74 THE ROYAL SOCIETY OF CANADA 
round the two lower aluminium plates with a collar of thin mica, shown 
in the figure. Therefore, 3,960 — K’ X -0085/91?, so that 
K’ = 3-81 X 10°. 
This is about two per cent greater than my previous value, 3-74 X 
10°. Although the capacity is determined more accurately with the 
guard ring and dise electroscope, it probably yields too large a value 
of K’, owing to some secondary radiation from the aluminium plates. 
The results gave, therefore, a satisfactory verification of the first set of 
determinations. 
Number of Ions Due to B Rays. 
When an attempt is made to determine the values of quantities 
corresponding to K’ and N’, but relating to B rays instead of 7 rays, 
difficulties occur. If the radium is placed in a receptacle, the walls 
absorb some of the 8 rays, and if the radium is placed on a plate, there 
is “reflected” radiation from the plate. The method employed to 
overcome these difficulties was as follows :— 
The number of ions per cm per second, produced by the 8 
rays from Q curies of radium C, at a distance r, is given by 
ream gail 
if 
where K isthe constant for 8 raysand sis the co-efficient of absorption 
by air of the B rays. 
At the same distance, with the same amount of radium C, we have 
q — Re 5 
77 
using accented letters throughout for + rays, and unaccented for 8 rays. 
By division, q/q’ = K/K’-e-”, and as K’ has been found, suita- 
ble experiments will determine K. 
1. A capsule, containing radium bromide (-33 mg. radium), 
backed by ebonite and covered with thin mica, was placed at 1m. from 
the centre of the electroscope. The 8 and y rays together caused a 
leaf movement of 12-2 divisions/minute, and the 7 rays alone of 0-4 
divisions/ minute. Since e/” — 1-4, it follows that K/K’ = 11-8 X 1-4 
/-4— 41. This is, however, too large, on account of the g rays from 
radium B reaching the electroscope. Kovarik* has found with alumi- 
nium screens y — 13 for radium C, and u— 75 for radium B. Since 
* Phil. Mag., Nov., 1910. 
