subjected to Radium Rays. 
347 
being practically negligible. The test plate p x was then exposed 
to the radium rays, at a distance of about \ cm., without removing 
it from its position ; the radium, in a suitable holder, being 
inserted between the plate and the gauze electrode. The ex- 
posure having continued for a given time, the radium was 
removed, and the secondary radiation produced by the X-rays 
for the two plates again measured. The standard plate p 0 was 
protected from the action of the radium by the walls of the boxes, 
which were of thick brass, and by the lead screen S. 
The experiments were then repeated, using the X-rays as the 
fatiguing agent, as in the experiments of Prof. More ; the standard 
plate being protected from the rays by a thick lead shutter placed 
in front of the window of the box. 
The results obtained are given in Table III. The first column 
gives the length of exposure to the fatiguing agent in hours. The 
other columns give for the various metals tried, the ratio of the 
secondary radiation produced by X-rays from the test plate, to 
that produced from the standard plate, after the former has been 
exposed to one or other of the fatiguing agents for the times given 
in the first column. 
It will be seen that the effects in the two cases are practically 
the same. In the case of polished zinc and lead, both X-rays 
and radium rays cause an increase in the secondary Rbntgen 
radiation. For copper there is in both cases a slight decrease. 
