88 tUYAL SOCIETY OF CANADA 
nut charcoal in granulated form. The outside of the electroscope was 
earthed and the ionization currents measured by the rate of movement 
of the gold leaf. The ionization current, or activity, at any time 1s 
proportional to the amount of emanation present in the emanation 
reservoir. 
When radium emanation was admitted into and retained in the 
electroscope, it was found that the decay of activity did not follow an 
exponential law, for while at the first the activity fell to half-value in 
1-0 days, in the course of five or six days the rate was half-value in 1-6 
or 1-7? days. 
When the emanation reservoir was refilled with emanation and the 
charcoal vessel removed, so that the emanation could diffuse to the opea 

@ 
= 
2 
Q 
5 
& ie TTERY 
| Vik = 
DRYING TUBE. 
4 
CHARCOAL 
THOR. HYOROX ES 
TEST. VESSEL 
MANOMETER. 
AIR DOME. + a 2 y, 
BRANCH CIRCUIT FOR SPEED ADJUSTMENT . 
ELECTROMETER 

Fie. 2. 
air, the decay of activity did follow an exponential law, the time for 
diminution to half-value being 1:0 days. This result may be expected, 
for it means that the amount of emanation diffusing to the open air 
per second is proportional to the amount of emanation in the reservoir. 
P. Currie and Danne ! performed experiments of this kind with capillary 
tubes as the communicaticn from the emanation reservoir to the out- 
side air, and found that the loss of emanation from the reservoir was 
exponential. 

*P. Currie and Danne, Comptes Rendues, 136, p. 1314, 1903. 
