Thus is explained the fact that we can separate them and that we can produce a sort of spectrum by the action of the magnet, or, again, as M.Deslandres has shown in a very interesting experiment, by that of an electrostatic field.

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.