Societies and Academies

Abstract

LONDON Physical Society, April 15.—H. E. Beckett: The measurement of reflection coefficients for radiation at oblique incidence. The material is spread upon the metal receiver of a thermopile which, when exposed to radiation, yields an e.m.f. proportional to the absorption coefficient of the surface. Results obtained with black and white paints and with polished copper are discussed.—W. Ewart Williams: A new type of interference refractometer. The beam from the central part of the collimator objective is divided and each half laterally displaced. After passing through the gas tubes, the beams are again reunited so that the interference pattern at the focal plane of the telescope objective is similar to that from a two-plate transmission echelon. The brightness of the fringes is approximately twenty times greater than with the usual Rayleigh interferometer, so that the instrument can be combined with a spectrograph for dispersion measurements. A new method, based on Benoit's ‘fractional part’ principle, is developed for this purpose.—L. G. Grimmett: A direct reading γ-ray electroscope. A dead-beat direct-reading “γ-ray electroscope having a linear scale graduated in milligrams of radium is described. It is a combination of a special ionisation chamber, Lindemann electrometer, and high resistance, and allows the estimation, in less than three seconds, of the activity of small γ-ray sources of the order 1 mgm. radium with an accuracy of 0.5 per cent on a full-scale deflexion.