The prisoner looked up incredulously.  “You say it forces him to betray himself?”

“That’s practically what it does.  There may be men strong enough and self-controlled enough to resist but we haven’t found such a person yet.  It’s true the system is quite recently devised, it hasn’t been thoroughly tested, but so far we have had wonderful results and—­it’s just the thing for your case.”

Groener was listening carefully.  “Why?”

“Because, if you are guilty, we shall know it, and can go on confidently looking for certain links now missing in the chain of evidence against you.  On the other hand, if you are innocent, we shall know that, too, and—­if you are innocent, Groener, here is your chance to prove it.”

If the prisoner’s fear was stirred he did not show it, for he answered mockingly:  “How convenient!  I suppose you have a scales that registers innocent or guilty when the accused stands on it?”

Hauteville shook his head.  “It’s simpler than that.  We make the accused register his own guilt or his own innocence with his own words.”

“Whether he wishes to or not?”

The other nodded grimly.  “Within certain limits—­yes.”

“How?”

The judge opened a leather portfolio and selected several sheets of paper ruled in squares.  Then he took out his watch.

“On these sheets,” he explained, “M.  Coquenil and I have written down about a hundred words, simple, everyday words, most of them, such as ‘house,’ ‘music,’ ‘tree,’ ‘baby,’ that have no particular significance; among these words, however, we have introduced thirty that have some association with this crime, words like ‘Ansonia,’ ‘billiards,’ ‘pistol.’  Do you understand?”

“Yes.”

“I shall speak these words slowly, one by one, and when I speak a word I want you to speak another word that my word suggests.  For example, if I say ‘tree,’ you might say ‘garden,’ if I say ‘house,’ you might say ‘chair.’  Of course you are free to say any word you please, but you will find yourself irresistibly drawn toward certain ones according as you are innocent or guilty.

“For instance, Martinez, the Spaniard, was widely known as a billiard player.  Now, if I should say ‘billiard player,’ and you had no personal feeling about Martinez, you might easily, by association of ideas, say ‘Spaniard’; but, if you had killed Martinez and wished to conceal your crime then, when I said ‘billiard player’ you would not say ‘Spaniard,’ but would choose some innocent word like table or chalk.  That is a crude illustration, but it may give you the idea.”

“And is that all?” asked Groener, in evident relief.