anium was followed about two years later by
the discovery that thorium, and the minerals containing thorium,
possess properties similar to those of uranium. This discovery was
made independently and at about the same time by Schmidt and Madame
Skaldowska Curie. But the importance of this discovery was soon
completely overshadowed by the discovery of radium by Madame Curie,
working with her husband, Professor Pierre Curie, at the Ecole
Polytechnique in Paris. Madame Curie, stimulated by her own discoveries
and those of the other scientists just referred to, began a series of
examinations upon various substances by numerous complicated methods
to try and find a possible new element, as certain peculiarities of the
substances found in the pitch-blende seemed to indicate the presence of
some hitherto unknown body. The search proved a most difficult one
on account of the peculiar nature of the object in question, but the
tireless enthusiasm of Madame Curie knew nothing of insurmountable
obstacles, and soon drew her husband into the search with her. Her first
discovery was that of the substance polonium--so named by Madame Curie
after her native country, Poland. This proved to be another of the
radio-active substances, differing from any other yet discovered, but
still not the sought-for element. In a short time, however, the two
Curies made the great discovery of the element radium--a substance
which, according to their estimate, is some one million eight hundred
thousand times more radioactive than uranium. The name for this element,
_radium_, was proposed by Madame Curie, who had also suggested the term
"radio-activity."

The bearing of the discovery of radium and radioactivity upon theories
of the atom and matter will be considered in a moment; first the more
tangible qualities of this wonderful substance may be briefly referred
to. The fact that radio-active emanations traverse all forms of matter
to greater or less depth--that is, pass through wood and iron with
something the same ease that light passes through a window-glass--makes
the subject one of greatest interest; and particularly so as the
demonstration of this fact is so tangible. While the rays given out by
radium cannot, of course, be seen by the unaided eye, the effects of
these rays upon certain substances, which they cause to phosphoresce,
are strikingly shown. One of such substances is the diamond, and a
most striking illustration of the power of radium in