78 ROYAL SOCIETY OF CANADA 
To obtain a fair amount of radioactivity a large volume of air 
is necessary. From a closed box of about 1,000 litres no appreciable 
amount could be obtained. Several times the wire was charged posi- 
tively, but not the slightest effect could be obtained. Experiments 
were tried to see the effect of voltage on the amount that could be 
collected. Owing to the difficulty of getting satisfactory conditions 
no definite relation could be obtained. At — 4,000 volts the rate of 
leak after charging a certain time was 19 divs. per sec., whilst at 
— 28,000 volts the rate of leak was 67 divs. per sec. for the same 
time of charge. 
CoNCLUSIONS. 
From these experiments we may draw the following conclusions: 
The excited radioactivity from air is similar in its properties to that 
produced by thorium and radium, but is of a more penetrating char- 
acter than either, and decays much more rapidly than that of thorium. 
It does not seem likely that it is caused by an emanation from the 
soil or vegetation, because it is more abundant in winter when the 
ground is covered with snow. The fact that we can obtain more 
when it is very windy is probably due to the fact that fresh carriers 
are continually being brought into the wire. 
It is probably due to an emanation of positive electrons in the 
air, ever present though in varying quantities. This emanation in 
the ordinary state shows no tendency to collect on substances except 
when there is an electric field to draw them into the negative by 
charged wire. For a given volume of inclosed air there should be 
a saturation voltage at which all the carriers would be brought in. 
Experiments are at present being done on this point. In conclusion, 
I wish to express my gratitude to Prof. Rutherford for suggesting 
this subject, and to his kindly supervision of the work. 
