"Well," began Darrow, "it's a little difficult to get started. But let's begin with the phenomena themselves. I've told you before, how, when I was in jail, I worked out their nature and the fact that they must draw their power from some source that could be exhausted or emptied. You have read Eldridge's reasoning as to why he thought Monsieur X was at a distance and on a height. He took as the basis of his reasoning one fact in connection with the wireless messages we were receiving--that they were faint, and therefore presumably far distant or sent by a weak battery. He neglected, or passed over as an important item of tuning, the further fact that the instrument in the Atlas Building was the only instrument to receive Monsieur X's messages. "Now, that fact might be explained either on the very probable supposition that our receiving instrument happened in what we may call its undertones to be the only one tuned to the sending instrument of Monsieur X; or it might be because our instrument was nearer Monsieur X's instrument than any other. This was unlikely because of the quality of the sound--it sounded to the expert operator as though it came from a distance. Nevertheless, it was a possibility. Taken by itself, it was not nearly so good a possibility as the other. Therefore, Eldridge chose the other. "There were a number of other strictly scientific considerations of equal importance. I do not hesitate to say that if I had been influenced only by the scientific considerations, I should have followed Eldridge's lead without the slightest hesitation. But as I told him at the time, a man must have imagination and human sympathy to get next to this sort of thing. "Leaving all science aside, for the moment, what do we find in the messages to McCarthy? First, a command to leave within a specified and brief period; second, a threat in case of disobedience. That threat was always carried out." Darrow turned to Mrs. Warford. "With your permission, I should like to smoke," said he. "I can follow my thought better." "By all means," accorded the lady. Darrow lighted his cigarette, puffed a moment, and continued: "For instance, at three o'clock he threatens to send a 'sign' unless McCarthy leaves town by six. McCarthy does not leave town. Promptly at six the 'sign' comes. What do you make of it?" Nobody stirred. "Why," resumed Darrow, "how, if Monsieur X was a hundred miles or so away, as Eldridge figured, did he know that McCarthy had not obeyed him? We must suppose, from the probable fact of that knowledge, that either Monsieur X had an accomplice who was keeping him informed, or he must be near enough to get the information himself." "There is a third possibility," broke in Jack. "Monsieur X might have sent along his 'sign' at six o'clock, anyhow, just for general results." Darrow nodded his approval.