results of the experiments must be accepted by science. Scientifically it makes no difference whether the subject on whom any such experiment is performed is honest or dishonest; the experiments are to be made without any reference to the moral character of the subject.
Fourth Source of Error: Unintentional collusion of third parties.—By third parties are meant audiences, witnesses, bystanders, or assistants seen or unseen.
The best illustration of error from this source is the aid which audiences in the mind-reading experiments give to the performer by their silence, when he wanders away from the object looked for, and by their murmurs and applause when he approaches or reaches it. This is quite analogous to the cry of "hot" or "cold" in the game of "blind-man’s buff." So natural is it for errors from this cause to enter these investigations that I found it necessary, in all my researches in that department, to send all witnesses from the room, or to insist on then: being absolutely silent, and even motionless, at every stage of the experiments.
Fifth Source of Error: Intentional collusion of third parties.—Under this head comes the aid which assistants, known or unknown, designedly give to the subject experimented on. This, in the abstract, is one of the more readily suspected of all the six sources of error, but in the concrete very difficult to guard against, or even to detect, as is so brilliantly illustrated in the conjuring tricks of Houdin and Heller, and it may be added also, in the operations of so-called "confidence-men."
The best and most mystifying tricks of illusionists, and sleight-of hand performers of all kinds, are almost always done through some form of collusion, the time and method of which are so artfully arranged that only those of unusual acuteness or expert skill can at once detect them. The astounding success of clairvoyants and mediums in telling people what they already know, but which they suppose can not be known to the witch they are consulting, is oftentimes explained by this fifth source of error.
Intentional, deliberate deception, where no money is to be gained by deception, is much more common among the better classes than those who have not specially studied this subject would be willing to believe: it is an instructive fact in the psychology of lying, that some persons—usually, though not always, women—whose general character is of the highest, are in some special direction absolutely systematically untruthful all their lives long. An old merchant of New York once told me that a clerk in his employ, trustworthy in all business affairs, exact, scrupulous, just, had a habit of telling large stories in regard to what he had seen and done so firmly fixed that it was organically impossible for him to restrict himself to the facts, and that his statements in regard to matters outside of business were worthy of absolutely no credence.
I was once requested by a valued medical friend to aid him in some experiments with a case of alleged sixth sense, or the asserted power of
