ane hit an unusually bad
air bump, and through the window they caught a glimpse of one of the
circling Air Guardsmen. Then suddenly there appeared in the air within
the room a point of flame. It hung in the air above the safe for an
instant, described a strangely complicated set of curves; then, as it
hung for an instant in mid-air, it became a great flare. In an instant
this condensed to a point of intensely brilliant crimson fire. This
described a complex series of curves and touched the top of the safe. In
an inconceivably short time, the eight-inch thickness of tungsto-iridium
alloy flared incandescently and began to flow sluggishly. A large circle
of the red flame sprang out to surround the point of brilliance, and
this blew the molten metal to one side, in a cascade of sparks.

In moments, the torch had cut a large disc of metal nearly free;
seemingly on the verge of dropping into the safe. Now the flame left the
safe, again retracting itself in that uncanny manner, no force seeming
either to supply it with fuel or to support it thus, though it burned
steadily, and worked rapidly and efficiently. Now, in mid-air, it hung
for a second.

"I'm going to work the projector for a few moments by hand so that you
may see this next bit of film." Arcot moved a small switch and the
machine blinked, giving a strange appearance to the seemingly solid
images that were thrown on the screen.

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
Guar