McCurtianp— On Secondary Radiation and Atomic Structure. 
stances has not been studied in detail. 
The secondary radiation from lead was 
It should be here pointed out that the intensity of the secondary radiation is 
measured by the ionisation it produces in the vessel 7’, and, if the radiations from 
different substances are not exactly similar in character, this method may be open 
to some objection—for example, if the secondary rays from one substance are more 
easily absorbed than those from another. 
studied in detail as described in the previous paper, and it was found to be very 
similar to the primary 6 rays; but the secondary radiation from the other sub- 
In any case the remarkable dependence 
of the secondary radiation thus measured on the atomic weight of the substance 
holds true. 
SECONDARY RapiATION FROM DIFFERENT SUBSTANCES. 
The following Table shows the results of the investigation :— 
TABLE. 
Substances. secondary | Atomic Weight. Paaeucns Density. 
EXTEN Tye Atomic Weight. 
Uranium, 100 239°5 *4] 18°7 
Bismuth, 97 208°5 “46 9°8 
Lead, | 97 206°9 "46 11:4 
Mercury, 96 200°3 “47 13°6 
Platinum, 93 194°8 ‘47 21°5 
Tungsten, 88 184:0 “47 19°1 
Jodine, 85:5 127°0 67 5:0 
Antimony, 85 120-0 7 It 6:7 
Tin, 84 118°5 sia 73 
Cadmium, 82 112°4 73 8°6 
Silver, 81 107:9 75 10°5 
Molybdenum, 78 96:0 “81 8-6 
Selenium, 74 79:1 “94 4°3 
Arsenic, 133 75:0 ‘97 57 
Zine, 72 65:4 1-10 72 
Jopper, 71 63°6 Ieitil 8:9 
Cobalt, 67 59-0 1:18 8-9 
Nickel, 67 58°7 1-14 8:5 
Tron, 65 55:9 1:16 hat 
Chromium, 63 §2°1 1:20 65 
