 Later that year, Rutherford and Owens noticed variations when trying to measure radiation from thorium oxide.Rutherford noticed that the compounds of thorium continuously emit a radioactive gas that remains radioactive for several minutes, and called this gas "emanation" (from , to flow out, and , expiration), and later "thorium emanation" ("Th Em").In 1900, Friedrich Ernst Dorn reported some experiments in which he noticed that radium compounds emanate a radioactive gas he named "radium emanation" ("Ra Em").