Discovery of X-Rays (1895): Wilhelm Röntgen's Accidental Find

The discovery of X-rays by Wilhelm Conrad Röntgen on 8 November 1895, in his laboratory at the University of Würzburg in Germany, revealed a new kind of invisible radiation that could pass through flesh but not bone. Within weeks of his announcement, doctors around the world were using X-rays to look inside the living body, making it one of the fastest transfers from laboratory to medicine in history.

Background: the puzzle of cathode rays

In the later nineteenth century many physicists were studying what happened when an electric current was passed through glass tubes from which most of the air had been pumped out. Such tubes, developed by researchers including Johann Hittorf, William Crookes and Philipp Lenard, produced streams known as cathode rays, which made the glass glow where they struck it.

Wilhelm Conrad Röntgen was born in 1845 in Lennep, in the Prussian Rhineland, and grew up partly in the Netherlands. He studied mechanical engineering at Zurich before turning to physics, and by 1888 he was professor of physics and head of the Physical Institute at Würzburg in Bavaria. He was a careful experimentalist, known for precise work rather than bold theories.

In the autumn of 1895 Röntgen began repeating and extending Lenard’s experiments, investigating whether cathode rays could pass out of the tube through its glass wall.

What happened on 8 November 1895

On the evening of 8 November 1895 Röntgen was working with a discharge tube that he had wrapped completely in black cardboard to block its visible glow, in a darkened room. When he switched on the current, he noticed that a small screen coated with barium platinocyanide, a fluorescent chemical, began to shimmer some distance away from the tube.

Cathode rays were known to travel only a few centimetres in air, so the glow could not be caused by them. Röntgen concluded that the tube was giving off some new kind of ray that passed through cardboard and air. He then tested it with other materials, finding that it passed easily through paper, wood and thin metal sheets, less easily through denser materials such as lead. When he held objects in the beam he could see their shadows on the screen, and he saw the outline of the bones of his own hand.

Because he did not know what the rays were, he called them X-rays, using the mathematical symbol for an unknown.

Seven weeks of secret work

For the next seven weeks Röntgen worked intensively and almost alone, telling few people what he was doing. Later accounts say he took his meals in the laboratory and even slept there, though some of these details may have been embellished over time.

He found that the rays travelled in straight lines, were not bent by magnets as cathode rays were, could not be noticeably reflected or refracted, and darkened photographic plates. He used photographic plates to make permanent images, including pictures of a set of weights in a closed wooden box, a compass and a door.

On 22 December 1895 he made the image that became famous: an X-ray photograph of the left hand of his wife, Anna Bertha Röntgen, showing the bones of her fingers and the dark shape of her ring. The exposure is usually said to have lasted about 15 minutes. According to a widely repeated anecdote, she was disturbed at seeing her own skeleton and felt she had glimpsed her death.

Announcement and worldwide sensation

On 28 December 1895 Röntgen submitted a short paper, “Über eine neue Art von Strahlen” (On a New Kind of Rays), to the Würzburg Physical-Medical Society, which printed it quickly. On 1 January 1896 he posted copies, together with prints of his X-ray photographs, to leading physicists across Europe.

The news spread with astonishing speed. One recipient in Vienna showed the images to friends, and on 5 January 1896 the Viennese newspaper Die Presse published a report. Within days the story was carried by newspapers in London, New York and beyond. Röntgen demonstrated the rays to Kaiser Wilhelm II in Berlin in mid-January.

On 23 January 1896 Röntgen gave his only public lecture on the discovery, in Würzburg. During it he made an X-ray of the hand of the elderly anatomist Albert von Kölliker, who proposed that the rays be named after their discoverer. In German, and many other languages, they are still called Röntgenstrahlen, or Röntgen rays.

Rapid medical use

Doctors understood the importance immediately. Within weeks, physicians in Europe and North America were using X-rays to locate needles and bullets in the body and to examine broken bones. In January 1896 the British pioneer John Hall-Edwards in Birmingham used an X-ray to find a needle in a patient’s hand, and in February 1896 Edwin Frost and his brother, a doctor, imaged a broken wrist at Dartmouth College in the United States.

Hospitals soon opened X-ray departments; the one at Glasgow Royal Infirmary, set up by John Macintyre in 1896, is often cited as one of the first. Armies also adopted the technology quickly, using it to locate bullets in wounded soldiers in conflicts of the late 1890s.

Thomas Edison worked on improved fluorescent screens and promoted the fluoroscope, which let doctors watch moving images in real time. X-ray machines also appeared at fairs and in studios as a public novelty.

The hidden danger

At first nobody understood that X-rays could harm living tissue. Early workers suffered skin burns, hair loss and later cancers. Clarence Dally, a glassblower who worked on X-ray tubes in Edison’s laboratory, developed severe injuries and died in 1904, and Edison abandoned his X-ray research. Many early radiologists died of radiation-related disease.

Gradually protective measures, such as lead shielding, shorter exposures and dose limits, were introduced. In the twentieth century, however, some uses that now seem reckless continued, such as shoe-fitting fluoroscopes in shoe shops from the 1920s to the 1950s.

Key people

• Wilhelm Conrad Röntgen (1845–1923), professor of physics at Würzburg, discovered and first described X-rays. He moved to the University of Munich in 1900.
• Anna Bertha Röntgen (1839–1919), his wife, whose X-rayed hand became the most famous early radiograph.
• Albert von Kölliker (1817–1905), Swiss-born anatomist, whose hand was X-rayed at the 1896 lecture and who proposed the name Röntgen rays.
• Philipp Lenard (1862–1947), whose cathode-ray experiments Röntgen was extending, and who later bitterly disputed the credit.

Consequences for science

X-rays transformed physics as well as medicine. Their discovery inspired the French physicist Henri Becquerel to look for similar rays from fluorescent materials, which led to the discovery of radioactivity in 1896 and then to Marie and Pierre Curie’s discovery of polonium and radium in 1898. X-rays also became a standard laboratory tool for studying how gases are ionised, research pursued by J. J. Thomson and his students at Cambridge.

The nature of X-rays remained unclear for years. In 1912 Max von Laue and his colleagues showed that crystals diffract X-rays, proving that they are electromagnetic waves with very short wavelengths. This also created X-ray crystallography, which later revealed the structure of molecules, including DNA. In 1913 Henry Moseley’s measurements of X-ray spectra helped confirm the picture of the atom that had emerged from Rutherford’s work on the atomic nucleus.

Myths and facts

• Myth: The discovery was pure luck. Fact: Röntgen noticed the glow by chance, but he was deliberately investigating cathode rays, and he spent weeks testing the effect systematically before publishing.
• Myth: Nobody had produced X-rays before 1895. Fact: Other researchers had unknowingly produced them with similar tubes; in 1890, for example, Arthur Goodspeed in Philadelphia made a photographic image he could not explain. Röntgen was the first to recognise and describe them.
• Myth: Röntgen made a fortune from his discovery. Fact: He refused to patent X-rays, believing that discoveries belonged to humanity, and he gave his Nobel Prize money to his university.

Legacy

In 1901 Röntgen received the first Nobel Prize in Physics. He died in Munich on 10 February 1923. His name is honoured in the röntgen, an old unit of radiation exposure, and in roentgenium, chemical element 111. His laboratory in Würzburg is preserved as a memorial.

Medical imaging built on his discovery grew into a vast field, from routine chest and dental X-rays to computed tomography (CT) scanners introduced in the 1970s. X-rays are also used in airport security, industrial inspection, astronomy and art history.

Timeline

• 1845, 27 March: Wilhelm Conrad Röntgen is born in Lennep, Prussia.
• 1888: Röntgen becomes professor of physics at Würzburg.
• 1895, 8 November: Röntgen observes the effect of an unknown radiation.
• 1895, 22 December: He makes the X-ray image of his wife’s hand.
• 1895, 28 December: He submits “On a New Kind of Rays” to the Würzburg society.
• 1896, 5 January: The first newspaper report appears in Vienna.
• 1896, 23 January: Röntgen lectures in Würzburg and X-rays Kölliker’s hand.
• 1896, February–March: Becquerel’s experiments lead to the discovery of radioactivity.
• 1901, 10 December: Röntgen receives the first Nobel Prize in Physics.
• 1912: Max von Laue’s team demonstrates X-ray diffraction by crystals.

Why it matters

Röntgen’s discovery gave doctors their first way to see inside the living body without surgery and launched the field of radiology. It also opened the door to radioactivity, atomic physics and crystallography, making 1895 one of the turning points between classical and modern science.