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 still pouring into the molds in powder form, or being tamped down, or being sintered to solidity. Joe leaned on the gallery-railing and said unhappily, "I can't help worrying, even though the Platform hasn't been shot at since we landed." That wasn't an expression of what he was thinking. He was thinking about matters the enemies of the Platform would have liked to know about. Sally knew these matters too. But top secret information isn't talked about by the people who know it, unless they are actively at work on it. At all other times one pretends even to himself that he doesn't know it. That is the only possible way to avoid leaks.