APS News | This Month in Physics History

November 8, 1895: Roentgen's Discovery of X-Rays

Published Nov. 1, 2001

Few scientific breakthroughs have had as immediate an impact as Wilhelm Conrad Roentgen's discovery of X-rays, a momentous event that instantly revolutionized the fields of physics and medicine. The X-ray emerged from the laboratory and into widespread use in a startlingly brief leap: within a year of Roentgen's announcement of his discovery, the application of X-rays to diagnosis and therapy was an established part of the medical profession.

Wilhelm Conrad Roentgen

Roentgen's scientific career was one beset with difficulties. As a student in Holland, he was expelled from the Utrecht Technical School for a prank committed by another student. His lack of a diploma initially prevented him from obtaining a position at the University of Würzburg even after he received his doctorate, although he eventually was accepted. His experiments at Würzburg focused on light phenomena and other emissions generated by discharging electrical current in so-called "Crookes tubes," glass bulbs with positive and negative electrodes, evacuated of air, which display a fluorescent glow when a high voltage current is passed through it. He was particularly interested in cathode rays and in assessing their range outside of charged tubes.

On November 8, 1895, Roentgen noticed that when he shielded the tube with heavy black cardboard, the green fluorescent light caused a platinobarium screen nine feet at away to glow — too far away to be reacting to the cathode rays as he understood them. He determined the fluorescence was caused by invisible rays originating from the Crookes tube he was using to study cathode rays (later recognized as electrons), which penetrated the opaque black paper wrapped around the tube. Further experiments revealed that this new type of ray was capable of passing through most substances, including the soft tissues of the body, but left bones and metals visible. One of his earliest photographic plates from his experiments was a film of his wife Bertha's hand, with her wedding ring clearly visible.

One of the earliest photographic plates from Roentgen's experiments was a film of his wife, Bertha's hand with a ring, produced on Friday, November 8, 1895.

To test his observations and enhance his scientific data, Roentgen plunged into seven weeks of meticulous planned and executed experiments. On December 28, he submitted his first "provisional" communication, "On a New Kind of Rays," in the Proceedings of the Würzburg Physico-Medical Society. In January 1896 he made his first public presentation before the same society, following his lecture with a demonstration: he made a plate of the hand of an attending anatomist, who proposed the new discovery be named "Roentgen's Rays."

The news spread rapidly throughout the world. Thomas Edison was among those eager to perfect Roentgen's discovery, developing a handheld fluoroscope, although he failed to make a commercial "X-ray lamp" for domestic use. The apparatus for producing X-rays was soon widely available, and studios opened to take "bone portraits," further fueling public interest and imagination. Poems about X-rays appeared in popular journals, and the metaphorical use of the rays popped up in political cartoons, short stories, and advertising. Detectives touted the use of Roentgen devices in following unfaithful spouses, and lead underwear was manufactured to foil attempts at peeking with "X-ray glasses."

As frivolous as such reactions may seem, the medical community quickly recognized the importance of Roentgen's discovery. By February 1896, X-rays were finding their first clinical use in the US in Dartmouth, MA, when Edwin Brant Frost produced a plate of a patient's Colles fracture for his brother, a local doctor. Soon attempts were made to insert metal rods or inject radio-opaque substances to give clear pictures of organs and vessels, with mixed results. The first angiography, moving-picture X-rays, and military radiology, were performed in early 1896.

In addition to the diagnostic powers of X-rays, some experimentalists began applying the rays to treating disease. Since the early 19th century, electrotherapy had proved popular for the temporary relief of real and imagined pains. The same apparatus could generate X-rays. In January 1896, only a few days after the announcement of Roentgen's work, a Chicago electrotherapist named Emil Grubbe irradiated a woman with a recurrent cancer of the breast, and by the end of the year, several researchers had noted the palliative effects of the rays on cancers. Others found remarkable results in the treatment of surface lesions and skin problems while others investigated the possible bacterial action of the rays. X-rays even found cosmetic uses in depilatory clinics set up in the US and France.

Roentgen was awarded the first Nobel Prize in physics in 1901 for his discovery. When asked what his thoughts were at the moment of discovery, he replied, true to form, "I didn't think, I investigated." Today, Roentgen is widely recognized as a brilliant experimentalist who never sought honors or financial profits for his research. He rejected a title that would have given him entry into the German nobility, and donated his Nobel Prize money to his university. While he accepted the honorary degree of doctor of medicine offered to him by his own university, he never took out any patents on X-rays, to ensure that the world could freely benefit from his work. His altruism came at considerable personal cost: at the time of his death in 1923, Roentgen was nearly bankrupt from the inflation following World War I.

Alan Chodos

Alan Chodos is the former editor of APS News.

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