Electrical Charge of the Active Deposit of Actinium. 737 
6. The square root of the percentage differences of ioniza- 
tion, due to a reversal of potential of the radiator, is inversely 
proportional to the secondary radiation from the radiator. 
This is a rough approximation for radiators of equal areas 
made of different substances. 
McGill University, Montreal, 
February 1908. 
Note added 25th April, 1908. 
In this paper I have upheld the old view that the 
secondary rays due to radium are not merely scattered 
primary. The experiments of H. W. Schmidt (Phys. Zeit. 
June 1, 1907) have to some extent weakened this theory. 
But the same observer has also shown that the j3 particle 
does not lose speed in passing through matter; and, if that is 
the case, the secondary electrons should have the same velocity 
as the primary; and they have not. Again, y rays (we will 
suppose them to be aether pulses) give rise to secondary rays 
with velocities nearly equal to those of the secondary rays due 
to ft particles. There seems no reason to suppose that the 
j3 rays could not cause the same projection of electrons from 
the atoms of the secondary radiator which we know that the 
7 rays cause. It is true that the view, advocated by Bragg, 
of the material nature of the y rays is not out of harmony 
with observed facts ; and, if that theory is correct, we may 
regard all secondary radiations, consisting of electrons with 
high velocities, as scattered primary rays. 
LXVI. On the Electrical Charge of the Active Deposit of 
Actinium. By Sidney Russ, Demonstrator in Physics, 
Manchester University*, 
EXPERIMENTS by several observers have shown that 
the active deposit of Thorium is almost entirely directed 
to a negative electrode. 
If into a vessel containing thorium emanation two wires 
be inserted, one charged negatively, the other positively, the 
amount of active deposit obtained on the negative wire is 
more than one hundred times that on the positive ; this 
number, however, shows a considerable redaction if the 
pressure in the vessel is diminished to a few millimetres. 
* Communicated by Prof. E. Kutherford, F.R.S. 
