Roentgen ray: Term coined around 1890 that preceded X-ray and is now synonymous with it. Named for Wilhelm Roentgen, a German professor of physics. Roentgen wanted to prove his hypothesis that cathode rays could penetrate substances besides air. When he saw that he could film his thumb and forefinger and their bones on a screen, the story goes that he replaced the screen with a photographic plate and X-rayed his wife's hand. Roentgen's report of his findings, "On a New Kind of Rays," was published by the Physical-Medical Society of Wurzburg in December 1895. See: X-ray.