1896-97.] Electrification of Air by Rontgen Rays. 
395 
negatively electrified when no screen or an aluminium screen was 
interposed between the Rontgen lamp and the near end of the lead 
cylinder. The air was found not electrified at all, or very slightly 
negative, when a lead screen was interposed. 
When the Rontgen lamp was removed or stopped, and air was 
still pumped through the filter, no deflection was observed on the 
electrometer. This proved that the air of the quadrangle was not 
electrified sufficiently to show any deflection when thus tested by 
filter and electrometer. 
Similar results were obtained with the end of the suction pipe 
placed so as to touch the floor of the lead cylinder, or the roof, or 
the sides. Whether the air was pumped away from a place in the 
cylinder permeated, or from a place not permeated, by the Rontgen 
rays, it was in all cases found to be negatively electrified. 
The following are some of the results obtained on December 16 
and 17. The electrometer was so arranged as to give 140 scale 
divisions per volt. 
Conditions . — Large lead cylinder metallically connected with 
sheath of electrometer. Rontgen lamp surrounded by a lead 
sheath, which latter was also connected to electrometer-sheath. 
There was a window in this lamp-sheatli 2*5 cms. broad and 5 cms. 
high. This window could be screened by aluminium or by lead. 
These screens were always connected metallically to sheaths. 
During all the experiments a Bunsen lamp (not shown in the 
diagram) was kept constantly burning, with its flame about 30 cm. 
below the Rontgen lamp. 
Results . — Rontgen lamp in action ; air drawn from lowest point 
of end of lead cylinder next to the R. lamp. 
December 16 : — 
3.55 p.m. - 61 scale divisions in 2 mins, with aluminium screen. 
,, -63 ,, ,, ,, no screen. 
,, -14 ,, ,, ,, lead screen. 
4.20 p.m. Air drawn from point on lowest line of lead cylinder 
26 cms. distant from R. L. end. 
,, - 14 scale divisions in 2 mins, with lead screen. 
? 5 
-78 
5 > 
J J 
5 5 
no screen. 
? > 
-24 
) ) 
) 5 
> 5 
lead screen. 
; ? 
-83 
5 > 
5 5 
alumin. screen. 
n 
- 13 
? 5 
? > 
lead screen. 
