The N-Ray Affair in Overview: Scale, Failed Replications, Priority Claims and the Historical Literature

N-rays were a form of radiation that the French physicist Prosper-René Blondlot announced in 1903 and named after the University of Nancy, where he was professor of physics. Other laboratories confirmed them at first; they were later found to be illusory. This page draws on Wikipedia's summary of the affair, which is a second-hand account built on a handful of historical studies. It is useful for the things shorter retellings leave out: how many people were involved, who could not see the rays, how the detector worked, and which historian stands behind which detail.

How big was the affair, and who was in it?

The scale is the first surprise. According to a figure credited to R. T. Lagemann's 1977 paper in the American Journal of Physics, Blondlot, Augustin Charpentier, Arsène d'Arsonval and approximately 120 other scientists reported detecting the rays, in 300 published articles. A second count comes from a 2018 Skeptical Inquirer review of the book The Skeptics' Guide to the Universe: "Three hundred scientific papers were published by one hundred experimenters over three years, all declaring this imaginary phenomenon to be real." The two agree on the papers and differ slightly on the people, and nothing in the summary reconciles them.

Almost everything was said to give off the rays. Human bodies were on the list of emitters; the odd exceptions, in a detail that appears to come from R. T. Carroll's Skeptic's Dictionary, were green wood and certain treated metals.

Blondlot was not a fringe figure. The same Lagemann paper is cited for his standing: the French Academy of Sciences had only eight physicists among its corresponding members and he was one of them, and the Academy had given him its Gaston Planté prize (1893) and its LaCaze prize (1899). M. J. Nye's 1980 study is cited for the fact that J. J. Thomson and Henri Poincaré had praised his work on measuring how fast electromagnetic waves travel.

The moment also favoured him. Nye is the cited source for the run of discoveries that came just before: Victor Schumann's vacuum ultraviolet radiation (1893), Wilhelm Röntgen's X-rays (1895), Henri Becquerel's radioactivity (1896) and Thomson's electron (1897). I. M. Klotz's 1980 Scientific American article is cited for the consequence, that scientists expected more kinds of radiation to turn up. Blondlot himself had taken up X-rays soon after they were found, hoping to settle whether they were particles or waves, and it was while trying to polarize them that he made his announcement.

The clearest sign of how seriously the rays were taken is that people fought over them. Klotz is cited for three rival claimants, the physicists Gustave le Bon and P. Audollet and the spiritualist Carl Huter, each of whom said the discovery was his. A commission of the Académie des sciences was set up to decide priority; the reference for it is a note by d'Arsonval in the Comptes rendus dated 11 April 1904. What the commission decided is not stated.

What was the detector, and why was it unreliable?

Blondlot's first evidence was a spark. He placed a spark gap in an X-ray beam, thought he saw the spark's brightness change, photographed it, and afterwards put the change down to a new radiation.

Most of those who followed him used something simpler: a faintly phosphorescent surface, with the observer's own impression of its brightness serving as the measurement. Wikipedia's summary says that work done in the same period had already shown such brightening to be physiological, a product of the eye and not of any real change in the light. The one reference attached to that statement is a paper by H. Guilleminot in the Archives d'électricité médicale, whose title says the rays had no influence on the resistivity of selenium. No date or data for it are given, so the summary does not show how the physiological explanation was demonstrated.

Who failed to reproduce the rays, and how did Wood test them?

Four prominent physicists are named as having tried and failed: Lord Kelvin, William Crookes, Otto Lummer and Heinrich Rubens. The American physicist Robert W. Wood failed too, and is said to have counted the attempt as a morning lost. That remark is cited to a Stanford-hosted web page about Wood, not to Wood's own writing.

Wood then went to Nancy, and the summary says it was the British journal Nature that prevailed on him to go. A story is attached about the choice of visitor. Wood is said to have proposed Rubens, who had been embarrassed at having to tell Kaiser Wilhelm II, after two weeks of trying at the Kaiser's request, that he could not reproduce the French results; Rubens is said to have preferred Wood, because Blondlot had been so courteous in answering Rubens's own questions. The passage carrying this story is marked as lacking a citation and should be treated as unverified.

Two tests are described, both carried out in the darkened laboratory without the experimenters' knowledge. The first is the subject of Robert Wood's 1904 Visit to Nancy: The Removed Prism and the Collapse of N-Rays: Wood took away a prism the apparatus depended on, and the rays were reported anyway. In the second, a large file was meant to be a source of the rays; Wood put a plain block of wood in its place, and the observers still saw the effect.

Wood's report appeared in Nature on 29 September 1904. In it he wrote that after three hours or more of watching experiments he had seen nothing that pointed to the rays existing, and had come away convinced that those getting positive results were deluded in some way. He addressed the report to the many physicists who had put long effort into the experiments without managing to reproduce them. The summary reads his conclusion as a verdict that the effect lay in the observers, whose results followed what they expected to find.

One further suggestion concerns Blondlot personally. Citing a one-page 1978 note by Spencer Weart in the American Journal of Physics, the summary says there is reason to think he was misled by his laboratory assistant, who confirmed every observation. It does not say what that reason is.

What happened afterwards?

Belief collapsed quickly but not completely. Lagemann is cited for the statement that by 1905 nobody outside Nancy accepted the rays, while Blondlot is reported to have been convinced of them still in 1926.

A darker version of his later life circulates. Martin Gardner, in Fads and Fallacies in the Name of Science (1957), drew on William Seabrook's biography of Wood and blamed the scandal for a decline in Blondlot's mental health and for his death. Lagemann is cited against this: the evidence is said to show the story is at least partly exaggerated.

The word outlasted the phenomenon. Dictionaries are said to have described N-rays as real until at least the 1940s, and a 1946 Webster's is quoted: "An emanation or radiation from certain hot bodies which increases the luminosity without increasing the temperature: as yet, not fully determined."

In Nancy the memory faded. Blondlot left his house and garden to the city, which turned them into a public park that carries his name. James Randi, cited from his 1982 book Flim-Flam!, reported that many townspeople and members of the university faculty did not remember hearing of the rays or of the man.

Among scientists the episode became a warning about experimenter bias, and Irving Langmuir used it as an example of pathological science, a theme taken up in Sheldon Stone's "Pathological Science" (2000): N-Rays, Langmuir's Six Symptoms and the Threshold of Seeing.

The summary also places N-rays in an older line. It claims that a radiation with nearly the same properties had been described about 50 years earlier by Carl Reichenbach, in an 1850 treatise relating magnetism, electricity, heat and light to a vital force, and before that by Franz Mesmer in a 1779 memoir on animal magnetism. It states that Paris researchers working with Blondlot knew Reichenbach's work, and that there is no proof Blondlot did.

How reliable is each claim?

None of this is first-hand. Wikipedia's summary reports no observation of its own, quotes nothing from Blondlot, and gives only Wood's side of the visit. How far each claim can be trusted depends on the work behind it.

• Scale, reputation and aftermath rest on Lagemann's four-page paper in the American Journal of Physics (1977). It is the cited source for the count of scientists and articles, the Academy membership and prizes, the dates 1905 and 1926, and the doubt about Blondlot's breakdown. The summary does not show how the count of 300 articles was made. The second count comes from a book review, not from a historical study.
• Background rests on Nye's paper in Historical Studies in the Physical Sciences (1980): the earlier discoveries, Blondlot's post at Nancy, and the praise from Thomson and Poincaré. Nothing about the collapse is attributed to it.
• Expectations and priority claims rest on Klotz's article in Scientific American (May 1980), along with Blondlot's interest in whether X-rays were particles or waves.
• The two substitutions rest on Wood's own report in Nature.
• The assistant rests on Weart's single-page note, and the story of Blondlot's decline on Gardner's retelling of Seabrook. Each would need to be read directly before being repeated as fact.
• The Reichenbach connection is the weakest. Its reference names the Revue Scientifique but gives no title or date, so it is a lead and not a documented line of influence.
• The Rubens story has no source at all.

Also listed, though not used for any particular claim, are the 1905 English translation of Blondlot's own book on the rays and a 1993 paper by M. Ashmore in Social Studies of Science whose title names a prism, a pocket and a piece of wood.