“I see how it works,” mused David, “except for one thing. How do you introduce the thought you want to measure?”
“If I explain that the experiment wouldn’t be possible,” said Leighton with a laugh. “The thought must come through unconscious suggestion, or our Ghost of the Forgotten will refuse to appear. In a way, it is like a game—and is more interesting than most games. Did you ever play the game of twenty questions?”
“I have,” interjected Una. “It’s this way. Something—a book, a piece of furniture, anything at all—is chosen by one set of players to be guessed by the other set. Then the set who know the secret have to answer twenty questions about it, asked by the other side. The questions sound silly, but they usually discover the secret.”
“Is your experiment like Una’s game?” asked David.
“Not exactly. Sit down in this chair and you’ll see.”
Seated as directed, the psychometer stood a little back and at one side of him.
“Now,” said Leighton, giving him the electrodes, “hold these, one in each hand.”
“It’s like an electrocution!” exclaimed Una. “Are you very uncomfortable?”
“Oh, quite the contrary! Now, Mr. Leighton——”