we begin with the fact that there were several clever attempts made to murder Mr. Henley. This was by putting out the gas which he habitually left burning in his room. It happened four times in all; thus proving that it was an attempt to kill him. If it had been only once it might have been accident, even twice it might have been accident, but the same accident does not happen four times at the same time of night.
“Mr. Henley finally grew to regard the strange extinguishing of the gas as an effort to kill him, and carefully locked and barred his door and windows each night. He believed that some one came into his apartments and put out the light, leaving the gas flow. This, of course, was not true. Yet the gas was put out. How? My first idea, a natural one, was that it was turned off for an instant at the meter, when the light would go out, then turned on again. This, I convinced myself, was not true. Therefore still the question—how?
“It is a fact—I don’t know how widely known it is—but it is a fact that every gas light in this house might be extinguished at the same time from this room without leaving it. How? Simply by removing that gas jet tip and blowing into the gas pipe. It would not leave a jet in the building burning. It is due to the fact that the lung power is greater than the pressure of the gas in the pipes, and forces it out.
“Thus we have the method employed to extinguish the light in Mr. Henley’s rooms, and all the barred and locked doors and windows would not stop it. At the same time it threatened the life of every other person in the house—that is, every other person who used gas. It was probably for this reason that the attempt was always made late at night, I should say three or four o’clock. That’s when it was done, isn’t it?” he asked suddenly of the valet.
Staring at The Thinking Machine in open-mouthed astonishment the valet nodded his acquiescence before he was fully aware of it.
“Yes, that’s right,” The Thinking Machine resumed complacently. “This was easily found out—comparatively. The next question was how was a watch kept on Mr. Henley? It would have done no good to extinguish the gas before he was asleep, or to have turned it on when he was not in his rooms. It might have led to a speedy discovery of just how the thing was done.
“There’s a spring lock on the door of Mr. Henley’s apartment. Therefore it would have been impossible for anyone to peep through the keyhole. There are no cracks through which one might see. How was this watch kept? How was the plotter to satisfy himself positively of the time when Mr. Henley was asleep? How was it that the gas was put out at no time of the score or more nights Mr. Henley himself kept watch? Obviously he was watched through a window.
“No one could climb out on the window ledge and look into Mr. Henley’s apartments. No one could see into that apartment from the street—that is, could see whether Mr. Henley was asleep or even in bed. They could see the light. Watch was kept with the aid offered by the flagpole, supplemented with a mirror—this mirror. A screw was driven into the frame—it has been removed now—it was swung on the flagpole rope and pulled out to the end of the pole, facing the building. To a man standing in the hall window of the third floor it offered precisely the angle necessary to reflect the interior of Mr. Henley’s suite, possibly even showed him in bed through a narrow opening in the curtain. There is no shade on the windows of that suite; heavy curtains instead. Is that right?”
Again the prisoner was surprised into a mute acquiescence.
“I saw the possibility of these things, and I saw, too, that at three or four o’clock in the morning it would be perfectly possible for a person to move about the upper halls of this house without being seen. If he wore a heavy bath robe, with a hood, say, no one would recognize him even if he were seen, and besides the garb would not cause suspicion. This bath robe has a hood.
“Now, in working the mirror back and forth on the flagpole at night a tiny scarlet thread was pulled out of the robe and clung to the rope. I found this thread; later Mr. Hatch found an identical thread in these apartments. Both came from that bath robe. Plain logic shows that the person who blew down the gas pipes worked the mirror trick; the person who worked the mirror trick left the thread; the thread comes back to the bath robe—that bath robe there,” he pointed dramatically. “Thus the person who desired Henley’s death was in these apartments, or had easy access to them.”
He paused for a moment and there was a tense silence. A great light was coming to Hatch, slowly but surely. The brain that had followed all this was unlimited in possibilities.
“Even before we traced the origin of the crime to this room,” went on the scientist, quietly now, “attention had been attracted here, particularly to you, Mr. Cabell. It was through the love affair, of which Miss Lipscomb was the center. Mr. Hatch learned that you and Henley had been rivals for her hand. It was that, even before this scarlet thread was found, which indicated that you might have some knowledge of the affair, directly or indirectly.
“You are not a malicious or revengeful man, Mr. Cabell. But you are hot-tempered—extremely so. You demonstrated that just now, when, angry and not understanding, but feeling that your honor was at stake, you shot a hole in the floor.”
“What?” asked Detective Mallory.
“A little accident,” explained The Thinking Machine quickly. “Not being a malicious or revengeful man, you are not the man to deliberately go ahead and make elaborate plans for the murder of Henley. In a moment of passion you might have killed him—but never deliberately as the result of premeditation. Besides you were out of town. Who was then in these apartments? Who had access to these apartments? Who might have used your bath robe? Your valet, possibly Miss Austin. Which? Now, let’s see how we reached this conclusion which led to the valet.
“Miss Regnier was found dead. It was not suicide. How did I know? Because she had been reading with the gas light at its full. If she had been reading by the gas light, how was it then that it went out and suffocated her before she could arise and shut it off? Obviously she must have fallen asleep over her book and left the light burning.
“If she was in this plot to kill Henley, why did she light the jet in her room? There might have been some defect in the electric bulb in her room which she had just discovered. Therefore she lighted the gas, intending to extinguish it—turn it off entirely—later. But she fell asleep. Therefore when the valet here blew into the pipe, intending to kill Mr. Henley, he unwittingly killed the woman he loved—Miss Regnier. It was perfectly possible, meanwhile, that she did not know of the attempt to be made that particular night, although she had participated in the others, knowing that Henley had night after night sat up to watch the light in his rooms.
“The facts, as I knew them, showed no connection between Miss Regnier and this man at that time—nor any connection between Miss Regnier and Henley. It might have been that the person who blew the gas out of the pipe from these rooms knew nothing whatever of Miss Regnier, just as he didn’t know who else he might have killed in the building.
“But I had her death and the manner of it. I had eliminated you, Mr. Cabell. Therefore there remained Miss Austin and the valet. Miss Austin was eccentric—insane, if you will. Would she have any motive for killing Henley? I could imagine none. Love? Probably not. Money? They had nothing in common on that ground. What? Nothing that I could see. Therefore, for the moment, I passed Miss Austin by, after asking you, Mr. Cabell, if you were Miss Austin.
“What remained? The valet. Motive? Several possible ones, one or two probable. He is French, or says he is. Miss Regnier is French. Therefore I had arrived at the conclusion that they knew each other as people of the same nationality will in a house of this sort. And remember, I had passed by Mr. Cabell and Miss Austin, so the valet was the only one left; he could use the bath robe.
“Well, the motive. Frankly that was the only difficult point in the entire
