Hatred of science and the joy of opposing it, combined with an uncritical tendency to mysticism, explain how it is that occultists acknowledge a belief in such heterogeneous domains of the the phenomenal as those of the divining-rod, animal magnetism, homoeopathy, and the action of the magnet on human beings. // would be safe to bet 10 to 1 that, if science were to give official recognition to animal magnetism and transposition of the senses, a very large number of occultists would at once commence an attack on those beliefs.

2. As further sources of error, I must mention sense-delusions and all kinds of errors of perception. Spiritists are particularly prone to sense-delusions. One can readily observe at spiritistic seances the way in which semi-darkness facilitates the appearance of all kinds of forms, and how everything is magnified by imagination. I remember a stance at which, on a lady declaring she could see an apparition, a gentleman present told her to close her eyes, because she was obviously not seeing with them, but with her stomach; and that, therefore, she could see much better with her eyes closed. It is often very difficult to distinguish accurately from what direction the sounds and noises come. For this reason, spiritists who are in a dark room believe they hear the music of guitars that are floating about in the air, whereas the instruments really remain in the same place all the time. It is the same with the "raps" which spiritists declare proceed from the tablecloth or the table itself, although they are really produced by the medium's foot.

These illusions of perception extend even farther.. Any one who wishes to see inanimate objects move of their own accord, and who for a considerable time vividly expects the occurrence of the phenomena, is very likely to see such movements, although the objects never stir from their respective positions. It was precisely in the case of Harnack's subject (p. 505) that I saw how easily tension of the apparatus of attention leads to the illusory perception of movements which objective investigation proves never took place.

3. Illusions of memory constitute another source of error. I have already pointed out their importance when discussing cases of the supposed appearance of dying persons to friends or relatives at a distance, and will only add that Christian considers illusions of memory a special source of error in telepathic experiments. In clairvoyance, also, it may happen that when a phenomenon occurs many people may believe that they have seen it before. Mnemonic adaptation, which has already been mentioned, is just as important as illusions of memory, because details that do not favour an occultistic interpretation of the phenomena may be subsequently eliminated by a capricious use of the imagination.

There is one special form of illusion of memory that has to be considered in many cases. It has been described by Bernard Leroy, a French author, who calls it Illusion de fausse reconnaissance, but Sander, Kraepelin and others had previously reported cases of the kind. The phenomenon consists in a person having the impression that he sees or experiences something for a second time, which is really perfectly new to him. Although in most cases the error is at once corrected and the illusion recognized, there are others in which this does not occur. This is particularly the case in mental disease, but it may also happen when the subject is perfectly normal. The effect produced on some people by this phenomenon is peculiar. They neither consider the whole affair an illusion, nor do they believe that the incident had ever really once happened to them; on the contrary, they are convinced that this is its first occurrence, but they believe that they have once had a mental vision of it This leads them to the conviction that they possess the power of prevision, and some, indeed, declare they are clairvoyant in their dreams, others in the waking state.

Undoubtedly this mnemonic error explains many cases of prophetic dreams and also of second sight, which latter, according to Perty, is but the vision of a present or coming event seen in a rapidly-passing delirium occurring in the waking state.

We have also to reckon with a further source of error that lies in the memory. It consists in a person being under a delusion as to what he recollected at a particular time. An example of this. X. went to a clairvoyante who told him of something that had happened to him years before. He admitted the accuracy of her statement, but subsequently explained that he had completely forgotten that episode of his life until the clairvoyante reminded him of it. From this he would have us believe that the clairvoyante could not have acquired any knowledge of his past either by telepathy or from any signs made by him. A careful investigation of several of these cases has provided me with almost irrefutable evidence that X. may quite well have recollected the episode during the stance but have afterwards believed that he had previously forgotten all about it until reminded of it. During the stances the clairvoyante by her remarks drew X.'s attention to things he had forgotten, and the associations thereby aroused refreshed his memory on various points. The excitement that prevailed and X.'s feeling of expectance favoured the stirring up of such recollections. As we saw when discussing telepathy, directly a subject recollects anything the fact is easily betrayed by his making some sign.

The prevailing excitement smooths the way for subsequent mnemonic errors, so that X. is quite unable to decide later on whether he remembered the episode at a certain moment or whether the clairvoyante made him think of it at that moment. We know that this kind of confusion of memory often occurs, and I consider it far from improbable that the seances of the "great medium" Mrs. Piper may be partly explained in this way.

Mrs. Piper is an American medium. It is said of Mrs. Piper - or, rather, of the spirit that is supposed by spiritists to act through her - that, in the course of some very carefully conducted experiments, she spoke of things of which she could previously have had no knowledge. The most frequently cited cases are those in which she held stances with Professor Hyslop, to whom she communicated facts concerninghis dead relatives, which apparently she could not have learned in any ordinary way. Max Dessoir does not consider this a case of simple fraud, and we must admit that if it was, the fraud was perpetrated very cunningly. But Max Dessoir also thinks that the telepathic theory fails to afford an explanation, for the very reason that Hyslop may very well at one time have known of these matters, but that he was certainly unaware of them when the medium related them. Now, Max Dessoir thinks that there is certainly no instance of a medium having acquired by telepathic means a knowledge of what is unconsciously retained in another person's memory. Since Hyslop, moreover, was unconscious of these matters at the time the medium mentioned them, it seems that we may exclude the possibility of his having guided her by signs.