Mr Richardson , On an attempt to detect radiation , etc. 169 
storage cells and a spark-gap of three centimetres was generally 
used. In this way the spark could be kept going almost con- 
tinually for hours. The apparatus was set up in a dark room and 
in addition to this the excited wire was enclosed in a blackened 
wood box, inside which the photographic plates were exposed. 
In the first experiments a brass rod about 1 cm. thick was used, 
but this was soon replaced by a brass wire *7 mm. in diameter. 
Aluminium and copper wires of about 6 mm. and a fine steel 
wire of '09 mm. diameter were also tested. Exposures of 5, 10, 20 
and 60 minutes were given successively to different plates. At first 
the plates were about 2 cms. from the wire, and it was expected 
they would be more fogged along the line of projection of the 
wire on the plate than elsewhere. The fog observed on developing 
was however quite uniform and so further exposures were given 
with plates covered by thick copper with a square hole in the 
middle. Nothing was observed except when the plate was close 
up to the wire, when the outline of the square was distinctly seen 
on developing. This was ultimately shown to be due to a very 
faint glow between the wire and the edge of the copper. Since, 
if the rays were very soft ones, they might have been absorbed 
by 1 — 2 cms. of air at ordinary pressures, the copper plate was 
now removed and the photographic plate brought up close to the 
wire. When the wire was only 3 — 5 mm. from the plate, an 
appearance similar to that produced by drawing an interrupted 
straight line on blotting paper was obtained on developing. 
The interr&ptedness is due to the fact that the wire could not 
be made quite straight on account of its stiffness ; so that it was 
nearer the plate in some parts than others. The edges of the 
linear spots presented in places a peculiar jagged appearance when 
magnified. The nature of the phenomenon was investigated by 
inserting thin plates of various material between the wire and the 
photographic plate. The action was found to be transmitted 
through transparent substances ( e.g . thin glass and mica) but 
was stopped by the thinnest aluminium foil. It was traced 
finally to a very faint glow which occasionally passed along the 
wire. The effect seemed identical in every respect with that 
recently investigated by M. T. Tomassina 1 . It was found im- 
possible to make sure of this glow never occurring, so that the only 
thing left was to try for an effect at low pressures when any 
radiation which might be given off would not be absorbed by 
the air. 
In the form of apparatus used at first, the excited wire simply 
passed in at one end of a wide tube which could be exhausted 
and out again through a short side tube fixed at right angles to 
Comptes Rendus, May 1900. 
