674 Mr. A. 8. Eve on the Secondary Radiation 
On plotting the results for density and the y secondary 
radiation, it was found that the substances held the same 
relative position as for 8 and y rays jointly. The change 
appears to be one of intensity, not of kind. The coefficients 
of absorption by aluminium and brass were also calculated, 
and their values averaged 17 per cent. more than those from 
the collective 8 andy rays. It is clear that the secondary 
radiations from 8 and from y¥ rays are of the same character. 
The secondary radiation from the y rays alone is less intense 
and less penetrating, but some of this difference is due to the 
loss of intensity by the y rays in passing through 6 mm. 
of lead. 
From the above results it appears that the @ rays caused 
about 85 per cent. of the secondary radiation, and the y rays 
15 per cent. This was confirmed by using a strong magnetic 
field whereby the 8 rays were deflexed, and then absorbed 
by lead, so that the y rays only remained. 
It is now possible to compare Townsend’s results with 
Rontgen rays with those for y rays. 
TasLE [f.—Secondary Radiations. 
a 
Radiator. Band y Rays.| y Rays. | Rontgen Rays. 
bieades ak epic 100 100 100 | 
Dapper’. nue: 57 | 61 291 
| ase clot ese, 58 . 59 263 
MN ot ease os dT rt ) 282 
Aluminium ...... 30 | 30 / 25 
ARES 3. poses rare ol 35 | 31 
Paraffin ..........-. Cm gia TM i hag 
In the above table lead has been selected as the standard 
for each column. 
It will be seen that the Réntgen rays give results widely 
divergent from the order expected from considerations of 
density. The radiation from lead is actually less than that 
from paraffin. It seemed possible that a hard bulb might 
give results differing from those found by Townsend. As a 
test case the secondary radiations from lead and brass were 
compared. The results from brass were a little larger than 
than those from lead, so that Townsend’s order was confirmed, 
for hard as well as soft rays, in the case of these two 
substances. 
As Townsend used an aluminium screen, *24 mm. thick, it 
