ON THE PROPERTIES AND NATURES OF VARIOUS 
ELECTRIC RADIATIONS. ¢ 
By W. H. Brace, M. A., EF. R.S., 
Elder Professor of Mathematics and Physics in the University of Adelaide. 
We are now aware of the existence of a number of different types 
of radiation, each of which is able to ionize a gas, to act on a photo- 
graphic plate, and to excite phosphorescence in certain materials. 
Of these the a and canal rays consist of positively charged particles 
of atomic magnitude; the cathode and £ rays are negative rays, and 
consist of electrons; the X and y rays are supposed to be ether pulses; 
and ultra-violet light consists of short ether waves. The 8 rays stand 
by themselves, for, though they consist of negative electrons like the 
cathode and £ rays, they have so small a velocity that they possess no 
appreciable ionizing powers. | 
The present paper contains, in the first place, an attempt to find 
whether there is anything to be learned from a comparison of the 
properties of the various rays; and, in the second place, a discussion 
of the possibility that the y and X rays may be of a material nature. 
It appears to me to be a first deduction from such a comparison 
that in all cases the bulk of the ionization which the rays effect is of 
the same character, and consists in the displacement of slow-moving 
electrons, or 8 rays, from the atoms of the gas or other substance 
which they traverse. Let us consider the various rays in turn. 
In the case of the cathode rays this principle has been clearly 
established by Lenard in the course of his long series of beautiful 
experiments. He has shown that cathode rays of the most varied 
speeds, impinging on bodies of various kinds, or traversing different 
gases, cause the liberation of slow-speed electrons from the atoms of 
the solid or gas.. The speed of the electrons is in every case that due 
to the fall through less than ten volts. This is in no way a contradic- 
tion of the fact that cathode rays of high speed are also liberated 
from a solid surface struck by primary cathode rays; or from atoms 
7 Read before the Royal Society of South Australia in two parts: the first on 
May 7, 1907, the second on June 4, 1907. Reprinted, by permission, fromthe 
Philosophical Magazine for October, 1907. 
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