of the fourth dimension, he would reply to us as we replied to the
"flat-land" people: "The problem is absurd and impossible if you
confine your line to space as you understand it. But for me there
is a fourth dimension in space. Draw your line through that
dimension, and the problem will be solved. This is perfectly
simple to me; it is impossible to you solely because your
conceptions do not admit of more than three dimensions."

Supposing the inhabitants of "flat-land" to be intellectual beings
as we are, it would be interesting to them to be told what
dwellers of space in three dimensions could do. Let us pursue the
analogy by showing what dwellers in four dimensions might do.
Place a dweller of "flat-land" inside a circle drawn on his plane,
and ask him to step outside of it without breaking through it. He
would go all around, and, finding every inch of it closed, he
would say it was impossible from the very nature of the
conditions. "But," we would reply, "that is because of your
limited conceptions. We can step over it."

"Step over it!" he would exclaim. "I do not know what that means.
I can pass around anything if there is a way open, but I cannot
imagine what you mean by stepping over it."

But we should simply step over the line and reappear on the other
side. So, if we confine a being able to move in a fourth dimension
in the walls of a dungeon of which the sides, the floor, and the
ceiling were all impenetrable, he would step outside of it without
touching any part of the building, just as easily as we could step
over a circle drawn on the plane without touching it. He would
simply disappear from our view like a spirit, and perhaps reappear