1) Roentgen was working in a laboratory in late 1890s with some cathode ray tubes. He evacuated the tubes from air and filled a special gas in the tubes. When he applied a potential difference across it, he observed fluorescents to glow. He then covered the tubes with a black paper but still observed a green light appearing on the screen few feet's away from the tubes. This lead to the discovery of X-rays.
2) In 1896, Henry was conducting an experiment where he was interested in the phenomena of fluorescence in which some materials glow when exposed to sunlight.