In 1895, Wilhelm Conrad Röntgen (1845-1923), professor of physics at the University of Wurzburg, discovered a previously unknown type of radiation that was capable of penetrating matter.
Röntgen was conducting experiments with a Crookes’ tube – an early type of cathode ray tube. This was a glass bulb containing electrodes at each end. After the air in the tube was emptied and a high voltage was applied, streams of electrons (cathode rays) were emitted from the negative electrode and the tube produced a fluorescent glow.
He shielded the tube with heavy black paper, but was surprised to notice green light coming from a fluorescent screen some distance away. Convinced that his tube covering was light-tight, he theorised that the screen was responding to some new kind of radiation that could penetrate the paper, and began a series of further experiments to test his idea. He soon found that these unknown ‘X-rays’ could pass through many substances, including...