r circuit by about a mile of space. A
mile, seen at a distance of ninety thousand feet, would be little
indeed.

It was almost midday when they had their first stroke of luck.

The buzzer sounded at the very moment Eyer uttered an ejaculation.

"The Jersey fellow says there is nothing between his lens and your plane
to obstruct the view."

"O.K.," retorted Jeter. "At the moment your buzzer sounded our plane
suddenly jumped upward. That means an upcurrent of air indicating an
obstruction under us. It must however, be invisible."

He severed the connection. His brow was furrowed thoughtfully. He was
remembering Sitsumi and his rumored discovery.

They circled back warily. The eyes of both were fixed downward, staring
into space. Their jaws were firmly set. Their eyes were narrowed.

And then....

There was that uprush of air again! It appeared to rise from an angle of
about sixty degrees. They got the wind against their nose and started a
humming dive, feeling in the alien updraft for the obstruction which
caused it.

CHAPTER VII

_Invisible Globe_

The buzzer of their radiophone was sounding, but so intent were they on
this phenomenon they were facing, they paid it no heed. Their eyes were
alight, their lips in firm straight lines of resolve, as they dived down
upon the invisible obstruction--whatever it was--from whose surface the
telltale updraft came.

It was Eyer who made the suggestion:

"Let's measure it to see what its plane extent is."

"How?" asked Jeter.

"Measure it by following the wind disturbance. We travel in one
direction until we lose it. There is one extremity. In a few minutes we
can discover exactly how big the thing is. What do you think it is?"

Jeter shook his head. There was no way of telling.

Jeter nodded agreement to Eyer. Then he spoke into the radiophone,
telling Hadley what they had found, to which he could give no name.

"The world awaits in fear and trembling what you will have to report,
Jeter," said Hadley. "What if you become unable to report, as Kress
did?"

"Don't worry. We will or we won't. If we succeed we'll be back. If we
fail, send up the other.... No, perhaps you hadn't better send up the
new planes. But I think Eyer and I have a chance to discover the nature
of this strange--whatever-it-is. If you can't contact us, delay
twenty-four hours before doing anything. I--well, I scarcely know what
to tell you to do. We'll just be shooting in the dark u