of Solutions by the action of Light and Rontgen Rays. 433 
wire placed in the thin layer of liquid parallel to and half-way 
between the electrodes. 
As has been said it was hoped that a distinct and readily 
measurable effect would have been obtained. But after deducting 
the ordinary temperature effect, it was found that the increase 
of conductivity of the solutions experimented with, due to illu- 
mination of an arc particularly rich in ultra-violet light, never 
amounted to as much as one per cent, of the conductivity of the 
given solution prepared and kept in the dark. It was greatest 
for solutions of ammoniacal silver chloride, uranyl nitrate, and 
colloidal silver, but the actual figures obtained could not be 
relied upon. 
With Rontgen Rays there was a distinct small effect in the 
following order: — strong solutions of Hoffmann’s violet (3‘7 per 
cent, increased conductivity) down to very dilute solutions (3’44 
per cent.) ; dilute solution of colloidal silver (08 per cent.) ; am- 
moniacal solution of silver chloride (025 per cent.) ; silver nitrate, 
and uranyl nitrate (no measurable change). 
These experiments were carried out in the Cavendish Labora- 
tory at the beginning of the year 1900 — 1901, and I am indebted 
to Professor Thomson and to Mr Whetham for many valuable 
suggestions. 
