* * * * *

Harding shook his head again. "Norman, your theory would be all right
if it were not for the cold fact that no such satellite has ever been
glimpsed."

"Can you glimpse a bullet passing you?" Norman retorted. "The two
fliers at Sweden and Lower California vanished within three hours of
each other, on opposite sides of the Earth. That means that this
second satellite, as I've computed, circles Earth once every six
hours, and travelling at that terrific speed it is no more visible to
us of Earth than a rifle bullet would be."

"Moving through Earth's atmosphere at such speed, indeed, one would
expect it to burn up by its own friction with the air. But it does
not, because its own gravitational power would draw to itself enough
air to make a dense little atmosphere for itself that would cling to
it and shield it as it speeds through Earth's upper air. No, I'm
certain that this second satellite exists, Harding, and I'm as certain
that it's responsible for the vanishing of those four fliers."

"And now you and Hackett have figured when it will be passing over
here and are going up in an X-type yourselves to look for it,"
Harding said musingly.

"Look for it?" echoed Hackett. "We're not going to climb forty miles
just to get a look at the damn thing--we're going to try landing on
it!"

"You're crazy sure!" the field superintendent exploded. "If Fellows
and those others got caught by the thing and never came down again,
why in the name of all that's holy would you two want--" He stopped
suddenly. "Oh, I think I see," he said, awkwardly. "Fellows was rather
a buddy of you two, wasn't he?"

"The best that ever flew a crippled Nieuport against three Fokkers to
pull us out of a hole," said Norman softly. "Weeks he's been gone, and
if it had been Hackett and I he'd be all over the sky looking for
us--the damned lunatic. Well, we're not going to let him down."

"I see," Harding repeated. Then--"Well, here comes your mechanic,
Norman, so your ship must be ready. I'll go with you. It's an event to
see two Columbuses starting for another world."

* * * * *

The gray dawn-light over the flying field was flushing to faint rose
as the three strode out to where the long X-type stood, its strangely
curved wings, enclosed cabin and flat, fan-like tail gleaming dully.
Its motor was already roaring with power and the plane's stubby wheels
strained against