Its salts are luminous in the dark, but this luminosity, at first very bright, gradually diminishes as the salts get older.

We have here to do with a secondary reaction correlative to the production of the emanation, after which radium undergoes the transformations which will be studied later on.
The method of analysis founded by M.and Madame Curie has enabled other bodies presenting sensible radioactivity to be discovered.

The alkaline metals appear to possess this property in a slight degree.
Recently fallen snow and mineral waters manifest marked action.

The phenomenon may often be due, however, to a radioactivity induced by radiations already existing in the atmosphere.

But this radioactivity hardly attains the ten-thousandth part of that presented by uranium, or the ten-millionth of that appertaining to radium.
Two other bodies, polonium and actinium, the one characterised by the special nature of the radiations it emits and the other by a particular spectrum, seem likewise to exist in pitchblende.