Wilhelm Röntgen

• 1. Introduction

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  In the late afternoon of the 8th of November 1895, the German physicist Wilhelm Röntgen stood in a darkened laboratory in Würzburg and noticed something that should not have been there. He was alone, he was testing nothing more dramatic than a cardboard cover, and he turned away from his apparatus to prepare the next step. Then the glow caught his eye.

  Röntgen was an experimental physicist, a man who built equipment, pushed electricity through it and watched what happened. In the weeks after that evening he stopped going home to sleep. What was he actually looking at? Who was the first person to see the result of his work with their own eyes, and how did they react? And why would a man who had found something so valuable decide he did not want to own it? Before any of that, there is a simpler puzzle. How did a boy without a country, a diploma or a settled home end up in that room?

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• 2. Lecture Halls and Borders

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  Wilhelm Conrad Röntgen was born on the 27th of March 1845 in Lennep, a town that is now part of Remscheid in Prussia. He was the only child of Friedrich Conrad Röntgen, a merchant and cloth manufacturer, and Charlotte Constanze Frowein. In 1848 the family moved to the Netherlands, where his mother's relatives lived, and the move left the boy stateless.

  In 1862 Röntgen enrolled at Utrecht Technical School and followed its courses for almost two years. In 1865 he was thrown out. Someone had drawn a caricature of one of the teachers, and Röntgen was accused of it. The accusation was false, because another student had drawn it.

  Without a high school diploma, Röntgen could attend Dutch universities only as a visitor. His 1865 attempt to enter Utrecht University failed for lack of the required credentials. So he moved to Switzerland, passed the entrance examination of the Federal Polytechnic School in Zurich, now called ETH Zurich, and became a mechanical engineering student. In 1869 he received his doctorate from the University of Zurich. There, Professor August Kundt made him a favorite student.

  Kundt's career became Röntgen's route through German academia. Röntgen followed him to the University of Würzburg after graduating, and then to the University of Strassburg in 1873. In 1874 he became a lecturer at Strassburg. The next year he was a professor at the Academy of Agriculture in Hohenheim. In 1876 he came back to Strassburg as Professor of Physics, and in 1879 he took the physics chair at the University of Giessen.

  In 1888 Röntgen regained German citizenship, after roughly 40 years without any. The same year he took the physics chair at Würzburg. In 1900 the Bavarian government made a special request, and he moved to the University of Munich.

  Röntgen had relatives in Iowa and planned to emigrate to the United States. He accepted an appointment at Columbia University in New York City and bought tickets for the crossing. The outbreak of World War I changed his plans, and he stayed in Munich for the rest of his career.

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• 3. Tubes and Cardboard

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  In 1895, at the Physical Institute of the University of Würzburg, Röntgen was studying what happens when an electric discharge passes through a vacuum tube. His bench held equipment associated with Heinrich Hertz, Johann Hittorf, William Crookes, Nikola Tesla and Philipp Lenard.

  Early in November he was repeating an experiment with one of Lenard's tubes. Lenard had fitted it with a thin aluminium window so that cathode rays could leave the glass. A cardboard cover protected that aluminium from the strong electrostatic field which produces the rays.

  Röntgen knew the cardboard stopped light. Even so, a small cardboard screen painted with barium platinocyanide fluoresced when he held it near the window. The cause had to be the invisible cathode rays. It then occurred to him that the Crookes-Hittorf tube, whose glass wall was much thicker than the Lenard tube, might produce the same effect.

  On the late afternoon of the 8th of November he set out to test that idea. He built a black cardboard cover like the one used on the Lenard tube and fitted it over the Crookes-Hittorf tube. Electrodes connected the tube to an induction coil. Before bringing out the painted screen, he darkened the room to confirm that the cover was light-tight.

  He sent the coil's charge through the tube, and the cover held. As he turned to prepare the next stage, a faint shimmering appeared on a bench a few feet from the tube. He ran several more discharges, and the shimmer returned each time. Then he struck a match. The glow came from the barium platinocyanide screen he had planned to use next. It was a Friday evening, and he had the whole weekend ahead of him.

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• 4. Weeks in the Laboratory

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  Regular, sharply formed shadows convinced Röntgen that he was dealing with rays. Because the 8th of November was a Friday, he spent the weekend repeating his experiments and wrote his first notes.

  Over the following weeks he ate and slept in his laboratory while he studied the properties of the new rays. For the time being he called them X-rays, using X as the mathematical symbol for an unknown. English kept that name. German and some languages of Central and Eastern Europe built their word from his surname instead, and the images became Röntgenograms.

  At one point he was checking which materials could stop the rays. He held a small piece of lead in position while a discharge was running. On the screen appeared the first radiographic image, and it showed his own flickering, ghostly skeleton.

  About six weeks after the discovery, Röntgen made a radiograph of the hand of his wife, Anna Bertha. When she saw her own skeleton, she exclaimed, "I have seen my death!" He later made a better picture, of the hand of his friend Albert von Kölliker. He took that one at a public lecture, so the rays were no longer a secret kept in one darkened room.

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• 5. The Rays Reach the World

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  On the 28th of December 1895 Röntgen's paper appeared under the title Ueber eine neue Art von Strahlen, which means On a New Kind of Rays. On the 5th of January 1896 an Austrian newspaper reported the discovery of a new type of radiation. Between 1895 and 1897 he published three papers on the subject in total.

  Physicists reacted with enormous excitement. Henri Becquerel went looking for a connection between the new rays and phosphorescence, and in 1896 he discovered spontaneous radioactivity. Marie and Pierre Curie were also drawn to the X-ray work. When they heard of Becquerel's findings, they turned to isolating and identifying radioactive isotopes, and that work led to the recognition that the radiation was generated at the atomic level.

  Honors arrived quickly. The University of Würzburg gave him an honorary M.D. In 1896 the Royal Society awarded him the Rumford Medal, jointly with Philipp Lenard, who had already shown that part of the cathode rays could pass through a thin metal film such as aluminium. That year he also received the Matteucci Medal from the Accademia dei XL. The Franklin Institute gave him its Elliott Cresson Medal in 1898, with the citation "For the discovery of X-rays." He joined the American Philosophical Society as an international member in 1897, and the Royal Netherlands Academy of Arts and Sciences made him a foreign member in 1907. In 1911 Wilhelm II conferred the order Pour le Mérite on him.

  The Royal Swedish Academy of Sciences made Röntgen the first recipient of the Nobel Prize in Physics, in 1901. The citation read "in recognition of the extraordinary services he has rendered by the discovery of the remarkable rays subsequently named after him." Röntgen was shy about public speaking and declined to give a Nobel lecture. Like Marie and Pierre Curie, he also refused to take out patents on his discovery. He wanted society as a whole to benefit from its practical uses.

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• 6. The Café in Zurich

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  In 1866, in Zurich, Röntgen met Anna Bertha Ludwig at her father's café, which was called Zum Grünen Glas. They became engaged in 1869, but they did not marry until the 7th of July 1872, in Apeldoorn in the Netherlands.

  The long wait had a reason. Anna was six years older than Wilhelm, and his father disapproved of her age or of her humble background. After the wedding, money was tight, because the family support Röntgen had once received had ceased.

  In 1887 Anna's only brother died. The couple adopted his daughter, Josephine Bertha Ludwig, who was six years old at the time. She was the only child they raised. Röntgen was a member of the Dutch Reformed Church.

  Anna died in 1919 at the age of 80, after 47 years of marriage. Röntgen outlived her by only a few years, and they were hard ones.

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• 7. Afterlives

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  Inflation after World War I pushed Röntgen into bankruptcy. He spent his final years at his country home in Weilheim. He died of colorectal cancer on the 10th of February 1923 in Munich, at the age of 77.

  His will gave instructions about his papers. With few exceptions, his personal and scientific correspondence was destroyed after his death. The will also left gifts to several places, including his hometown of Lennep and the Physical Institute of the University of Würzburg.

  In November 2004 the IUPAC named element number 111 roentgenium, with the symbol Rg. The IUPAP adopted the name in November 2011. A collection of his surviving papers is held at the National Library of Medicine in Bethesda, Maryland.

  In Remscheid-Lennep stands the Deutsches Röntgen-Museum. In Würzburg, a non-profit organization maintains his laboratory and offers guided tours of the Röntgen Memorial Site. As of 2023-55 stamps from 40 countries have been issued to commemorate him as the discoverer of X-rays. Röntgen Peak in Antarctica carries his name, and so does the minor planet 6401 Roentgen. In 2010 a Google doodle honored his discovery.

  Since 2012, medical imaging has had a day of its own. World Radiography Day is held each year on the 8th of November, the anniversary of that Friday in Würzburg. The European Society of Radiology, the Radiological Society of North America and the American College of Radiology launched it together.

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