ABSTRACT
The American Physical Society in Washington last December, at which the interesting paper of Dr. MacLennan and Mr. Burton, referred to by Prof. J. J. Thomson, presents an account was given by Mr. H. L. Cooke and myself of some results shows that a very penetrating radiation was given off from the walls of buildings and from the surface of the earth itself. The primary object of this investigation was to see if the natural ionisation of air observed in closed vessels was due, in part at least, to an external radiation which passed through the walls of the vessel. The purposes the rate of discharge of a gold leaf electroscope in a brass vessel of about 1 litre capacity was observed. Metals exposed for some time outside the buildings showed a marked increase of activity over the metal which had been carefully cleaned. The similar effect observes when the electroscope was immersed in a deep water tank.
