But the literature of Psychical research abounds with instances where objects are alleged to have been introduced into such closed and sealed rooms and boxes—or removed from them, which comes to the same thing—without breaking the seals. This is the phenomenon of "apport" properly so called and it forms a special case of the more general class of "apparent penetration of matter by matter."
Other cases of the latter are the tying of knots in an endless cord of such a nature that they can only be untied by breaking the cord or separating its previously sealed ends; or the passing, on to the wrist or ankle of some person or other, of a ring so small that it could not possibly be pushed on over the hand or foot.
A very good test would be the interlinking of two rings turned from different sorts of wood—as was attempted without success in the Slade-Zöllner investigation; or the passing of a piece of weldless drawn steel tube on to the middle portion of an ordinary wooden dumb-bell.
With regard to these phenomena I propose, first, to show in what their very great importance lies and then to discuss the nature of the evidence we have for their actual occurrence.
If the reader will refer back to the first chapter, he will at once perceive why I laid what must have appeared to be unnecessary stress on the fact that "rooms" and "boxes" which would appear to be absolutely closed to a two space being would be perfectly open to us who live in a three space world. Just as every point in the interior of a two space figure is absolutely open in the direction of the third dimension, so we must suppose from analogy that the interior of a closed three space figure—a box or room—is perfectly accessible from the direction of the fourth dimension.
Consequently on the hypothesis that four space actually exists as a reality, and is peopled by intelligent beings, possessed of the necessary "apparatus"—whatever that may be—the explanation of the phenomenon of apport is quite simple.
We have only to suppose that the object in question is moved out of the containing space, in the direction of the fourth dimension, and then put down again into three space outside the box or room in which it originally was. Or conversely, when it is a question of introducing an object into a closed space.
During transit, the object would, of course, be located entirely outside of three space.
I will not go at length into the question of how the tying of knots in an endless cord could be performed in four space. Any reader who cares to tie together the two ends of a piece of string for himself, will soon realise that it is not possible then to tie a simple knot in the string without untying the ends. If such an operation were to be performed, under test conditions, it would clearly be a case of apparent penetration of matter by matter.
Consider this case which is analogous to that of the steel tube and the dumb-bell suggested above: