340 
Mr Crowtlier, On the Fatigue of Metals 
On the Fatigue of Metals subjected to Radium Rays. By 
J. A. Crowther, B.A., St John’s College. 
[ Read 28 October 1907.] 
Introduction. 
The object of the following experiments was to discover if the 
continuous impact of radium rays upon a solid surface caused any 
diminution in the amount of secondary radiation emitted by it. 
It is well known that the amount of negative electricity discharged 
from a metal plate when exposed to the action of ultra-violet 
light, diminishes rapidly if the exposure to the rays is prolonged. 
Much work has been done on this subject, but the results obtained 
by different observers are so diverse that it still remains in some 
obscurity. There can be no doubt, however, that it varies 
(i) for different metals, 
(ii) with the gas in which the metal is placed, 
(iii) with the quality of the ultra-violet light *. 
It also depends upon the state of polish of the surface. A plate 
when fatigued can be restored to its original activity by careful re- 
polishing. 
Large numbers of corpuscles are also given off from a surface 
exposed to the action of radium rays. It was thought of interest 
to investigate whether in this case also there were any phenomena 
of fatigue similar to those observed with ultra-violet light. 
Experiments were performed using 
(i) yS and <y rays only, 
(ii) a, /3, and <y rays, 
and extended over a considerable space of time. 
Section 1. 
In the first series of experiments, using only the pene- 
trating /3 and y rays of radium the apparatus employed took the 
form represented in figure 1. The rays from the radium R, fell 
upon a plate of the metal under investigation A, which was 
mounted upon a block of wood W, at an angle of 45° with the 
horizontal. The rays proceeding from the surface of the metal A, 
* Conduction of Electricity through Gases, p. 288 (1906). 
