Figure IV
When a vacuum is produced in the receiver,
, which contains air charged with the emanation, and when the radiation of the receiver is measured immediately after the extraction of the air, it is found that the radiation has not changed at the moment when the active air is withdrawn. The Becquerel radiation of air charged with the emanation does not, then, produce any action in this experiment. This radiation probably exists, but it is composed of very slightly penetrating rays, incapable of passing through the glass wall. In this connection the following experiment can be performed. One of the ends of the metallic tube,
(Fig. IV.), communicates at
by means of a rubber tube with a receiver,
, in which is a solution of a radium salt. The other end of the tube,