"Why not," smiled Darrow, "until he has scared McCarthy out?" "Which will it be next time, do you think?" "Whatever happens, don't be frightened," said Darrow enigmatically. "It seems to me there is something absurd about all this," said Helen. "A man with such a discovery, such powers, using them in such a manner, for such a petty purpose!" "He is, of course, crazy," Darrow said quietly; "the methodical logical lunatic--the most dangerous sort." "What is it he has discovered?" asked Jack. "I do not know, yet." "But you suspect?" Darrow nodded, but would not explain. "What will be the outcome?" "I am going to cut loose from science and guess wildly," said Darrow, after a moment. "To-morrow morning, somewhere about ten, McCarthy will disappear." "You said that before!" cried Jack. "Well, I say it again," drawled Darrow. CHAPTER IX THE GREAT SILENCE Percy Darrow sat quite calmly, though a little hungrily, through the first of the two hours of the Great Silence. As it fell, he looked at his watch; then went on reading. Strangely terrified faces flitted by the open door of his little room. About seven o'clock Darrow, struck by a sudden idea, arose, walked down the corridor outside, and quite deliberately set to work to force the light door. As has been intimated, either by direct order of McCarthy or because of some vagueness of the orders, the young man had been confined, not in the jail proper, but in one of the living apartments of the wing. Few realize how important a role sound plays in what might be called the defensives of our every-day life. Sight is important, to be sure, but it is more often corroborative than not; it is more often used to identify the source of the alarm that has been communicated through other channels. When we are told of the hero--or the villain--that he stood "with every sense alert", our mental picture, in spite of the phrasing, is that of a man listening intently for the first intimations of what may threaten. So it is in prison. The warders can, of necessity, remain within actual view of but a few of the prisoners a small proportion of the time. But through those massive and silent corridors sound stands watch-dog for them. The minute scratch of a file, the vibrations attendant on the most cautious attempts against the stone structure, the most muffled footfall reports to the jailer that mischief is afoot. Instantly he is on the spot to corroborate by his other faculties the warnings of the watch-dog of the senses.