the
power of emitting rays, that is, to be radio-active. We know to-day that
nearly every form of matter can be stimulated to radio-activity; which,
as we shall see, means that _its atoms break up into smaller and
wonderfully energetic particles which we call "electrons."_ This
discovery of electrons has brought about a complete change in our ideas
in many directions.

So, instead of atoms being indivisible, they are actually dividing
themselves, spontaneously, and giving off throughout the universe tiny
fragments of their substance. We shall explain presently what was later
discovered about the electron; meanwhile we can say that every glowing
metal is pouring out a stream of these electrons. Every arc-lamp is
discharging them. Every clap of thunder means a shower of them. Every
star is flooding space with them. We are witnessing the spontaneous
breaking up of atoms, atoms which had been thought to be indivisible.
The sun not only pours out streams of electrons from its own atoms, but
the ultra-violet light which it sends to the earth is one of the most
powerful agencies for releasing electrons from the surface-atoms of
matter on the earth. It is fortunate for us that our atmosphere absorbs
most of this ultra-violet or invisible light of the sun--a kind of light
which will be explained presently. It has been suggested that, if we
received the full flood of it from the sun, our metals would
disintegrate under its influence and this "steel civilisation" of ours
would be impossible!

But we are here anticipating, we are going beyond radium to the
wonderful discoveries which were made by the chemists and physicists of
the world who concentrated upon it. The work of Professor and Mme. Curie
was merely the final clue to guide the great search. How it was followed
up, how we penetrated into the very heart of the minute atom and
discovered new and portentous mines of energy, and how we were able to
understand, not only matter, but electricity and light, will be told in
the next chapter.

THE DISCOVERY OF THE ELECTRON AND HOW IT EFFECTED A REVOLUTION IN IDEAS

What the discovery of radium implied was only gradually realised. Radium
captivated the imagination of the world; it was a boon to medicine, but
to the man of science it was at first a most puzzling and most
attractive phenomenon. It was felt that some great secret of nature was
dimly unveiled in its wonderful manifestations, and there now
concentrated upon it as