Abstract
LONDON. Royal Society, January 23.—Sir J. J. Thomson, president, in the chair.—Admiral Sir Henry Jackson and Prof. G. B. Bryan: Experiments demonstrating an electrical effect in vibrating metals. Experiments are described which demonstrate the, electrical effect produced by vibration in wires and other metallic bodies, and a method of detecting and recording them by means of searching coils connected to delicate recording apparatus. The diminution of the effect when the surface of a steel, wire is rusted is dealt with, in continuation of a paper by one of the authors on the subject of vibrating wires. The inductive effect of a vibrating wire on a neighbouring circuit is mentioned; and this led up to the fact that all metallic bodies experimented with, whatever their shape or material, generate eddy currents, which can be detected in them by using suitable searching coils. That this effect is primarily due to the vibrating conductor cutting the lines of the earth's magnetic field is proved by the experiments, but that there seems to be a residual effect, not at present fully accounted for, which is greater than can be attributed to experimental errors. Details of the tests are described. These have been carried out with wire bridges, tubes, utensils of various forms and materials, and also with Chladni plates.—Prof. T. H. Havelock: Wave resistance: some cases of three-dimensional fluid motion. It is shown how to calculate the wave resistance when the surface pressure is two-dimensional and the wave-pattern like that of ship-waves. Certain cases are examined in detail, and the method can be extended to more complex systems. Interpreting some of the results in terms of the related problem of a submerged body, expressions are obtained for the wave resistance of a prolate spheroid and of other bodies.—W. S. Abell: Chances of loss of merchant ships. This communication discusses the effect of damage to vessels in respect of chances of loss of bulkbeads and the consequent chances of loss of vessels. If the extent, of damage be fairly constant, as in torpedo explosions, it would appear that there is an inferior limit to the spacing of bulkheads. Further, as the carriage of cargo is impeded by subdivision, there is an economic reason for calculating the number, of bulkheads sufficient for reasonable safety, Such calculation involves the discussion of chances of loss of one or more bulkheads, and of the relation of size of vessel to bulkhead spacing. Assuming that water-tightness is destroyed within radius R from centre of damage, it is shown that where (1) bulkhead spacing = 2R + a, the “odds on” for loss of one bulkhead are 2R/a; (2) spacing = 2R-a, “odds on” for loss of two bulkheads are a/(2R-2a); and (3) spacing = R-a, “odds on” for loss of three bulkheads are 2a/(R-3a). These results are applied to the case of ordinary cargo-carrying vessels of fixed type, but of varying lengths, with R = 20 ft. representing longitudinal extent of torpedo damage. Diagrams accompanying indicate that (1) for a given standard of subdivision, decrease of size of Jarge vessels only slightly increases chances of loss; (2) for small vessels, risk of loss is relatively high, and it is doubtful whether any subdivision whatever is effective for vessels below 320-ft. length; (3) safety increases markedly with length of vessel; and (4) intermediate bulkheads are more useful in larger vessels, but may also, in certain cases, increase risk of loss. By suitable assumptions the method may be used to discuss subdivision of passenger vessels exposed to ordinary marine risks.—Prof. W. M. Hicks: A critical study of spectral series. Part v.: The spectra of the monatomic gases. This part deals with the series relationships in the second or blue spectra of the rare gases. Not only are the S, D, and F series allotted, but the discussion serves to amplify and sustain the laws developed in preceding parts, and illustrates their value for the purpose of the analysis of spectra in general. Amongst new methods may be mentioned the use of the links, discovered in part iv. of these communications, for the purpose of dealing with lines expected from formulae or other considerations which lie outside the observed region. Thus, in the case of a wave-number n of a line in the ultra-violet n-e, or n-u, or vice versa if in the ultra-red n + e, n + u, where e, u are definite and calculable quantities, may be wave-numbers in the observed region and correspond with lines actually seen. In this way it is possible to obtain evidence of the existence and wave-length of lines belonging to the spectrum, although not actually measured. Of importance also in the general theory of spectra is the discovery of summation series. Thus in the case of the ordinary well-known series the wave-numbers are represented as the difference of two quantities A-ø(m), where m is the order in the series. It is shown that in the case of the F series at least there are, in addition to these difference frequencies, also a corresponding series of summation frequencies given by n = A + ø(m). For S, D series, such series, if existing, would occur far down in the ultra-violet.
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Societies and Academies. Nature 102, 459–460 (1919). https://doi.org/10.1038/102459a0
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DOI: https://doi.org/10.1038/102459a0