I once heard a cautionary tale about the dangers of the observer-expectancy effect. It was at least presented as a true example from the history of science, but I'm having trouble identifying the incident now.

A team of experimental physicists announced they had discovered a previously unknown effect of some sort. The experiment involved some solid sample (a metal or crystal?) of something reasonably available. The setup somehow produced an image related to the sample or its surroundings (maybe a diffraction pattern?). When some additional stimulus or condition was added, the effect was said to cause a specific sort of pattern in the image.

Other groups were interested, but attempts to replicate the experiment were inconsistent at best. The original group explained the experiment is delicate, and invited others to come to their lab to observe it.

The demo went pretty normally: the hosts first showed and explained the apparatus. One researcher set things up for a few "control" runs, and another reported each time the pattern was not visible in the image. Then a few runs were done with the extra condition applied, and the viewer reported each time the pattern was visible.

As the demo concluded, one visiting skeptic revealed they had removed the sample before the measurements started! (My vague memory suggests possibly this skeptic is also known for other things in science or philosophy?)

Does this describe some actual incident, perhaps embellished a bit? If so, what was it?

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    $\begingroup$ This sounds like N rays, as explained in en.wikipedia.org/wiki/N_ray . $\endgroup$ Commented Jul 21, 2019 at 4:40
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    $\begingroup$ @kimchilover Yes, that was the name of it! (Though I did recall some details wrong.) Care to make it an answer? $\endgroup$
    – aschepler
    Commented Jul 21, 2019 at 11:29

1 Answer 1


This is the story of the "discovery" of "N Rays", as described in a Wikipedia article. The gist of the story told there is as follows:

In 1903 the physicist Prosper-René Blondlot (1849 – 1930) thought he found something similar to the then-new X rays but not the same. Since the phenomenon could not be duplicated in others' laboratories the community smelled a rat. Robert W. Wood (1868-1955) attended a demonstration in Blodot's lab. After the effect was once again exhibited, Wood revealed that he had surreptitiously removed an important part of Blondot's apparatus, so what was exhibited was not the result of the experiment as described.

The effect was the result of a kind of self-delusion.

  • $\begingroup$ This is the most famous case, and the one least subject to the "TrueBeliever Syndrome." We could add perpetual motion machines, PSI power people, and cold fusion to the latter category. $\endgroup$ Commented Jul 22, 2019 at 14:15
  • $\begingroup$ BTW -- hey, Robert Wood died before he was born, huh? :-) . -- I think his birth year is 1869 ? $\endgroup$ Commented Jul 22, 2019 at 14:15
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    $\begingroup$ @CarlWitthoft Wood was obviously a man before his times! Thanks for the catch. $\endgroup$ Commented Jul 22, 2019 at 14:19

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