644 Mr. E. D. Kleeman on Different Kinds of y Rays 
celluloid dish 14 cm. long and 11 cm. broad, and comparing 
the radiation from the mercury with that from a lead plate 
having the same length and breadth as the dish. The depth 
of the mercury in the dish was 10 mm. and the thickness of 
the lead plate was 6 mm. In these measurements the screens 
were placed in a horizontal position underneath the ioniza- 
tion-chamber, and the mercury dish or lead plate placed in a 
horizontal position underneath the screen. The radiation 
Table 
I. 
Radiator 1 
and its I 
thickness J 
Pb. 
T8 mm. 
Zn. 
6*5 mm. 
Fe. 
6*5 mm. 
S. 
9 mm. 
Al. 
7"5 mm. 
C. 
20 mm. 
Card- 
board. 
4 mm. 
Pb 
100 
100 
100 
100 
100 
100 
100 
Hg .- 
64-1 
64-1 
67-6 
68-5 
67-0 
676 
64-1 
Zn 3 mm 
156 
268 
253 
225 
214 
186 
186 
Cu3 „ ... 
183 
330 
303 
278 
257 
233 
223 
Fe 3 „ ... 
172 
311 
304 
264 
244 
214 
230 
S 2 „ ... 
150 
260 
249 
223 
186 
187 
A17-5 „ ... 
151 
267 
273 
377 
239 
347 
334 
209 
208 
C 20 mm.... 
167 
343 
274 
284 
Table II. 
Radiator. 
Pb. 
Zn. 
Fe. 
S. 
Al. 
C. 
Card- 
board. 
Pb 
64-1 
37-3 
39-5 
44-4 
467 
53-7 
53-8 
Hg 
411 
100 
23-9 
267 
30-4 
313 
363 
34-5 
Zn 
190 
100 
100 
100 
100 
100 
Cu 
117 
123 
120 
122 
120 
125 
120 
Fe 
110 
116 
120 
117 
114 
115 
127 
S 
96-3 
96-8 
97 
996 
98-4 
108 
106 
104 
99-8 
112 
101 
112 
Al 
C 
107-2 
128 
140 
154 
156-2 
147 
153 
from the lead plate was taken equal to 100. The radiation 
from each of the other radiators was compared with that 
from a lead plate 1*8 mm. thick, and o£ the same length and 
breadth as these radiators, each of which was 28 cm. long 
and 24 cm. broad. The radiation from lead was taken, as 
before, equal to 100. 
Table II. gives the same observations as Table I. except 
