X-Rays Discovered
In late 1895, the German physicist Wilhelm Conrad Röntgen discovered a previously unknown form of penetrating radiation that he called X-rays. The "X" signified an unknown. Within weeks the discovery had spread around the world, giving doctors their first way to see inside the living body without surgery and opening a path to some of the most important developments in twentieth-century physics.
Röntgen was a professor at the University of Würzburg, where he was experimenting with cathode ray tubes, sealed glass tubes in which an electric current passes through a near-vacuum. Physicists such as Philipp Lenard and William Crookes had already studied the glowing "rays" produced inside these devices, and many laboratories had similar equipment. It is likely that others had unknowingly produced X-rays before him, since some had noticed fogged photographic plates near such tubes without pursuing the cause.
According to the accounts that survive, Röntgen noticed in the autumn of 1895 that a screen coated with a fluorescent chemical glowed faintly across his darkened laboratory, even though the tube was covered with black cardboard. Something invisible was passing through the cover and striking the screen. Over the following weeks he worked largely alone, finding that the rays passed through paper, wood and flesh but were stopped by denser materials such as bone and metal. He produced photographic images, including a famous one of his wife's hand showing her bones and a ring. He reported his findings in a paper at the end of December 1895.
The reaction was extraordinary. Newspapers carried the story in early 1896, and physicians began using X-rays to locate bullets, broken bones and swallowed objects almost immediately. The technology was also met with fascination and some anxiety, including jokes and rumors about its power to see through clothing. The dangers of radiation exposure were not understood at first, and early experimenters and operators suffered burns, hair loss and, in some cases, serious long-term illness before safety practices developed.
The scientific consequences were just as great. Inspired by Röntgen's work, Henri Becquerel investigated whether other substances emitted penetrating rays and discovered radioactivity in 1896, a step that led to the work of Marie and Pierre Curie. Röntgen's discovery also helped drive research into atomic structure and, later, X-ray crystallography, which would reveal the arrangement of atoms in crystals and eventually the structure of DNA. In 1901 Röntgen received the first Nobel Prize in Physics. He declined to patent his discovery, which allowed it to be adopted freely. Today, X-rays remain central to medicine, industry, security and astronomy.