Societies and Academies

Abstract

LONDON Royal Society, January 18. B. F. J. SCHONLAND and H. COLLENS: Progressive lightning. Eleven lightning flashes, comprising fifty separate strokes from two separate thunderstorms, have been photographed with a rotating lens camera based upon the design of C. V. Boys. The speed was fast enough to permit the study of the propagation of the discharge. The majority of the strokes were double and consisted of a dart-like downward-moving leader stroke, followed immediately upon arrival at the ground by a more intense flame-like upward-moving main stroke. The mean velocity of the leader strokes was 1-1×109 cm./sec. along the tortuous track in two dimensions and 7-0×108 cm./sec. in the vertical direction. The dart was less than 54 metres long. Corresponding mean velocities for the main strokes were 6-0×109 cm./sec. and 3-8×109 cm./sec. The leader strokes are identifiable with electron avalanches and the main strokes with thermally ionised channels. The cloud base was negative and the earth positive. A. O. RANKINE: A simple method of demonstrating the paramagnetism and diamagnetism of substances in magnetic fields of low intensity. The instrument described is the result of an attempt to construct a magnetic gradiometer capable of measuring small distortions of the earth's magnetic field in the same way that the Eotvos torsion balance measures non-uniformities of gravity. Although this purpose has not yet been achieved, the first model of the instrument has revealed itself as a means of demonstrating the paramagnetism or diamagnetism of substances of small susceptibility. Moreover, the magnetising fields employed are much smaller than has hitherto been customary, being of the order of 50 gauss or less. The system used also provides a basis for the construction of a new form of very sensitive galvanometer. C. W. GILBERT: The production of showers by cosmic radiation. Experiments made with triple coincidence counters showed that the frequency of showers produced in lead by the passage of cosmic radiation is proportional to the general cosmic radiation. The transition curves for air to lead were obtained at 3,500 m., and it was found that there the energy of the shower particles was greater than at sea-level. To explain the curves obtained, three types of radiation are needed, a primary radiation, a shower-producing radiation and the shower particles.