Societies and Academies

Abstract

LONDON Royal Society, May 26.—E. V. Appleton and R. Naismith: Some measurements of upper atmospheric ionisation. Experimental work on the reflexion of wireless waves by the upper atmosphere has shown that if the frequency of waves, projected vertically upwards, is steadily increased, the Kennelly-Heaviside layer (Region E) is ultimately penetrated and reflexion takes place at the upper region (Region F). The critical penetration frequency varies diurnally and seasonally. From measurements of the critical penetration frequency made in south-east England, the maximum ionisation content of the Kennelly-Heaviside layer is at noon, and a minimum occurs just before dawn. The diurnal variation curves correspond very closely to the theoretical curves obtained by S. Chapman in his study of the atmospheric ionisation produced by a solar stream of monochromatic radiation. Summer noon ionisation is found to be about 2.5 times as intense as winter noon ionisation.—J. D. Cockcroft and E. T. S. Walton: Experiments with high velocity positive ions (1 and 2). In order to obtain high steady potentials for the acceleration of protons, a method has been developed by which the voltage of a transformer can be rectified and multiplied several times by an arrangement of valves and condensers. A rectifier system has been built consisting of four glass cylinders placed end to end and arranged in the form of a tower 12 ft. high, the cylinders containing suitable electrodes and hot filaments and being evacuated continuously. With this apparatus and four condensers, a potential of more than 700 kv. has been obtained, which is steady to within a few per cent. The method used is a special case of a more general method of transforming steady potentials from low to high voltages and in the reverse direction. The voltage of the rectifier is applied to an experimental tube which is built to allow positive ions to be accelerated by the full voltage available. Positive ions of hydrogen are directed down the axis of two glass cylinders and focused by suitable electrodes, current of the order of 10 microamperes being obtained. Protons having energies up to 710 kv. have been produced, and have been transmitted through a mica window into an experimental chamber at atmospheric pressure, where their ranges are measured (see also NATURE, April 30, p. 649).