The bearded Wilhelm Roentgen, in the few photographs of him taken in his lab, with the help of unintentionally dramatic lighting resembled nothing so much as a mad scientist – which in some ways he was. He was working at the frontiers of science, experimenting with the passage of electricity through glass vessels filled with gas at extremely low pressure — cathode rays, essentially. These experiments were tried before, but Rontgen’s attempts led to an unexpected discovery.

On this day, November 8, in 1895, in his experiments on cathode rays, Wilhelm Rontgen discovered a new kind of light, able to pass through solid matter, like the heavy cardboard cover of the tube.

Rontgen’s X-Rays — so named because he did not have an idea of what to call the mysterious light — had another curious feature: they were absorbed by most metals and, as it happens, human bone. That last discovery turned out to be a great boon for physicians, who could now analyze the structure of the human skeleton on living people, and precisely diagnose broken bones.