Geology Reference
In-Depth Information
attending the session held in the Physics and Mathematics
Section where all the talk was of 'mysterious rays'. The previ-
ous year, 1895, William Röntgen, a German physicist, had
observed a mysterious source of energy being emitted as invis-
ible rays. When he placed the hand of his wife over a photo-
graphic plate and in the path of these rays, Röntgen was able to
develop a remarkable photograph that showed the bones in her
hand, surrounded by the shadow of her flesh. This extraordinary
image was the first X-ray ever taken.
The following year Henri Becquerel, a French physicist, won-
dered whether there was any connection between the newly dis-
covered X-rays and the reason why uranium glowed in the dark
after it had been exposed to sunlight. He placed some uranium
in a drawer with a photographic plate covered with black paper.
Sure enough, on removing the paper the plate was seen to be
fogged, proving that uranium too emitted invisible rays which
were at least capable of passing through the black paper.
Radioactivity had been discovered, and the first step towards
finding the true age of the Earth had been taken. Speculation at
the BAAS meeting as to what these mysterious rays were cen-
tred upon 'some kind of light', but at that time even the best
brains in the business were mystified. However, set scientists a
good problem and someone will try to solve it.
Initially, Becquerel's discovery did not arouse much attention,
overshadowed as it was by Röntgen's X-rays because of the
medical possibilities which X-rays opened up. But working in
Paris at that time was a newly married couple, Pierre and Marie
Curie, both of whom were physicists. Following the birth of
their first child in 1897 Marie needed a project to work on and
decided to make a systematic investigation of Becquerel's mys-
terious 'uranium rays'. Progress was quick. Within a few days
she had discovered that another element, thorium, gave out the
same rays as uranium. Then she noticed that regardless of what
uranium was combined with, the strength of the radiation being
emitted depended only on one thing: the amount of uranium
