X-rays were discovered casually by Wilhelm Konrad Röntgen (1845-1923) while studying discharges in tubes with rarefied gases. He was observing the fluorescence that the cathodic rays produced on the walls of the tube when, to his great surprise, he became aware that even a screen of barium platinocyanide, which was close to the discharge tube, became fluorescent every time the tube was working and he found that the fluorescence appeared on that screen up to a distance of two metres from the tube.
Röntgen studied the properties of the rays that produced this fluorescence and established that they could not be identified with cathodic rays, but were generated by them in colliding with the walls of the discharge tube. He reported this to the Physical-Medical Society of Wurzburg in December 1895.
Having established that they produce shadows with sharp outlines and therefore propagate in a straight line, Röntgen called them rays and, since their nature was unknown to him, he added the X.
In 1901 he was awarded the Nobel Prize "for his discovery of x-rays".
In the course of his research on x-rays, he found that: they excite the fluorescence of certain substances; they are invisible; they impress a photographic plate; they ionize gases; they propagate along straight lines; they penetrate through bodies that are opaque in visible and ultraviolet light and are absorbed differently by bodies having different densities; they are not deviated by magnetic fields, even when quite intense. ...continues