100 ROYAL SOCIETY OF CANADA 
(IIL.) RADIOACTIVITY COMMUNICATED TO NEGATIVELY CHARGED 
BoDIES. 
For the purpose of the investigation, a series of circular discs was 
cut from a thin sheet of zine of such a diameter as to fit snugly into 
the movable base, G. The method followed in the experiments was 
to place one of these discs, after having cleaned it carefully with 
fine emery paper, on the base of the electroscope, charge the gold 
leaf to 150 volts and then observe its rate of fall under the conduc- 
tivity arising from spontaneous ionization in the vessel. When this 
rate was ascertained, the dise was removed from the electroscope and 
suspended by an insulating support in some selected position. A 
wire was led from it to one terminal of a Toepler Holtz machine and 
the second terminal of the machine was joined to earth through a 
water main. 
The dise was then maintained at a potential of about 11,000 
volts, positive or negative as desired, for a selected time, and after- 
wards replaced in the electroscope and the rate of leak again deter- 
mined. Any increase observed in the rate of fall of the gold leaf 
was taken as a measure of the intensity of the radioactivity acquired 
by the zine plate during its exposure. 
A preliminary set of measurements was made on the amount of 
radioactivity excited in a series of discs suspended in a large room in 
the Physical Laboratory at different distances from the electrical 
machine which charged them. All were exposed for the same length 
of time under the same negative potential. On testing the discs 
after exposure, it was found that the radioactivity excited was much 
less on those discs which were suspended in close proximity to the 
machine than on those which occupied positions more remote. 
From this result it seemed evident that air when confined in 
a room does not possess the power of imparting radioactivity to bodies 
to an unlimited degree, and that whatever property of this kind the 
air may possess initially, it is gradually deprived of it in the pressure 
of an electric field such as that produced by an electrical machine in 
action. 
In corroboration of this conclusion, it may be stated that some 
observations were made upon the radioactivity excited in a series of 
discs exposed consecutively in the same position in the room while the 
air was kept as far as possible unchanged. The room was well aired 
before the experiments began, and the doors and windows were kept 
closed during the whole period of exposure. The results of one 
test are given in Table I., and they indicate a gradual decrease in the 
activity excited. 
