The pictures seemed to show the flame slowly descending till it again touched the metal. The tungsto-iridium glowed briefly; then, as suddenly as the extinguishing of a light, the safe was gone! It had disappeared into thin air! Only the incandescence of the metal and the flame itself were visible. "It seems the pirate has solved the secret of invisibility. No wonder the Air Guardsmen couldn't find him!" exclaimed Arcot, senior. The projector had been stopped exactly on the first frame, showing the invisibility of the safe. Then Arcot backed it up. "True, Dad," he said, "but pay special attention to this next frame." Again there appeared a picture of the room, the window beyond, the mail clerk asleep at his desk, everything as before, except that where the safe had been, _there was a shadowy, half visible safe_, the metal glowing brightly. Beside it there was visible a shadowy man, holding the safe with a shadowy bar of some sort. And through both of them the frame of the window was perfectly visible, and, ironically, an Air Guardsman plane. "It seems that for an instant his invisibility failed here. Probably it was the contact with the safe that caused it. What do you think, Dad?" asked Arcot, junior. "It does seem reasonable. I can't see off-hand how his invisibility is even theoretically possible. Have you any ideas?" "Well, Dad, I have, but I want to wait till tomorrow night to demonstrate them. Let's adjourn this meeting, if you can all come tomorrow." * * * * * The next evening, however, it seemed that it was Arcot himself who could not be there. He asked Morey, junior, to tell them he would be there later, when he had finished in the lab. Dinner was over now, and the men were waiting rather impatiently for Arcot to come. They heard some noise in the corridor, and looked up, but no one entered. "Morey," asked Fuller, "what did you learn about that gas the pirate was using? I remember Arcot said he would have some samples to analyze." "As to the gas, Dick found out but little more than we had already known. It is a typical organic compound, one of the metal radical type, and contains one atom of thorium. This is a bit radioactive, as you know, and Dick thinks that this may account in part for its ability to suspend animation. However, since it was impossible to determine the molecular weight, he could not say what the gas was, save that the empirical formula was C_{62}TH H_{39}O_{27}N_{5}. It broke down at a temperature of only 89 deg. centigrade. The gases left consisted largely of methane, nitrogen, and methyl ether. Dick is still in the dark as to what the gas is." He paused, then exclaimed: "Look over there!" The men turned with one accord toward the opposite end of the room, looked, and seeing nothing particularly unusual, glanced back rather puzzled. What they then saw, or better, failed to see, puzzled them still more. Morey had disappeared!