Throughout all this excitement Percy Darrow did absolutely nothing. He spent all his time, save that required for meals and the shortest necessary sleep, in a round-armed wooden chair in the wireless station of the Atlas Building. Jack Warford sat with him. Darrow rarely opened his mouth for speech, but smoked slowly a few cigarettes, and rolled many more, which he held unlighted in the corner of his mouth until they dropped to pieces. He watched quietly all that went on; glanced through such messages as came in from Monsieur X, read the papers, and dozed. To reporters he was affable enough in his drawling slow fashion, but had nothing to say.

"Eldridge is doing this," he said to them; "I'm only in the position of an interested spectator."

Eldridge had taken hold in a thoroughly competent way. Back of the cold precision of his undoubted scientific attainments lurked, unexpected by most, a strong ambition and a less admirable hankering for the lime-light. His opportunity to gratify all these appetites—science, advancement, and fame—was too good not to cause him the deepest satisfaction.

"I have determined," he told the reporters, "that this particular instrument alone receives the messages from the unknown perpetrator. Our investigations must be initiated, therefore, in this apartment."

"How do you explain it?" asked one of the reporters.

"I can not explain it scientifically," admitted Eldridge, "but I can surmise that the fact either purposely or accidentally has to do either with this instrument's location or with some slight and undetermined peculiarity of its tuning."

"You could easily tell which by moving the instrument to another station where they aren't getting the messages now," suggested Darrow lazily.

"Certainly," snapped Eldridge, "any child could deduce that. But I fail to see the use or necessity for the determination at all unless in a spirit of frivolous play. Our task is not to discover where the messages can be received, but whence they are sent."

He gazed frostily at the man who had interrupted him. Darrow smiled softly back.

"How far will your instrument carry in sending?" Eldridge asked Simmons.

"Its extreme is about two hundred miles."

"Then we can safely assume that a circle drawn with a two-hundred-mile radius would contain this man you call Monsieur X"—the newspapers had adopted Darrow's nickname for the Unknown—"since you have succeeded in communicating with him."

"Marvelous," said Darrow to Jack—but under his breath.

"As the sending of Monsieur X is faint, it follows that he is somewhere near the periphery of this circle, or that he is possessed of a primitive or weak instrument. By the doctrine of probabilities we should be justified in concluding against the latter supposition."

"How's that, Professor?" asked the Morning Register man. "It doesn't get to me."

"He is evidently a man not only of scientific attainments, but of immense scientific possessions—as is evidenced by these phenomenal results he is able to accomplish. But we are not justified in reasoning according to the doctrine of probabilities. Therefore, we shall proceed methodically. I have already made my preparations."

Eldridge looked about him with an air of triumph.

"I am fortunate enough to have, in the present crisis, unlimited financial backing," he said. "Therefore, I am in a position to carry out the most exhaustive of experiments."

He stretched his hand out for a long roll, which he laid flat upon the table, pinning down the corners.

"Here is a map of the Eastern States," said he. "I have drawn a circle on it with a two-hundred-miles radius. At this moment a private instrument with a full crew to string sending and receiving wires is two hundred miles from here on the New York Central Railroad. It has for its transportation a private train, and it will be given a clear right of way." He turned to Simmons. "Have you found yourself able to communicate with this Monsieur X at any time?"

"Communicate!" echoed Simmons. "Why, he's easier to talk to than a girl who wants an ice-cream soda!"

"Then send this: 'Your messages have been communicated to the people. Be patient.'"

Simmons touched the key. The spark leaped crashing.

"What do you get?" asked Eldridge, after a moment.

"Oh, a lot of the same sort of dope," answered Simmons wearily. "Do you want it?"

"No, it is not necessary," replied Eldridge. "But listen for another message from about the same distance when he has finished."

Silence fell on the room. At the end of ten minutes Simmons raised his head.

"I get 'O K Q' over and over," said he. "Want that?"

"That," replied Eldridge with satisfaction, "indicates that my crew on the special train in the Adirondacks two hundred miles away has heard your message to Monsieur X." He glanced at his watch. "Now, if you would be so good as to afford me a moment's assistance," he requested Simmons, "I wish to disconnect from your battery one of your powerful Leyden jars, and to substitute for it one of weaker voltage. I ventured to instruct my delivery man to leave a few in the outer hall."

"That will weaken the sending power of my instrument," objected Simmons.

"Exactly what I wish to do," replied Eldridge.

"He's clever all right," Darrow murmured admiringly to Jack. "See what he's up to?"

"Not yet," muttered Jack.

The substitution completed, Eldridge again glanced at his watch.

"Now," he instructed Simmons, "send the letters 'Q E D,' and continue to do so until you again hear the letters 'O K Q.'"

Simmons set himself to the task. It was a long one. At last he reported his answer.

"He sends 'O K Q ten,'" he said.

Eldridge turned to the reporters.

"That means that the substitution of the smaller Leyden jar for one of the larger reduced the sending power of this instrument just ten miles," said he. "My crew has quite simply moved slowly forward until it caught our sending here."

"Next," he instructed Simmons, "see if you can communicate with Monsieur
X."

The operator speedily reported his success at that. Eldridge removed his glasses and polished their lenses.

"Thus, gentlemen," said he, "from our circle of two-hundred-mile radius we have eliminated a strip ten miles wide. Naturally if this weakened sending reaches only one hundred and ninety miles, and our antagonist receives our messages, he must be nearer than one hundred and ninety miles. We will now further reduce the strength of our sending and try again."

The younger men present broke into a shout,

"Good work!" somebody cried. They crowded about, keenly interested in this new method of man-hunting. Only Darrow, tipped back in his chair against the wall, seemed unexcited.

To Jack's whispered question he shook his head.

"It's ingenious," he acknowledged, "but he's on the wrong track." That was as far as he would explain, and soon dropped into a slight doze.

Throughout the greater part of the night the experiment continued. Battery by battery the sending power of the instrument was weakened. Mile by mile the special train drew nearer until, by catching the prearranged signal, it determined just how far the new sending reached. Then Simmons tried Monsieur X. As the latter invariably answered, it was, of course, evident that he remained still in the narrowing zone of communication. It was fascinating work, like the drawing of a huge invisible net.

The reporters on the morning papers mastered only with difficulty their inclination to stay. They had to leave before their papers went to press, but were back again in an hour, unwilling to lose a moment of the game. A tension vibrated the little office. Only Percy Darrow dozed alone in the corner, leaning back in his wooden armchair.

At near four o'clock in the morning Simmons raised his head after a long bout of calling to announce that he could get no reply from Monsieur X.

"He's got tired of your fool messages," remarked the Register man. "And
I don't wonder! Guess he's gone to bed."

Eldridge said nothing, but replaced the Leyden jar he had but just removed.

"Try one," said he.

"I get him," reported Simmons, after a moment.

"Send him anything plausible and reassuring," commanded Eldridge hastily. He turned to his small and attentive audience in triumph. "Thus, gentlemen," he announced, "we have proven conclusively that our man is located between forty and fifty miles from New York. If we draw two circles, with this building as center, the circumference of one of which is fifty, the other forty miles away, we define the territory within which the malefactor in question is to be found."

The people in the room crowded close about the table to examine the map upon which Professor Eldridge had drawn the circles.

"There's an awful lot of country—some of it pretty wild," objected the Bulletin man. "It will be a long job to hunt a man down in that territory."

"Even if it were as extensive a task as a hasty review of the facts might indicate," stated Eldridge, "I venture to assert that enough men would be forthcoming to expedite such a search. But modifying circumstances will lighten the task."

"How's that?" asked the Banner man, speaking for the others' evident interest.

"We have no means of surmising the method by which this man succeeds in arresting vibratory motions of certain wave-lengths," said Eldridge didactically, "any more than we are able to define the precise nature of electricity. But, as in the case of electricity, we can observe the action of its phenomena. Two salient features leap out at us: one is that these phenomena are limited in time; the other that they are limited in space. The latter aspect we will examine, if you please, gentlemen.

"The phenomena have been directed with great accuracy (a) at the Atlas Building; (b) at this city and some of its immediate suburbs. The peculiarity of this can not but strike an observant mind. How is this man able, at forty or fifty miles distance, to concentrate his efforts on one comparatively small objective? We can only surmise some system of insulating screens or focal mirrors. I might remark in passing that the existence of this power to direct or focus the more rapid ethereal vibrations would be a discovery of considerable scientific moment. But if this is the method employed, why do we not cut a band of vibratory nullifications, rather than touch upon a focal point?"

"Repeat softly," murmured the irrepressible Register man.

"Why," explained Eldridge patiently, "are not the people and buildings between here and the unknown operator affected? The only hypothesis we are justified in working upon is that the man's apparatus is at a height sufficient to carry over intervening obstacles. This hypothesis is strengthened by the collateral fact that the territory we have just determined as that within which he must be found lies in the highlands of our own and neighboring states. We may, therefore, eliminate the low-lying districts within our radius."

Percy Darrow opened one eye.

"Perhaps he's up in a balloon," he drawled languidly; "better take along an aeroplane."

Eldridge cast on him a look of cold scorn. Darrow closed the eye.