* * * *

And that was all he knew about the danger, real or imaginary, that had
driven two men into insanity. He would have six months in which to find
the answer. Six months minus-- He looked at the chronometer and saw that
twenty minutes had passed since he left the cruiser. Somehow, it seemed
much longer ...

He moved to light a cigarette and his metal soles scraped the floor with
the same startling loudness he had noticed before. The bubble was as
silent as a tomb.

It was not much larger than a tomb; a sphere eighteen feet in diameter,
made of thin sheet steel and criss-crossed outside with narrow
reinforcing girders to keep the internal air pressure from rupturing it.
The floor under him was six feet up from the sphere's bottom and the
space beneath held the air regenerator and waste converter units, the
storage batteries and the food cabinets. The compartment in which he sat
contained chair, table, a narrow cot, banks of dials, a remote-control
panel for operating the instruments mounted outside the hull, a
microfilm projector, and a pair of exerciser springs attached to one
wall. That was all.

There was no means of communication since a hyperspace communicator
would have affected the delicate instruments with its radiations but
there was a small microfilm library to go with the projector so that he
should be able to pass away the time pleasantly enough.

But it was not the fear of boredom that was behind the apprehension he
could already feel touching at his mind. It had not been boredom that
had turned Horne into a suicide and Silverman into--

Something cracked sharply behind him, like a gunshot in the stillness,
and he leaped to his feet, whirling to face it.

It was only a metal reel of data tape that had dropped out of the
spectrum analyzer into the storage tray.

His heart was thumping fast and his attempt to laugh at his nervousness
sounded hollow and mirthless. _Something_ inside or outside the bubble
had driven two men insane with its threat and now that he was
irrevocably exiled in the bubble, himself, he could no longer dismiss
their fear as products of their imagination. Both of them had been
rational, intelligent men, as carefully selected by the Observation
Bureau as he had been.

He set in to search the bubble, overlooking nothing. When he crawled
down into the lower compartment he hesitated then opened the longest
blade of his knife before searching among the dark