LONDON. Royal Society, Feb. 20.—A. C. Davies, F. Horton, and E. Blundell: Critical potentials for the excitation of soft X-rays from iron. Critical potentials for excitation of soft X-rays from solids, and for production of secondary electrons from solids, under electronic bombardment, do not conform with the view that characteristic displacements take place of electrons forming the outermost extranuclear groups in the bombarded atoms. The experiments deal with critical potentials for soft X-ray excitation from iron, rolled into thin strip from a drawn wire, for different temperatures and also for the same specimen at room temperatures, after being subjected to various heat treatments. Many critical potentials were produced, mostly persisting throughout the subsequent conditions of the target, once they had made their appearance; only one—at 201 volts—justifies the conclusion that its presence was dependent upon the iron strip being at a high temperature.—L. M. T. Gray and D. W. G. Style: The absorption of light by chlorine, bromine, and their gaseous mixtures. The independence of the absorption of chlorine of the intensity or nature of the incident radiation was tested by various methods. Extinction coefficients of bromine vapour have been determined at room temperature for certain mercury arc lines. The absorptions of mixtures of chlorine and bromine confirmed the existence of RrCl.