Wilhelm Conrad Röntgen

German physicist

• Born: March 27, 1845
• Birthplace: Lennep, Prussia (now Remscheid, Germany)
• Died: February 10, 1923
• Place of death: Munich, Germany

Röntgen made important contributions to several areas of physics but is best known for his revolutionary discovery of X rays and his investigations of their properties.

Early Life

Wilhelm Conrad Röntgen (RAHNT-gehn) was the only child of Friedrich Conrad Röntgen, a German textile manufacturer and merchant, and Charlotte Constanza Frowein, who came from a Dutch family of merchants. When “Willi,” as he was called as a child, was three, his family moved to Apeldoorn, his mother’s hometown in Holland. There Willi attended primary public school and later became a student at Kostschool, a private boarding school. In 1862, he went to Utrecht, where he entered a secondary technical school, from which he was later expelled for refusing to inform on a fellow student who had drawn an unflattering caricature of a teacher. Although he attended some classes at the University of Utrecht, he was unable to become a formal student because he lacked a secondary-school diploma. He resolved his academic problems by passing the difficult entrance examination of the recently established Federal Institute of Technology (or Polytechnic) in Zurich, Switzerland.

In November of 1865, Röntgen began his education as a mechanical engineer. Over the next three years, he studied various technical courses but found his greatest fulfillment in a physics course taught by Rudolf Clausius, a distinguished scientist who helped found modern thermodynamics. Röntgen eventually passed his final examinations with excellent grades and received his diploma on August 6, 1869.

Röntgen remained in Zurich after graduation to work in the laboratory of August Kundt, a Polytechnic physics professor who had befriended him. Röntgen studied different gases to see if they all expanded uniformly with increases in temperature, as predicted by Gay-Lussac’s law, and discovered that some had expanded to greater volumes than the law predicted. Less than a year later, he submitted his dissertation, “Studies on Gases,” to the University of Zurich, which granted him a doctorate on June 22, 1869. While working in Zurich, Röntgen met his future wife, Anna Bertha Ludwig, who shared his interests in natural history and hiking. In 1871, when Kundt accepted a position at the University of Würzburg, Röntgen accompanied him as his assistant, and the following year he married Bertha.

Life’s Work

Röntgen’s lack of a secondary-school diploma again hindered his academic advancement at Würzburg, so he and his wife subsequently moved, with Kundt, to the Kaiser Wilhelm University in Strasbourg. On the basis of the success of his scientific investigations with Kundt, he received an offer of a full professorship from the Agricultural Academy in Hohenheim, Württemberg, in 1875. However, he was unhappy with that institution’s experimental facilities and returned to Strasbourg one and one-half years later as an assistant professor in theoretical physics.

Röntgen wrote a series of papers on the properties of gases that exhibited his growing skills as an experimental physicist, and in 1879 he was offered the chair of physics at the University of Giessen. During his ensuing nine years at Giessen, he did important work on crystals, their generation of electricity when subjected to heat (pyro-electricity), and their generation of electricity when subjected to mechanical stress (piezoelectricity). His greatest discovery, however, was his confirmation of a prediction made by the Scottish physicist James Clerk Maxwell that a magnetic field would be generated within dielectrics such as glass plates when they are moved back and forth between two electrically charged plates. The Dutch physicist Hendrik Antoon Lorentz named this effect, which Röntgen detected with a sensitive device, the “roentgen current.” Röntgen later considered this discovery as an important step in his work on X rays.

Recognition of Röntgen’s accomplishments in physics brought him offers from other universities. In 1888, he turned down the chair of physics at the University of Utrecht but accepted the University of Würzburg’s proposal to occupy Kundt’s former position. During his first six years at Würzburg, he published seventeen papers on such topics as the properties of solids and liquids. His fame as a physicist and respect for his political sagacity led to his election in 1894 to the rectorship of the university. One year later, he left his position as rector and took up a new field of scientific research.

Philipp Lenard, a Hungarian-German physicist, had been studying cathode rays by means of an apparatus he constructed that allowed what some called “Lenard rays” to enter the air beyond the apparatus. Röntgen became interested in exploring these rays, and on November 8, 1895, he wrapped a cathode-ray tube with a “close-fitted shield of black paper” to observe the narrow beam of rays from the tube. By chance, he noticed that a paper coated on one side with barium platinocyanide and located some distance from the tube glowed with a brilliant fluorescence. This puzzled him because cathode rays had an effective range of only a few centimeters. He therefore suspected that he might have come upon a previously unknown kind of radiation.

Over the next several weeks, Röntgen investigated these new rays by directing the invisible beam through paper, wood, and thin sheets of aluminum, copper, silver, gold, and platinum. He was amazed to discover that these materials were transparent to the rays, which were impeded only by sheets of lead. He also discovered that these “X rays”—as he called them, “for the sake of brevity”—traveled in straight lines, were unaffected by magnets or electrically charged plates, and could ionize gases. Unlike light rays, X rays could neither be reflected from a mirror nor refracted in a prism. On the other hand, they could, like light rays, blacken photographic plates; when Röntgen directed an X-ray beam through his wife’s hand and onto a photographic plate, an image of the bones wondrously appeared.

On December 28, 1895, when Röntgen announced his discoveries to the world, both scientists and the public were fascinated by these mysterious rays that could reveal the skeletons inside living humans. Physicians in Europe and America quickly put them to medical use in diagnosing broken bones and foreign objects in human bodies. Röntgen knew that his rays had commercial potential, but, out of altruism, he refused to patent his discovery.

Kaiser William II was the first dignitary to honor Röntgen with an award, on January 14, 1896. The kaiser’s award was following by many others, culminating in Röntgen’s reception of the first Nobel Prize in Physics in 1901. By that time he had accepted a distinguished position as professor of experimental physics and head of the physical institute at the University of Munich, where he would remain for the next twenty years. During that period, he witnessed X rays being used by physicians to treat skin diseases and cancer and by physicists to study atomic arrangements in crystals. His own work centered on crystals, their electrical conductivity, and the influence of radiation on them.

During his professorship at Munich, Röntgen dedicated himself to what he saw as his sacred duty to advance scientific knowledge. However, he also had to take time to defend himself against the claims that other scientists had observed the effects of X rays before him. However, although Lenard may have observed fluorescence near a Crookes tube, he never investigated this observation in the way that Röntgen later did.

Although Röntgen received many honors on the occasion of his seventieth birthday in 1915, the privations brought by World War I had a negative influence on his scientific work. After the war he was deeply affected by the sufferings of his wife, who died in 1919 after a long illness. Furthermore, he, like most Germans, was troubled by postwar political turmoil, ruinous inflation, and food shortages. His own health began to fail, and other physicists took over his work. Röntgen diagnosed his condition as carcinoma of the intestine. He died in Munich during the morning of February 10, 1923, and his ashes were later deposited at the family grave in Giessen.

Significance

The medical applications of X rays were quickly recognized, but the impact of X rays on physics and chemistry proved to be even more momentous. For example, Henry Becquerel’s investigation of X rays led directly to his discovery of radioactivity. In 1912, Max von Laue suggested that X rays might be diffracted by crystals, and scientists soon discovered that diffracted rays allowed them to determine the three-dimensional structures of many crystals. The English physicist Henry Moseley discovered characteristic X rays emitted by each of the chemical elements, leading to a deeper understanding of the periodic table. So significant were these and other discoveries that some scholars called Röntgen’s discovery of X rays the event that initiated the “Second Scientific Revolution” because it ushered in the modern physics of the twentieth century, just as the discoveries of Galileo Galilei, Johannes Kepler, and Isaac Newton had forged the New Science of the seventeenth century.

With the passage of time, practical uses of X rays multiplied. So many medical applications were developed that an entirely new medical specialty, radiology, was created. Engineers used X rays to study stresses in various materials and the strengths of welds. Dentists used them to detect cavities in teeth. Archaeologists used them to study mummies and other artifacts without harming the objects. Computer technicians used them to etch integrated circuits. Workers and airports and seaports used them to inspect luggage and cargo. Astronomers studied X rays emanating from different parts of the universe to help them understand stars, pulsars, and black holes. In computerized axial tomography scientists used high-resolution X-ray pictures to study healthy and diseased human brains. These examples do not exhaust the significant applications that continue to be discovered over a century after Röntgen first found and characterized these powerful rays.

Bibliography

Baigrie, Brian S. Scientific Revolutions: Primary Texts in the History of Science. Upper Saddle River, N.J.: Pearson Prentice Hall, 2004. This anthology, based on the conviction that scientific discoveries are best understood through classic texts, contains a chapter, “Shadow Pictures,” with an English translation of Röntgen’s “On a New Type of Rays” preceded by a helpful historical introduction.

Bleich, Alan Ralph. The Story of X-Rays from Röntgen to Isotopes. New York: Dover, 1960. Bleich, a professor of radiology, devotes the first two chapters of his book to Röntgen’s discovery of X rays and the remaining chapters to their applications in medicine, industry, scientific research, and art.

Glasser, Otto. Wilhelm Conrad Röntgen and the Early History of Roentgen Rays. Springfield, Ill.: Charles C Thomas, 1995. This reprint, with a new introduction, derives from what was once the standard Röntgen biography first published in 1931, expanded in a second edition in 1945 to commemorate the centennial of Röntgen’s birth, and revised again in 1959.

Kevles, Bettyann H. Naked to the Bone: Medical Imaging in the Twentieth Century. New Brunswick, N.J.: Rutgers University Press, 1997. This narrative history for the nonscientist analyzes how X rays fostered such new technologies as computerized tomography and magnetic resonance imaging. The author also discusses how X rays transformed medicine, criminology, and certain visual, literary, and fine arts.

Nitski, W. Robert. The Life of Wilhelm Conrad Röntgen, Discoverer of the X Ray. Tucson: University of Arizona Press, 1971. This popular biography, which incorporates primary source material into the narrative, concentrates on Röntgen’s researches before, during, and after the discovery of X rays. Chronology, bibliography, and index, with English translations of Röntgen’s three most famous papers.