DECEMBER 31, 1896) 
NATURE 
“go 
heard of the cultivation of woad, Zsa¢zs t2ncforia ; but ‘‘ wood- 
wax ” (? woad-wax), Genzsta ténctoréa, which grows plentifully 
in that neighbourhood in pastures on marly soil, used to be 
collected by the peasant-women for dyeing purposes at the 
cloth factories in Trowbridge. The plant being very tough to 
pull up, ‘* wood-waxing ” was Very laborious work. I am not 
aware whether it is still carried on there. 
Croydon, December 16. , H. FRANKLIN PARSONS. 
ELECTRIFICATION OF AIR BY RONTGEN 
RAYS? 
me? test whether or not the Réntgen rays have any 
electrifying effect on air, the following arrangement 
was made. 
A lead cylinder 76 cms. long, 23 cms. diameter, was 
constructed ; and both ends were closed with paraffined 
cardboard, transparent to the Rontgen rays. Outside the 
end distant from the electrometer (see diagram) a 
pumped away froma place in the cylinder permeated, 
or from a place not permeated, by the Réntgen rays, it 
was in all cases found to be negatively electrified. 
The following are some of the resu!ts obtained on 
December 16and 17. Theelectrometer was so arranged 
as to give 140 scale divisions per volt. 
Conditions.—Large lead cylinder metallically con- 
nected with sheath of electrometer. Rontgen lamp 
surrounded by a lead sheath, which latter was also con- 
nected to electrometer-sheath. There was a window in 
this lamp-sheath 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 c.m. below the Rontgen lamp. 
Results.—Rontgen lamp in action; air drawn from 
lowest point of end of lead cylinder next to the R. 
lamp. 
Krom windows 
n 
q co 
To air-pump. 
Rontgen lamp? was placed. In the other end two 
holes were made, one in the middle, through which 
passed a glass tube (referred to below as suction pipe) 
of sufficient length to allow the end in the lead cylinder 
to be put into any desired place in the cylinder. By 
means of this, air was drawn through an electric filter * 
by an air pump. The other hole, at a little distance from 
the centre, contained a second glass tube by which air 
was drawn through indiarubber tubing from the open-air 
quadrangle outside the laboratory. 
In one series of experiments the end of the suction pipe 
was kept in the axial line of the lead cylinder at various 
points 10 cms. apart, beginning with a point close to the 
end distant from the Réntgen lamp. 
In every case the air drawn through the filter was 
found to be negatively electrified when no screen or an 
aluminium screen was interposed between the Réntgen 
Jamp 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 Réntgen 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 
1 “Electrification of Air by Réntgen Rays.’ By Lord Kelvin, Dr. J. C. 
Beattie, and Dr. M. Smoluchowski de Smolan. (Read before the Royal 
Society of Edinburgh, Monday, December 21, 1896.) 
2 The Réntgen lamp was a vacuum vessel with an oblique platinum plate 
(Jackson pattern). : 
3 Kelvin, Maclean, Galt, Proc. R.S., London, March 14, 1895. 
NO. 1418, VOL. 55 | 
December 16 :— 
3°55 p-m. — 61scale divisions in 2 mins. with aluminium screen, 
— 63 ” 9 2 oA no screen. 
= ie nt) re a5 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. 
- 78 5, ne s no screen. 
aw 33 2 Df lead screen 
-— 83 a3 ee ; alumin. screen. 
— 13 5 ae re lead screen. 
December 17. k.L. acting, and air drawn through filter. 
End of suction pipe kept 
in axial line of cylinder 
10.47 a.m. ems. 
—44 in 2 mins, with alumin, screen... 68 from R. L. end. 
oO 3 Ss lead 53 . 68 4 <a 
— 28 a9 ” no ” 58 ” 
~ 24 7 cE) no ” 48 b) 9 
fe) a es lead I 48 ce 
= 23 a5 Bs alumin. ,, 48 5 
—26 ae es alumin. ,, 38 9 1 
=a, 29 32 lead bE 38 oP) 
=i) » », lead ” 28 ; » 
— 26 of es alumin. ,, 28 ot 1 
— 36 3 af alumin. ,, 18 3 - 
- 21 alumin. 8 OC 
” ” 9 23 
We had previously made experiments with a sheet- 
iron funnel 1 metre long, 14°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 Réntgen 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. 
