6.—Sir J. J. Thomson, president, in the chair.—A. Mallock: Note on the elasticity of metals as affected by temperature. The present note is an account of some preliminary experiments on the variations with temperature of Young's modulus for fifteen selected metals. The choice was influenced largely by the ease with which specimens could be procured. No alloys are included. The metals chosen were rhodium, platinum, iron, palladium, nickel, copper, gold, silver, magnesium, aluminium, zinc, lead, cadmium, bismuth, and tin. The procedure was to determine the frequency of the vibrations of a stiff rod carried at its lower end by a small thin plate of the material to be tested, the other end of the plate being clamped to a fixed support. The plate and its support could be immersed in fluid of any desired temperature without wetting the rod or in any way interfering with the mounting. The temperatures employed were those of liquid air, 0° Centigrade, ordinary temperature (10°–15°), and as near 100° C. as was practicable. The measured frequencies of vibration at these temperatures furnished the necesary data for determining the changes in Young's modulus. The results showed that the more infusible the metal, the less the modulus was affected for a given change of temperature, and this suggested that there might be a real connection between the variation of the modulus (M) and the melting point θM in Absolute temperature. A diagram is given comparing the experimental results with what they would have been had the relation dM/dθ = θM been true. If this relation holds, and 11, θ2 are two temperatures for which the moduli are M1, M2, then would M1/M2=θM-θ1/θM-θ2, and if θ1 is Absolute zero and θ2=0° C., then in this M1/M3 = melting point Absolute/melting point Centigrade for any two temperatures differing by 270° C. The experimental results show a distinct resemblance to those obtained on this supposition.—W. L. Cowley and H. Levy: Vibration and strength of struts and continuous beams under end thrusts. In a previous communication, “The Critical Loading of Struts and Structures,” the authors investigated the stability of a strut under end thrust and simply supported at a number of intermediate points. The method of analysis has been extended in the present paper to include the more general problem of the vibration of such a system when the lateral load is periodic and the supports are assumed in a state of vibration. The flexural rigidity and the end thrust, constant along each bay, are taken for further generality to vary from bay to bay. These conditions correspond closely with those originated in a wing spar of an aeroplane when in flight and influenced by engine-throbbing. A very general form of the equation of three moments is derived, and the conditions for resonance and crippling are expressed in a convenient determinantal form. The general case where the end thrust, the flexural rigidity, and the mass per unit length vary between the supports according to any assumed law is discussed, and the method of solution illustrated in the particular case of the crippling of a strut of variable flexural rigidity. The result is expressed in a form extremely convenient for graphical treatment.—A. Dey: A new method for the absolute determination of frequency. (With a prefatory note by C. V. Raman.)