Pathological science
Pathological science is the process in science in which "people are tricked into false results ... by subjective effects, wishful thinking or threshold interactions". The term was first used by Irving Langmuir, Nobel Prize-winning chemist, during a 1953 colloquium at the Knolls Research Laboratory. Langmuir said a pathological science is an area of research that simply will not "go away" long after it was given up on as 'false' by the majority of scientists in the field. He called pathological science "the science of things that aren't so".  Bart Simon lists it among practices pretending to be science: "categories  pseudoscience, amateur science, deviant or fraudulent science, bad science, junk science, and popular science  pathological science, cargo-cult science, and voodoo science ..".
On the other hand, Professor Emeritus Henry H. Bauer said that " 'pathological science' is not scientific misconduct (nor is it pathological)", that "it lacks justification in contemporary understanding of science studies (history, philosophy, and sociology of science)", and that "it is time to abandon the phrase".
Examples of pathological science may include N-rays, polywater, water memory, and cold fusion.

# Definition
Pathological science, as defined by Langmuir, is a psychological process in which a scientist, originally conforming to the scientific method, unconsciously veers from that method, and begins a pathological process of wishful data interpretation (see the Observer-expectancy effect cognitive bias). Some characteristics of pathological science are:
- The maximum effect that is observed is produced by a causative agent of barely detectable intensity, and the magnitude of the effect is substantially independent of the intensity of the cause.
- The effect is of a magnitude that remains close to the limit of detectability, or many measurements are necessary because of the very low statistical significance of the results.
- There are claims of great accuracy.
- Fantastic theories contrary to experience are suggested.
- Criticisms are met by ad hoc excuses.
- The ratio of supporters to critics rises and then falls gradually to oblivion.
Langmuir never intended the term to be rigorously defined; it was simply the title of his talk on some examples of "weird science". As with any attempt to define the scientific endeavor, examples and counterexamples can always be found.

# Langmuir's examples

## N-rays
Langmuir discussed the issue of N-rays as an example of pathological science.
The discoverer, Rene-Prosper Blondlot, was working on X-rays (as were many physicists of the era) and noticed a new visible radiation that could penetrate aluminium. He devised experiments in which a barely visible object was illuminated by these N-rays, and thus became considerably "more visible". Blondlot claimed that N-Rays also produced a small visual reaction, which could only be seen when most "normal" light sources were removed and the target was just barely visible to begin with.
After a time another physicist, Robert W. Wood, decided to visit Blondlot's lab, where he had since moved on to the physical characterization of N-rays. The experiment passed the rays from a 2 mm slit through an aluminum prism, from which he was measuring the index of refraction to a precision that required measurements accurate to within 0.01 mm.
Wood asked how it was possible that he could measure something to 0.01 mm from a 2 mm source, a physical impossibility in the propagation of any kind of wave. Blondlot replied, "That's one of the fascinating things about the N-rays. They don't follow the ordinary laws of science that you ordinarily think of."
Wood then asked to see the experiments being run as usual, which took place in a room required to be very dark so the target was barely visible. Blondlot repeated his most recent experiments and got the same resultsdespite the fact that Wood had reached over and covertly sabotaged the N-ray apparatus.

## Other examples
Langmuir offered additional examples of what he regarded as pathological science in his original speech:
- The Davis-Barnes effect (1929) After Professor Bergen Davis from Columbia University
- The Mitogenetic rays of (1923) Alexander Gurwitsch and others
- The Allison effect (1927) After Fred Allison	
- Extrasensory perception (1934)
- Flying saucers

# Newer examples
Since Langmuir's original talk, a number of newer examples of what appear to be pathological science have appeared.

## Polywater
Polywater was a form of water which appeared to have a much higher boiling point and much lower freezing point than normal water; many articles were published on the subject, and research on polywater was done around the world with mixed results. Eventually it was determined that many of the properties of polywater could be explained by biological contamination and when more rigorous cleaning of glassware and experimental controls were introduced polywater could no longer be produced. It took several years for the concept of polywater to die in spite of the later negative results.

## Cold fusion
Since the announcement of Pons and Fleischmann in 1989, cold fusion has been considered  by many to be an example of pathological science.  In 2004, a US Department of Energy panel identified several areas where more research might resolve the continuing scientific issues, but did not recommend federal funding for cold fusion research.  While the reviewers were split on the evidence of excess heat, most did not find the evidence of nuclear origin conclusive.

# Scientific theories that are not pathological science
As with any definition, it is useful to consider examples that do not apply but have features that may be in common. This can be a useful filter to separate closely related concepts.
For instance, according to the "scientist's account" of the progress of science, theory generally follows from experiment, and those theories are always open to change when new evidence is presented.

## The cubical atom
Langmuir himself was at one time a supporter of the cubical atom, a simple model of atomic theory. This model was later abandoned in favor of the Bohr atom, which offered a much simpler and richer understanding of the collected experimental results. There was no "pathology" taking place: when Bohr's model came along, the supporters of the cubical atom had no particular interest in it anymore, and it quickly disappeared.

## Continental drift
The theory of continental drift was proposed in 1912 by Alfred Wegener but not taken seriously by geologists until well into the 1960s.  While it sounded fantastic in the first half of the last century it did make clear predictions about the movement of the continental plates, and as soon as the mechanisms driving plate tectonics (the theory which replaced continental drift) and seafloor spreading were elucidated, the theory gained wide acceptance. There was no pathology involved  the evidence appeared, grew, and was eventually accepted. So simply "not being accepted" at a point in time also proves not to be a useful demarcation line.

## Lysenkoism
Lysenkoism is named after Trofim Lysenko and refers to a period of Soviet science in which political ideas superseded scientific rigour. Lysenko was an influential political figure, but his ideas were devoid of scientific merit; many scientists of the time were forced into publicly recanting politically unacceptable ideas such as genetics and heredity (those that refused were imprisoned or executed). Once again, there was no pathology involved in the legitimate scientific community. Rather, it was imposed by the political system.

# Notes
-  Irving Langmuir, "Colloquium on Pathological Science", held at The Knolls Research Laboratory, December 18, 1953. A recording of the actual talk was made, but apparently lost, though a recorded transcript was produced by Langmuir a few months later. A transcript is available on the Web site of Kenneth Steiglitz, Professor of Computer Science, Princeton University. But see also: I. Langmuir, "Pathological Science", General Electric, (Distribution Unit, Bldg. 5, Room 345, Research and Development Center, P. O. Box 8, Schenectady, NY 12301), 68-C-035 (1968); I. Langmuir, "Pathological Science", (1989) Physics Today, Volume 42, Issue 10, October 1989, pp.36-48
-  Park, Robert (2000). Voodoo Science: The Road from Foolishness to Fraud. Oxford University Press. ISBN 0-19-513515-6..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
-  Bart Simon, "Undead Science: Science Studies and the Afterlife of Cold Fusion" (2002) ISBN 0-8135-3154-3. Simon refers to: Thomas F. Gieryn, "Cultural Boundaries of Science : Credibility on the Line" (1999) University Of Chicago Press, ISBN 0-226-29262-2
-  Jump up to: 4.0 4.1 Henry H. Bauer, "'Pathological Science' is not Scientific Misconduct (nor is it pathological)" HYLE--International Journal for Philosophy of Chemistry, Vol. 8, No.1 (2002), pp. 5-20
-  For a review and bibliography, see Hollander and Claus, J. Opt. Soc. Am., 25, 270-286 (1935).
-  F. Allison and E.S. Murphy, J. Am. Chem. Soc., 52, 3796 (1930). (b) F. Allison, Ind. Eng. Chem., 4, 9 (1932). (c) S. S. Cooper and T. R. Ball, J. Chem Ed., 13, 210 (1936), also pp. 278 and 326. (d) M. A. Jeppesen and R. M. Bell, Phys. Rev., 47, 546 (1935). (e) H. F. Mildrum and B. M. Schmidt, Air Force Aero Prop. Lab. AFAPL-TR-66-52 (May 1966).