The Ray That Wasn't -

Wiki:

N-rays (or N rays) are a hypothesized form of radiation, described by French physicist Prosper-René Blondlot, and initially confirmed by others, but subsequently found to be illusory.

In 1903, Blondlot, a distinguished physicist who was one of 8 physicists who were corresponding members of the French Academy of Science announced his discovery while working at the University of Nancy attempting to polarize X-rays. He had perceived changes in the brightness of an electric spark in a spark gap placed in an X-ray beam which he photographed and he later attributed to the novel form of radiation, naming it the N-ray for the University of Nancy. Blondlot, Augustin Charpentier, Arsène d'Arsonval and approximately 120 other scientists in 300 published articles claimed to be able to detect N-rays emanating from most substances, including the human body with the peculiar exception that they were not emitted by green wood and some treated metals. Most researchers of the subject at the time used the perceived light of a dim phosphorescent surface as "detectors", although work in the period clearly showed the change in brightness to be a physiological phenomenon rather than some actual change in the level of illumination. Physicists Gustave le Bon and P. Audollet and spiritualist Carl Huter even claimed the discovery as their own, leading to a commission of the Académie des sciences to decide priority.

The "discovery" excited international interest and many physicists worked to replicate the effects. However, the notable physicists Lord Kelvin, William Crookes, Otto Lummer and Heinrich Rubens failed to do so. Following his own failure, self-described as "wasting a whole morning", American physicist Robert Wood, who had a reputation as a popular "debunker" in the period, was prevailed upon by the journal Nature to travel to Blondlot's laboratory in France to investigate further. Wood suggested that Rubens go since he had been the most embarrassed when the Kaiser asked him to repeat the French experiments and then after two weeks he had to report his failure to do so. Rubens, however, felt it would look better if Wood went since Blondlot had been most polite in answering his many questions.

In the darkened room, Wood secretly removed an essential prism from the experimental apparatus, yet the experimenters still said that they observed N-rays. He also secretly replaced a large file that was supposed to be giving off N-rays with an inert piece of wood, yet the N-rays were still "observed". His report on these investigations, published in Nature, suggested that N-rays were a purely subjective phenomenon, with the scientists involved having recorded data that matched their expectations. By 1905 no one outside Nancy believed in N-rays even as Blondlot himself is reported to have still been convinced of their existence in 1926.^[1] Martin Gardner, referencing Wood's biographer William Seabrook's account of the affair, attributed a subsequent decline in mental health and eventual death of Blondlot to the resulting scandal, but there is evidence that this is at least an exaggeration of the facts.