"Instantly a sliding mirror suggested itself to me to fit all these conditions. He saw the apparition in the door, then saw only half of it, then all of it disappeared. He passed through the spot where it had been. All of this would have happened easily if a large mirror, working as a sliding door, and hidden in the wall, were there. Is it clear?"
"Perfectly," said Mr. Weston.
"Yes," said Hatch, eagerly. "Go on."
"This sliding mirror, too, might have made the noise which Mr. Hatch imagined was a rat. Mr. Hatch had previously told me of four large mirrors in the living- and dining-rooms. With these, from the position in which he said they were, I readily saw how the reflection could have been made.
"In a general sort of way, in my own mind, I had accounted for the phantom. Why was it there? This seemed a more difficult problem. It was possible that it had been put there for amusement, but I did not wholly accept this. Why? Partly because no one had ever heard of it until the Italian workmen went there. Why did it appear just at the moment they went to begin the work Mr. Weston had ordered? Was it the purpose to keep the workmen away?
"These questions arose in my mind in order. Then, as Mr. Hatch had told me of a tragedy in the house and hidden jewels, I asked him to learn more of these. I called his attention to the fact that it would be a queer circumstance if these jewels were still somewhere in the old house. Suppose some one who knew of their existence were searching for them, believed he could find them, and wanted something which would effectually drive away any inquiring persons, tramps or villagers, who might appear there at night. A ghost? Perhaps.
"Suppose some one wanted to give the old house such a reputation that Mr. Weston would not care to undertake the work of repair and refurnishing. A ghost? Again perhaps. In a shallow mind this ghost might have been interpreted even as an effort to prevent the marriage of Miss Everard and Mr. Weston. Therefore Mr. Hatch was instructed to get all the facts possible about you, Mr. Weston, and members of your family. I reasoned that members of your own family would be more likely to know of the lost jewels than anyone else after a lapse of fifty years.
"Well, what Mr. Hatch learned from you and your cousin, George Weston, instantly, in my mind, established a motive for the ghost. It was, as I had supposed possible, an effort to drive workmen away, perhaps only for a time, while a search was made for the jewels. The old tragedy in the house was a good pretext to hang a ghost on. A clever mind conceived it and a clever mind put it into operation.
"Now, what one person knew most about the jewels? Your cousin George, Mr. Weston. Had he recently acquired any new information as to these jewels? I didn't know. I thought it possible. Why? On his own statement that his mother, then a bride, got the story of the entire affair direct from his grandmother, who remembered more of it than anybody else--who might even have heard his grandfather say where he intended hiding the jewels."
The Thinking Machine paused for a little while, shifted his position, then went on: