In 1895, physicist Wilhelm Röentgen noticed a mysterious glow while experimenting with cathode rays. Even with the tube covered, a nearby screen lit up—something invisible was passing through solid objects.

He called it “X-rays,” with “X” for unknown. When he held his hand up to the ray, he saw his bones—creating the first X-ray image. His wife, upon seeing her own hand and wedding ring on screen, gasped, “I have seen my death!”

The discovery transformed medicine overnight. For the first time, doctors could peer inside the human body without surgery. Röentgen earned the first Nobel Prize in Physics in 1901, and X-ray fever swept the world.