Wilhelm Konrad Roentgen (1845-1923), German experimental physicist and discoverer of X-rays. In 1895, while using a discharge tube (in which an electric discharge is passed through a gas at low pressure) in a darkened room, Roentgen noticed that a card coated with barium platinocyanide glowed when the tube was switched on. The effect could penetrate walls and metal sheets. Roentgen named this effect X-ray radiation, and suggested that it consisted of electromagnetic rays with a shorter wavelength than light. He was awarded the first Nobel Prize for Physics in 1901. X-rays are today widely used in medicine as a diagnostic tool. Artwork from A Travers l'Electricite (G. Dary, Paris, 1900).