344 
electrometer sheaths was used. 
metallic bar was placed, supported by its ends on small 
blocks of paraffin so situated as not to be shone on by 
the Roéntgen rays. This insulated metal was connected 
by a copper wire to the insulated terminal of the electro- 
meter. To protect it from inductive effects it was 
enclosed in a lead tube connected to the other terminal 
and to sheaths (see Diagram 1). 
The Réntgen lamp was placed in a lead cylinder con- 
nected to sheaths. The rays passed into the tube of 
aluminium through a window in the lead cylinder, which 
could be screened or unscreened at will, as described in 
our former paper (Proc. R.S.E., December 1896). 
The course of the experiment was the same with each 
insulated metal. The metal was charged first positively, 
then negatively; the R6éntgen rays were then shone 
on it through the aluminium cylinder surrounding it, and 
the electrometer readings taken at fixed intervals, until a 
steady reading on the electrometer was obtained. The 
Along the axis of this a | 
WATORE 
| 
| 
point at which the electrometer reading remained steady 
with the rays acting we shall call the vays-zero. ‘ 
Finally, the insulated metal was discharged by metallic 
connection in the electrometer, and re-insulated ; the 
- 
Qawinisen J ube 
DiaGRaM 1. 
rays were again shone on it until the rays-zero was | 
again reached. 
The following figures, taken from the laboratory book, 
show the effect obtained in this way when the insulated 
metal was amalgamated zinc. 
The zero with the electrometer quadrants in metallic 
connection we shall afterwards speak of as the mefad/ic 
Zero. 
December 31, 1896, 5.56 p m.— Readings with one pair of 
| to sheaths. 
electrometer quadrants insulated, and with Rontgen lamp | 
acting. 
— 72 scale divisions from metallic zero after 5 secs. 
= ti) » » > » 10,5 
= 191 » ” ” ” 15 ys 
— 92 2 3 33 eS)! fe 
= 115} ” 2 mins. 
Afterwards steady. 
Thus the difference between the rays-zero and the 
metallic zero is in this case — 93 scale divisions, or | 
— 0°66 of a volt. 
[Sensibility of electrometer 140 divs. per volt.] 
This deviation from the metallic zero was not stopped 
by placing an aluminium screen over the window of the 
lead cylinder ; on the other hand, it was stopped if a lead 
screen was used. If a positive or a negative charge was 
given to the insulated metal and the Réntgen rays were | 
shone through the aluminium cylinder surrounding it, 
the discharge went on till the rays-zero was reached ; 
only then was the electrometer reading steady. 
In the following table, Column II. gives the potential 
differences of the rays-zero from the metallic zero for 
twelve different metals insulated within the unpolished 
aluminium cylinder as described above. 
gives the differences for two of the same metals in the 
NO. 1424 VOL. 55] 
[FEBRUARY IT, 1897 
interior, but with the surrounding aluminium cylinder 
altered by its inner surface being polished by emery 
paper. 
: Il. III. 
Insulated metal. 
Magnesium tape —0°671 of a volt 
Amalgamated zine —0°66 ;, 5, 
Polished aluminium SIOTAGS: 55... 55 
Polished zinc PeETOrSAS 5, 
Unpolished aluminium EO:340 5, 55 +0°35 ofa volt 
Polished lead SIORZRT 55 55 
Polished copper ORN29) 55 55 
Polished iron nail - +o'r82 ,, ,, 
Palladium wire ORGS. 55° 55 
Gold wire +0'204 ,, 5: +0°930 of a volt 
Carbon ... EORA20 4) 55 
It is to be noted that the preceding experiments tell us 
insufficiently as to what would happen had we shone the 
rays on an insulated metal 
surrounded by an absolutely 
identical metallicsurface con- 
nected to sheaths. Another 
experiment towards answer- 
ing this question will be 
described in a later part of 
our paper. 
The preceding results of 
the action of Réntgen rays 
are very similar to, and 
wholly in accordance with, 
the results found by Mr. 
Erskine Murray, and de- 
scribed by him in a com- 
munication to the Royal Society of London, March 19, 
1896. 
They are analogous to those found for ultra-violet light 
by Righi (Rend. R. Acc. dei Lincet, 1888, 1889) ; 
Hallwachs ( Wedemann’s Annalen, 34, 1888) ; Elster and 
Geitel (Wiedemann’s Annalen. 38, 41, 1888); Branly 
(Comptes rendus, 1888, 1890), and others. 
We have also made some experiments with ultra-violet 
light, in which this similarity is further brought out. 
The'method we have employed is that of Righi. 
A cage of brass wire gauze was made and connected 
Inside it the insulated metal was placed on 
a block of paraffin, and connected to the insulated terminal 
of the electrometer by a thin copper wire protected 
Lad Sheaths 
ol € Atoms fxr 
er 
‘Mekal Dise Foo SSSR Sc = 
DIAGRAM 2. 
against inductive effects. The light from an arc lamp 
was then shone through the gauze so as to fall on the 
insulated metal perpendicular to its surfaces (see 
Diagram 2). 
The experiments were of the same nature as those 
with the Réntgen rays, except that wire gauze letting 
through the ultra-violet light was substituted for the non- 
perforated aluminium cylinder transparent to the Rontgen 
rays. The insulated metal disc was 2 cms. distant from 
the gauze of brass wire. The steady electrometer read- 
| ings after the two pairs of quadrants were insulated and 
Column III. | 
the ultra-violet light shining (which we shall hereafter 
refer to as the w/tra-violet-light-zero) was observed. 
