Röntgen Discovers X Rays Summary

  • Last updated on November 10, 2022

Wilhelm Conrad Röntgen’s discovery of X rays had both practical and philosophical consequences. The penetrating power of this wavelength of electromagnetic radiation led to its wide use in medical and industrial applications. Meanwhile, the vision of the world revealed by X-radiography seemed to confirm the late nineteenth century worry that the world was less solid and less stable than it seemed.

Summary of Event

X rays were discovered in 1895 by Wilhelm Conrad Röntgen, a professor of physics at the University of Würzburg. He was investigating the radiation produced in a partially evacuated glass bulb when a high voltage was applied. Sir William Crookes in 1869 had published a research report in which he described the bright glow that occurred inside such a bulb. Another physicist, Philipp Lenard Lenard, Philipp , had then shown that the electrical discharge inside the glass bulb could penetrate a thin aluminum window, producing an external beam that traveled through several centimeters of open air. This beam was called a “cathode ray,” because it originated at the negative voltage terminal, or cathode. Lenard was able to trace the path of cathode rays by coating a small screen with fluorescent paint that glowed in the dark when radiation struck it. He showed that cathode rays could be deflected by a magnet. X rays Medicine;X rays Röntgen, Wilhelm Conrad [kw]Röntgen Discovers X Rays (Nov. 9, 1895) [kw]Discovers X Rays, Röntgen (Nov. 9, 1895) [kw]X Rays, Röntgen Discovers (Nov. 9, 1895) X rays Medicine;X rays Röntgen, Wilhelm Conrad [g]Germany;Nov. 9, 1895: Röntgen Discovers X Rays[6060] [c]Physics;Nov. 9, 1895: Röntgen Discovers X Rays[6060] [c]Science and technology;Nov. 9, 1895: Röntgen Discovers X Rays[6060] [c]Inventions;Nov. 9, 1895: Röntgen Discovers X Rays[6060] [c]Photography;Nov. 9, 1895: Röntgen Discovers X Rays[6060] Crookes, Sir William Hertz, Heinrich Lenard, Philipp Zehnder, Ludwig

Röntgen was an experienced experimentalist with twenty-five years of laboratory research and more than forty technical publications. Using the same type of apparatus as Crookes Crookes, Sir William and Lenard had used, he first confirmed their observations for himself. In order to see the external beam more clearly, he surrounded the glass bulb with opaque, black paper, so the light produced inside the bulb would be blocked out and the external beam would show up more clearly. On November 9, 1895, according to his laboratory notebook, he noticed something quite unusual. A piece of cardboard coated with fluorescent paint, lying on the table more than a meter away, started to glow whenever the electric discharge was turned on. This was a startling observation, because cathode rays could not travel that far. Was there another, unknown type of radiation coming through the black paper?

Wilhelm Conrad Röntgen.

(Library of Congress)

Working by himself, Röntgen began a systematic investigation of the mysterious radiation. He observed fluorescence at a distance of as much as two meters from the discharge tube. Since the radiation had penetrated opaque, black paper, he decided to test various other materials for their transparency. Even behind a book of one thousand pages, he found that the fluorescent screen lit up brightly. Blocks of wood and sheets of aluminum transmitted the radiation fairly well, but two millimeters of lead was enough to block it. When holding his hand between the discharge apparatus and the fluorescent screen, Röntgen was able to see the shadow of the bones inside the faint outline of his fingers.

Further experiments showed that photographic Photography;and X rays[X rays] X rays;and photography[Photography] plates were sensitive to the radiation. This enabled Röntgen to make a permanent record of his observations. He had to be careful not to store unused photographic plates near the apparatus, however, or they would become fogged by stray radiation. In his publications, Röntgen referred to the new type of radiation as “X rays,” because they were a mystery. He used a glass prism to see if X rays could be refracted like ordinary light, but the result was negative. He also found that X rays were not reflected by a mirror and could not be focused by a lens. Diffraction gratings, which had been used to measure the wavelengths of visible light with high precision, had no effect on X rays, and a magnet caused no deflection in their path.

On December 22, 1895, Röntgen asked his wife to help him in the laboratory. He placed an X-ray tube just underneath a table, while she held her hand on the table surface with a photographic Photography;and X rays[X rays] X rays;and photography[Photography] plate above her hand. The exposure time was about five minutes. When Röntgen developed the photograph, it showed the bones in her hand with her wedding ring on one finger. A photography assistant made multiple prints from this and several other negatives. On January 1, 1896, Röntgen sent a ten-page article with photographs to the Physical-Medical Society of Würzburg, as well as to colleagues at other universities. The pictures created a sensation. Nothing like them had ever been seen before.

Within a few days, newspapers all over Europe had published stories and photographs about this new scientific development. A flood of messages came to Röntgen with invitations to give lectures and demonstrations. He turned them all down, except one that he could not refuse from the emperor of Germany, William I. On January 13, Röntgen traveled to Berlin with his X-ray apparatus and showed to the assembled court how metal objects inside a closed box could be photographed Photography;and X rays[X rays] X rays;and photography[Photography] . On January 23, he gave a lecture to the faculty and students at his own university. He told the audience about his experiments, giving credit for earlier contributions to Heinrich Hertz Hertz, Heinrich , who had discovered radio waves in 1888, and to Lenard Lenard, Philipp . Toward the close of the lecture, Röntgen made an X-ray photograph of a faculty colleague’s hand, which was quickly developed and passed around the room. Prolonged applause came as the lecture ended.

Over the next several weeks, Röntgen received letters from many scientists who were experimenting with X rays. One person sent a photograph of a fish showing its detailed bone structure. His friend Ludwig Zehnder Zehnder, Ludwig , whom he had known since graduate school in Zürich, took several photographs of the human body, which he pasted together to obtain a complete skeleton from head to foot. There were some crackpot letters, such as the one asking for a sum of money to solve the secrets of weather forecasting with X rays. The greatest honor for Röntgen was to be awarded the Nobel Nobel Prizes Prize in 1901, the first year in which the award was given.


Röntgen felt that the benefits of X rays should be available to humankind without restrictions. He therefore did not take out a patent on his discovery, although doing so could have made him wealthy. His apparatus was not expensive or difficult to duplicate. The most difficult aspect of its construction was the need for a professional glass blower to make a specialized glass bulb with two metal electrodes inside that were connected by wires going through the glass to two terminals on the outside. Many hospitals and research laboratories were able to set up their own X-ray machines. Within one year of Röntgen’s initial publication, nearly one thousand articles on X rays had appeared in various technical journals.

The medical profession enthusiastically welcomed X rays as a new diagnostic tool. Doctors were able to determine the severity of broken bones and to locate swallowed objects or bullets embedded in the body. Annual chest X rays for school children became a routine procedure to diagnose early signs of tuberculosis Tuberculosis . Irradiation of cancerous tumors was found to be a beneficial therapy, as long as the dose was carefully regulated. In the 1970’s, a major improvement in X-ray technology, called the CT scan, was developed. A narrow beam of X rays was swept across a portion of the body from many different angles, and the information was then correlated by a computer to produce a picture on a screen.

Among its industrial applications, the X-ray apparatus came into common use at airports to inspect baggage before boarding. X rays have been used to search for hidden microphones in the wall of a room before a diplomatic conference. In the pipeline industry, after individual sections of pipe had been welded together, portable X-ray machines have been used to detect possible hairline cracks at the welds that might later allow fluid to leak out. X-ray analysis has been widely used by chemists Chemistry;and X rays[X rays] to determine the structure of complex molecules, such as the deoxyribonucleic acid (DNA) DNA;and X-ray analysis[X ray analysis] helix. Röntgen’s discovery of X rays stands as a good example of pure research that led to a multitude of practical applications that could not have been anticipated.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Farmelo, Graham. “The Discovery of X-rays.” Scientific American, November, 1995, 86-91. Describes Röntgen’s experimental setup and contains reprints of the earliest X-ray photographs, including the one of his wife’s hand.
  • citation-type="booksimple"

    xlink:type="simple">Hart, Michael H. The One Hundred: A Ranking of the Most Influential Persons in History. New York: Galahad Books, 1982. A fascinating collection of short biographies about the most famous artists, political leaders, theologians, and scientists, including Röntgen.
  • citation-type="booksimple"

    xlink:type="simple">Kevles, Bettyann. Naked to the Bones: Medical Imaging in the Twentieth Century. Reading, Mass.: Addison-Wesley, 1998. Discusses Röntgen’s discovery and its medical applications, with modern improvements in imaging technology using computers; intended for the general reader.
  • citation-type="booksimple"

    xlink:type="simple">Nitske, W. Robert. The Life of Wilhelm Conrad Röntgen: Discoverer of the X Ray. Tucson: University of Arizona Press, 1971. The best biography of Röntgen available in English, containing fascinating anecdotes about his personal life and scientific career. Photographs, a bibliography, and translations of his three X-ray publications.
  • citation-type="booksimple"

    xlink:type="simple">Turner, G. L. “Röntgen, Wilhelm Conrad.” Dictionary of Scientific Biography. Vol. 11. New York: Charles Scribner’s Sons, 1981. An authoritative, short biography of Röntgen’s life and professional career.
  • citation-type="booksimple"

    xlink:type="simple">Walker, James S. Physics. 2d ed. Upper Saddle River, N.J.: Pearson/Prentice Hall, 2004. College-level textbook describing the operation of an X-ray tube, including Röntgen’s contribution.

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