<P> There are conflicting accounts of his discovery because Röntgen had his lab notes burned after his death, but this is a likely reconstruction by his biographers: Röntgen was investigating cathode rays from a Crookes tube which he had wrapped in black cardboard so that the visible light from the tube would not interfere, using a fluorescent screen painted with barium platinocyanide . He noticed a faint green glow from the screen, about 1 meter away . Röntgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow . He found they could also pass through books and papers on his desk . Röntgen threw himself into investigating these unknown rays systematically . Two months after his initial discovery, he published his paper . </P> <P> Röntgen discovered their medical use when he made a picture of his wife's hand on a photographic plate formed due to X-rays . The photograph of his wife's hand was the first photograph of a human body part using X-rays . When she saw the picture, she said "I have seen my death ." </P> <P> There was immediate interest from researchers for the X-ray . A.A. Campbell - Swinton and Nikola Tesla were amongst the firsts to test the new discovery . In 1896, Thomas Edison investigated materials' ability to fluoresce when exposed to X-rays, and found that calcium tungstate was the most effective substance . Around March 1896, the fluoroscope he developed became the standard for medical X-ray examinations . Nevertheless, Edison dropped X-ray research around 1903, even before the death of Clarence Madison Dally, one of his glassblowers . Dally had a habit of testing X-ray tubes on his hands, and acquired a cancer in them so tenacious that both arms were amputated in a futile attempt to save his life . </P> <P> The first use of X-rays under clinical conditions was by John Hall - Edwards in Birmingham, England on 11 January 1896, when he radiographed a needle stuck in the hand of an associate . On February 14, 1896 Hall - Edwards was also the first to use X-rays in a surgical operation . In early 1896, several weeks after Röntgen's discovery, Ivan Romanovich Tarkhanov irradiated frogs and insects with X-rays, concluding that the rays "not only photograph, but also affect the living function". </P>

When was the first x ray machine invented