Retardation of Electroscopic Leak by means of Recognised Radio-Active Substances

Abstract

IN a communication made to the Royal Society on April 5, 1906, and subsequently published in the “Archives of the Middlesex Hospital,” vol. vii., I described certain experiments which I regarded as showing that substances exist which retard the leak of an earthed metal electroscope. I further asserted that an aluminium plate which had been kept in proximity to, but not in contact with, uranium, thoria, or pitchblende, also retards the electroscopic leak. This retardation does not necessarily occur immediately after introduction of the modified aluminium plate into the electroscope, for after proximity to thoria there is a period, lasting three or four days, during which the leak is accelerated, and after proximity to radium I failed to find any evidence of retardation whatever. My results were received with scepticism, except by Sir William Ramsay, who had independently observed the same phenomenon in his laboratory. It is impossible to occupy your space with details, but it may be stated that gold-leaf electroscopes made of -inch lead were used, that the earthing of electroscopes and aluminium was complete, that effects of induction and alteration of capacity of the electroscope were eliminated, and that the general conditions were kept as constant as possible.