Societies and Academies

Abstract

LONDON. Royal Society, February 27.—Sir J. J. Thomson, president, in the chair.—Hon. R. J. Strutt: Scattering of light by solid substances. Glasses of all kinds show a strong internal scattering of light. The beam viewed laterally is strongly, but not completely, polarised. Yellow and smoky quartz also show a strong scattering. One specimen gave a polarisation so nearly complete that an analysis set for minimum intensity transmitted only 0.7 of 1 per cent. of the scattered light. if a polarised beam is passed along the axis of such a quartz crystal, there are for a given wave-length maxima and minima of scattered light along the length of the beam. This is due to the rotatory property. Owing to rotatory dispersion the period is different, for different wave-lengths, and coloured bands result. The clearest and whitest quartz has some scattering power, though much less than that of glass or liquids. In one case examined the intensity was about eight times that due to dust-free air at atmospheric pressure. This small scattering is considered to be due to inclusions, as in the case of visibly smoky or yellow quartz. The regular atomic structure, which has a period small compared with the wave-length of ordinary light, should give no scattering. For very short wave-lengths (X-rays) the well-known diffraction effects of crystals come in.—Sir James Dobbie and Dr. J. J. Fox: The constitution of sulphur vapour. Investigations based on the determination of the vapour density leave the question of the existence of sulphur molecules intermediate in complexity between S8 and S2 unsettled. The present paper contains an account of an attempt to solve the problem by the study of the absorptive power of the vapour of sulphur for light under various conditions of temperature. When light from a suitable source is passed through the vapour and examined with the spectroscope at successively higher temperatures it is found that the amount of absorption caused by the vapour gradually increases up to about 650° C., after which it decreases as the temperature rises until 900° C. is reached, above which no further change occurs.—Dr. W. G. Duffield, T. H. Burnham, and A. H. Davis: The pressure upon the poles of the electric arc. for many reasons the projection of electrons from the cathode of an electric arc is to be expected, and the mechanism of the arc appears to require it. If this projection exists, it is likely to occasion a mechanical recoil upon the cathode. A pressure was looked for in 1912 and discovered. It remained to determine if the magnitude was such as to be accounted for by electronic projection. Numerous sets of observations upon anode and cathode were taken with varying current and arc-length and different dispositions of apparatus. The pressure was found to be about 0.17 dyne per ampere, or when convection current effects were eliminated so far as possible, 0.22 dyne per ampere. The effect does not appear to be due to radiometer action, and is about two hundred times too small to be referred to the expulsion of carbon atoms at the boiling-point of that element. Such evidence as has been obtained thus favours the recoil being due to the projection of electrons.