1896-97.] Apparent and Beal Diselectrijication. 
397 
in some cases acquired negative electricity, under the influence of 
Rontgen rays; and we were thus led to investigate the effect of 
Rontgen rays on air unelectrified to begin with. 
§ 3a. The arrangement described in § 1 was again used to test 
whether or not air was electrified by ultra-violet rays. The ultra- 
violet rays were produced by an arc lamp. This lamp was placed 
about a cm. distant from the closed end of the large lead cylinder. 
The rays passed into the cylinder through a quartz window. The 
air in the cylinder from the immediate neighbourhood of this 
window was drawn through an electric filter. No effect was pro- 
duced on the electrometer. An exactly corresponding arrange- 
ment — § 1 — with Rontgen rays gave negative electrification of 
the air. 
Art. II. — On Apparent and Real Diselectrificatiqn of 
Solid Dielectrics Produced by Rontgen Rays and 
by Flame. 
(Read February 15, 1897.) 
§ 4. The fact that air is made conductive by flame, by ultra- 
violet light, by Rontgen rays, and by the presence of bodies at a 
white heat, has been shown by many experimenters. We propose 
in this communication to give some results bearing on this conduc- 
tivity of air, based chiefly on experiments of our own. 
§ 5. We have examined more particularly the behaviour of paraffin 
and of glass. 
In our first experiments with paraffin we used a brass ball of 
about an inch diameter, connected to the insulated terminal of an 
electrometer by a thin copper wire soldered to the ball. The ball 
and the wire were both coated to the depth of about Jth of 
an inch with paraffin. The ball was then laid on a block of par- 
affin in a lead box with an aluminium window, both of which 
were in metallic connection with the case of the electrometer. 
By this means we avoided all inductive effects. 
The electrometer was so arranged as to read 140 scale divisions 
per volt. 
After testing the insulation the paraffin ball was charged posi- 
