Roentgen, Wilhelm

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ROENTGEN, WILHELM (1845–1923), Prussian scientist, discoverer of x-rays.

Wilhelm Conrad Roentgen was born on 27 March 1845 in Lennep, Prussia (now Remscheid, Germany). During the Revolution of 1848, the family moved to Apeldoorn, Netherlands, Roentgen's home until 1870. He then returned to Germany, dying in Munich on 10 February 1923.

After earning a doctorate in physics from the University of Zurich in 1869, Roentgen worked at various German universities before becoming, in 1879, professor and chair of physics at the Hessian Ludwigs University in Giessen. There, he became increasingly well-known for research into the effect of electricity on gases and crystals, an investigative area that was revealing a relationship between electricity, light rays, and magnetism. In 1888, Roentgen provided experimental proof of the Faraday-Maxwell theory of electrodynamic power, which earned him an invitation to head the Physics Institute at the Julius Maximilians University in Wurzburg. He remained there until 1900, becoming president of the university in 1894, then moved to Munich to direct the Physics Institute at the Ludwig Maximilians University, retiring in 1920.

During his early years at Wurzburg, Roentgen focused his research on the effect of pressure on water and other liquids. In mid-1894, however, his interest was piqued by progress in the study of cathode rays, a surge of electrons produced when electricity passes through a vacuum tube. In order to familiarize himself with recent research in that area, Roentgen began repeating experiments reported by other physicists. It was the work of Philipp Lenard that led him to his groundbreaking discovery of x-rays on 8 November 1895.

An invention by Lenard allowed scientists to study cathode rays flowing out of a vacuum tube, in addition to rays confined inside one. In air, the rays caused a board coated with barium platinocyanide to fluoresce, but since they faded quickly, the board had to stand inches from the equipment. Preparing to witness this phenomenon for himself, Roentgen switched on the electricity activating the tube but accidentally left the board propped some feet away. To his surprise, it was nevertheless glowing. Since cathode rays could not be present at that distance, the vacuum tube must also have been emitting another form of radiation. Unable to identify that, Roentgen himself dubbed it an "x-ray."

Over the next few weeks, Roentgen spent most of his waking hours studying x-rays. After determining that they traveled farther in air than any ray yet known to science, he wondered whether they would pass through solid objects. Earlier, the German physicist Hermann von Helmholtz had argued that very-short-wave light rays should do so. X-rays proved this theory correct, penetrating even metal, except for lead. Objects held in front of the vacuum tube caused shadowy marks within the fluorescence, and it was while testing a piece of lead that Roentgen saw the shape of his own finger bones, a chilling observation that temporarily made him doubt his own sanity. Would anyone believe him? Other scientists would need to see such a sight for themselves. Again, Roentgen drew inspiration from Lenard, who had reported that fluorescence from cathode rays darkened a photographic plate. The photographs Roentgen made to document his discovery of x-rays were sensational: the best known of them shows the bones in Mrs. Roentgen's hand.

In late December, Roentgen communicated his findings to the Physical-Medical Society of Wurzburg, which published his paper in its last journal issue for 1895. By the first week of January, the news was already spreading around the world. Roentgen's discovery sparked a revolution in both medicine and physics. So simple was the technology involved that the first diagnostic use of x-rays occurred on 7 January 1896, and physicians were soon also using them to treat skin diseases and tumors. The discovery also inspired other physicists investigating radiation: the atomic age was just around the corner.

Roentgen became a celebrity, receiving innumerable awards, including the first Nobel Prize for physics in 1901. Some people thought the honors more properly belonged to Lenard and other cathode ray researchers, whose work had led directly to the discovery. The Nobel Prize committee was struck, however, not only by Roentgen's actual identification of x-rays but also by the scope of his consequent gift to humanity. His observations had generated successful treatments for hitherto fatal or crippling diseases and injuries. "Roentgen's discovery has already brought so much benefit to mankind," said the presenter at the award ceremony, "that to reward it with the Nobel Prize fulfils the intention of the testator [Alfred Nobel] to a very high degree."

See alsoBody; Nobel, Alfred; Science and Technology.


Gherman, Beverly. The Mysterious Rays of Dr. Röntgen. Illustrated by Stephen Marchesi. New York, 1994. For younger readers.

Glasser, Otto. Wilhelm Conrad Röntgen and the Early History of the Röntgen Rays. Edited by Jessie C. Tucker. Springfield, Ill., 1934. Translation of Wilhelm Conrad Roentgen und die Geschichte der Roentgenstrahlen (1931). Primarily concentrates on technology. Contains the text of Roentgen's three papers on x-rays, and a chapter of reminiscences by Margret Boveri, a Roentgen family friend.

Mould, Richard F. A Century of X-rays and Radioactivity in Medicine: With Emphasis on Photographic Records of the Early Years. Bristol, U.K., and Philadelphia, 1993. Contains an extensive and entertaining collection of illustrations.

Nitske, W. Robert. The Life of Wilhelm Conrad Röntgen: Discoverer of the X Ray. Tucson, Ariz., 1971. Includes a chapter on claims by others to have discovered x-rays.

"The Nobel Prize in Physics 1901." Available from

L. Margaret Barnett