caused by the B and y Rays of Radium. 675 
is easy to calculate the coefficient of absorption in aluminium 
from secondary radiation caused by Rontgen rays. The 
values for @ and y rays and for y rays alone are placed by 
the side for comparison with those from Réntgen rays. The 
results from y rays are not very accurate, as the quantities to 
be measured were small when the screen was used. 
Tasre ITI.—’ for Aluminium, Secondary Rays. 
Radiator. Bandy. | Y: | Rontgen. 
a 19 23 | 5D 
BGP PER .. 0.51.26. 20 25 133 
[Snes ee ak 27 131 
2/2 ee 21 23 169 
| Aluminium ...... 24 32 22 
i re | 24 ae 37 
fearaein.....:.....- 21 | 2 26 
| 
| 
This table further accentuates the difference between the 
secondary radiations from y and from Réntgen rays, the 
Jatter having much less penetrating power, particularly in 
the case of zinc, brass, and copper, whilst lead behaves in a 
manner apparently anomalous. 
In order to test the character of the secondary radiations 
due to radium, layers of paper were placed in front of the 
electroscope, lead being used as radiator. The results are 
shown graphically in fig. 5. The logarithms of the ordinates 
— 
Scale Divisions. 
‘a 
: a 
20 
J asnferen| | 
° so 
20° 
Sheets of poper 
when plotted give a straight line, so that the curve has a 
simple exponential equation [=I,e-*’* where \’=9. 
