416 
Proceedings of Poycd Society of Edinburgh. 
SESS. 
With the light shining on both through a window 7 cms. broad, 
13 cms. high, both positive and negative charges given to the insu- 
lated metal were discharged, and the ultra-violet light deviated from 
the metallic zero by - 152 scale divisions. 
This difference was reduced to about - 30 scale divisions when 
the experiments were repeated after the apparatus had been left to 
itself for a night. 
§ 24. To make similar experiments with the Rontgen rays, it was 
found necessary to cover the window near the lamp with tinfoil 
gauze connected to sheaths, and the window on the opposite side 
Avas covered with non-perf orated tinfoil. In this Avay direct 
electrostatic induction was avoided. We had also a thin sheet 
aluminium Avindow betAveen the tinfoil gauze and the Rontgen 
lamp. 
When the Rontgen rays fell on both insulated and disinsulated 
metal the rays-zero AA r as - 5 scale divisions from the metallic zero, 
and both positive and negative charges fell to this zero in a few 
seconds. 
With the rays shining only on the insulated metal the same small 
difference of zeros Avas obtained, and both positive and negative 
charges fell to the rays-zero, though much more sloAvly than before, 
in about four minutes. 
With the Rontgen rays shining on the insulated tinfoil through 
the disinsulated tinfoil gauze, the rays-zero was - 9 scale divisions 
from the metallic zero, and both positive and negative charges Avere 
removed in about a minute. 
On substituting an aluminium gauze for the tinfoil gauze, and 
sending rays through it on the insulated tinfoil, the rays-zero Avas 
+ 25 scale divisions from the metallic zero. 
[Added February 6. — With a polished zinc disc as the insulated 
metal, and with the same Avindows to the tinfoil box, the Rontgen 
rays Avere shed in betAveen the insulated zinc and the opposite 
AA T all of tinfoil from a slit in a lead screen outside. This slit 
was 4 cms. long by 1 cm. broad. The distance betAveen the two 
metals Avas 7 cms. The rays illuminated only part of the air space 
betAveen the tA\ r o, and also a part of the tinfoil covering the tAvo 
AvindoAvs. 
