s or x-rays fall on matter they give rise to ss-rays.
The mechanism involved is not known but it is possibly a result
of the resonance of the atom, or of parts of it, to the short
light waves. And it is remarkable that the y-rays which, as we
have seen, are shorter and more penetrating waves than the
x-rays, give rise to ss-rays possessed of greater velocity and
penetration than ss-rays excited by the x-rays. Indeed the ss-rays
originated by y-rays may attain a velocity nearly approaching
that of light and as great as that of any ss-rays emitted by
transmuting atoms. Again there is demonstrable evidence that
ss-rays impinging on matter may give rise to y-rays. The most
remarkable demonstration of this is seen in the x-ray tube. Here
the x-rays originate where the stream of ss- or cathode-rays

247

are arrested on the anode. But the first relation is at present
of most importance to us--_i.e._ that the y-or x-rays give rise to
ss-rays.

This relation gives us additional evidence of the identity of the
physical effects of y-, x-, and light-rays --using the term light
rays in the usual sense of spectral rays. For it has long been
known that light waves liberate electrons from atoms. It has been
found that these electrons possess a certain initial velocity
which is the greater the shorter the wave length of the light
concerned in their liberation. The whole science of
"photo-electricity" centres round this phenomenon. The action of
light on the photographic plate, as well as many other physical
and chemical phenomena, find an explanation in this liberation of
the electron by the light wave.

Here, then, we have spectral light waves liberating
electrons--_i.e._ very minute negatively-charged particles, and we
find that, as we use shorter light waves, the initial velocity of
these particles increases. Again, we have x-rays which are far
smaller in wave length than spectral light, liberating much
faster negatively electrified particles. Finally, we have
y-rays--the shortest nether waves of all-liberating negative
particles of the highest velocity known. Plainly the whole series
of phenomena is continuous.

We can now look closer at the actions involved in the therapeutic
influence of the several rays and in

248

this way, also, see further the correlation between what may be
called photo-therapeutics and radioactive therapeutics.

The ss-ray, whether we obtain it directly from the transforming
radioactive atom