dsman 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!

"Why--why where--ohhh! Quick work, Dick!" The senior Arcot began
laughing heartily, and as his astonished and curious companions looked
toward him, he stopped and called out, "Come on, Dick! We want to see
you now. And tell us how it's done! I rather think Mr. Morey here--I
mean the visible one--is still a bit puzzled."

There was a short laugh from the air--certainly there could be nothing
else there--then a low but distinct click, and both Morey and Arcot were
miraculously present, coming instantaneously from nowhere, if one's
senses could