N-rays: a physicist's 'discovery' 120 scientists believed — until a visitor debunked it

In 1903, Prosper-René Blondlot, a respected professor of physics at the University of Nancy in France, announced that he had discovered a new form of radiation, which he named 'N-rays' after his university. This came right after a string of real, thrilling discoveries — X-rays, radioactivity, the electron — and the scientific world was primed to believe another was coming. Blondlot claimed N-rays were emitted by most substances and could be detected as a faint brightening of a spark.

The 'discovery' caused a sensation, especially in France. Around 120 scientists published some 300 papers confirming N-rays and elaborating on their properties. But prominent physicists elsewhere — Lord Kelvin, William Crookes, and others — tried to replicate the effect and failed. The detection method was subjective: observers reported a barely perceptible change in brightness, which was easy to imagine when you expected to see it.

The affair was settled by the American physicist Robert W. Wood, who traveled to Blondlot's lab at the request of the journal Nature. In the darkened demonstration room, Wood secretly removed a crucial prism from the apparatus — and the experimenters still reported observing N-rays. He also swapped a metal file that was supposedly emitting N-rays for a piece of wood, with no change in the 'results.' Wood's report in Nature showed that N-rays were a subjective illusion; by 1905, no one outside Nancy believed in them. The episode became a classic example of 'pathological science.'