[M'LENNAN & POUND] RADIOACTIVITY Of LEAD AND OTHER METALS 11 
second. The lowest value, 23, was obtained with the lead which had 
deen in the laboratory between twenty-five and thirty years, and had 
probably been a very much longer time away from the mine. With the 
cylinder No. 4, which was made from an old drain pipe, the value of 
“q” was found to be 78, a somewhat higher value than that obtained 
with No. 1. Although both of these cylinders were made of compara- 
tively old lead it is highly probable that No. 4, from the nature of its 
use had become contaminated with some active substance. It may 
possibly too have possessed a higher activity than No. 1 when originally 
mined. 
With cylinder No. 5 the value obtained for “q” was 34 ions per 
ce. per second. This lead, we have reason to believe, was mined not 
more than two or three years ago, and under the circumstances might 
have been expected to show a much higher activity. Its activity, how- 
ever, was practically the same as that of No. 3, which was selected at 
random from a commercial sheet of lead which probably had been on the 
market for some years. 
Cylinders No. 6 and No. 7 possessed a moderate activity compared 
with the others of the same metal. The number of ions per cc. 
generated in air per second with them being 55 and 61 respectively. 
With cylinder No. 2, the greatest ionization was obtained, the value 
of “q” in this case being 160 ions per cc. per second. 
This cylinder was treated precisely the same as the others, but on 
account of its high activity special measurements were made with it in 
order to investigate more fully the character of the radiation which it 
emitted. 
Measurements on the radiation from this cylinder showed it to be 
in great measure an easily absorbed one. When aluminum linings 
0.73 mm. thick were inserted in cylinders No. 1 and No. 2, and No. 3 
and measurements made on their saturation currents the values of “ q” 
were found to be 12.0, 13.3, and 14.4, respectively. These numbers it 
will be seen, are slightly lower than those found for aluminium alone, 
which is exactly as one would expect owing to the absorption of the 
penetrating rays from the earth by the lead. ‘The value for “q” 13.5 
found for No. 2 is slightly greater than that “q ’’==12 given by No. 1, 
although this lead cylinder was 2.25 mm. thick, while No.1 was only 
1.85. This would seem to indicate the existence of a slight penetrating 
type of radiation issuing from No. 2 which was absent from cylinder 
No. A 
A second series of measurements was made with cylinder No. 2 to 
investigate the distribution of the substance which was the cause of its 
high activity. Readings were taken on the saturation current first with 
