ntil it was a million times thinner than the atmosphere, he made the
experiment of sending an electric discharge through it, and found a very
curious result. From the cathode (the negative electric point) certain
rays proceeded which caused a green fluorescence on the glass of the
tube. Since the discharge did not consist of the atoms of the gas, he
concluded that it was a new and mysterious substance, which he called
"radiant matter." But no progress was made in the interpretation of
this strange material. The Crookes tube became one of the toys of
science--and the lamp of other investigators.

In 1895 Rontgen drew closer attention to the Crookes tube by discovering
the rays which he called X-rays, but which now bear his name. They
differ from ordinary light-waves in their length, their irregularity,
and especially their power to pass through opaque bodies. A number of
distinguished physicists now took up the study of the effect of sending
an electric discharge through a vacuum, and the particles of "radiant
matter" were soon identified. Sir J. J. Thomson, especially, was
brilliantly successful in his interpretation. He proved that they were
tiny corpuscles, more than a thousand times smaller than the atom of
hydrogen, charged with negative electricity, and travelling at the
rate of thousands of miles a second. They were the "electrons" in which
modern physics sees the long-sought constituents of the atom.

No sooner had interest been thoroughly aroused than it was announced
that a fresh discovery had opened a new shaft into the underworld. Sir
J. J. Thomson, pursuing his research, found in 1896 that compounds of
uranium sent out rays that could penetrate black paper and affect the
photographic plate; though in this case the French physicist, Becquerel,
made the discovery simultaneously' and was the first to publish it. An
army of investigators turned into the new field, and sought to penetrate
the deep abyss that had almost suddenly disclosed itself. The quickening
of astronomy by Galilei, or of zoology by Darwin, was slight in
comparison with the stirring of our physical world by these increasing
discoveries. And in 1898 M. and Mme. Curie made the further discovery
which, in the popular mind, obliterated all the earlier achievements.
They succeeded in isolating the new element, radium, which exhibits the
actual process of an atom parting with its minute constituents.

The story of radium is so recent that a few line