First Dental Radiograph (1896)

In 1895, the German physicist, Wilhelm Conrad Röntgen (1845-1923), who was 50 years old by then, studied cathode rays with Crookes tubes. He was more precisely concerned with the penetration of the rays through the glass. At the time, it had already been established that cathode rays could pass through the tube wall and penetrate a few centimetres in the air. In the evening of November 8, during his preliminary work, he decided to cover the tube with a black cardboard pannel. He thus observed that a screen which was covered with a layer of platinocyanide barium and which had been placed incidentally in front of the tube became fluorescent during the discharge. However, he knew that at this distance, the fluorescence could not be caused by cathode rays. He thus pushed further the screen and noticed the persistence of fluorescence despite the increasing layer of air it had to cross. Then, he inserted objects between the light bulb and the screen: a sheet of paper, aluminium foil, wood, glass and even a thousand-page book. Each time, the fluorescence persisted: he concluded that he had just discovered some ray which was distinct to that produced by the cathode and which was very penetrating for it was able to go through matter. As those rays were unknown by then, he named them “the X rays”, after the unknown in mathematics. He devoted the last weeks of 1895 to manipulate X rays by himself, and managed to allocate them the following features: