60 THE ROYAL SOCIETY OF CANADA 
Electroscopes. 
One electroscope (20 X10 X10 cm.) was built of a framework of 
light steel knitting needles. This was covered with tissue paper, 
blackened inside with pencil, weighing -002 grams to the square centi- 
metre, so that the stopping power of the wall was less than that of 2 em. 
oi air. The framework was suspended, and held firmly by light steel 
wires, near the middle of the room, well removed from other bodies. 
The observer approached the electroscope only for a few seconds at the 
beginning and towards the end of a reading. The microscope could 
be similarly removed and replaced, but this proved to be unnecessary 
as the consequent error was larger than the negligible correction. The 
mica windows were exceedingly thin, and the light aluminium leaf 
system was charged through a trap door in the paper. Considerable 
variation in the natural leak occurred at first, and was traced to day- 
light entering the tissue paper, and making the sulphur insulator a 
partial conductor. This trouble was obviated by working in a darkened 
room, and subsequently by using amber insulators. The effect of day- 
light on sulphur was discovered by Bates of Macdonald College, and 
it has been suggested that sulphur shares to a small degree the well 
known property of selenium. In the usual thick-walled electroscope 
the effect is slight, and may escape notice. 
Another electroscope consisted of a framework of thin knitting 
needles mounted on tall light wooden pillars. In this case the frame- 
work was covered with aluminium leaf -0003 cm. thick, weighing about 
-0008 grams to the square centimetre, with a stopping power of about 
7 mm. of air. It is easily shown by experiment that when the walls 
are covered with two or three times this thickness of aluminium leaf, 
neither the 8 nor the y ray ionizations are altered to an extent which 
can be detected. 
Thus the experimental conditions ensure the desired result, that is, 
the investigation of an elementary volume of air, practically removed 
from any important modification due to reflected or scattered or second- 
ary radiation from surrounding bodies, excepting the air and radiating 
source. 
Long Range Experiments. 
It was found possible to detect the direct 7 radiation from 14-6 mg. 
of pure radium bromide (8-5 mg. of radium) placed within two test 
tubes, at a distance of 7 metres, and to make fairly accurate measure- 
ments at 6 metres. The test tubes reduced the # radiation from radium 
C to about half value, and the radiation from radium B was negligible. 
A single experiment may be given in detail, when the ionization 
from f and y rays together was measured at ranges from 1 to 6 metres. 
