Societies and Academies

Abstract

LONDON.Royal Society, June 14.Sir J. J. Thomson, president, in the chair.Prof. T. H. Ilavelock: Some cases of wave motion due to a submerged obstacle. In this paper Prof. Lamb's solution for a submerged circular cylinder is carried a stage further in the approximation, and the wave resistance is calculated directly from the resultant fluid pressure on the cylinder. Similar methods are then applied to a three-dimensional problem, the waves produced by a submerged sphere.Prof. L. V. King: The propagation of sound in the free atmosphere and the acoustic efficiency of fog-signal machineryH. J. Shannon, F. F. Renwick, and B. V. Storr: The behaviour of scattering media in fully diffused light. The paper deals with the relationships between the. rejectance (proportion of in- cident light rejected), the obstruction (ratio of incident light to transmitted light), light capacity (ratio of accepted light to transmitted light) when a sheet of diffusing medium is illuminated on one side by diffuse light, and also the relative obstruction, and relative density, when, as in various instruments, the source of light is a first sheet of diffusing medium in contact with the 'sheet being examined. The experimental part of the paper discusses the method of using the theoretical equations obtained for determining the con- stants of a specimen of diffusing medium, certain requirements of the instrument used, and precautions to be taken. Examples are given showing the close agreement between observed and calculated valpes up to seven thicknesses of opal for both air and oil con- tact.J. W. T. Walsh: The theory of decay in radio- active luminous compounds. The theory of destruction of “ active centres “ put forward by Ruthrford to account for the decay of luminosity of radio-active luminous compounds leads to a simple exponential relation in the special case of a compound of constant activity. It has been found for radium zinc suiphide compounds that this relation expresses the observed results to a sufficient accuracy over short periods of less than 200 days, but that it fails to do so over longer periods, such as 500 days, the rate of decay of luminosity becoming gradually slower and slower, so that the brightness tends to a limiting value which is not zero. The paper is an attempt to find a luminosity time relation which will allow of the prediction of the ultimate behaviour of compounds of varying composition, and it assumes the operation of some factor acting in a direction opposite to that of the destruction of the active centtes.