Abstract
LONDON. Physical Society, February 27.—Dr. R. T. Glazebrook, F.R.S., president, in the chair. -A paper by Prof. Fleming and Mr. Clinton, en the measurement of small capacities and inductances, was read by Prof. Fleming.. The measurement of small capacities and inductances has become important in connection with Hertzian wave wireless telegraphy. The authors have designed a rotating eommutator which renders the measurement of small capacities a matter as easy as the measurement of resistance on a Wheatstone bridge. The appliance is described in the paper, and the authors claim that they have worked out a thoroughly satisfactory form of rotating commutator, designed more from the point of view of an engineer than an-electrical instrument maker. For use with the instrument a moving-coil differential galvanometer has been designed. The authors have made a number of experiments upon th.e capacity of aerial wires, such as are used in Hertzian, wave telegraphy/ and have also, investigated the laws governing the capacity, of such wires when grouped together in certain ways' and verified, experimentally, as far as possible, the. formula ".for the capacity of insulated wires in various'position's in regard to,the: earth, ! The experiments are given:at ' length in the paper, and the results practically obtained are compared with those derived from theoretical considerations. In all cases the total measured capacity of? wires is less than?times the capacity of one wire.—Mr. A. Campbell exhibited the commutator used for condenser tests at the National Physical Laboratory. It is similar to that designed by Mr. Searle and used by him and Prof. J. J. Thomson in their determination of the value of "v."In this commutator the ebonite insulation does not fill the spaces between the segments, and is never touched by the brushes, thus giving satisfactory insulation. By its aid many measurements have been made of the B.A. air-condensers, the capacity of each of these being about 0?2 m.fd.—A paper on the thickness of the liquid film formed by condensation at the surface of a solid was read by Dr. G. J. Parks. It was known more than half a century ago that when a solid is placed in a gas or vapour there is a condensation of the latter on the surface of the solid, and in particular that glass has the power of condensing water-vapour at temperatures above the dew-point. In order to determine the thickness of the liquid film, the author has exposed masses of cotton-silicate of known area to the action of water-vapour. The author has compared his results with those obtained by other experimenters with different substances and under widely different conditions, and concludes that in all cases where condensation of moisture takes place at a solid surface, and at temperatures not below the dew-point, the thickness of the surface-film varies from IOXIO"6 to 8ox io˜˜6 cms., according to the substances used and the conditions of temperature and pressure.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies . Nature 67, 429–432 (1903). https://doi.org/10.1038/067429b0
Issue Date:
DOI: https://doi.org/10.1038/067429b0