For the first two decades of his scientific career, Wilhelm Conrad Röntgen (1845-1923) studied a fairly diverse variety of topics, including the specific heats of gases, the Faraday effect in gases, magnetic effects associated with dielectric materials, and the compressibility of water. He is most famous, however, for his discovery in 1895 of X rays, which had a revolutionary effect not only on physics but also on a number of other areas, particularly medicine, and for this he was awarded the first Nobel Prize in physics in 1901.
Wilhelm Conrad Röntgen was born in Lennep, Germany, on March 27, 1845. He was the only child of Friedrich Conrad Röntgen and the former Charlotte Frowein. His father was a textile merchant who came from a long line of metal workers and cloth merchants. His mother had been born in Lennep but then moved with her family to Amsterdam, where they had become wealthy as merchants and traders. When Röntgen was three years old, his family moved to Apeldorn, Holland. Otto Glasser speculates in Dr. W. C. Röntgen that the revolution of 1848 may have been a factor in this move because the family lost its German citizenship on May 23, 1848, and became Dutch citizens a few months later. In any case, Röntgen received his primary and secondary education in the public schools of Apeldorn and at a private boarding school in Middelann.
In December 1862, Röntgen enrolled at the Utrecht Technical School. His education at Utrecht was interrupted after about two years, however, when a childish prank went awry. He confessed to having drawn a caricature of an unpopular teacher for which another student had been responsible. As punishment, Röntgen was expelled from school, and his education was stalled until January 1865, when he was given permission to attend the University of Utrecht as an irregular student. There he attended classes on analysis, physics, chemistry, zoology, and botany. His future still seemed bleak, however, and, according to Glasser, "both Wilhelm and his parents had become resigned to his seeming inability to adjust to the requirements of the Dutch educational system and to obtain the credentials necessary to become a regular university student."
A friend of Röntgen's told him about the liberal admission policies at the Swiss Federal Institute of Technology in Zurich. Röntgen applied and was admitted at Zurich, and he arrived there to begin his studies in the mechanical technical branch of the institute on November 16, 1865. Over the next three years, Röntgen pursued a course of study that included classes in mathematics, technical drawing, mechanical technology, engineering, metallurgy, hydrology, and thermodynamics. On August 6, 1868, he was awarded his diploma in mechanical engineering. His degree had come in spite of his rather irregular attendance at classes. He later told Ludwig Zehnder that the lake and mountains surrounding Zurich were "too tempting." As a result, he became a devoted mountain climber and boater but an undistinguished student. Only when one of his professors told Röntgen that he would fail his examinations did he settle down to his studies.
At Zurich, the most important influence on Röntgen was the German physicist August Kundt. Kundt suggested to him that he do his graduate studies in physics rather than engineering, and Röntgen took his advice. On June 22, 1869, he was granted his doctoral degree for a thesis entitled "Studies about Gases." Kundt then asked him to become his assistant, an offer he quickly accepted. A year later, when Kundt was offered the chair of physics at the University of Würzburg in Germany, he brought Röntgen with him as his assistant.
While still in Zurich, Röntgen had met his future wife, Anna Bertha Ludwig, the daughter of a German revolutionary who had emigrated to Switzerland. They were married on January 19, 1872, after his move to Würzburg. The couple never had children of their own, although in 1887 they did adopt his wife's six-year-old niece Josephine Bertha.
After two years at Würzburg, Kundt moved once more, this time to the newly established University of Strasbourg in France. Again, he asked Röntgen to accompany him as his assistant. At Strasbourg, in March 1874, Röntgen finally achieved a long-delayed ambition: He was appointed a privatdozent at the university, his first official academic appointment. The appointment was the result of more liberal policies at Strasbourg; his lack of the necessary credentials had prevented him from receiving a formal appointment in any German university.
In 1875, Röntgen accepted a position as professor of physics at the Hohenheim Agricultural Academy. Missing the superb research facilities to which he had become accustomed in Strasbourg, however, he returned there in 1876 as associate professor of physics. Three years later he was appointed professor of physics at the University of Giessen in Germany, where he remained until 1888. He then returned to the University of Würzburg to take a joint appointment as professor of physics and director of the university's Physical Institute. Röntgen would remain at Würzburg until 1900, serving as rector of the university during his last six years there.
Röntgen wrote forty-eight papers on a diverse range of phenomena including the specific heats of gases, the heat conductivity of crystals, the Faraday and Kerr effects, the compressibility of solids and liquids, and pyroelectricity and piezoelectricity. Probably his most significant contribution during this period was a continuation of research originally suggested by James Clerk Maxwell's theory of electromagnetism. That theory had predicted that the motion of a dielectric material within an electrostatic field would induce a magnetic current within the dielectric material. During his last year at Giessen, Röntgen completed studies that confirmed this effect, a phenomenon for which Hendrik Lorentz suggested the name "röntgen current."
Yet there is no doubt that the discovery for which Röntgen will always be most famous is that of X rays. In 1894 Röntgen began research on cathode rays, which was then one of the most popular topics in physics. Much of the fundamental research on this topic had been carried out in the 1870s by the English physicist William Crookes. Crookes had found that the discharge of an electrical current within a vacuum tube produces a beam of negatively charged rays that causes a fluorescence on the glass walls of the tube. A number of scientists had followed up on this research, trying to discover more about the nature and characteristics of Crookes's cathode rays.
After repeating some of the earlier experiments on cathode rays, Röntgen's own research took an unexpected turn on November 8, 1895. In order to observe the luminescence caused by cathode rays more clearly, Röntgen darkened his laboratory and enclosed the vacuum tube he was using in black paper. When he turned on the apparatus, he happened to notice that a screen covered with barium platinocyanide crystals about a meter from the vacuum tube began to glow. This observation was startling, because Röntgen knew that cathode rays themselves travel no more than a few centimeters in air. It was not they, therefore, that caused the screen to glow.
Over the next seven weeks, Röntgen attempted to learn as much as he could about this form of energy. He discovered that its effect could be detected at great distances from the vacuum tube, suggesting that the radiation was very strong. He learned that the radiation passed easily through some materials, such as glass and wood, but was obstructed by other materials, such as metals. At one point, he even saw the bones in his hand as he held out a piece of lead before it. He also discovered that the radiation was capable of exposing a photographic plate. Because of the unknown and somewhat mysterious character of this radiation, Röntgen gave it the name X strahlen, or X rays.
On December 28, 1895, seven weeks after his first discovery of X rays, Röntgen communicated news of his work to the editors of a scientific journal published by the Physical and Medical Society of Würzburg. Six days earlier, he had made the world's first X-ray photograph, a picture of his wife's hand. Within weeks, news of Röntgen's discovery had reached the popular press, and the general public was captivated by the idea of seeing the skeletons of living people. On January 13, 1896, Röntgen was ordered to demonstrate his discovery before the Prussian court and was awarded the Prussian Order of the Crown, Second Class, by the Kaiser.
Röntgen actually devoted only a modest amount of attention to his momentous discovery. He wrote two more papers in 1896 and 1897, summarizing his findings on X rays, and then published no more on the subject. Instead, he went back to his work on the effects of pressures on solids. Röntgen chose not to ask for a patent on his work and refused the Kaiser's offer of an honorific "von" for his name. He did, however, accept the first Nobel Prize in physics, awarded to him in 1901. Even then, however, he declined to make an official speech and gave the prize money to the University of Würzburg for scientific research. His discovery had generated a surprising number of personal attacks, with many dismissing it as an accident or attributing it to other scientists. Glaser speculates that "Röntgen's reticence, bordering on bitterness with advancing years, was doubtless a defense against these attacks."
Röntgen had declined offers from other universities for many years, but in 1900, at the special request of the Bavarian government, he abandoned his chair at Würzburg in order to accept a similar position at the University of Munich. The decision was not an easy one for Röntgen because, as Zehnder later noted, "the nice quiet laboratory at Würzburg suited him so well." Röntgen remained at Munich until 1920 when he retired, a decision he made at least partly because of his grief over his wife's death a year earlier. She had suffered from a lingering disorder during which she became addicted to morphine. Zehnder was later to write that she was always "Röntgen's most understanding and truest friend."
Germany's defeat in World War I also had its effect on Röntgen: The inflationary period following the war resulted in his bankruptcy. He spent the last few years of his life at his country home at Weilheim, near Munich. He died there on February 10, 1923, after a short illness resulting from intestinal cancer. Among the many awards given to him were the Rumford Medal of the Royal Society (1896), the Royal Order of Merit, Bavarian (1896), the Baumgaertner Prize of the Vienna Academy (1896), the Elliott-Cresson Medal of the Franklin Institute (1897), the Barnard Medal of Columbia University (1900), and the Helmholtz Medal (1919).
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