The discovery of X-rays
In December 1895 the German physicist Wilhelm Rontgen noticed that some barium platinocyanide crystals glowed brightly in the neighbourhood of a working cathode ray tube even when the tube was covered up. He also noticed that some wrapped photographic plates left near the tube had become fogged. It appeared that some kind of invisible radiation proceeded in straight lines from the tube and was able to penetrate substances opaque to ordinary light. He subsequently found that this
radiation, which he called X-rays, was coming from the fluorescent glass wall of the tube at the place where it was struck by the cathode rays. The rays were otherwise known as Rontgen rays, in honour of their discoverer.
Rontgen found that if a sheet of cardboard covered with barium platinocyanide was placed in the path of the X-rays it became luminous. On placing his hand between tube and screen a faint shadow of the hand was formed in which the bones were clearly visible, since they were more opaque to the X-rays than flesh. It was found that the newly discovered X-rays were not deflected by magnetic or electric fields, from which it was concluded that they could not consist of electrically charged particles. Rontgen assumed that the X-rays were some kind of longitudinal wave motion, but we now know them to be of the same nature as light waves but with a very much shorter wavelength.