Abstract
LONDON. Royal Society, December 9.—Prof. C. S. Sherring-ton, president, in the chair.—Lord Rayleigh: Double refraction and crystalline structure of silica glass. Although glasses in general have no double refraction, except that due to bad annealing, yet silica glass is found to have a doubly refracting structure which cannot be so accounted for, and must rather be regarded as crystalline. The double refraction is very weak, of the order of 1/60 that of crystalline quartz. In a mass of silica which has been melted, but not drawn or blown, the structure consists of doubly refracting grains with dimensions of about 1/2 mm., oriented at random. If the grained material is drawn out while soft, the grains are elongated into crystalline fibres or ribbons. Fused silica sometimes contains isolated, small inclusions of quartz with angular outlines which have escaped vitrification. These are conspicuous in the polariscope by the strain effects they produce in the surrounding glass.—Prof. J. W. Nicholson and Prof. T. R. Merton: The effect of asymmetry on wave-length determinations. (1) The apparent displacement of an unsymmetrical spectrum line caused by the finite resolving power of the spectroscope can be calculated on certain simple assumptions. (2) The displacement is independent of the actual widths of the lines. (3) It is considered that the general practice of measuring spectrum lines to a degree of accuracy far transcending the resolving power is not justified.—Prof. T. R. Merton: The effect of concentration on the spectra of luminous gases. Certain spectroscopic phenomena appear to be associated with the concentration of the radiating atoms in the source. An increase in concentration may result in a broadening of the lines, a change in the structure of the lines, and changes in the relative intensities. Sources containing lithium exhibit these three phenomena, and the broadening is familiar in sodium flames. A study has been made of the behaviour of sources containing sodium and lithium. The results seem to exclude a temporary association of atoms as the cause of the changes, for the addition of large quantities of sodium to a source containing a trace of lithium produces no change in the lithium spectra. Mixtures of hydrogen and helium have also been investigated. The broadened lines of both these elements from vacuum tubes excited by condensed discharges are accounted for completely bv the electrical resolution of the lines bv the electric fields of neighbouring charged particles.—Prof. E. Wilson: The measurement of low magnetic susceptibility by an instrument of new type. The paper deals with the design, construction, and working of an instrument for the measurement of susceptibility (of low order) over a wide range of magnetic force, and thus avoids the difficulty met with in the Curie balance, the defections of which follow the square law, and, in fact, limit the measurement of suscerjtibilitv of a given specimen to a very narrow range of magnetic force. The force due to torsion in a suspending fibre is replaced by an electromagnetic system in which the mechanical force is due to two components—one proportional to the magnetic force impressed upon the specimen and the other variable if the susceptibility varies. The expression for the susceptibility is that of the reciprocal of a resistance multiplied by a constant, and thus the instrument lends itself to great accuracy in the detection of variations in susceptibility.—Prof. W. T. David: The internal energy of inflammable mixtures of coal-gas and air after explosion. In the first part of this paper an empirical law of cooling of exploded mixtures of coal-gas and air contained in a closed vessel has been formulated. This is based upon measurements of the heat loss by conduction and by radiation made during the explosion and later cooling of the inflammable mixtures. In the second part the heat-loss measurements have been applied to the estimation of the internal energy of the gaseous mixtures at the moment of maximum temperature and at various stages during cooling.—Prof. A. McAulay: Multenions and differential invariants. The paper is a summary of the properties of a linear associative algebra suitable for electromagnetic relations, differential invariants, arid relativity. There are n fundamental units, otherwise it is the same algebra as that considered in a paper bv W. J. Johnson and read to the Royal Society on November 20, 1919.
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Societies and Academies. Nature 106, 553–555 (1920). https://doi.org/10.1038/106553a0
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DOI: https://doi.org/10.1038/106553a0