Dirk said humbly, "Great must have been the wisdom of your forebears to be able to transfer themselves from a sinking island to this place. I understand, now, your interest in Earth. It is more than just sympathy for us ... it is a natural love for a land which once was yours."
"Yes," said the Ptan. "A land which once we ruled, and now have lost forever. But enough of this, my son. You were telling me of your adventures—?"
"Yes," said Dirk, remembering. "There was one thing happened which I do not understand. In the boudoir of the Princess Lenore, Ptan Slador, I was visible for a few seconds! Why was that?"
Slador stared at him in astonishment.
"Visible! Impossible!"
"That's what I thought. But it is true, sir. I saw my own image in the Princess' mirror—"
"Mirror! Ah!" exclaimed the Ptan. "Now I begin to understand. This mirror ... it was not plain, silvered glass? It was, perhaps, quartz?"
"Possibly," admitted Dirk. "I would not know about such things, sir."
"Undoubtedly," mused his advisor, "it must have been a rock-quartz mirror. That is the only Earthly substance of dual isotopic form. Its converse refractions hold and trap not only the normal vibrations of your system, but harmonic vibrations as well. Surely your scientists know this. Many hundreds of years ago, I know they experimented with the use of quartz substances in both light and sound transmission.
"But we are not so interested now in causes as in results. Do you think the Princess saw you in this mirror?"