Societies and Academies.

Abstract

LONDON. Physical Society, November 8.—Prof. A. Schuster, F.R.S., president, in the chair.—H. R. Nettleton: A method of measuring the Thomson effect. The distribution of temperature down a conductor conveying an electric current and at the same time moving uniformly through two fixed temperature sources is investigated. The effect of the Thomson heat on the distribution is exactly similar to the effect of a small impressed velocity. This result was applied to mercury to measure the Thomson effect by comparing the alteration of temperature Δθ1 at a point near the middle of the gradient caused by reversing a current of C amperes with the alteration of temperature Δθ2 at the same point due to a flow of mercury of m grams per second. Without any approximation as to emis-sivity loss or magnitude of Joulian heat, 2Cσ/ms = Δθ1/Δθ2, where s is the specific heat of mercury and σ the specific heat of electricity. Working with currents of from 4 to 9 amperes and with flows of different magnitudes—but never exceeding 1 cm. per hour—consistent values of σ were obtained, the value at 61° C. being –1.52 × 10–6 calories per degree Centigrade per coulomb. The thermo-junctions, which were of iron and constantan, were fused through the glass tubes with inappreciable distortion.—F. W. Jordan: An improved Joule radiometer and its applications. The first part relates to improvements made in order to convert the original Joule convection apparatus into an instrument for the exact measurement of small steady rates of evolution or absorption of heat. These improvements consisted in (1) replacing the badly conducting glass enclosure and cardboard partition by others made of brass and copper; (2) replacing the uncertain and variable magnetic control of the movement of the vane in Joule's apparatus by the elastic control of a quartz fibre; (3) shaping the channels, in which the vanes moved, so that the angular deflection of the vanes was proportional to the rate of evolution of heat; (4) reducing the size, so that uniform temperatures of its various parts could be maintained by (5) placing the radiometer within a concentric brass tube to exclude all extraneous heat excepting that which might be directed through apertures in its side towards the radiometer. The sensibility of the instrument was measured and found to be equal to 0.52 mm. per microwatt, as measured on a scale at a distance of one metre from the mirror. Thus the instrument may be used for the measurement of feeble oscillating currents. To convert the apparatus into an instrument for the measurement of radiant heat it is suggested that the radiant heat be directed through a small rock salt or fluorite window in the side of a compartment on to a thin blackened metal disc supported centrally. Its use for the quick measurement of the heat given out by radium is also suggested. The second part relates to a suggested method of measuring the Thomson effect with this radiometer. The method hinges on an experiment described by the author in NATURE, May 18, 1911.—Miss A. Somers: Note on the attainment of a steady state when heat diffuses along a moving cylinder. The paper dealt with the case of a column of mercury moving with uniform speed between two fixed temperature sources. The differential equation for the temperature within the column was stated and its solution given, and it was shown how the time of attainment of a steady state could be obtained from the latter. Dr. S. W. J. Smith: Thermomagnetic study of steel. Thermomagnetic measurements make it increasingly evident that the magnetic properties of steels are frequently those of mixtures of magnetic substances, each possessing characteristic properties, which contribute in a comparatively definite way to the properties of the material as a whole. In the case of a simple ferromagnetic substance, magnetising fields can be found in which the permeability variation with temperature is small except in the neighbourhood of the critical temperature. In such fields there is a marked peak in the permeability temperature curve for the substance. The explanation of this peak suggests that the phenomenon should be found common to all ferromagnetic substances. The paper shows that it is exhibited by the carbide of iron (cementite) in annealed carbon steels.