If now we suppose the cube to be an inch in each dimension, and to pass across, from right to left, through the plane, then we should explain the appearances presented to the plane being by saying: First of all you have the face of a cube, this lasts only a moment; then you have a figure of the same shape but differently coloured. This, which appears not to move to you in any direction which you know of, is really moving transverse to your plane world. Its appearance is unaltered, but each moment it is something different—a section further on, in the white, the unknown dimension. Finally, at the end of the minute, a face comes in exactly like the face you first saw. This finishes up the cube—it is the further face in the unknown dimension. The white line, which extends in length just like the red or the yellow, you do not see as extensive; you apprehend it simply as an enduring white point. The null point, under the condition of movement of the cube, vanishes in a moment, the lasting white point is really your apprehension of a white line, running in the unknown dimension. In the same way the red line of the face by which the cube is first in contact with the plane lasts only a moment, it is succeeded by the pink line, and this pink line lasts for the inside of a minute. This lasting pink line in your apprehension of a surface, which extends in two dimensions just like the orange surface extends, as you know it, when the cube is at rest. But the plane creature might answer, “This orange object is substance, solid substance, bounded completely and on every side.” Here, of course, the difficulty comes in. His solid is our surface—his notion of a solid is our notion of an abstract surface with no thickness at all. We should have to explain to him that, from every point of what he called a solid, a new dimension runs away. From every point a line can be drawn in a direction unknown to him, and there is a solidity of a kind greater than that which he knows. This solidity can only be realised by him by his supposing an unknown direction, by motion in which what he conceives to be solid matter instantly disappears. The higher solid, however, which extends in this dimension as well as in those which he knows, lasts when a motion of that kind takes place, different sections of it come consecutively in the plane of his apprehension, and take the place of the solid which he at first conceives to be all. Thus, the higher solid—our solid in contradistinction to his area solid, his two-dimensional solid, must be conceived by him as something which has duration in it, under circumstances in which his matter disappears out of his world. We may put the matter thus, using the conception of motion.