that the same is the case for the deflected β-rays of radium. The deviable β-rays of radium are charged with negative electricity.
(Note.—Let the radio-active substance be placed on one of the plates of a condenser, this plate being connected to earth; the second plate is connected to an electrometer, it receives and absorbs the rays emitted by the substance. If the rays are charged, a continuous flow of electricity into the electrometer should be observed. In this experiment, carried out in air, we were not able to detect a charge accompanying the rays, but such an experiment is not delicate. The air between the plates being caused by the rays to conduct, the electrometer is no longer isolated, and can only respond to charges if these be sufficiently strong. In order that the a-rays may not interfere with the experiment, they may be suppressed by covering the source of radiation with a thin metallic screen. We repeated this experiment, without more success, by causing the rays to pass through the interior of a Faraday cylinder in connection with the electrometer).
According to the preceding experiments, it was evident that the charge of the rays of the radiating body employed was a weak one.
In order to fix a feeble evolution of electricity upon the conductor which absorbs the rays, this conductor should be completely insulated; this is effected by screening it from the air, either by placing it in a tube with a very perfect vacuum, or by surrounding it with a good solid dielectric. We employed the latter arrangement.
A conducting disc, m m (Fig. 6), is connected by the wire,
Fig. 6.
t, to the electrometer; the disc and wire are completely enveloped by the insulating substance i i i i; the whole is again surrounded with the metallic covering, e e e e, which is in electric connection with the earth. The insulator, p p, and the metallic envelope are very thin upon one of the faces of the disc. This face is exposed to the radiation of the barium and radium salt, r, placed outside in a lead receptacle. The rays emitted by the radium penetrate the metallic envelope and the insulating lamina, p p and are absorbed by the metallic disc, m m. The latter
