“It is owing to the difference in these provisional colouring matters that it is possible to distinguish between writing written with different kinds of ink. I was able easily to obtain samples of the inks used by the Vandams, by Mrs. Popper, by Mr. Farrington, and by the druggist. I have compared the writing of the original prescription with a colour scale of my own construction, and I have made chemical tests. The druggist’s ink conforms exactly to the writing on the two pillboxes, but not to the prescription. One of the other three inks conforms by test absolutely to the ink in that prescription signed ‘Dr. C. W. H.’ as a blind. In a moment my chain of evidence against the owner of that bottle of ink will be complete.”
I could not help but think of the two pendulums on the shelf behind the curtain, but Craig said nothing for a moment to indicate that he referred to that apparatus. We sat dazed. Farrington seemed nervous and ill at ease. Mrs. Popper, who had not recovered from the hysterical condition of her exposure, with difficulty controlled her emotion. Vandam was crushed.
“I have not only arranged this laboratory so as to reproduce Mrs. Popper’s séance-room,” began Craig afresh, “but I have had the cabinet placed in relatively the same position a similar cabinet occupies in Mr. Vandam’s private séance-room in the Vandam mansion.
“One night, Mr. Jameson and myself were visiting Mr. Vandam. At precisely twelve-thirty we heard most unaccountable rappings from that cabinet. I particularly noted the position of the cabinet. Back of it ran a hallway. That is duplicated here. Back of this cabinet is a hallway. I had heard of these rappings before we went, but was afraid that it would be impossible for me to catch the ghost red handed. There is a limit to what you can do the first time you enter a man’s house, and, besides, that was no time to arouse suspicion in the mind of anyone. But science has a way out of every dilemma. I determined to learn something of these rappings.”
Craig paused and glanced first at Farrington, then at Mrs. Popper, and then at Mr. Vandam.
“Mr. Jameson,” he resumed, “will escort the doctor, the inspector, Mr. Farrington, Mrs. Popper, and Mr. Vandam into my imitation hall of the Vandam mansion. I want each of you in turn to tiptoe up that hall to a spot indicated on the wall, back of the cabinet, and strike that spot several sharp blows with your knuckles.”
I did as Craig instructed tiptoeing up myself first so that they could not mistake his meaning. The rest followed separately, and after a moment we returned silently in suppressed excitement to the room.
Craig was still standing by the table, but now the pendulums with the magnets and needles and the drums worked by clockwork were before him.
“Another person outside the Vandam family had a key to the Vandam mansion,” he began gravely. “That person, by the way, was the one who waited, night by night, until Mrs. Vandam took the fatal capsule, and then when she had taken it apprised the old man of the fact and strengthened an already blind faith in the shadow world.”
You could have heard a pin drop. In fact you could almost have felt it drop.
“That other person who, unobserved, had free access to the house,” he continued in the breathless stillness, “is in this room now.”
He was looking at O’Connor as if for corroboration. O’Connor nodded. “Information derived from the butler,” he muttered.
“I did not know this until yesterday,” Kennedy continued, “but I suspected that something of the sort existed when I was first told by Dr. Hanson of the rappings. I determined to hear those rappings, and make a record of them. So, the night Mr. Jameson and I visited Mr. Vandam, I carried this little instrument with me.”
Almost lovingly he touched the pendulums on the table. They were now at rest and kept so by means of a lever that prevented all vibration whatever.
“See, I release this lever—now, let no one in the room move. Watch the needles on the paper as the clockwork revolves the drums. I take a step—ever so lightly. The pendulums vibrate, and the needles trace a broken line on the paper on each drum. I stop; the lines are practically straight. I take another step and another, ever so lightly. See the delicate pendulums vibrate? See, the lines they trace are jagged lines.”
He stripped the paper off the drums and laid it flat on the table before him, with two other similar pieces of paper.
“Just before the time of the rapping I placed this instrument in the corner of the Vandam cabinet, just as I placed it in this cabinet after Mr. Jameson conducted you from the room. In neither case were suspicions aroused. Everything in both cases was perfectly normal—I mean the ‘ghost’ was in ignorance of the presence, if not the very existence, of this instrument.
“This is an improved seismograph,” he explained, “one after a very recent model by Prince Galitzin of the Imperial Academy of St. Petersburg. The seismograph, as you know, was devised to register earthquakes at a distance. This one not only measures the size of a distant earthquake, but the actual direction from which the earth-tremors come. That is why there are two pendulums and two drums.
“The magnetic arrangement is to cut short the vibrations set up in the pendulums, to prevent them from continuing to vibrate after the first shock. Thus they are ready in an instant to record another tremor. Other seismographs continue to vibrate for a long time as a result of one tremor only. Besides, they give little indication of the direction from which the tremors come.
“I think you must all appreciate
