Among this class of scientific blunders is the custom of applying the calculations of chances to experiments with living human beings. Thus in the now well-known mind-reading performances it was averred that by a mathematical calculation there would be but one chance in several hundred thousand of finding any object in a house or hall or assemblage; hence it was inferred that a new force, or manifestation of force, had been revealed to the world. The fallacies in this philosophy do not require a very long search; of the many objects in any house, or indeed in any public building, but a small minority would be accessible in any mind-reading test, and of these few only a limited number are of a sufficiently positive nature and description to be thought of by the subject of such experiments; then, in addition, are all the errors that come from intentional and unintentional assistance of audiences and bystanders.
Practically the only way to eliminate, in a scientific manner, the error of chance or coincidence in all experiments of that character, is by making comparative experiments in the same line, with all the sources of error closed except chance, and to repeat these a sufficient number of times to make an absolute domonstration. In this way it was shown that mind-reading, so called, was really muscle-reading. In these and in all studies of like character it is to be recognized that coincidences of the most extraordinary and astonishing nature are liable to occur at any instant, and that they are as likely to occur on the first trial as on the last of a long series. To determine whether any conjunction of events is simple coincidence, or the result of some new fact or law in science, is possible oftentimes only through a series of comparative experiments. In the researches which I made in muscle-reading it was shown over and over that by pure chance alone—every other element of error being excluded—the blindfold subject would, under certain conditions, find the object looked for in one case and sometimes in two cases out of twelve.
It would seem that the errors from chance and coincidence were the most patent of all the errors that complicate and confound scientific investigation, and so clear even to the unskilled and unthinking mind, that trained investigators would never be deluded by them. But in practice it vitiates the research and the philosophizing of educated men, even more perhaps than any other of the six, excepting the involuntary action of mind on body which, as we have seen, has been the stone of stumbling for physiologists ever since physiology was introduced into science.
Hay-fever, for half a century and more, has supplied an unusual richness of material for false reasoning of a similar type. An English physician, a victim of this disorder, notices that he is worse as he crosses a field of grass, and concludes that at last he has found the one source of the mystery, and so gives the affection a misleading name which it can never lose; Helmholtz, a leader both in physics and physiology, puts the nasal secretions under the microscope, discovers some
