"I see your mistake," he said. "You come from the old world, where the old type of house is still in existence. The history of the old world is the special study of my friend, the Professor. But of course there is general knowledge that every educated being may be supposed to possess, and I know the type of house you mean. I have seen pictures of it in the museum. Now in Thule, when many centuries ago aviation became the cheapest and most popular form of transit, it also became obviously impossible that we should have houses above ground. Aviation is a source of danger to such houses, and the houses themselves were dangerous to the aviator. Our buildings are all subterranean. We avoid danger of every kind. We dislike risk. You cannot see my house to which I am taking you, but as a matter of fact it is less than a quarter of a mile away."
He went so slowly that I had to abate my usual pace, lest I should outstrip my guide. As he moved, he looked a little like a very small tired elephant.
"Aviation," I said. "I suppose that with you that has been carried to a great point of perfection."
"On the contrary," he said, "it is superseded. It is a back number. We no longer use it. But we have seen no reason to change our style of domicile, which possesses many advantages."
"And what is it?" I asked, "that has superseded aviation?"
"It is the power to dissipate and subsequently reconstruct identically at some different point the atoms of any organism or group of organisms."
"I don't think I understand," I said.
"It is natural that you should not. However, here we are at my house."
It looked to me rather as if we had come to an ordinary well, the interior of which was occupied by a spiral descending incline.
"You will observe," he said, "that when I am weary of exertion and return to my house, I descend. In the old type of house it was customary to ascend."