"I'm afraid it's getting rather late, Professor?" I said.

"Yes, indeed," said the Professor. "I must take you all through the Ivory Door again. You've stayed your full time."

"Mightn't we stay a little longer!" pleaded Sylvie.

"Just one minute!" added Bruno.

But the Professor was unyielding. "It's a great privilege, coming through at all," he said. "We must go now." And we followed him obediently to the Ivory Door, which he threw open, and signed to me to go through first.

"You're coming too, aren't you?" I said to Sylvie.

"Yes," she said: "but you won't see us after you've gone through."

"But suppose I wait for you outside?" I asked, as I stepped through the doorway.

"In that case," said Sylvie, "I think the potato would be quite justified in asking your weight. I can quite imagine a really superior kidney-potato declining to argue with any one under fifteen stone!"

With a great effort I recovered the thread of my thoughts. "We lapse very quickly into nonsense!" I said.