Iv] NATURE OF THE RADIATIONS 135 
between A and B varies as e~*, i.e. it decreases according to an 
exponential law with the distance traversed. 








Current 









0 5 Distance in mms. 10 15 
Fig. 29. 
The variation of the current between A and B with the distance 
from a thin layer of uranium oxide is shown in Fig. 29 for different 
gases. The initial measurements were taken at a distance of about 
3°5 mms. from the active surface. The actual values of this mitial 
current were different for the different gases, but, for the purposes 
of comparison, the value is in each case taken as unity. 
It will be seen that the current falls off with the distance 
approximately in a geometrical progression, a result which is in 
agreement with the simple theory given above. The distance 
through which the rays pass before they are absorbed is given 
below for different gases. 
Distance in mms. to 
Gas absorb half of radiation 
Carbonic acid mas 3 
ANP 56 ae ane 4:3 
Coal-gas_... ‘ite 75 
Hydrogen ... as 16 
The results for hydrogen are only approximate, as the absorp- 
tion is small over the distance examined. 
