It was not so much as a physicist but rather as a keen amateur photographer that Wilhelm Conrad Roentgen uncovered the secret of the X-ray and its potential use as a tool in medical diagnosis in 1895.
As Professor of Physics at Wurzburg University in Germany, Roentgen was working in his laboratory when he made his discovery - by accident. He was experimenting with an electric current flow through a gas-filled tube when he noticed a strange glow coming from a small scree, covered in a chemical called barium platino-cyanide, which he had left lying around. Putting his hand between the tube and screen he saw, to his surprise, the shadowy images of the bones of his hand in eerie outline. With his keen interest in photography, Roentgen hit upon the idea of substituting a photographic plate for the screen. Using his wife's left hand he took the first known X-ray picture: a clear, permanent image of the bone structure of her hand, obscured only at the place where she was wearing her gold ring.
At first he did not understand what the rays were - he simply called them 'X-rays'. We now know that X-rays are invisible rays of the same general kind as the rays of heat, light and radiowaves. Roentgen did not know this, but he appreciated their value for photography inside the living body and published a paper entitled 'On a new kind of ray' in the Transactions of the Wurzburg Physical-Medical Society. X-rays were soon put to use in Vienna for medical diagnosis, gaining Roentgen worldwide fame for his chance discovery. The rays became known as 'Roentgen rays' and, in 1901, he received the very first Nobel prize for physics.