In this case too it is associated with radioactive matter, which is almost ubiquitous.
Another radioactive substance - ionium - was isolated from carnotite, a uranium mineral, by B.
Strutt has found that phosphatized nodules and bones are rich in radioactive constituents, and has brought this into relation with their geological age.
And Mme Curie subjected a large amount of pitchblende to a laborious process of fractionation, with the result that in 1898 they announced the existence in it of two highly radioactive substances, polonium and radium.
In 1901 Elster and Geitel found that a radioactive emanation is present in the atmosphere.