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Jay Andre: On the night of December 1st, the control rods were locked. The 57th layer would make the pile go critical. Only little more material would be needed to finish it. Further work was postponed until the following day. On the morning of December 2nd, 1942, the steam lines under the stands were again out of commission. It was cold, drafty. The environment inside never created a false sense of security. Groups of scientists began to gather in the racquets court. On the balcony at the east end were Fermi, Zinn, and Anderson, grouped around some instruments. On the floor, beneath the balcony, young George Wile was standing by to handle the final control rod. On a platform above the pile stood the liquid control squad. Crawford Greenewalt describes the scene:
Crawford Greenewalt: The whole atmosphere there was one of calmly observing an experiment being made. To be sure there was a suicide squad that you could see on the other end of the platform with their cadmium nitrate ready to pour in if it didn't work. But it became obvious very quickly that it was going to be controlled.
Jay Andre: The experimental procedure was one of calm routine. The pile had been built up slowly, layer by layer. At 9:45am, Fermi asked that the cadmium strips be pulled out and the neutron density checked. Next he ordered the electrically-operated control rods withdrawn. Shortly after 10 o'clock he asked for the emergency rod to be pulled out and tied. Walter Zinn and Herb Anderson describe the scene:
Walter Zinn: Fermi, of course, gave the instructions, he made the calculations which were not really very elaborate, but had to be done correctly at the time. He got information to make his calculations from recorders. He also got measurements from Leona Woods, a station that had some counting equipment which is in another part of the room.
Herb Anderson: He made an initial test of the activity, then called for withdrawal of the control rod, and made another measurement of the radioactivity generated, and then with a sliderule, he calculated what would be the effect if he took the rod out somewhat more, announced this. He said now you look at this, and it will rise this high. And they pulled out the rod and it went that high, and the counters clicked a little more, and kept this up a number of times, each time being right about it.
Jay Andre: At 11 o'clock the clicking of the counters speeded up again. The pin climbed a few more points. At 11:25 the automatic control rod was reinserted and again Fermi predicted the increased rate. His calcuations were so exact, they said he was able to predict to the exact brick the point at which the reactor would become self-sustaining. Norman Hilberry contributes some insight to Fermi's uncanny accuracy:
Norman Hilberry: Fermi had, the night before, sat down and computed what the trace on the recording galvanometer would be for every single position of the control rod. Clearly, if there were any new law of physics, it would begin to show up in an actual deviation of the observed graphs from those he had computed, and each time it hit absolutely right on the nose. I am sure that long before Fermi finally said "George pull it out another ten inches," the question had long since been settled in his mind, and it had long since settled mine, too.
Jay Andre: Eleven thirty-five, the automatic safety rod was withdrawn and set. Another withdrawal of the control rod and the counters began clicking faster and faster. Suddenly there was a loud thud, then silence. The safety point at the automatic rod had been set too low, and it had slammed home. Fermi called a recess for lunch, and the group headed for the student cafeteria.