[Broo 
VIII. 
THE PENETRATING RADIUM RAYS. 
By J. A. McCLELLAND, M.A., 
Professor of Experimental Physics, University College, Dublin. 
[Read, Apriz 19, 1904. ] 
THERE has been some difficulty in deciding as to the nature of the very 
penetrating or y rays given by radium, whether they are electromagnetic 
pulses like Rontgen rays, or a flight of charged particles like the a and B rays. 
In some respects, the y rays act like the a and 6 rays, which we know to consist of 
charged particles; while, on the other hand, no deflection of the rays in a 
magnetic field has been detected ; and, further, we should expect to get Rontgen 
rays from a body like radium which is emitting charged particles travelling with 
a great velocity. 
The chief reason for considering the y rays to consist of charged particles lies 
in the fact that the absorption of these rays by different substances is propor- 
tional to the density of the substance—a law obeyed by a and 6 rays, and by 
Cathode rays, but not obeyed by Réntgen rays. It should be stated here that 
since the experiments described in this Paper were commenced, Mr. Eve* 
has found that, when only very penetrating Rontgen rays are used, the 
absorption produced by different substances becomes more nearly proportional 
to the density of the substance—a result which tends to remove the chief 
difficulty in deciding that the y rays are of the same nature as Rontgen 
rays. 
The method I have used to decide whether or not the y rays are charged 
particles is to endeavour to directly detect the charge carried by the rays, 
if any. 
First EXPERIMENT. 
A block of lead was taken, and a hole drilled to a small depth in the centre of 
one of its faces; 50 milligrams of a good sample of radium bromide, enclosed in an 
air-tight vessel with a very thin mica top, were placed in the hole. The rays from 
* Nature, March 10th, 1904. 
TRANS, ROY. DUB. SOC., N.S., VOL. VIII., PART VIII. ») 
