Investigation of the Nature of the y Rays. 663 
radiation which is not able to get out of the plate — is 
probably transformed into secondary cathode radiation and 
other forms of energy. 
It is very probable that similar relations exist between 
primary and secondary X rays. The writer hopes to make 
some experiments in the near future to test this point. 
In conclusion I wish to thank Prof. Thomson for his keen 
interest and ever ready advice during these experiments. 
Cavendish Laboratory, February 18, 1908. 
LX, An Experimental Investigation of the Suture of the 
7 Rays. By W. H. Bkagg, M.A., F.R.S., Elder 'Pro- 
fessor of Mathematics and Physics in the University of 
Adelaide, and J. P. Y. Madsex, D.Sc, Lecturer on 
Electrical Engineering *. 
IX papers recently published in the Proceedings of the 
Poyal Society of South Australia (May and June 1907) 
aud in the Philosophical Magazine (October 1907) an attempt 
was made to show that the sether-pulse theory of 7 and X 
rays might prove to be incorrect after all, and that most of 
the known properties of these rays could be explained more 
simply and directly on the supposition that they were 
material and consisted of neutral pairs. The arguments 
were based on a comparison of known phenomena with 
deductions from each of the two opposing hypotheses. At 
that time there did not seem to be any opportunity of appeal 
to a decisive experiment. 
The object of this paper is to give a preliminary account 
of an investigation which appears to us to give the final 
answer as regards the y rays, and to show that they are 
material in nature. 
The argument is as follows : — 
Secondary radiation which is excited in an atom by a 
passing wave or pulse must be distributed symmetrically 
with regard to a plane passing through the atom perpen- 
dicular to the direction of motion of the pulse. If we speak 
of the primary pulse as going forwards, the secondary radiation 
is just as likely to go backwards as forwards. This is a 
well-recognized principle. For example, J. J. Thomson 
divides the secondary radiation due to 7 rays into two equal 
parts which he supposes to move away symmetrically in 
opposite directions, and, for convenience of calculation, 
parallel to the direction of the primary rays (' Conduction of 
* Communicated by the Physical Society: read April 10, 1908. 
2 Y 2 
