Iv] NATURE OF THE RADIATIONS 105 
absorb all the a particles, but thin enough to allow most of the 
B particles to escape. A sealed tube, contaming the radium, was 
attached at one end to a pair of thin gold leaves in metallic 
connection with the radium, and was insulated inside a larger 
tube by means of a quartz rod. The air in the outer tube was 
exhausted as completely as possible by means of a mercury pump, 
in order to reduce as much as possible the ionization in the gas, 
and consequently the loss of any charge gained by the gold leaves. 
After an interval of 20 hours, the gold leaves were observed to 
diverge to their full extent, indicating that they had acquired 
a large positive charge. In this experiment Strutt used 4 gram 
of radiferous barium of activity only 100 times that of uranium. 
It can readily be calculated that 10 milligrams of pure radium 
bromide would have caused an equal divergence of the leaves 
in a few minutes. 
A determination of the amount of the charge carried off by the 
rays of radium has been made recently by Wien’. A small quantity 
of radium, placed in a sealed platinum vessel, was hung by an 
insulating thread inside a glass cylinder which was exhausted to 
a low pressure. A connection between the platinum vessel and an 
electrode sealed on the external glass cylinder could be made, when 
required, by tilting the tube. Wien found that in a good vacuum 
the platinum vessel became charged to about 100 volts. The rate 
of escape of negative electricity from the platinum vessel containing 
4 milligrams of radium bromide corresponded to 2°91 x 10-” am- 
peres. Ifthe charge on each particle is taken as 11 x 10-* electro- 
magnetic units, this corresponds to an escape of 2°66 x 10’ particles 
per second. From 1 gram of radium bromide the corresponding 
number would be 6°6 x 10° per second. Since some of the 8 rays 
are absorbed in their passage through the walls of the containing 
vessel, the actual number projected per second from 1 gram of 
radium bromide must be greater than the above value. 
75. Determination of e/m. J.J. Thomson has shown that 
in their passage between the plates of a condenser the cathode 
rays are deflected towards the positive plate. Shortly after the 
discovery of the magnetic deviation of the @ rays from radium, 
1 Phys. Zeit. 4, No. 23, p. 624, 1903. 
