Today in History—November 8: X-Rays Seen for the First Time

On this day in 1895, the invisible became visible. German physicist Wilhelm Conrad Röntgen discovered the X-ray—by accident.

Röntgen’s original experiment focused on something else: whether cathode rays could pass through glass. Cathode rays (these are hard to explain, so stick with us) are essentially beams of electrons emitted from a vacuum tube. Röntgen’s particular tube was covered by thick black paper—which is why he was surprised to see a glowing green light emanating from the tube onto a screen nearby. Cathode rays wouldn’t have been able to permeate the paper…meaning that Röntgen was looking at something else entirely.

Röntgen dubbed his newly discovered glow the X-ray, with the “X” standing for “I don’t know what’s happening here.” (Okay, technically “X” means “unknown.”) He spent weeks in the lab obsessively studying the rays, which passed through some solids, including human skin, and left impressions of others, including bone. One of the first X-rays captured via photograph showed the skeleton of Röntgen’s wife’s hand.

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“All hell broke loose” when Röntgen published his findings—and that’s a direct quote from the physicist himself.

Newspapers from Vienna to London to New York spread X-ray fever, dubbing the discovery “sensational,” “revolution[ary],” and even “naughty.” (That last one begs explanation: Some misinformed members of society feared X-rays’ potential to expose what was underneath their clothes. At least one London store took advantage of the panic by selling “X-ray proof underclothing.”)

Even as Röntgen’s discovery changed the world, ushering in new eras of medicine, physics, and atomic science, he refused to patent his work. He believed the amazing X-ray belonged to everyone.