Abstract
LONDON. Physical Society, May 9.—E. J. Williams: (1) The induction of electromotive forces in a moving liquid by a magnetic field, and their application to the investigation of the flow of liquids. Preliminary experiments on the flow through straight tubes show that potential differences of the order of 10″4 to 10 a volt set up by a magnetic field in a moving liquid consisting of an aqueous solution of copper sulphate can be satisfactorily measured.—(2) The motion of a liquid in an enclosed space. The increase of resistance of a column of mercury in a magnetic field is due to the internal motion of the liquid produced by the action of the ampere forces between the magnetic field and the electric current traversing the mercury. The hydrodynamic significance of the results of such experiments is considered; e.m.f.'s as small as 10.6 to 10.7 volt, induced by a magnetic field in moving mercury, can be accurately measured.—E. Simeon: The generation of sound by the siren principle. The paper discusses various undesirable features of the simple siren considered as a sound-source for technical work, and describes a siren with a reasonably pure note, the intensity of which can be kept constant throughout a range of pitch from about 70 to about 7500 cycles.—L. Hartshorn: Surface resistivity measurements of solid dielectrics. The paper describes (1) a new form of electrode suitable for surface resistivity measurements on insulating materials in sheet form, and (2) a method for the determination of the ‘volume leakage’ correction for any system of electrodes. Data are given on the volume leakage correction for the various types of electrode in general use, and on the ‘leakage resistivities’ of materials commonly used in the construction of laboratory instruments.
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Societies and Academies. Nature 125, 765–767 (1930). https://doi.org/10.1038/125765b0
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DOI: https://doi.org/10.1038/125765b0