"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.