On a New Kind of Rays
An invisible ray that passes through flesh, is stopped by bone, and photographs the skeleton within.
In the winter of 1895 a German physicist noticed a glow he couldn't explain — and within weeks the world could see the bones inside a living hand.
The idea, unpacked
Röntgen had found an invisible kind of ray that streams out of an electrified vacuum tube and passes straight through paper, wood, and the soft parts of the body. Denser things slow it down; bone soaks up far more of it than flesh, and metals like lead stop it almost completely.
Point these rays at a hand held in front of a glowing screen, or a photographic plate, and the parts that absorb the most cast the darkest shadows. The bones show up clearly inside the faint outline of the flesh. For the first time in history, you could look inside a living body without cutting it open.
Where it came from
On 8 November 1895, working alone in his Würzburg laboratory, Röntgen had a discharge tube completely wrapped in black cardboard in a darkened room — yet a screen nearly a metre away shimmered. No ordinary light could have escaped the shield. Gripped, he barely left the lab for seven weeks, reportedly eating and sleeping there while he tested what the rays would and would not pass through.
On 22 December he photographed his wife Anna Bertha's hand; the story goes that, seeing her own skeleton and wedding ring, she said, "I have seen my death." He submitted his short report on 28 December, and by January the news — and the eerie image — had raced around the world.
Why it mattered
Medicine was transformed in months. Doctors could now locate broken bones, bullets and swallowed objects without exploratory surgery, and X-rays reached battlefield hospitals within the first year. Because Röntgen could not say what the rays actually were, he named them with the mathematician's symbol for an unknown: X. And he refused to patent the discovery, believing it belonged to everyone — later giving away the money from his Nobel Prize.
A way to picture it
Think of fog at night. A car's headlights cut through thin fog but are swallowed by thick fog. X-rays do the dramatic version: flesh is like thin fog and lets most of the rays through, bone is like thick fog and blocks a lot more, and a sheet of lead is like a solid wall. The shadow you see on the screen is simply a map of how much fog each part of you was.
Where it sits
Röntgen's rays opened a remarkable burst of discovery. They prompted Henri Becquerel to look for related effects and stumble onto radioactivity in 1896, which led Marie and Pierre Curie to radium in 1898 (the Library tells that story too). What the rays actually were stayed a puzzle until 1912, when they were diffracted by a crystal and shown to be light of very short wavelength — and that same diffraction later became the tool that revealed the structure of DNA.
A discharge from a large induction coil is passed through a Hittorf's vacuum tube, or through a well-exhausted Crookes' or Lenard's tube. The tube is surrounded by a fairly close-fitting shield of black paper; it is then possible to see, in a completely darkened room, that paper covered on one side with barium platino-cyanide lights up with brilliant fluorescence when brought into the neighbourhood of the tube.
For brevity's sake I shall use the expression 'rays'; and to distinguish them from others of this name I shall call them 'X-rays.'
If the hand be held before the fluorescent screen, the shadow shows the bones darkly, with only faint outlines of the surrounding tissues.