Radioactivity of the Atmosphere. 149 
In view of the importance of these results, experiments 
were undertaken to see if the Montreal tap-water derived 
from the River St. Lawrence showed similar properties. 
For this purpose a large cylindrical zinc tank, diameter 
102 ems. and height 150 cms., was used. In the centre of 
this was suspended a brass cylinder 5 cms. in diameter, which 
passed through an ebonite plate at the top of the tank, and 
was connected to the electrometer. The outer cylinder was 
connected to a battery of 300 volts. Between the two cylinders 
- was arranged a guard-ring connected to earth. A rubber 
tube passed from the bottom of the tank to an ordinary water 
pump, from which a return tube entered the top of the tank. 
The natural leak of the tank filled with ordinary air was 
first observed, and found to vary from 4 to 5 divs. per sec. 
The water pump was then started, and the moist air circu- 
lated through the tank, while readings of the conductivity 
were taken every minute. The conductivity of the air in the 
tank immediately began to increase, and reached a maximum 
in about five minutes, reaching in one test 25 divs. per sec., 
or nearly six times the natural leak. When the water pump 
was stopped this increased conductivity at once began to 
decrease, and reached the natural leak in about six to eight 
minutes. The maximum varied from time to time, but was 
always from four to six times the natural leak. This modified 
air, when passed through pumice-stone saturated with sul- 
phuric acid before reaching the tank, only gave 8 divs. per 
sec. as the maximum, but as soon as the pumice-stone was 
removed gave 20 divs. per sec. It was found that the quicker 
the air was drawn through the tank the greater was the con- 
ductivity produced. Passing the air through a cotton-wool 
plug destroyed a large portion of the conductivity. It was 
also found thet when the moist air was passed through a 
spiral tube immersed in liquid air, ora tube heated to redness, 
the increase of conductivity previously observed was com- 
pletely absent. The experiment was tried of allowing a 
quantity of liquid air to evaporate inside the tank, but no 
increase of conductivity could be observed. 
A brass rod was suspended in the tank, and kept charged 
to a high negative potential for several hours, whilst the air 
charged with water-spray was circulating through. It was 
then removed and tested in another vessel, but no signs of 
any excited activity could be detected. 
I think we may conclude from these experiments that 
the increased conductivity is not caused by an emanation 
in the water-spray, since it will not stand the tests to 
which an emanation may be subjected. Neither is there any 
