1896-97.] Conductive Effect in Air by Rontgen Rays. 
409 
The zero with the electrometer quadrants in metallic connection 
we shall afterwards speak of as the metallic zero. 
December 31, 1896. 5.56 p.m. — Readings with one pair of electrometer 
quadrants insulated, and with Rontgen lamp acting. 
- 72 scale divisions from metallic zero after 5 secs. 
-87 
3 3 
3 3 
3 3 
33 
10 
3 3 
-91 
3 3 
3 3 
33 
3 3 
15 
3 3 
-92 
S 3 
3 3 
3 3 
3 3 
30 
3 3 
-93 
33 
3 3 
3 3 
3 3 
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 Avas stopped if a lead screen was used. If a positive 
or a negative charge was given to the insulated metal, and the 
Rontgen rays were shone through the aluminium cylinder surround- 
ing 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. Column III. gives the differences for two of the same 
metals in the interior, but with the surrounding aluminium cylinder 
altered by polishing its inner surface with emery paper. 
i. 
Insulated metal. 
Magnesium tape 
Amalgamated zinc 
Polished aluminium . 
Polished zinc 
Unpolished aluminium 
Polished lead . 
Polished copper 
Polished iron nail 
Palladium wire 
Gold wire 
Carbon 
It is to be noted that the preceding experiments tell us in- 
YOL. XXI. 2/7/97. 2 D 
n. 
- 0*671 of a volt 
0*66 
- 0*465 
- 0*343 
- 0*349 
- 0*257 
+ 0*129 
+ 0*182 
+ 0*255 
4- 0*264 
+ 0*429 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
33 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
3 3 
III. 
+ 0*35 of a volt. 
+ 0*930 of a volt. 
