ied body is one that has lost some of its
corpuscles."*4* According to this view, then, electricity is not a form
of energy but a form of matter; or, to be more precise, the electrical
corpuscle is the fundamental structure out of which the atom of matter
is built. This is a quite different view from that scarcely less recent
one which regards electricity as the manifestation of ether strain,
but it must be admitted that the corpuscular theory is supported by a
marvellous array of experimental evidence, though it can perhaps hardly
be claimed that this brings the theory to the plane of demonstration.
But all roads of physical science of late years have seemed to lead
towards the electron, as will be made further manifest when we consider
the phenomena of radio-activity, to which we now turn.

RADIO-ACTIVITY

In 1896, something like a year after the discovery of the X-ray,
Niewenglowski reported to the French Academy of Sciences that the
well-known chemical compound calcium sulphide, when exposed to sunlight,
gave off rays that penetrated black paper. He had made his examinations
of this substance, since, like several others, it was known to exhibit
strong fluorescent or phosphorescent effects when exposed to the cathode
rays, which are known to be closely connected with the X-rays. This
discovery was followed very shortly by confirmatory experiments made by
Becquerel, Troost, and Arnold, and these were followed in turn by the
discovery of Le Bon, made almost simultaneously, that certain bodies
when acted upon by sunlight give out radiations which act upon a
photographic plate. These manifestations, however, are not the effect of
radio-activity, but are probably the effects of short ultra-violet
light waves, and are not produced spontaneously by the substances. The
radiations, or emanations, of the radio-active substances, on the other
hand, are given out spontaneously, pass through substances opaque to
ordinary light, such as metal plates, act upon photographic plates, and
discharge electrified bodies. The substances uranium, thorium, polonium,
radium, and their compounds are radioactive, radium being by far the
most active.

The first definite discovery of such a radio-active substance was made
by M. Henri Becquerel, in 1896, while making some experiments upon
the peculiar ore pitch-blende. Pitch-blende is a heavy, black,
pitchy-looking mineral, found principally at present in some parts of
Saxony and Bohemia on t