102 McCietitanp—TZhe Penetrating Radium Rays. 
filled with shot, so that it absorbed a pencil of y rays passed along it. 
The 50 milligrams of radium bromide producing the y rays were contained 
in a small vessel R placed in a hole in a block of lead, so as to limit 
its radiation to a diverging pencil with its axis parallel to the axis of the 
shot cylinder, and thus prevent the rays from falling on other parts of the 
apparatus. 
A wire from the inner cylinder leads to the electrometer placed some yards 
away, the wire being led along the axis of an earthed metal tube filled with 
paraffin. The inner cylinder and the wire leading from it were thus not exposed 
to air ionised by the radium. 
The vessel « was thick enough to stop all the a rays; the 8 rays could be 
stopped when desired by placing a sheet of lead between the radium and the 
vessel © 
Electro 
meter 
MONON AS 
MNS 
NNN 
Lead Shot 
6 
Fig. 1. 
In this way the charge got by the shot-cylinder could be measured when it 1s 
absorbing both 8 and y rays, and also when absorbing y rays only. 
When the shot-cylinder absorbs both 8 and y rays, it rapidly gets a negative 
charge; when it absorbs only y rays, no charge could be detected.. 
This experiment shows that the y rays do not carry any charge sufficient to be 
detected by the above apparatus. | 
The sensitiveness of the apparatus, and therefore the value of the experiment, 
can best be estimated by considering the deflection obtained with the B rays. A 
pencil of rays diverges from & wide enough to include practically the whole 
end of the cylinder 4. This pencil produces a deflection of 38 scale-divisions 
per minute when absorbed by the shot-cylinder. The whole charge carried by 
