Societies and Academies

Abstract

LONDON. Royal Society, November 3.—Prof. C. S. Sherrington, president, in the chair.—T. R. Merton: The spectra of lead isotopes. Comparison of the wave-lengths of five lines in the spectra of ordinary lead and lead from Australian carnotite shows differences wrhich are not constant, but vary for the different lines. The difference in wave-length observed for the principal line, λ= 4058 Å., is about two hundred times as great as that expected on theoretical grounds.—G. I. Taylor; Experiments with rotating fluids. Methods are described by which experiments pa spheres, cylinders, and vortex rings moving through rotating fluids can be projected in a lantern and instantaneous photographs taken. If any small motion be given to a rotating fluid, the resulting flow will be such that concentrated masses of coloured liquid should be drawn out into thin films, parallel to the axis of rotation. Photographs taken by a camera placed vertically above a rotating basin of water show that the liquid moves in this way.—L. Bairstow, Miss B. M. Cave, and Miss E. D. Lang: The two-dimensional slow motion of viscous fluids. In its restricted form the equation of motion of a viscous fluid is ∇4ψ = 0, where ψ is Stokes's stream function. If the molecular rotation in the fluid be defined by ξ≡∇2ψ the equation of motion may be expressed alternatively as ∇2ξ=0. The equation ∇4ψ=0 is transformed by means of Green's theorem to a form in which the only unknown is the distribution of the ξ doublets on the boundaries. The strengths of the doublets are found by solving the resulting integral equation. An example shows the motion of fluid past a circular cylinder in an infinite parallel-walled channel. If d be the diameter of the cylinder, ρ the density of the fluid, v the kinematic coefficient of viscosity, and U the velocity of the fluid in the centre of the channel at infinity, then, when the width of the channel is 5d, the resistance per unit length of cylinder is R=7.10ρvdU. The value of Ud/v to which this formula applies is not to exceed 0.2.—H. C. H. Carpenter and Constance Elam: The production of single crystals of aluminium and their tensile properties. The parallel portion of the test pieces of the sheet was 4 in. × 1 in.×0.125 in., consisting of about 1,687,000. The conversion of this area into a single crystal involved heat treatment for six hours at 550° C., tensile stress of 2.4 tons per square inch, producing an average elongation of 1.6 per cent. on 3 in., and final heat treatment beginning at 450° and extending up to 600° C. On an average, one test piece in four produces a single crystal over its parallel portion, which frequently grows up into the shoulders of the test piece. The tenacity of single crystals varied from 2.8 to 4.08 tons per sq. in., while the extension on 3 in. varied from 34 to 86 per cent., according to the orientation of crystal relative to stress. Five types of specimens were recognised. Stress tests of test pieces consisting of two and three crystals show the strengthening influence of one crystal upon another. Experiments on round bars resulted in the production of single crystals in the parallel portion pf bars 0.564 and 0.798 in. in, diameter. The total volumes of the crystals were more than 1 cb.in., and more than 2 cb.in. respectively. The tensile properties were determined, and in every case a wedge-shaped fracture was produced, the bar diminishing principally, in one dimension only. Remarkable twinning effects were observed in certain cases.—C. V. Raman and B. Ray: The transmission colours of sulphur suspensions. When a few drops of sulphuric acid are added to a dilute solution of sodium thiosulphate and a precipitate of sulphur gradually forms in the liquid, the suspension becomes practically opaque to the shorter wave-lengths first and the longer wave-lengths later, and afterwards regains its transparency partially, the shorter wave-lengths re-appearing first and later the longer wave-lengths. A theoretical explanation is offered.—E. F. Burton and Miss E. Bishop: The law of distribution of particles in colloidal solution.