This also probably
explains the phenomena studied by M. Villard, and previously pointed
out.
Sec. 2. RADIOACTIVE SUBSTANCES
Even in ordinary conditions, certain substances called radioactive
emit, quite outside any particular reaction, radiations complex
indeed, but which pass through fairly thin layers of minerals, impress
photographic plates, excite fluorescence, and ionize gases. In these
radiations we again find electrons which thus escape spontaneously
from radioactive bodies.
It is not necessary to give here a history of the discovery of radium,
for every one knows the admirable researches of M. and Madame Curie.
But subsequent to these first studies, a great number of facts have
accumulated for the last six years, among which some people find
themselves a little lost. It may, perhaps, not be useless to indicate
the essential results actually obtained.
The researches on radioactive substances have their starting-point in
the discovery of the rays of uranium made by M. Becquerel in 1896. As
early as 1867 Niepce de St Victor proved that salts of uranium
impressed photographic plates in the dark; but at that time the
phenomenon could only pass for a singularity attributable to
phosphorescence, and the valuable remarks of Niepce fell into
oblivion.
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