The Accidental Discovery of X-Rays

For most of human history, there was no way to see inside a person’s body without cutting it open. But at the end of the 19th century, German physicist Wilhelm Conrad Röntgen discovered a type of radiation he labeled X-rays that could penetrate flesh and capture images of bones and organs.

An immediate sensation, X-rays revolutionized medicine and science as well as pop culture, while also presenting health risks to unsuspecting users.

Scientists had known for decades that by applying an electric current inside a glass vacuum tube they could produce a brilliant fluorescent glow. Yet, lacking knowledge of electrons, they struggled to understand exactly what caused this colorful phenomenon.

Röntgen, a physicist at the University of Würzburg in central Germany, was among those trying to unravel the mystery. On November 8, 1895, as he conducted cathode ray experiments in his darkened laboratory, he caught a glimpse of a glow, not within the glass tube itself, but rather on a chemically coated screen he had placed nearby. “And what did you think?” a reporter later asked him. “I did not think; I investigated,” he responded.

For the next seven weeks, Röntgen isolated himself in his lab, speaking to no one about his work and attempting to understand as much as possible about what he correctly deduced were newfound rays produced by cathode rays.

He called them X-rays for their unknown nature, X being the standard unknown variable in physics and math.

“He wanted to be absolutely sure about his discovery,” says Anna-Katharina Kätker, deputy museum director of the German Röntgen-Museum.

As Kätker points out, other scientists experimenting with cathode rays had undoubtedly already produced X-rays. But until Röntgen, “nobody noticed them,” she says. Kätker adds that his work was so thorough that no significant new physical properties of X-rays were discovered until 1912, when Max von Laue found they were similar to light waves except with shorter wavelengths that made them invisible to the human eye.

When Röntgen placed various objects, including a 1,000-page book, a double pack of cards, tinfoil, wooden boards and rubber sheets, in the path of X-rays, they passed right through, lighting up the chemically coated screen on the other side. Lead—later used to protect patients getting X-rays—was one of the few materials dense enough to absorb them.

At some point, Röntgen observed that X-rays also penetrated flesh, allowing him to see the shadow of his own bones. An enthusiastic photographer, he then exposed the X-rays to photographic plates, capturing images of his wife’s hand, with her finger bones and wedding ring clearly visible, and of metal weights inside a closed box.

By late December 1895, Röntgen was ready to go public with his findings. He released a scientific report and X-ray photographs that immediately caused an international stir. In a biography of Röntgen, author Otto Glasser wrote, “Rarely in the history of science has information concerning a new discovery or invention been disseminated so rapidly or has it made such a deep impression upon the general public.” Glasser added that “Röntgen’s name suddenly had become known in the most distant outposts of human culture.”

Rival physicist Philipp Lenard, who would later become a keen supporter of the Nazi Party, groused that Röntgen would be unknown without his own work on cathode rays. Lenard refused to even use the term X-rays, preferring instead high-frequency rays. Yet his jealousy did nothing to stop Röntgen’s fame from spreading. It helped that Röntgen’s results were easily reproduced by other scientists, many of whom, like Nikola Tesla, captured their own X-ray images.

“Because experimenting on cathode rays was so popular at the time, almost every physical laboratory had everything you needed to produce X-rays,” Kätker says. “From early on, they started to X-ray almost everything,” she adds, from mummies and fossils to weapons.

Within months, X-rays were also being used as a diagnostic tool—the birth of radiology—and to treat ailments ranging from tumors to skin lesions. During Italy’s failed colonization attempt of Ethiopia in 1896 and during the Greco-Turkish War of 1897, they were purportedly used on wounded soldiers to locate bullets and shrapnel prior to surgery. Promoted by Marie Curie, mobile X-ray units later patrolled battlefields during World War I.

X-rays likewise entered popular culture. In 1896, an English company purportedly advertised “X-ray-proof underclothing.” That same year, magazines published poems and cartoons regarding Röntgen’s discovery, and the following year, a short comedy film called “The X-Rays” came out. By the 1930s, Superman was fighting crime with the help of X-ray vision, and shoe stores carried X-ray machines so that customers could see the bones in their feet.

Röntgen, who would win several scientific awards, including the first Nobel Prize in Physics in 1901, did not enjoy all the attention. He agreed to give an X-ray demonstration to Kaiser Wilhelm II, but he declined other prominent public appearances and gave only one known press interview about his discovery to U.S.-based McClure’s Magazine. “I think the press wanted to make him a superstar,” Kätker says, “and he much detested that.”

Röntgen’s work indirectly contributed to other exciting findings. In 1896, for example, a French scientist investigating the properties of X-rays accidentally discovered radioactivity. The British discoverer of electrons in 1897 likewise studied X-rays, which in turn laid the groundwork for Albert Einstein’s discovery of the photoelectric effect. “It was a time of scientists who really were into the invisible,” Kätker says.

Of course, the side effects of X-rays were evident almost from the beginning, ranging from burns to eye damage to leukemia. In 1896, an Austrian dermatologist treated a young girl’s birthmark with X-rays, causing an ulcer. Not long after, a British surgeon had his hand amputated after working extensively with X-rays —a not uncommon occurrence at the time. In fact, the German Röntgen Museum, located in Röntgen’s birthplace, has an amputated hand with visible radiation damage in its collection. Meanwhile, in 1904, an assistant to Thomas Edison died of skin cancer, prompting Edison to discontinue his work with X-rays.

Even as the most perilous and unnecessary practices, such as shoe store X-rays, were gradually abandoned, X-rays remain in wide use. To this day, they play a key role in medical and dental imaging, material analysis and airport security. The majority of Americans get at least one X-ray every year, according to the U.S. Food and Drug Administration, which supports their use when medically needed despite the potential risks. “[It] can even save your life,” the FDA says.