It would at first sight appear as if Poltergeists should provide a useful standard of comparison for arriving at an opinion as to what causes, supernormal or otherwise, produce similar phe nomena in the seance room. Unfortunately, they give little assis tance. In the earlier cases (up to, say, 185o or thereabouts), the observers, even where they were intelligent and responsible per sons like the Wesleys, did not know what were the significant points to which to direct their attention ; and nowadays the inves tigator who knows what to look for does not usually arrive on the scene until a crowd of enterprising journalists, dogmatic spiritualists, and sensation-hunting members of the public has hopelessly "queered the pitch," and prevented the collection of first-hand, uncoloured evidence. The best Poltergeist cases, from the student's point of view, are those investigated in the latter half of the 19th century. There is a good collection of cases occurring between 1883 and 1896, and analysed by F. Pod more, in S.P.R. Proceedings vol. xii. ; and the spirited controversy between Podmore and Andrew Lang in vol. xvii. of the Proceed ings is instructive.
Poltergeist cases show a degree of uniformity which is remark able, in view of their being so widely distributed in time and space. It can almost invariably be shown that there is some one agent whose presence is essential for the production of the phenomena, although occasionally a secondary agent assists in their production ; if the principal agent is removed the phenomena cease at once. The agent is usually a person of some marked mental or physical abnormality, often a girl in her "teens," less often a boy of the same age, and only rarely an adult. In some cases there is obvious trickery, easily discoverable by any fairly good observer; in others the trickery is so cleverly done that only a skilled investigator can find it out; in a few cases does not seem to be an adequate explanation of the facts, assum ing these to have been accurately reported. Finally, there is an absence of any apparent motive sufficient, from the point of view of a sane adult, to account for all the trouble to which the agent puts himself and others; nothing is gained by the agent but the notoriety of a nine-days' wonder.
The problem is whether the undoubted existence of fraud (usu ally "hysterical fraud") in many of the cases justifies us in assuming that the same factor has operated in the unexplained residue. Podmore thought that it did; Lang that it did not. The controversy remains very much where they left it, owing to the paucity of well-recorded cases in recent years.
Although Poltergeists, for the reasons stated, are not as help ful in the study of experimental" physical phenomena as might be expected, or as they would be if competent observers were given a fair chance to observe them, there are, nevertheless, two ways in which they throw a useful light on doubtful problems of the seance-room. First, on the question of motive: with the evidence derived from Poltergeist cases in mind, it is less difficult to imagine that "physical" mediums, who often have a strong vein of childish vanity, may think that the sensation they create by their performances is in itself, quite apart from any material advantage, a sufficient compensation for maintaining over a long period an elaborate scheme of deception, sometimes imposing on the medium no little physical discomfort. Secondly, as to the
ease and rapidity with which skill in deception is acquired: a child after a few weeks' practice and relying on its own perverted ingenuity, may produce phenomena as baffling as a professional medium who has had years in which to perfect his technique, and who has some knowledge of the methods of other mediums.
It is impossible to classify, or even enumerate, all the kinds of "physical" phenomena which have been reported ; they in clude apparent breaches of all the generally accepted laws gov erning matter. Two kinds, however, have received closer study and attained more credence than the rest, telekinesis and tele plasm (also called ectoplasm).
Telekinesis is the movement of objects without the applica tion of any physical force known to science, and has a history dating back to the early days of spiritualism. Horne, Eusapia Palladino, Kathleen Goligher, Willy Schneider and "Margery" (Mrs. Crandon) may be named amongst the best known tele kinetic mediums.
Teleplasm is a "substance" extruded from the medium's body; it may be either wholly invisible, or visible but amorphous, or it may take the form of a complete human figure, apparently endowed with energies of its own, like "Katie King," to whose reality Crookes testified. Among recent teleplastic mediums may be mentioned Eva C., Kluski, Kathleen Goligher, "Margery." It will be noted that two names are common to the telekinetic and teleplastic lists, and as the result, especially of Crawford's experiments with Kathleen Goligher, it is a general opinion among those students who accept the genuineness of both classes of phenomena (and they include several scientists of repute, es pecially on the Continent), that it is by force exerted through teleplastic rods or structures that telekinetic movements of objects are effected. For teleplasm itself the "ideoplastic" theory has gained wide acceptance. According to this theory, teleplasm is moulded into definite shape by the thoughts of the medium and the sitters ; attempts have been made to fortify the theory by analogies from the real or supposed facts of normal biology, the influence, e.g., of a mother's thoughts on the development of the child within her womb.