"You see how it was done? Grantham turned his switches, and as the tourmaline disk was turned slowly in its framework you saw it growing more and more transparent until when it had been turned a quarter-turn in the framework it was perfectly transparent and so invisible to your eyes in the strong sunlight streaming through it. Grantham let it remain so but a moment and then with his switch or rheostat control turned it back again a quarter-turn. It grew more and more cloudy and black until at a quarter-turn it was again black and opaque against the light. He reached for it, and when he turned to you again palmed it and could hand you the paper-weight disk."
Carton shook his head like one dazed. "And it seemed such a perfectly open demonstration," he said.
"But that doesn't explain the Invisible Master!" Ellsworth exclaimed. "If Grantham's power was faked, who committed those three crimes that no one but an invisible person could have committed? Who took the money last night?"
Wade Reconstructs
"I think I can reconstruct the thing from the first," Wade said, "though some of the secret died with Grantham here. You told me yourself that he and Gray had long been prevented from engaging in the lines of research they desired because of their lack of funds. Well, I think that Grantham grew resentful at this, and then determined, and that he and Gray resolved to lay hands on the money they needed in their own fashion. To do it they worked out an elaborate and incredibly ingenious plan, that hinged upon Grantham's known reputation as a great physicist.
"Grantham and Gray prepared the tourmaline-crystal set-up, and then let it be known in one way or another that Grantham had discovered a method of making things invisible. Of course there was excitement, and of course the reporters, Carton among them, rushed out here to learn all about it. Then Grantham reluctantly consented to a demonstration, and after pulling this tourmaline-crystal stunt, sent them away, and you too, perfectly convinced that he had actually found a way to make matter invisible. That was his first great step—to implant in the minds of reputable witnesses the absolute conviction that he had really the power of making things invisible.
"Just what happened on that afternoon between Grantham and Gray may never be known fully, but there seems little doubt that Gray, who had been sullen at the demonstration that morning, had come to the point where he had resolved not to go on with the scheme. Probably he threatened to expose Grantham if he did not stop it, and no doubt Grantham saw exposure and oblivion on the way. Fearing Gray's confession, he killed him, and disposed of his body here in the laboratory. He had the knowledge to do that, and I've found that on that afternoon he received from the supply-rooms here an inordinate order of acids which were without doubt used in the disposition of Gray's body. However it was done, there is not the slightest doubt that on that afternoon Gray, and even his body, passed out of existence in this laboratory.
"Then Grantham went on with his plan, changing it somewhat, no doubt, to fit in with this new circumstance. That night he struck himself a painful but not heavy blow on the head with some wooden object—you remember the doctor said the blow was from the side?—and pretended to be lying stunned when you, President Ellsworth, came in. When the police came he, without seeming to want to do so, threw the responsibility of the attack on Gray as much as possible, and told of his projector that had been stolen by his attacker, and that would make a man invisible. He had already prepared a mocking letter addressed to himself as from the Invisible Master, and while talking with Carton and me, laid the letter on the table where I found it. The officers at the door had seen no one go in or out, we knew or thought we knew that someone was at large with an apparatus for attaining invisibility, and since we never dreamed of Grantham having left the letter, we had no doubt whatever but that the Invisible Master, whether Gray or another, had actually entered the room invisibly and left the letter for us.
"This was Grantham's second step, his establishing the idea that someone was at large with a projector that could make him invisible, that the Invisible Master was at large and ready to commit any crime. That idea was established in all the city by the newspapers in the next day or so, and so strong was the evidence in the demonstration of his discovery that Grantham had given, and the greatness of his reputation as a scientist, that almost all did believe that such an invisible man, an Invisible Master, was at large.