He stumbled forward, dazed and groping as though he were in the dark, instead of merely in silence; a striking example in the uncertainty of his movements of how closely our senses depend on one another.

Jack spoke twice, then closed his lips in a grim straight line. He held his elbows close to his sides, and looked ready for anything.

A look of mild triumph illumined Percy Darrow's usually languid countenance. He stepped quickly to the wall, and turned the b.u.t.ton of the incandescent globe. The light instantly glowed. At this he nodded twice more. From his pocket he drew a note-book and pencil, wrote in it a few words, and handed it to the dazed and uncertain boss.

"I was right," Darrow had scrawled. "This proves it. It's by no means the end. Better be good."

McCarthy's bulldog courage had recovered from its first daze. He began to see that this visitation was not entirely personal, but extended also to his two companions. This relieved his mind, for he had suspected some strange new apoplexy.

"Did you expect this?" he wrote.

Darrow nodded.

Together the three ghosts left the phantom office, and glided down the phantom halls. Other ghosts in various stages of alarm were already making their way down the stairs. Some of them spoke, but no sound came. One woman, her eyes frightened, reached out furtively to touch her neighbor, apparently to a.s.sure herself of his reality. Urged by an uncontrollable impulse, a man thrust his hand through the ground gla.s.s of an office door. The gla.s.s shivered, and crashed to the tile floor.

The pieces broke--silently. It was as though the man had been the figure in a cinematograph illusion. He stared at his cut and bleeding hand. The woman who had touched the man suddenly threw back her head and screamed. They could see her eyes roll back, her face change color, could discern the straining of her throat. No sound came.

At this a panic seized them. They rushed down the stairs, clambering over one another, pushing, scrambling, falling. A mob of a hundred men fought for precedence. Blows were struck. No faintest murmur of tumult came from their futile heat. It might have been the riot of a wax-works in a vacuum.

They fell into the lower hallway, and fought their way to the street, and stood there dazed and staring, a strange, wild-eyed, white-faced, b.l.o.o.d.y crew. The hurrying avenue stopped to gaze on them curiously, gathering compact in a mob that blocked all traffic. Policemen pushed their way in and began roughly to question--and to question in real audible words.

But for the s.p.a.ce of a full minute these people stood there staring upward, drinking in the blessed sound that poured in on them lavishly from the life of the street; drinking deep gulps of air, as though air had lacked.

Darrow, and with him Jack Warford, had descended more leisurely. Before leaving the building Darrow placed the flat of his hands over his ears, and motioned Jack to do the same. Thus they missed the stunning effect of receiving the world of noise all at once; as a man goes to a bright light from a dark room. Furthermore, Darrow returned several times from the sound to the silence, trying to determine where the line of demarcation was drawn. Then, motioning to Jack, he began methodically to make his way through the crowd.

This proved to be by no means an easy task. Rumors of all sorts were afoot. Some bold spirits were testing a new sensation by venturing into the corridor of the building. The police were undecided as to what should be done. One or two reporters were already at hand, investigating.

McCarthy, his a.s.surance returned, was conversing earnestly with a police captain.

Percy Darrow, closely followed by Jack, managed to worm his way through the crowd, and finally debouched on Broadway.

"What was it? What struck us?" demanded Jack. "Do you know?"

"I can guess; in essence," said Percy. "I was pretty sure after last evening's trouble; but this underscores it, proves it. Also, it opens the way."

"What do you mean?"

"Along the lines of these phenomena there are two more things possible.

Possible, I say. They might be called certain, were we dealing only with theory; but there is still some doubt how the practical side of it may work out."

"I suppose you know what you're talking about," said Jack resignedly. "I don't."

"You don't need to, yet. But here's what I mean. If my theory is correct, we are likely to be surprised still further."

Jack ruminated; then his engaging young face lighted up with a smile.

"All right," said he; "I'm enlisted for the war. What have you got to do with it?"

"I'll explain this much," said Darrow; "more I'll not tell at present, even to you. If one breath should get out that any one suspected--well, this is a man-hunt."

"Who's the man?"

"An enemy of McCarthy."

"Whom you are going to find for him?"

"Perhaps."

"And you were putting up that job for me as part of your pay!"

Percy Darrow smiled slowly.

"As all of my pay--from McCarthy," said he. "I was just bedeviling him."

Jack Warford started to say something, but the scientist cut him short.

"This is bigger than McCarthy," he said decisively. "We are the only people in this city who suspect a human origin of these phenomena. Other men are yet working, and will continue to work, on the supposition that they are the results of some unbalanced natural conditions. The phenomena are, as yet, harmless. It will not greatly injure the city, once it is prepared, to be without electricity or without sound for limited periods.

I doubt very much whether the Unknown can continue these phenomena for longer than limited periods. But conceivably this man may become a peril.

He has, if I reason correctly, four arrows in his quiver; the fourth is dangerous. It is our duty to find him before he uses the fourth arrow--if indeed he has discovered the method of doing so. That is always in doubt."

Jack's eyes were shining.

"Bully!" he cried.

"He may conceivably possess the power to launch the fourth and dangerous arrow, but may withhold it unless he believes himself suspected or close pressed. His probable mental processes are obscure. At present he directs himself solely against McCarthy." Percy Darrow had been thinking aloud, and realized it with a smile. "This is one of your jobs, fellow detective," said he. "You've got to be a mark for me to think at."

"I wish you'd think a little more clearly," observed Jack. "It sounds interesting, but jumbled. I feel the way I did when I began to read Greek."

"McCarthy's incidental," observed Darrow in his detached tone.

"Eh?"

"Oh, I thought we might as well worry McCarthy by asking him for that job on the side. It's amusing."

"What do you want me to do?" asked Jack.

"This," said Darrow, with an unusual rapidity of utterance. "See that thick-set, quick man in gray clothes? He's a policeman. In a moment he'll arrest me."

"Arrest you--why?" demanded Jack, in tones of great astonishment.

"I reason that McCarthy will come to that conclusion. He is beginning to think I have something to do with what he calls his annoyances. I saw it in his eyes. This last curious manifestation came along too pat. You remember, it cut off the dressing-down he was going to give me." Darrow chuckled in appreciation. "Didn't the humor of that strike you?"

"Me? Oh, I was scared," admitted Jack.

"I want you to go home and tell Helen just what happened in the Atlas Building. Do not tell her that I believe the phenomena are due to any human agency. Say simply that if it is repeated, and she happens to be within the zone of its influence, to keep calm, and wait. It will pa.s.s, and it is not to be feared. Tell her I said so."

"Lord!" cried Jack. "You don't think it's going to happen again!"

"Within the next twenty-four hours," said Darrow.

"Oughtn't we to warn the people?"