lightly, and the
whole huge mold grew hotter and hotter and hotter. And after a time it
was allowed to cool.

But that did not mean a ceasing of activity. The plaster casts had been
made while the concreting process was worked out. The concreting
process--including the heating--was in action while fittings were being
flown to the Shed. But other hulls were being formed by metal-concrete
formation even before the first mold was taken down.

When the plaster sections came off, there was a long, gleaming,
frosty-sheened metal hull waiting for the fittings. It was a replacement
of one of the two shot-down space craft, ready for fitting out some six
weeks ahead of schedule. Next day there was a second metal hull, still
too hot to touch. The day after that there was another.

Then they began to be turned out at the rate of two a day, and all the
vast expanse of the Shed resounded with the work on them. Drills drilled
and torches burned and hammers hammered. Small diesels rumbled. Disk
saws cut metal like butter by the seemingly impractical method of
spinning at 20,000 revolutions per minute. Convoys of motor busses
rolled out from Bootstrap at change-shift time, and there were again
Security men at every doorway, moving continually about.

But it still didn't look too good. There is apparently no way to beat
arithmetic, and a definitely grim problem still remained. Ten days after
the beginning of the new construction program, Joe and Sally looked down
from a gallery high up in the outward-curving wall of the Shed. Acres of
dark flooring lay beneath them. There was a spiral ramp that wound round
and round between the twin skins of the fifty-story-high dome. It led
finally to the Communications Room at the very top of the Shed itself.

Where Joe and Sally looked down, the floor was 300 feet below. Welding
arcs glittered. Rivet guns chattered. Trucks came in the doorways with
materials, and there was already a gleaming row of eighty-foot hulls.
There were eleven of them already uncovered, and small trucks ran up to
their sides to feed the fitting-out crews such items as air tanks and
gyro assemblies and steering rocket piping and motors, and short wave
communicators and control boards. Exit doors were being fitted. The last
two hulls to be uncovered were being inspected with portable x-ray
outfits, in search of flaws. And there were still other ungainly white
molds, which were other hulls in process of formation--the metal s