ABSTRACT
Thorium oxide has been employed in most of the experiments, as it exhibits the emanation property to a greater degree than the other compounds; but what is true for the oxide is also true, but to a less extent, of the other thorium compounds examined, viz. the nitrate, sulphate, acetate, and oxalate. The intensity of thorium radiation, when examined by means of the electrical discharge produced, is found to be very variable; and this inconstancy is due to slow currents of air produced in an open room. The radioactive particles emitted by the thorium compounds gradually diffuse through the gas in its neighbourhood and become centres of ionization throughout the gas. The radioactive emanation passes through all metals if sufficiently thin. In order to make certain that the emanation passed through the material to be examined and did not diffuse round the edges, the radioactive substance was placed in a square groove of a thick lead plate.
