Abstract
LONDON. Royal Society, November 14.—Sir J. J. Thomson, president, in the chair.—A. Mallock: Sounds produced by drops falling on water.—G. H. Hardy and S. Ramanujan: The coefficients in the expansions of certain modular functions.—The Hon. R. J. Strutt: The light scattered by gases: its polarisation and intensity.—Dr. F. Horton and Ann C. Davies: An investigation of the ionising power of the positive ions from a glowing tantalum filament in helium. The ionising power of the positive ions from a glowing tantalum filament in helium has been investigated by a modification of the method due to Lenard. The positive ions were accelerated through a piece of platinum gauze into the ionisation chamber, and were there retarded by an opposing potential difference between the gauze and a movable collecting electrode, this retarding potential being constant during a series of experiments, and always greater than the greatest accelerating potential used in that series, so that none of the positive ions reached the collecting electrode. It was found that an increasing current was obtained in the ionisation chamber (the electrode collecting a negative charge) when the potential difference accelerating the positive ions was gradually raised above 20 volts. This result is similar to that obtained by Pawlow, and by Bahr and Franck, who concluded that helium atoms are ionised by the collisions of positive ions moving with 20 volts velocity. The experiments described in the paper have shown that the observed increasing o current, with increasing accelerating potentials above, about 20 volts, is mainly due to the positive ions liberating electrons from the walls of the ionisation chamber which they bombard, and that the positive ions do not ionise the helium atoms even when they collide with velocities up to 200 volts.
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Societies and Academies . Nature 102, 238–240 (1918). https://doi.org/10.1038/102238a0
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DOI: https://doi.org/10.1038/102238a0