high potential by an electric machine, and the cylinder connected with earth. A luminous spot of light was observed on the screen, which was brighter at the edge than at the centre. A conductor, connected with earth, brought near the luminous spot apparently repelled it. An insulator did not show such a marked effect. On removal of the active substance, the luminosity of the screen persisted for some time. This was probably due to the excited activity produced on the screen.
The results obtained by Giesel support the view that the carriers of excited activity of “emanium” have a positive charge. In a strong electric field the carriers travel along the lines of force to the cathode, and there cause excited activity on the screen. The movement of the luminous zone on the approach of a conductor is due to the disturbance of the electric field. Debierne25 found that actinium also gave off a large amount of emanation, the activity of which decayed very rapidly with the time, falling to half value in 3·9 seconds.
This emanation produces excited activity on surrounding objects, and at diminished pressure the emanation produces a uniform distribution of excited activity in the enclosure containing the emanation. The excited activity falls to half value in 41 minutes.
Debierne observed that the distribution of excited activity was altered by a strong magnetic field. The experimental arrangement is shown in Fig. 71A. The active matter was placed at M, and two plates A and B were