Friedrich Ernst Dorn
Friedrich Ernst Dorn was a German physicist who was the first to discover that a radioactive substance, later named radon, is emitted from radium.
Dorn was born in Guttstadt , Province of Prussia , and died in Halle, Province of Saxony. He was educated at Knigsberg and went on to teach at the university level. In 1885, at Halle University, Dorn took over the position of personal ordinarius professor for theoretical physics from Anton Oberbeck. Since Dorn was already an ordinarius professor, he was allowed to assume the title so as to not appear as having been demoted. In 1895, Dorn succeeded Hermann Knoblauch at Halle as the ordinarius professor for experimental physics and director of the physics institute. Dorns previous duties were assumed by Carl Schmidt, who had been a Privatdozent and was called as an extraordinarius professor for theoretical physics.
Source: Wikipedia