Societies and Academies

Abstract

LONDON Physical Society, May 19. W. F. FLOYD: Interference tones in superheterodyne receivers. The problem involves the reception of at least three signals, double detection, and a filter action between the two detectors. In the case of rectification by detectors with generalised characteristics, quantitative analysis is extremely complex. The form of the result, however, shows how large is the number of possible sources of interference tones. The specific case of square-law rectification is also considered. W. G. MARLEY: A method of measuring the specific heats of poor conductors. A brief review of existing methods of determining specific heats is given with reference to their suitability for poor conductors. The method of cooling, which has received scant attention in the past, is developed to afford an accurate and ready method. D. BROWN: The demonstration of eddy currents in conductors of various shapes. A method is described whereby it is possible to demonstrate visually the existence of eddy or Foucault currents in masses of conducting material, and the way in which the flow of the currents may be distorted or baffled by suitable slots or laminations. S. TOLANSKY: The absence of fine structure from the arc spectrum of silver. The arc spectrum of silver, produced in a water-cooled hollow-cathode discharge, has been examined for fine structure with a variable-gap silvered Fabry-Perot interferometer in the region 8300-4000 A. Results for the resonance lines at approximately 3300 A. are quoted also. Silver consists of two odd isotopes 107, 109, and although 5s, 6s, 7s, 5p, 6p, and 5d terms have been studied, no trace of fine structure has been found, in spite of very excessive over-exposing in many lines. All lines are extremely sharp and are worth considering as wave-length standards, being well distributed. Attention is directed to the fact that the analogous spectrum of CdII also shows no fine structure, so that it is concluded that the absence of structure is probably due to the electron configuration’ and not necessarily to smallness of the nuclear magnetic moment. This is remarkable, for penetrating s electrons are involved in some configurations. W. Y. CHANG and WILLIAM BAND: Thermomagnetic hysteresis in steel. The temperature variation of a new hysteresis of the thermomagnetic electromotive force in a steel wire is described. The hysteresis is of a negative or abnormal form with a maximum amplitude of about 2 microvolts between up and down branches. The accuracy of the apparatus and method is critically examined, and an error of more than 0.5 microvolt in any reading is considered to be unlikely. A qualitative explanation of the phenomenon is given.