Societies and Academies

Abstract

LONDON. Royal Society, January 21.—Sir William Crookes, president, in the chair.—Dr. C. Chree: Atmospheric electricity potential gradient at Kew Observatory, 1898–1912. A previous paper discussed results obtained from the Kelvin water-dropping eiectrograph at Kew Observatory for the period 1898–1904. The present paper discusses the data from the fifteen years 1898–1912. Particular attention is given to the character of the diurnal variation, as to how it varies throughout the year, and as to the nature of the differences apparent between different years. The predominance of the 12-hour term over the 24-hour term in the diurnal variation, which is especially conspicuous in summer, is found to vary greatly from year to year. The 12-hour term shows less fluctuations either in amplitude or phase than the 24-hour term.—Prof. A. E. H. Love: The transmission of electric waves over the surface of the earth.—Art analytical solution of the general equations of electrodynamics is obtained for the case of waves generated by a vibrating doublet in presence of a conducting sphere, and is adapted to obtain the known solution for perfect conduction, and the correction for moderate resistance, such as that of sea-water. The known solution is expressed by the sum of a series involving zonal harmonics, and the correction by a similar series. Different results have been obtained by different writers who have investigated the numerical value of the former sum. In the paper a new method of summing the series is explained, and worked,out in detail for the wave-length 5 km. In the case of perfect conduction the result confirms that found by H. M. Macdonald (Proc. Roy. Soc, Ser. A, vol xc, 1914, p. 50). The effect of resistance is found to be a slight increase of the strength of the signals at considerable distances, counteracting to some small extent the enfeebling effect of the curvature of the surface.—L. Silberstein: Electromagnetic waves in a perfectly conducting tube. The problem of waves in conducting tubes, which has already been treated by various authors, is here taken up with the purpose of developing some of its solutions which offer noteworthy peculiarities with respect to the velocity of the corresponding waves. The waves investigated are axially symmetrical and of permanent type. Their velocity of transfer along the tube is a comparatively simple function of the period of vibration and of the “order” of waves, and it exceeds, for each of these waves, the velocity of light in free space. The peculiarities of distribution of the lines of force are illustrated by two examples with annexed drawings. The paper closes with remarks concerning superpositions of waves of the specified kind, more especially of electromagnetic pulses.—H. B. Keene: An electrically-heated full radiator. The essential conditions in a determination of the constant of the Stefan-Boltzmann law of radiation are, either that both “emitter” and “receiver” are full radiators, or that the amount by which they fall short of full radiators is known—an amount difficult to determine with certainty. Hitherto, a measurement of this constant has not been made under full radiation conditions. This paper describes an electrically-heated “constant temperature enclosure” which has been constructed for temperatures in the neighbourhood of 1100° C. It consists of a hollow cylinder of alumina, about 8 in. in diameter, closed with conical end pieces of the same material. Three separate windings of platinum strip provide a means of adjusting the temperature distribution within the enclosure, which can be made uniform to within two or three degrees. At the apex of one of the cones is a circular aperture which emits radiation closely approximating to full radiation. It is intended to use this radiator in conjunction with a full receiver, described in an earlier paper, in order to determine the value of the radiation constant under “black-body” conditions.