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.

He was assisted, from time to time, in his investigations by Professors Weber, Fechner, and Scheibner all of whom were men of considerable eminence in one branch or another of mathematical or physical science.

The medium in whose presence the phenomena were produced was the well-known "Dr." Slade. This medium has been demonstrated to have resorted to fraud with a certainty that admits of no dispute.

But, as Mr. Hereward Carrington points out, we ought not to allow this fact to influence us in the consideration of any particular case. In the first place it is fairly certain that mediums who are capable of producing genuine phenomena under suitable conditions are also liable to resort to trickery when the genuine thing does not come off. (Cp. the case of Eusapia Palladino.) In the second, too great a reliance on antecedents is apt to produce an unreliable a priori prejudice. Every case should be considered on its merits alone and the medium's past history should only be allowed to influence our judgment if it can be shown that fraud has not been rigorously excluded and that the only argument against it is the argument from moral integrity.

In this case the argument from integrity is obviously inadmissible and as a matter of fact the precautions taken to guard against fraud were so very inadequate that we cannot accept the experiments in question as worth anything at all from the scientific point of view.

Zöllner's account of his experiments is to be found in his book "Transcendental Physics," translated into English by Mr. C.C. Massey in whom the author found an able and enthusiastic champion against his many critics.

Among the more important of his experiments were:

Production of knots in an endless string.

Slate writing under "test" conditions.

Disappearance and reappearance of solid objects.

Coins transferred from closed and fastened boxes.

Other instances of the apparent penetration of matter by matter.

The careful study of this book is of the greatest value as an exercise in the criticism of evidence and as a guide for anyone who proposes to study such matters at first hand.

I do not think that I can illustrate my meaning better than by a description of my own impressions in connection with the book.

When I first read it I was much impressed by the scientific eminence of those who bore witness to the authenticity of the events described.

I reflected that here we had a Physicist of no mean order, assisted by other scientists of European reputation, men trained, presumably, in the art of exact observation and not likely to be deceived by the manipulations of a conjuror. Surely we must believe their testimony if we are to assign any value to human evidence at all!

Then, as I thought over the matter more and became more convinced of the importance of the conclusions to be drawn from these experiments, if genuine, I felt that these considerations, although possessed of their own importance, were yet not sufficient to warrant acceptance of the evidence without careful examination of the intrinsic qualities of the latter.

On further study of the book I was struck by the fact that not one of the special experiments, carefully designed by Zöllner to establish the genuineness of the phenomena and the validity of the four-dimensional explanation beyond all doubt, had succeeded. This was suspicious, although not, of course, conclusive. Specially devised test experiments may very likely fail simply because they may involve the upsetting of some essential condition which is not fully understood by the experimenter. But when such experiments fail, while others of, apparently, identical general nature succeed, it gives one cause for thought.

Finally, when I came to examine the records of individual experiments in the light of the criticisms of Mr. Carrington, of Dr. Hyslop and others, I realised that the nature of the evidence was emphatically not good enough to justify our accepting as demonstrated the facts which Zöllner claimed to have established.

I shall not waste my own time and that of the reader by giving numerous instances of the sort of thing I mean.

I will confine myself to the case that we are more especially considering as being typical of the whole of this class of phenomena, i.e., the case of the removal of a coin from a closed and fastened box.

Zöllner describes how in December 1877 he put some coins in a small cardboard box and had closed it by glueing a strip of paper round the sides. He had done this in the expressed hope that Slade might be able to remove them and thus give a proof of the reality of the fourth dimension which was Zöllner's pet hobby. In May 1878 Slade came again to Leipsic and performed the feat, at any rate to the satisfaction of Zöllner.

The box was put on a table together with some slates and other objects and Slade and Zöllner and his colleagues sat round. Zöllner satisfied himself by shaking the box that the coin was still inside and in answer to Slade's enquiries explained the purpose of the experiment and its importance if successful. There was a little preliminary slate writing and then Slade began staring into a corner of the room and saying "I see funf and eighteen hundred seventy six." Then a hard object was heard to fall on the slate which Slade had held under the table all the time and on withdrawing the slate it was found to be a five mark piece of date 1876. Zöllner then snatched up the cardboard box and shook it only to find that it was empty.

This is a very highly condensed description of the proceedings but I do not think I have been guilty either of "suggestio falsi" or of "suppressio veri".

Interested readers can refer to the original.

Now, if Zöllner had been writing no more than a casual account of a well-known experiment, inserted for the sake of completeness or for similar reasons, it would be well enough.

But to offer his account, in the face of a very natural scientific incredulity, as a conclusive demonstration of a highly controversial point, was an insult to one's intelligence.

There are numerous criticisms that might be made, but I shall confine myself to pointing out only the more conspicuous of them.

In this experiment there are two main methods by which the result might have been obtained by fraudulent means.

There seems no doubt that the coin was really in the box at the beginning of the sitting. We may equally accept the statement that the box shaken at the end of the experiment did not contain a coin.

On the hypothesis of fraud, therefore, one of two things must have happened.

Either Slade must have contrived, during the sitting, to possess himself of the box, open it, abstract the coin, close the box again, and return it to the table; or else he must have substituted for the box, which at the beginning of the sitting contained the coin, another (empty) box, previously prepared to resemble the original.

I do not think the former method to be at all likely.

One cannot unstick a length of glued paper and stick it up again in a few seconds unobserved.

On the other hand everything lends itself to the supposition that the second method was actually adopted.

In the first place we know that the box was prepared some six months previous to the experiment.

It is true that Zöllner is a trifle hazy as to dates, saying at the outset that Slade's first visit to Leipsic was in December 1877, and, later, that the first and second visits were in November and December 1877.

But this is comparatively immaterial, the point being that Slade had presumably had ample time and opportunity for finding out all about these boxes and for preparing substitutes. I say "presumably" because in the absence of definite evidence to the contrary, we have no reason to suppose that these boxes were kept in an inaccessible place or that Zöllner had never mentioned his intentions with regard to them to Slade himself or to anyone else. I consider then that so far as the records go, we are perfectly entitled to suppose that Slade was able to prepare, and, in fact, actually did prepare, an empty counterfeit box, externally similar to that prepared by Zöllner. The second, and almost incredible, point to be noticed is that apparently no steps of any sort were taken by Zöllner to identify either the box or the coin after the sitting with those originally prepared by him.

In fact, he definitely says that he had completely forgotten, indeed had never so much as observed, the value or dates of the coins used!

With such gross carelessness in the control, the trick becomes exceptionally easy to perform.

Slade goes to the séance armed, among other things, with an empty, counterfeit box resembling Zöllner's, also with a five-mark piece of the right date—I think that even Zöllner would have been suspicious if the coin that fell on the slate had been dated 1878! Zöllner shakes his box—the genuine one—and satisfies himself that the coin is really there. Then follows a little preliminary play with the slate and so on, the simplest matter in the world to an artist like Slade. At the critical moment Slade diverts the attention of the experimenters from the table by the world-old conjuror's dodge of gazing fixedly in some other direction and murmuring "I see—see—funf," etc. While Zöllner and his colleagues are glancing in the same direction to see what he is looking at, Slade swiftly substitutes his counterfeit box for the original, and the trick is to all intents and purposes done. All he has now to do is to drop the coin which he brought with him on to the slate at any convenient moment and draw out the latter in triumph!

Given the astounding guilelessness of Zöllner and the complete lack of control revealed by the records, the thing was absurdly simple.

And yet Zöllner refers to it as having been performed under "such stringent conditions!"

The foregoing example will, I hope, make quite clear how much importance I attach to the Slade-Zöllner investigations.

I am not prepared to say that Slade never produced genuine phenomena, either with Zöllner or with anyone else.

On the contrary, I think it probable that he possessed a certain amount of genuine mediumistic power which, however, he did not hesitate to supplement by cheating when occasion offered.

Some, or for that matter all, of the Slade-Zöllner experiments may happen to have been genuine. But in view of the known untrustworthiness of Slade and the complete lack of proper scientific control revealed by a study of the published records we must write them off as quite valueless from a scientific point of view.

I have dealt with this particular case at some length partly on account of the vehemence of the controversies which have raged round it and partly because the discrediting of Zöllner's observations has done much to bring the whole idea of the fourth dimension into disfavour and even into ridicule. This, I feel, is unfair and I wish to make it clear that my present advocacy of the claims of the higher space hypothesis is in no way based on the Zöllner experiments.

There are, of course, in the literature of the subject a large number of other cases which are not so obviously unreliable—some, in fact, which are distinctly good.

Dr. S.A. Peters gives an account of an early experiment by Dr. Hare—one of the pioneer investigators—in which two small balls of platinum were transferred to the inside of two hermetically sealed glass tubes. It is not a bad case but is a very old one and the record gives no particulars of any special precautions taken to exclude fraud.

The Milan Committee appointed to investigate the mediumship of Eusapia Palladino failed to obtain any confirmation of Zöllner's experiments, but they seem to have been puzzled by an unaccountable incident where the medium managed to get into, or partially into, a coat while her hands were being held by the Committee. I do not myself regard this case as convincing.

The American Society for Psychical Research recorded some observations with a Mrs. Roberts of New York, who managed to liberate herself from a carefully made and sealed cage which was closed and sealed by members of the investigating committee. I do not know anything at first-hand about the credentials of this case. Dr. Paul Joire quotes it and I suppose, therefore, that he considers it reliable.

The same author also quotes at length a case observed by Dr. Pogorelsky and other Russian investigators with the medium Sambor. In this case a cane chair was passed on to the arms of two of the experimenters whose hands were clasped and bound together. That is to say, whereas to start with the chair was by itself and independent of them it was, at the end of the proceedings, found suspended from their arms by the opening at the back. As the opening was too small for either of them to have wriggled through even if they had wished to do so this was a clear case of apparent penetration of matter by matter.

The evidence in this case seems to be well above the average although it cannot be said to amount to mathematical certainty.

Mr. Gambier Bolton gives a distinctly good case in his book "Psychic Force," p. 65. Under exceptionally favourable conditions he observed the removal of a light table from a sort of tent which he had constructed and very carefully closed and secured. This is one of the best cases I know; it took place in the observer's own room, it was done impromptu, it was well observed in light, and all the objects concerned were the observer's property and not of a kind to admit of prestidigitation. It is difficult to see any way out of it and yet I must confess that I am not wholly satisfied. I feel that in every case there is just something more needed to carry complete conviction and I should very much like to see a good case myself.

Other instances are common. The records of the mediumship of Stainton Moses, for instance, abound with them. But as there were never any test conditions imposed, so far as I am aware, it follows that the question of the genuineness of the phenomena is simply a matter of the integrity of the medium. On this point every reader must be left to form his own opinion. Many authorities have professed the greatest confidence in Moses. Mr. Podmore, on the other hand, presents the suspicious features of the case in a very able criticism in his "Modern Spiritualism." Anyway on a point of such importance as this I do not think it would be right to allow the matter to be settled by any purely moral considerations of the type adduced in the case of Moses.

In general, then, I should say that the phenomena of the apparent penetration of matter by matter are not established with the same degree of certainty which characterises certain other phenomena, and which we ought to demand before accepting them as scientifically proven or utilising them without reserve as a basis for the construction of theories.

In the interests of the science it is in the highest degree important that experiments of this nature should be carried out under real test conditions.

Should any of my readers be so fortunate as to be acquainted with any medium capable of producing these very rare phenomena with regularity, I should esteem it a great favour if they would kindly inform me. I would very much like to arrange some definite experiments to settle the matter—if possible once and for all.

There is one other direction from which, in my opinion, we receive a strong hint that four-dimensional space is intimately connected with Psychic phenomena.

I refer to Crawford's work on table levitation. This investigation is undoubtedly destined to take rank as a "classical" research of the first magnitude and no one who professes to take an intelligent interest in the scientific and experimental aspects of Psychic investigations can afford to be without his book.[4]

In a later chapter I shall have occasion to refer to certain aspects of his results and to show how they fit in with those of other investigators working on very different lines.

In the present context I propose only to call attention to the rigidity of his "cantilever," a phrase which perhaps needs some explanation.

As a result of the most careful and painstaking researches extending over a period of nearly three years and performed under conditions which were singularly favourable for observation, he has been enabled to arrive at certain definite conclusions as to the mechanical causes of telekinesis in general and table levitation without contact in particular.

He finds that when the table is lifted clear of the floor it is supported by a definite structure or cantilever. This structure is invisible and impalpable, or nearly so, and appears to be organised out of some form of matter actually taken from the body of the medium.

Dr. Crawford has been able to work out the form and size of this structure with considerable accuracy. For the details of method and results the reader should consult his book. It is possible to pass a thin rod through this structure in any direction without causing a breakdown, and without encountering any perceptible resistance.

Nevertheless the structure can resist compressional, tensional and torsional stresses of very considerable magnitude as I am able to testify from personal experience.

I may mention here that I have witnessed these phenomena myself under good observing conditions and that I am prepared to certify in the most unequivocal manner that they are absolutely authentic; that is to say the result neither of fraud—conscious or unconscious—nor of illusion.

Indeed, I do not suppose that an intelligent person could suppose them to be due to anything of the sort after a careful study of Dr. Crawford's book, quite apart from any personal observation and I only add my own testimony as a small make-weight for what it may be worth.

We are here confronted with a sort of mechanical paradox. How can we conceive that the structure manages to combine the contrary attributes of rigidity and impalpability? Rigidity means simply the power of resisting deformation under stress. That is to say that in order for a body to be rigid it must be capable of developing within itself forces which shall counteract those which tend to deform it. If we apply a stress—a deforming force—to a rigid body, then this force must be met by some opposing force; otherwise the body will be deformed. Normally this is a matter of molecular cohesion, etc.

Now, this structure resists deformation under stress, and it therefore follows that the deforming forces must be counteracted by opposing forces.

But the structure is impalpable, and we can pass a rod through it in any direction without encountering any resistance.

This being so it is difficult to conceive how the forces resisting deformation can be applied from any direction in which we can move the rod, i.e., from any direction known and accessible to us.

The more one tries to think out what is involved in the idea of an impalpable and yet rigid structure, the more hopeless it seems.

But I think that the concept of four-dimensional space will help us even here.

We know two things. First that the structure is rigid and therefore that the deforming stresses are counteracted by opposing forces and, second, that these opposing forces are apparently not applied from any direction with which we are acquainted. But is it not possible that they may be applied from some direction with which we are not acquainted?

From some direction, in fact, of which the hypothetical fourth rectangular axis of space is a component.

Is it possible that the matter which is drawn from the body of the medium, and which forms the structure, is composed of molecules whose atoms are arranged not in space of three dimensions but in space of four dimensions?

I do not say that this is necessarily so; but I must confess that to me it looks rather like it. Still less am I prepared to say that the atoms are arranged four dimensionally. We do not know enough for that yet. But it is, I think, a possibility, although for all I know to the contrary there may be many other ways in which forces operating in four space might act on three-dimensional atoms and molecules.

Consider a two-dimensional analogy again.

Imagine a number of flat-headed drawing pins lying points upward on a flat surface. Taken collectively as a system they will have no rigidity. Now imagine a board pressed down on those points so that they penetrate into the board. The points and the board alike will be invisible to the two space beings inhabiting the surface and yet the drawing-pins, taken collectively as a system would have acquired rigidity. Deforming stresses would be resisted by cohesive forces operating outside the two space surface altogether.

This analogy is, naturally, imperfect; but I think that it enables us to form some idea of the way in which the rigidity of the levitating structure might result from its being held together by binding forces operating outside our space.

The only alternative is to suppose that the particles of which the structure is composed are rendered rigid by virtue of some peculiar motion of the ether of a nature entirely unknown to us and different from any type of ethereal motion with which we are at present acquainted. This is palpably unsatisfactory and has the grave defect, in an explanation, of failing even to begin to explain.

In an article published in "Light," for July 14, 1917, I discussed this point in somewhat greater detail.

This is all that I have to say with respect to the phenomena which are essentially "Psychical." In the next chapter I shall deal with two other applications of the theory to more general questions.