What Is Well Documented
Wilhelm Conrad Roentgen was a German physics professor at the University of Wurzburg. He is credited with discovering X-rays in the fall of 1895, and the date usually given is the evening of 8 November 1895. That much is solidly documented, including by Roentgen’s own paper. Some of the details of the story, such as exactly what he said or thought that night, rest on later retellings, because Roentgen was private and left little personal record of his work. He is said to have asked that his papers be destroyed after his death, so the surviving record is thin.
His name is also commonly spelled Rontgen or Roentgen, and in German it is written with an umlaut over the o.
The Evening in the Laboratory
Roentgen had been studying how electrical discharges behave in evacuated glass tubes, a subject many physicists were working on. According to the usual account, he had covered a tube with black cardboard so that no light could escape. Some distance away, a screen coated with a fluorescent chemical, commonly described as barium platinocyanide, began to glow while the tube was running. Light from the tube could not explain it, because the tube was covered. Something else was crossing the room and making the screen glow.
What followed is the part of the story that shows him as a careful experimenter. Over the next weeks, working largely alone and in secret, he tested the new rays. He found that:
- They passed through many materials, including paper, wood and thin sheets of metal, with different substances absorbing different amounts.
- They blackened photographic plates.
- They were not bent by a magnet, which suggested they were not the same as the cathode stream inside the tube.
- They did not seem to reflect or refract like ordinary light in any obvious way.
Not knowing what they were, he called them “X-rays,” using the mathematical symbol for an unknown. In German-speaking countries they were often called Roentgen rays, and that term persists in some languages.
The Hand Image
The picture that made the discovery famous showed the bones of a hand, with a ring visible on one finger. It is usually identified as the hand of his wife, Anna Bertha, and it is commonly dated to 22 December 1895. The exposure is said to have taken a long time, often given as around fifteen minutes, but this detail is reported differently in different sources.
The image was striking because it required no explanation. Anyone could look at it and grasp that the rays could show the inside of the body. Roentgen reportedly said that he had not been trying to do that at all, and it would be a mistake to treat the discovery as the planned outcome of a medical research program. It came out of basic physics.
The Paper and the News
Roentgen wrote a short report titled, in English, “On a New Kind of Rays,” and gave it to the secretary of the Physical-Medical Society of Wurzburg at the end of December 1895. It was printed quickly. In the first days of January 1896 he sent copies, along with some of his images, to a number of physicists in Europe. That small mailing turned out to be the spark.
A Vienna newspaper is commonly cited as publishing an account in early January 1896, and other papers quickly picked it up. By the middle of the month the story had appeared in the press of Britain, the United States and elsewhere. The speed of its spread was helped by the electric telegraph, which allowed news to cross borders in hours, and by the fact that the experiment was easy to repeat. Many laboratories already had tubes and induction coils. Within weeks, physicists in several countries reported making their own images.
Reactions: Excitement and Alarm
Public reaction mixed amazement with some silliness. Newspapers wrote about seeing through walls or clothing, and some commercial claims were absurd. There were jokes, cartoons and, according to stories from the period, anxiety about privacy and a few products marketed for supposed protection from the rays. These accounts are anecdotal, and it is hard to say how widespread any particular reaction was.
The medical response was faster and more serious. Doctors saw that a bone could be imaged and a bullet located. The first clinical images were made in 1896, and journals began to fill with X-ray photographs. Hospitals soon adopted the technique for X-ray diagnosis, and instrument makers began building X-ray machines for the purpose.
Credit, Honors and Roentgen’s Attitude
In 1901, the first Nobel Prize in Physics was awarded to Roentgen “in recognition of the extraordinary services” he had rendered by discovering the rays. He declined to take out patents and reportedly wished the discovery to be freely available. He is also said to have given the prize money to his university, though like many details of his life this is repeated in popular sources more often than it is proved in them.
It is worth noting that others had seen related effects before him. Some researchers had photographic plates fogged near their tubes without recognizing why. That earlier history is its own story, but the usual reasoning for giving Roentgen the credit is that he recognized that something new was happening, investigated it systematically and published promptly so that others could confirm it.
Why the Discovery Spread So Fast
Several things came together in late 1895: laboratory equipment was widely available, photography was mature enough to record the results, scientific journals and newspapers circulated quickly, and the images made the discovery visible to anyone. Few discoveries are so easy to prove with a single photograph. This is one reason the X-ray became the first of a series of imaging technologies, leading eventually to modern medical imaging.