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Societies and Academies

Nature volume 114, pages 108112 (19 July 1924) | Download Citation



LONDON. Physical Society, June 13.—Mr. F. E. Smith in the chair.—G. E. Bairsto: On a method for the synchronous and instantaneous illumination of objects rotating or vibrating at very high speeds. It is capable of giving instantaneous photographic records, and gives a precision of the order of half a microsecond. It is much more precise and able to give a more intense spark than any contact breaker and coil method.—E. A. Owen, N. Fleming, and Miss W. E. Fage: The absorption and scattering of?-rays. The absorption and scattering of 7-rays from radium filtered through 23 mm. of lead have been measured in magnesium, aluminium, zinc, tin, and lead. Assuming that the mean effective wave-length of the radiation employed is 0-021 A, the experimental results are consistent with the following statements: (i.) When 7-rays traverse matter, the characteristic radiations of the absorbing medium are excited; (ii.) the atomic fluorescent absorption coefficient of 7-rays depends upon the wave-length of the incident radiation and the atomic number of the absorber according to the law 3/4 2/3, which holds for X-rays; (iii.) the radiations which accompany this fluorescent absorption are the characteristic radiations of the K, L, M, … series of the absorbing elements; (iv.) the absorption of 7-rays in light elements is due almost entirely to scattering; (v.) the pure atomic scattering absorption coefficient is proportional to the atomic number of the absorber; (vi.) in addition to fluorescent and scattering absorption, a true absorption exists, the atomic coefficient of which is proportional to the atomic number. Comp-ton's formulae would account for the experimental results if the wave-length of the incident radiation were 0-020 A. Jauncey's formulae would require the wave-length to be 0-029 A.—W. N. Bond: The flow of compressible fluids, treated dimensionally. The method of dimensions treatment that is applicable to the pressure gradient at a point in a system through which non-compressible fluids of finite viscosity are passed, is extended by means of the thermo-dynamical equations for gas flow to the case where appreciable changes in density of the fluid occur, but where no heat passes across the walls of the system. The theory is developed in detail only for the case of flow “through a straight parallel-walled tube, and has been tested by experiments in which water and air at high velocities pass through small tubes. The air in some experiments had a velocity of more than two-thirds of the velocity of sound in the air. Errors due to moisture, pulsating flow, heat conduction through the walls, and proximity to the entrance to the tube are small; an error of moderate amount is attributed to the partial neglect of the variation of the variables over the transverse section of the tube.—D. B. Deodhar: Note on Israj, a remarkable Indian stringed instrument.

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