With a final warning to Simmons as to the dissemination of any information without consulting him, Darrow left the room. Hallowell listened to this advice with unmixed satisfaction; the afternoon papers would not be able to get at his source of information. The reporter felt a slight wonder as to how Darrow had managed his ascendency over the operator. An inquiry as to that met with a shake of the head.

"I may have to ask your help in that later," was his only reply.

At the corner, after pushing through a curious crowd, the men separated. Hallowell started for the wharf; Jack Warford for home--at Darrow's request. The scientist returned to his own apartments, where he locked himself in and sat for five hours cross-legged on a divan, staring straight ahead of him, doing nothing. At the end of that time he cautiously stretched his legs, sighed, rose, and looked into the mirror.

"I guess you're hungry," he remarked to the image therein.

It was now near mid-afternoon. Percy Darrow wandered out, ate a leisurely meal at the nearest restaurant, and sauntered up the avenue. He paused at a news stand to buy an afternoon paper, glanced at the head-lines and a portion of the text, and smiled sweetly to himself. Then he betook himself by means of a bus to the Warford residence.

Helen was at home, and in the library. With her was Professor Eldridge. The men greeted each other formally. After a moment of general conversation Darrow produced the newspaper.

"I see you have your theories in print," he drawled. "Very interesting. I didn't know you'd undertaken grammar-school physics instruction."

"I know I'm going to be grateful for any sort of instruction--from anybody," interposed Helen. "I'm all in the dark."

"Like the Atlas Building," Darrow smiled at her. "Well, here's a very good exposition in words of one syllable. I'll leave you the paper. Professor, what have you concluded as to the causes?"

"They are yet to be determined."

"Pardon me," drawled Darrow, "they have been determined--or at least their controlling power."

"In what way, may I ask?" inquired Professor Eldridge formally.

"Very simply. By the exercise of a little reason. I am going to tell you, because I want you to start fairly with me; and because you'll know all about it in the morning, anyway."

"Your idea--the one you told us yesterday--is to be published?" cried Helen, leaning forward with interest.

"The basis of it will be," replied Darrow. "Now"--he turned to Eldridge--"listen carefully; I'm not going to indulge in many explanations. Malachi McCarthy, political boss of this city, has made a personal enemy of a half-crazed or at least unbalanced man, who has in some way gained a limited power over etheric and other vibrations. This power Monsieur X, as I call him--the Unknown--has employed in fantastic manifestations designed solely for the purpose of frightening his enemy into leaving this country."

Eldridge was listening with the keenest attention, his cold gray eyes glittering frostily behind their toric lenses.

"You support your major hypothesis, I suppose?" he demand calmly.

"By wireless messages sent from Monsieur X to McCarthy, in which he predicts or appoints in advance the exact hour at which these manifestations take place."

"In advance, I understand you to say?"

"Precisely."

"The proof is as conclusive for merely prophetic ability as for power over the phenomena."

"In formal logic; not in common sense."

Eldridge reflected a moment further, removing his glasses, with the edge of which he tapped methodically the palm of his left hand. Helen had sunk back into the depths of her armchair, and was watching with immobile countenance but vividly interested eyes the progress of the duel.

"Granting for the moment your major hypothesis," Eldridge stated at last, "I follow your other essential statements. The man is unbalanced because he chooses such a method of accomplishing a simple end."

"Quite so."

"His power is limited because it has been applied to but one manifestation of etheric vibration at a time; and each manifestation has had a defined duration."

Darrow bowed. "You are the only original think-tank," he quoted Hallowell's earlier remark.

"You are most kind to place me in possession of these additional facts," said Eldridge, resuming his glasses, "for naturally my conclusions, based on incomplete premises, could hardly be considered more than tentative. The happy accident of an acquaintance with the existence of these wireless messages and this personal enmity gave you a manifest but artificial advantage in the construction of your hypothesis."

"Did I not see you in the corridor of the Atlas Building the day of the first electrical failure?" asked Darrow.

"Certainly."

"Then you had just as much to go on as I did," drawled Darrow, half closing his eyes. The long dark lashes fell across his cheek, investing him in his most harmless and effeminate look.

"I fail to--"

"Yes, you fail, all right," interrupted Darrow. "You had all the strings in your hands, but you were a mile behind me in the solution of this mystery. I'll tell you why: it was for the same reason that you're going to fail a second time, now that once again I've put all the strings in your hands."

"I must confess I fail to gather your meaning," said Professor Eldridge coldly.

"It was for the same reason that always until his death you were inferior to dear old Doctor Schermerhorn as a scientist. You are an almost perfect thinking machine."

Darrow quite deliberately lighted a cigarette, flipped the match into the grate, and leaned back luxuriously. Professor Eldridge sat bolt upright, waiting. Helen Warford watched them both.

"You have no humanity; you have no imagination," stated Darrow at last. "You follow the dictates of rigid science, and of logic."

"Most certainly," Eldridge agreed to this, as to a compliment.

"It takes you far," continued Darrow, "but not far enough. You observe only facts; I also observe men. You will follow only where your facts lead; I am willing to take a leap in the dark. I'll have all this matter hunted out while you are proving your first steps."

"That, I understand it, is a challenge?" demanded Eldridge, touched in his pride of the scientific diagnostician.

"That," said Percy Darrow blandly, "is a statement of fact."

"We shall see."

"Sure!" agreed Darrow. "Now, the thing to do is to find Monsieur X. I don't know whether your curiously scutellate mind has arrived at the point where it is willing to admit the existence of Monsieur X or not; but it will. The man who finds Monsieur X wins. Now, you know or can read in the morning paper every fact I have. Go to it!"

Eldridge bowed formally.

"There's one other thing," went on Darrow in a more serious tone of voice. "You have, of course, considered the logical result of this power carried to its ultimate possibility."

&quo............