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 lines will suffice to
recall as much as is needed for the purpose of this chapter. In
their study of the emanations from uranium compounds the Curies
were led to isolate the various elements of the compounds until
they discovered that the discharge was predominantly due to one
specific element, radium. Radium is itself probably a product of
the disintegration of uranium, the heaviest of known metals, with
an atomic weight some 240 times greater than that of hydrogen.
But this massive atom of uranium has a life that is computed in