spots the thickness of the bubble is about the
three-millionth part of an inch. If the whole bubble were as thin as
this it would be completely invisible.]

Sec. 3

THE DISCOVERY OF X-RAYS AND RADIUM

The Discovery of Sir Wm. Crookes

But these wonders of the atom are only a prelude to the more romantic
and far-reaching discoveries of the new physics--the wonders of the
electron. Another and the most important phase of our exploration of the
material universe opened with the discovery of radium in 1898.

In the discovery of radio-active elements, a new property of matter was
discovered. What followed on the discovery of radium and of the X-rays
we shall see.

As Sir Ernest Rutherford, one of our greatest authorities, recently
said, the new physics has dissipated the last doubt about the reality of
atoms and molecules. The closer examination of matter which we have been
able to make shows positively that it is composed of atoms. But we must
not take the word now in its original Greek meaning (an "indivisible"
thing). The atoms are not indivisible. They can be broken up. They are
composed of still smaller particles.

The discovery that the atom was composed of smaller particles was the
welcome realisation of a dream that had haunted the imagination of the
nineteenth century. Chemists said that there were about eighty different
kinds of atoms--different kinds of matter--but no one was satisfied with
the multiplicity. Science is always aiming at simplicity and unity. It
may be that science has now taken a long step in the direction of
explaining the fundamental unity of all the matter. The chemist was
unable to break up these "elements" into something simpler, so he called
their atoms "indivisible" in that sense. But one man of science after
another expressed the hope that we would yet discover some fundamental
matter of which the various atoms were composed--_one primordial
substance from which all the varying forms of matter have been evolved
or built up_. Prout suggested this at the very beginning of the century,
when atoms were rediscovered by Dalton. Father Secchi, the famous Jesuit
astronomer said that all the atoms were probably evolved from ether; and
this was a very favoured speculation. Sir William Crookes talked of
"prothyl" as the fundamental substance. Others thought hydrogen was the
stuff out of which all the other atoms were composed.

The work which finally resulted in the discovery of radium beg