406 
Proceedings of Poycd Society of Edinburgh. [sess. 
and - 2400 volts. At none of these potentials did we find any 
perceptible increase of conductance produced by the Rontgen rays 
above the natural conductance of the paraffin when undisturbed 
by them. 
§ 16. In the experiments with glass, the Leyden A consisted of 
a glass tube silvered on the inside. The inside silvering was placed 
in metallic connection with the inside coating of B. That part of 
the glass tube which projected beyond the lead sheath was covered 
with wet blotting-paper connected to the sheaths. We observed 
the behaviour of glass under the Rontgen rays at differences of 
potential of + 800, + 1500, + 2000 volts. We found no indication 
of increased conductance due to the rays at these voltages. 
We are forced to conclude that the experiments described by J. 
J. Thomson and McClelland do not prove any conductance to be 
induced in paraffin or glass by the Rontgen rays. It seems to us 
probable that the results described in their paper — pages 7 and 8 — 
are to be explained by electrifications induced on surfaces of glass 
or of paraffin in contact with air rendered temporarily conductive 
by the Rontgen rays. ‘(See § 7.) 
Art. IY. — On the Conductive Effect Produced in Am by 
Rontgen Rays and by Ultra-Violet Light. 
(Read February 1, 1897.) 
§ 17. We propose next to describe results of experiments on the 
electrical effects of Rontgen rays and of ultra-violet light when 
shone on metals, or through air between two metals mutually insu- 
lated; and electrified to begin with, by previously producing a 
difference of potentials between platinum electrodes of an electro- 
meter metallically connected with them. In some of our experi- 
ments this potential-difference was zero, and the initial ± electrifi- 
cations of the opposed surfaces depended solely on difference of 
volta-electric quality between their opposed surfaces. 
§ 18. To investigate the effects of Rontgen rays, a hollow 
cylinder of unpolished aluminium connected to the electrometer 
sheaths was used. Along the axis of this a metallic bar was placed, 
