348 
Mr Crowther, On the Fatigue of Metals 
We must conclude, therefore, that radium rays produce in 
metals the same sort of fatigue of the secondary Rontgen radiation 
as is produced by the continuous application of the Rontgen rays 
themselves. 
Table III. 
Secondary Rontgen Radiation. 
Exposure 
Zinc 
Copper 
Lead 
Radium 
X-rays 
Radium 
X-rays 
Radium 
X-rays 
hrs. 
0 
100 
100 
100 
100 
100 
100 
1 
104 
— 
98 
98 
— 
— 
2 
106 
104 
— 
— 
103 
105 
3 
— 
— 
97 
98 
101 
101 
4 
109 
106 
— 
— 
101 
— 
Section 3. 
Experiments were further made to discover if radium could 
produce or accelerate photo-electric fatigue ; that is to say, if 
the rate of discharge of negative electricity from a metal plate 
under the action of ultra-violet light was altered by an exposure 
of the surface to the action of radium rays. The apparatus 
employed was that of the last section, the X-ray bulb being 
replaced by a source of ultra-violet radiation. As a compensation 
method of measurement was adopted it was not necessary to have 
the source of radiation particularly constant. An electric arc 
between two sharpened rods of aluminium was employed, and was 
maintained by the secondary of a transformer, the primary of 
which was connected directly to the alternating lighting circuit. 
This was found to give a copious but somewhat unsteady supply 
of ultra-violet rays. 
The copper plates 4 cm. in diameter were carefully polished, 
with flour-emery, and finally with a clean silk rag, and placed in 
position in the two boxes ; the wire gauge electrodes being 
charged to a high positive potential. The earth connections of 
the plates and the gold-leaf systems were broken, and the arc 
started. The rates of leak in the two chambers were measured 
by the movements of the gold leaves of the electroscopes. 
The test plate p 1 was removed and exposed in a small vessel 
to a quantity of uncovered radium. It was thus exposed not 
