Blondlot announced N-rays — a visitor removed the prism and he still saw them

In 1903, René Blondlot — a respected professor of physics at the University of Nancy and a corresponding member of the French Academy of Sciences — announced a new form of radiation, which he named N-rays after Nancy. He claimed they were emitted by X-ray tubes, heated metals and the sun, and could be detected by a faint brightening of an electric spark or a dim phosphorescent screen — an impression only a trained eye could confirm.

The Academy published the work in its Comptes rendus, and the field boomed. Blondlot, physician Augustin Charpentier, physicist Arsène d'Arsonval and roughly 120 other scientists published about 300 papers claiming to detect N-rays — including rays given off by the human body. No instrument ever measured the rays; researchers 'detected' them by the perceived light of a dim phosphorescent surface.

In 1904, Robert W. Wood of Johns Hopkins visited the darkened lab in Nancy. He secretly removed an essential prism from the apparatus — the experimenters still described N-rays. He replaced the large iron file supposed to be emitting them with an inert piece of wood — still N-rays. Wood's report ran in Nature on 29 September 1904.

Within a year no one outside Nancy believed in N-rays, and the affair became the textbook case of self-deception in science. Blondlot's reputation never recovered — he was reportedly still convinced of the rays' existence in 1926. MIT Libraries, which keeps his 1904 book of communications, calls the episode 'an object lesson in the need for scrupulous control of variables.'