X rays

The development of X-ray photography, or radiology, was an enormous leap into the future: For the first time, physicians could see inside the body without opening it. With X rays surgeons could quickly diagnose fractures, tumors, and other ailments and plan more intricate operations. As a result, surgery rapidly grew in sophistication.
Early in 1895 German physicist Wilhelm Conrad Roentgen was experimenting with a Crookes tube—a pear-shaped glass tube emptied of air with electrodes (metal wires) sealed into opposite ends of the tube. When the negative electrode, or cathode, received a high-voltage electric current, it glowed white-hot and emitted a stream of invisible, electrically charged particles called cathode rays. These rays moved towards the positive electrode, or anode, of the tube. If only a little air remained inside the Crookes tube, the cathode rays striking the glass at the other end of the tube would produce a yellow-green fluorescence.
Roentgen's experiments had confirmed another physicist's observation that cathode rays could pass through an aluminum-covered window in the wall of a Crookes tube. To discover whether cathode rays could also go through the glass wall of a Crookes tube, he placed a piece of paper coated with a barium salt near the tube's anode. Such paper was known to fluoresce when hit with cathode rays. He expected the fluorescence to be faint, so he covered the tube with black cardboard to block the tube's fluorescence and to better help him see. He also darkened his laboratory.
While testing the tube to see whether any fluorescence was visible through the cardboard, Roentgen noticed a strange glow some distance away. Lighting a match for light to see, he discovered that the glow was coming from another piece of coated paper that was about a meter away from the Crookes tube. Repeatedly turning his tube on and off, he learned that the paper only glowed when the tube was on. The paper still fluoresced when he moved it even farther away and even when he shielded it, first with a pack of cards and then with a book.
Roentgen knew that cathode rays were not strong enough to cause this distant fluorescence. There could only be one explanation: The Crookes tube was producing previously unknown kinds of electromagnetic waves, which he later called X rays. Further experiments showed that these new X rays would not go through lead and would go only partly through other metals.
In December 1895 he X-rayed his own fingers holding a small lead pipe. To his astonishment, the developed pictures revealed not only the shadow of the pipe but also the bones of two of his fingers. He later X-rayed the left hand of his wife, Bertha, who had two gold rings on her fourth finger, and showed the terrified woman a picture of her own bones, complete with rings.
Roentgen's preliminary report, entitled On a New Kind of X Ray, was published only a few days after he submitted it, a record for rapid publication in science. In 1901 Roentgen became the first scientist ever to receive the Nobel Prize in physics.
X rays were used immediately for medical diagnosis but did not become a routine procedure until the 1920s. In the decades that followed, technological advances allowed X rays to outline individual organs and organ systems, as well as arteries and veins. In 1972 researchers developed the computerized tomography (CAT) scan, a sophisticated X-ray technology that produces computer-generated cross-sectional views of the body.
source: encarta encyclopedia