396 
Proceedings of Boy al Society of Edinburgh. [sess. 
Dec. 17. 
10.47 a.m 
R. L. acting, and air drawn 
through filter. 
End of suction pipe kept 
in axial line of cylinder. 
cms. 
- 44 in 
2 mins, with alumin. 
screen . 
. 68 from R. L. end. 
0 
3 3 3 3 
lead 
3 3 * 
. 68 
3 3 3 3 
-28 
? j 3 3 
no 
3 3 
00 
3 / 33 
-24 
3 3 * 3 
no 
3 3 
. 48 
3 3 3 3 
0 
3 3 3 3 
lead 
3 3 
. 48 
3 3 3 3 
-23 
3 3 3 3 
alumin. 
33 
. 48 
3 3 3 3 
-26 
3 3 3 3 
alumin. 
3 3 
. 38 
3 3 3 3 
- 9 
3 3 3 3 
lead 
3 3 • 
. 38 
3 3 3 3 
- 7 
3 3 3 3 
lead 
3 3 
. 28 
3 3 3 3 
-26 
3 3 3 3 
alumin. 
3 3 
. 28 
3 3 3 3 
-36 
3 3 3 3 
alumin. 
3 3 
. 18 
3 3 3 3 
-21 
3 3 3 3 
alumin. 
33 
. 8 
3 3 3 3 
§ 2. We had previously made experiments with a sheet-iron 
funnel 1 metre long, 1 4*5 cms. diameter ; and with a glass tube 
150 cms. long, 3‘5 cms. diameter; and with an aluminium tube 
60 cms. long, 4 - 5 cms. diameter. Air was pumped from different 
parts while the Rontgen rays were shining along the tube from one 
end, which was closed by paraffined paper stretched across it. In 
every case the air was found to be negatively electrified. 
In those earlier experiments the air drawn away was replaced 
by air coming in from the laboratory at the open end of the tube. 
We found evidence of disturbance due to electrification of air of 
the laboratory by brush discharges from electrodes between the 
induction coil and Rontgen lamp, and perhaps from circuit-break 
spark of induction coil. These sources of disturbance are elimi- 
nated by our later arrangement of lead cylinder covered with 
cardboard at both ends, as described above, and air drawn into it 
from open-air outside the laboratory. 
§ 3. We have also found a very decided electrification of air — 
sometimes negative, sometimes positive — when the Rontgen rays 
are directed across a glass tube or an aluminium tube, through 
which air was drawn from the quadrangle outside the laboratory, 
to the filter. 
A primary object of our experiments was to test whether air 
electrified positively or negatively lost its charge by the passage of 
Rontgen rays through it. We soon obtained an affirmative answer 
to this question, both for negative and positive electricity. We 
found that positively electrified air lost its positive electricity, and 
