xplode the instant
any section of the thin metal weakened.

It was supposed to be an alloy so extremely strong that it had a high
safety factor but he could not believe that any metal so thin could be
so strong. It was all right for engineers sitting safely on Earth to
speak of high safety factors but his life depended upon the fragile wall
not cracking. It made a lot of difference.

* * * * *

The next day he thought he felt the hook to which the exerciser spring
was attached crack loose from where it was welded to the wall. He
inspected the base of the hook closely and there seemed to be a fine,
hairline fracture appearing around it.

* * * * *

He held his ear to it, listening for any sound of a leak. It was not
leaking yet but it could commence doing so at any time. He looked out
the windows at the illimitable void that was waiting to absorb his
pitiful little supply of air and he thought of the days he had hauled
and jerked at the springs with all his strength, not realizing the
damage he was doing.

There was a sick feeling in his stomach for the rest of the day and he
returned again and again to examine the hairline around the hook.

The next day he discovered an even more serious threat: the thin skin of
the bubble had been spot-welded to the outside reinforcing girders.

Such welding often created hard, brittle spots that would soon
crystallize from continued movement--and there was a slight temperature
difference in the bubble between his working and sleeping hours that
would daily produce a contraction and expansion of the skin. Especially
when he used the little cooking burner.

He quit using the burner for any purpose and began a daily inspection of
every square inch of the bubble's walls, marking with white chalk all
the welding spots that appeared to be definitely weakened. Each day he
found more to mark and soon the little white circles were scattered
across the walls wherever he looked.

When he was not working at examining the walls he could feel the windows
watching him, like staring eyes. Out of self defense he would have to go
to them and stare back at the emptiness.

Space was alien; coldly, deadly, alien. He was a tiny spark of life in a
hostile sea of Nothing and there was no one to help him. The Nothing
outside was waiting day and night for the most infinitesimal leak or
crack in the walls; the Nothing that had been waiti