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THE ENERGY OF SECONDARY RADIATION. 
By J. A. M‘CLELLAND, M.A., Professor of Experimental Physics, University College, 
Dublin. 
[ Read, November 21; Received for Publication, November 24, 1905; Published, Frsrvary 6, 1906. | 
In previous papers* the author has studied the secondary radiation emitted 
by substances when exposed to the action of the 6 and y rays from radium. 
This secondary radiation consists of negatively-charged particles similar to 
the 8B rays; and a simple relation has been found to exist between the intensity 
of the radiation and the atomic weight of the substance emitting it, the 
secondary radiation from all the elements tested increasing with the atomic 
weight of the element. 
In establishing this relation, the relative intensities of the secondary radiations 
from a large number of elementary substances were compared, the incident 
radiation of 8 rays being the same in all cases; but no attempt was made to 
compare the energy of the secondary radiation with that of the primary radiation 
producing it. The present paper deals with this main point, together with a 
number of other points that arise in connexion with it. 
PRELIMINARY INVESTIGATION. 
The apparatus used in the previous work was of such a form as_ to 
exclude any easily-absorbed secondary radiation that might be produced when 
the incident 6 (and y) rays were absorbed by any substance; the secondary 
radiation experimented with consisted entirely of negatively-charged particles 
similar in penetrating power to the primary 8 rays. As our present object 
is to establish the relation between the total energy of the secondary radiation 
and that of the primary radiation producing it, it is necessary to determine, 
* Trans. Royal Dublin Soc., Vol. vili., Part xrv., 1905, p. 169, and Vol, ix., Part 1., 1905, p. 1. 
TRANS. ROY. DUB. SOC., NoS., VOL. IX., PART II, 6 
