Active Deposits of Radium, Thorium, and Actinium. 613 
formation of the active deposit and its transference to either 
electrode, as taking place in an exactly similar fashion. 
It has been shown by Miss Slater* that slowly moving 
/3 particles accompany the a particles which are ejected 
from thorium and radium emanations. If there are two such 
ft particles to every a particle, the remainder of the emana- 
tion atom, i. e. the active deposit, would be left with a 
positive charge. 
This supposition would explain the almost complete trans- 
ference of the active deposit of thorium to the cathode ; but 
the small, though quite definite, quantity of the active 
deposit of radium that is directed to the anode still presents 
a difficulty. It may be that a few of the active deposit 
particles gain negative ions from the gas in which they are 
moving, which must be present in very large numbers. 
In the case of actinium, although at a pressure of a few 
millims., far more activity is observed on the cathode than 
on the anode, as has already been found by Debierne f, yet 
we have seen that at higher pressures this inequality is very 
much reduced, there being almost as many negative carriers 
as positive. 
It is hoped that a more extended series of observations 
may throw some light on the apparently anomalous behaviour 
of actinium. 
In conclusion, I desire to thank Professor Rutherford for 
several suggestions during the latter part of the work. The 
research was begun with Mr. Makower, who, however, could 
not continue the collaboration owing to pressure of other 
work. I wish to express my thanks for the very considerable 
help he has given me in these experiments. 
Note added March 11th. 
Some recent experiments made with actinium tend to 
explain the anomalous behaviour referred to above. A pre- 
paration of actinium was placed at the bottom of a cylinder, 
and two parallel plates were suspended so as to hang verti- 
cally above it. These plates were connected to the terminals 
of a battery of 300 volts, and after an exposure at atmospheric 
pressure usually lasting several hours the activities of the 
two plates were compared by means of an electroscope. The 
distance of the plates from the actinium preparation could 
be altered as required. 
* Phil. Mag. Oct. 1905. 
f Comptes Rendus, vol. cxxxvi. p. 671. 
Phil. Mag. S. G. Vol. 15. No. 89. May 1908. 2 T 
