he Continent, in Cornwall in Great Britain, and
in Colorado in America. It is by no means a recently discovered mineral,
having been for some years the source of uranium and its compounds,
which, on account of their brilliant colors, have been used in
dye-stuffs and some kinds of stained glass. It is a complex mineral,
containing at least eight or ten elements, which can be separated from
it only with great difficulty and by complicated chemical processes.

Becquerers discovery was brought about by a lucky accident, although,
like so many other apparently accidental scientific discoveries, it was
the outcome of a long series of scientific experiments all trending in
the same direction. He had found that uranium, when exposed to the sun's
rays, appeared to possess the property of absorbing them and of then
acting upon a photographic plate. Since pitch-blende contained uranium,
or uranium salts, he surmised that a somewhat similar result might be
obtained with the ore itself. He therefore prepared a photographic plate
wrapped in black paper, intending to attempt making an impression on the
plate of some metal body interposed between it and the pitch-blende. For
this purpose he had selected a key; but as the day proved to be cloudy
he put the plate, with the key and pitch-blende resting upon it, in
a dark drawer in his desk, and did not return to the experiment for
several days. Upon doing so, however, he developed the plate without
further exposure, when to his astonishment he found that the developed
negative showed a distinct impression of the key. Clearly this was the
manifestation of a property heretofore unknown in any natural substance,
and was strikingly similar to the action of the Roentgen rays. Further
investigations by Lord Kelvin, Beattie, Smolan, and Rutherford confirmed
the fact that, like the Roentgen rays, the uranium rays not only acted
upon the photographic plate but discharged electrified bodies. And what
seemed the more wonderful was the fact that these "Becquerel rays," as
they were now called, emanated spontaneously from the pitch-blende.
But although this action is analogous to the Roentgen rays, at least as
regards its action upon the photographic plate and its influence on
the electric field, its action is extremely feeble in comparison, the
Roentgen rays producing effects in minutes, or even seconds, which
require days of exposure to uranium rays. The discovery of the
radio-active properties of ur