M.Becquerel established, after some hesitations natural in the face of phenomena which seemed so contrary to accepted ideas, that the radiating property was absolutely independent of phosphorescence, that all the salts of uranium, even the uranous salts which are not phosphorescent, give similar radiant effects, and that these phenomena correspond to a continuous emission of energy, but do not seem to be the result of a storage of energy under the influence of some external radiation.

Spontaneous and constant, the radiation is insensible to variations of temperature and light.
The nature of these radiations was not immediately understood,[32] and their properties seemed contradictory.

This was because we were not dealing with a single category of rays.

But amongst all the effects there is one which constitutes for the radiations taken as a whole, a veritable process for the measurement of radioactivity.

This is their ionizing action on gases.