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: Let A and B be two space objects. Fig 8. A two space being could not conceive of their being brought into the second position shown in the figure. [Illustration: _Fig. 8_] But we, having the advantage of a third dimension of space could very easily pick up the object A and put it down in the second position with regard to B. Similarly a four space being of sufficient knowledge and manipulative ability could, theoretically, slip on to the middle part of the dumb-bell a piece of steel tube of a diameter too small to be passed over the two large ends. There are, of course, a large number of variations which could be introduced into this class of experiment but the foregoing will be sufficient to indicate their salient features. For the purpose of detailed consideration I shall deal only with the case of the removal of a solid object from the interior of a closed and sealed box, which is typical of the whole of this class of phenomena.