12 ROYAL SOCIETY OF CANADA 
the lead cylinder entirely unscreened, then with the one half of the cylin- 
drical surface screened internally with aluminium 0.73 mm. thick, and 
finally with the whole of the inner cylindrical surface covered with the 
aluminium. 
The values are given in Table IT. 






Table Ii 
~ 
5 a > CS 
apes © à o © À 
ES ! s&s a3 8 
A © Cylinder No. 2. & à = SRE 
2 £ Be bon Ory 
aS ES DES 
AZ Sa esau 
2 5 | 
1 Completely, unscreened eyane een ese Neel cies 54.6 
22.2 
2 One-half inner cylindrical surface screened...... .... 32.4 
22.57 
3 All inner cylindrical surface screened................. 9.87 

and from them it will be seen that the decrease in conductivity was the 
same for each half of the cylindrical surface. This goes to show that 
the radioactive impurity in the lead was uniformly distributed over its 
surface. It was also very probably distributed in a uniform manner 
throughout the mass of the cylinder as repeated scourings with glass 
paper failed to remove it. In this connection it is of interest to note 
that during the last six months, measurements have been repeatedly 
made on the conductivity of air confined in this cylinder, but during 
that period no indication of a falling off in the intensity of the radiation 
from it has been observed. 
From the foregoing results it is abundantly evident that the high 
activity of lead which has from time to time been recorded by a number 
of observers can not be ascribed to any intrinsic property of the metal, 
but must be connected with the existence in it, in amounts varying with 
different specimens, of some foreign body of considerable activity. 
The low value obtained for the conductivity of air enclosed in 
cylinder No. 1 suggested the possibility that the difference between the 
reading for this cylinder and that obtained with the aluminium cylinder 
No. 9 was due entirely to a difference in the secondary rays excited in 
the two metals by the penetrating radiation from the earth. With the 
object of clearing up this point observations are still being made with 
the cylinders, and from results obtained already, it would seem that, 
apart from active impurities, differences in the secondary radiation will 
suffice to explain the differences in conductivity obtained with air con- 
- fined in vessels made of different metals. 
