N-Rays
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[edit] Definition
N-rays were supposedly a new sort of radiation discovered by the French scientist Professor René Blondlot in 1903. They don't really exist; and the story of how they were "discovered", and then debunked, provides an classic and often-repeated cautionary tale about the practice of science.
[edit] Discovery
The "discoverer" of N-rays was Professor René Blondlot. In using a cathode ray tube originally intended to produce X-rays, he found, or so he thought:
- A new species of radiations emitted by the focus tube, which traverse aluminum, black paper, wood, etc. These are plane-polarized from the moment of their emission, are susceptible of rotary and elliptic polarization, are refracted, reflected and diffused, but produce neither fluorescence nor photographic action. (Blondlot, communication to the French Academy of Sciences[2])
According to Robert Lagemann (American Journal of Physics 45 (3): 281-284, March 1977) about 120 scientists published almost 300 articles on N-rays during the years 1903-1906; he does not say what proportion of these articles were skeptical, but the bulk of them confirmed and extended Blondlot's findings.
[edit] Experiments and observations
The key flaw in Blondlot's experiments was in the way these supposed rays were detected: by visual observation on the changes they brought about in the luminosity of (in the original experiment) a small spark. In later experiments Blondlot used other sources of light such as a small flame, phosphorescent calcium sulfide, a platinum wire made incandescent by passing a current through it, and so forth, all with equal success.
You will notice that N-rays don't make things glow which aren't already glowing (unlike X-rays, for example) but just change the intensity of an object already luminous; or, rather, they changed the intensity as judged by Professor Blondlot. And this, of course, is where the possibility for error creeps in. Straining his eyes in the dark at his little spark or flame, the unfortunate professor saw what he wanted to see.
Here is his description of how to observe the effect of N-rays, traslated from the Comptes Rendus of the French Academy of Sciences:
- It is indispensable in these experiments to avoid all strain on the eye, all effort, whether visual or for eye accommodation, and in no way to try to fix the eye upon the luminous source, whose variations in glow one wishes to ascertain. On the contrary, one must, so to say, see the source without looking at it, and even direct one’s glance vaguely in a neighboring direction. [...] When viewing the screen or luminous object, no attempt at eye-accommodation should be made. In fact, the observer should accustom himself to look at the screen just as a painter, and in particular an "impressionist" painter, would look at a landscape. To attain this requires some practice, and is not an easy task. Some people, in fact, never succeed. [3]
The introduction into science of a new sort of radiation, as evidenced by an effect which only some physicists could learn to see, was bound to cause controversy. This divided itself mostly along national lines, with French scientists finding that they could see the effect, and German scientists finding that they couldn't. It is only fair to the French to suggest that if the rays had been "discovered" in Germany, the situation would have been reversed.
[edit] The photographs
![Photographic negatives showing spark intensity, as communicated by Blondlot to the French Academy of Sciences.[1]](/index.php/Image:N-ray_photographs.JPG)
If we rule out simple fraud on Blondlot's part, and there is no particular reason to suspect it, then we must look to problems in the design of his experiment. He was attempting to measure something just on the edge of measurability, never a good idea. In describing his experiment, he writes:
- It is of great importance that exceedingly feeble sparks should be employed, the brilliancy of which be little more than the minimum luminous intensity capable of producing some impression on the plate. (Blondlot, "Photographic Records of the Action of N-Rays", Scientific American, October 14, 1905 [4])
His equipment was erratic: he writes of "the impossibility of obtaining an absolutely exact regulation of the small spark". To compensate for this, he introduced an element of subjectivity into his supposedly objective experiment. In his words:
- The process used was practically the same as that employed previously, but for a telephone inserted in the secondary circuit of the induction coil. The assistant, by keeping the telephone receiver close to his ear, was in a position to check the regularity of the spark throughout the duration of the experiments. If the spark was extinguished owing to an excessive distance of the points, the sound in the telephone was also discontinued. If, on the contrary, the points touched each other, the sound became much more intense. Any irregularities in the spark might thus be detected, and if any were observed during a photographic experiment, the photographs were rejected. (Blondlot, "Photographic Records of the Action of N-Rays", Scientific American, October 14, 1905 [5])
So the assistant has to subjectively judge whether the experiment sounds right. Blondlot does not mention whether the assistant in these tests knew which photographs were meant to show the presence, and which the absence, of N-rays, or whether the assistant could see the spark; there is also the possibility that the assistant could, unconsciously, learn the difference between sparks that sounded right for N-rays and the weaker sparks that sounded right for the control experiments without N-rays.
As Blondlot doesn't describe the sort of careful double blind experimentation that would please a skeptic, we may reasonably assume that he didn't use it. At all events, by whatever means Blondlot managed to produce his results, his experiments failed to placate critics unable to replicate them.
[edit] Debunking
- He first showed me a card on which some circles had been painted in luminous paint. He turned down the gas light and called my attention to their increased luminosity, when the N ray was turned on. I said I saw no change. He said that was because my eyes were not sensitive enough, so that proved nothing. I asked him if I could move an opaque lead screen in and out of the path of the rays while he called out the fluctuations of the screen. He was almost 100 percent wrong and called out fluctuations when I made no movement at all, and that proved a lot, but I held my tongue. He then showed me the dimly lighted clock, and tried to convince me that he could see the hands when he held a large flat file just above his eyes. I asked if I could hold the file, for I had noticed a flat wooden ruler on his desk, and remembered that wood was one of the few substances that never emitted N rays. He agreed to this, and I felt around in the dark for the ruler and held it in front of his face. Oh, yes, he could see the hands perfectly. This also proved something.
- But the crucial and most exciting test was now to come. Accompanied by the assistant, who was by this time casting rather hostile glances at me, we went into the room where the spectroscope with the aluminum lenses and prism were installed. In place of an eyepiece, this instrument had a vertical thread, painted with luminous paint, which could be moved along in the region where the N ray spectrum was supposed to be turning a wheel having graduations and numerals on its rim. Blondlot took a seat in front of the instrument and slowly turned the wheel. The thread was supposed to brighten as it crossed the invisible lines of the N-ray spectrum. He read off the numbers on the graduated scale for a number of the lines, by the light of a small, darkroom red lantern. This experiment has convinced a number of skeptical visitors, as he could repeat his measurements in their presence, always getting the same numbers.
- I asked him to repeat his measurements, and reached over in the dark and lifted the aluminum prism from the spectroscope. He turned the wheel again, reading off the same numbers as before. (Robert Wood in William Seabrook's Doctor Wood: Modern Wizard of the Laboratory, 1941.[7])
Wood published his findings in Nature 70, 530-531 (29 September 1904)[8], writing:
- I am not only unable to report a single observation which appeared to indicate the existence of the rays, but left with a very firm conviction that the few experimenters who have obtained positive results, have been in some way deluded.
N-rays then died a quiet death as a physical phenomenon; but have retained a celebrated place in the annals of mass delusion.
[edit] Moral
There are a couple of morals to this story. The first is that we cannot rely on scientists (or anyone else) to be perfect unbiased observers giving reports uncolored by their preconceptions. Science must never be done based on the notion that scientists are ideal observers, but rather on the principle that they are not. The essential problem with the N-ray experiments was that they made human and fallible scientists into an essential part of their own experimental apparatus. This has nothing to do with how good they are as scientists: Blondlot and the many other scientists who confirmed his results were no slouches at science, but an aptitude for and educuation in science doesn't make a person less prone to unintentional self-deception.
The second thing to note is that when we are, reluctantly, forced to rely on the judgement or expertise of scientists (or anyone else) we can test whether they really do have this judgement by testing it in situations where they don't know what their judgement should be telling them. This is just what Wood did with his experiments with the lead screen, the substitution of the wooden ruler for the metal file, and the removal of the aluminum prism.
Similar situations don't often arise in physics, where objective measuring equipment is usually used in the investigation of claims. However, tests similar to those performed by Wood are often useful in the investigation of paranoramal claims, where the claims are often intrinsically subjective in nature. For example, experiments similar to Wood's lead screen experiment have been done to test the claims of some practitioners of alternative medicine to be personally sensitive to the chi (or "life force") of other people. The obvious way to test such a claim is to see whether they report detecting chi only in those cases when another person is in fact present, under circumstances where the psychic healer in question is unaware of whether or not there is anyone present whose chi s/he should be detecting, so that with each test the psychic has no preconceptions as to what results s/he ought to be reporting.
[edit] Further Reading
- Some of Blondlot's papers on N-rays can be found here.
- Robert Wood's book of comic verse, How To Tell The Birds From The Flowers, can be found here.
