"Without now stopping to consider any _a priori_ speculations as to the scientific possibility or impossibility of such a thing; the mere historic evidence in the case would certainly seem to point to the conclusion that fraud and nothing but fraud has been operative throughout and is quite sufficient to account for all the phenomena observed (save in the case of W.S. Moses, perhaps, that stumbling block to the rationalistic psychical researcher), in the presence of professional mediums.... In fact _all_ these cases sift themselves down to the one primary consideration: could the medium, in spite of the searching, have introduced into the séance room, unseen by his sitters, the objects materialised." It should be noted that the above refers to cases where the séance room is found, after the sitting, to contain objects which were certainly not there before. In this connection the last sentence of the passage quoted above is eminently justifiable and it is for this reason that I prefer to deal with varieties of the phenomenon which are more amenable to experimental control on the part of the experimenter; as for instance the removal of a solid object from the sealed box which we are considering. Compare with this first quotation the following taken from Mr. Gambier Bolton's book "Psychic Force." "During my sixteen years of experimental investigation into the question of the existence of this Psychic Force, the apparent penetration of matter by matter has been such a common occurrence at our experimental meetings, that unless this happens to take place in connection with some unusually large and ponderous object that is suddenly brought into our midst, or removed from the place where we are holding our meetings, I take but very little note of it. I could fill a large volume with instances where this has taken place in my own presence.... I am not engaged in an attempt to explain such things, but am merely recording phenomena which I myself have witnessed and which have been witnessed hundreds, nay thousands, of times by well-known investigators like Sir William Crookes and Dr. Alfred Russel Wallace under the strictest test conditions." These two views are, to say the least of it, somewhat divergent. We must, therefore, see what is to be gathered from such original records as are available. The _locus classicus_ of this sort of phenomenon is the Slade-Zöllner investigation of 1877-9. This investigation has received so much attention that it is impossible to avoid giving it somewhat careful consideration here. Johann Carl Friedrich Zöllner was born in 1834. He was Professor of Physics and Astronomy at the University of Leipsic, a member of many learned and scientific societies and the author of a number of scientific treatises.