rn off the tape and continue
for as many cycles as you can."

"How long? A man could do that for a month, provided he didn't have to
sleep."

"I think you'll be a little surprised. You will continue until your
accumulation of errors becomes so great that the entire procedure
collapses."

"It still looks like a kid's game to me," Harper said confidently.
"Let's get started."

Carefully, they fitted the multiple electrodes of the
electro-encephalograph recorder to his skull. The tape instructor was
turned on, and Harper began the first cycle.

Behind the one-way glass of the observation room, Paul sat with Nat Holt
and Professor Barker and two assistants, watching. The rocket engineer
began jauntily, contemptuous of the simple actions required of him,
impatient to have it over with and get back to his duties at the
take-off stand.

The instructions coming over the speaker had some variations from the
normal handling of a ship, including the items necessary to record
observations and responses. Harper listened to these for a half dozen
cycles. Then, confident that he could breeze through the procedure for
the rest of the day if he had to, he switched off the tape and settled
back to take it easy.

One by one, he watched the meters, noted their information, made the
proper adjustments, added compensations, waited for results, checked and
re-checked--

"He'll go a long time," said Nat Holt confidently. "He's had top
training. If it breaks down, we may find out a few things."

"Cummins had top-drawer training, too," Paul said. "His break point
seemed to have no adequate antecedents. I don't think we're going to
find Harper holding out very long."

After an hour, the attitude of contempt had left Harper's face, and he
was proceeding with obvious boredom. He had made no error yet, but there
was evident a faint trace of anxiety as he concentrated on the
instruments and levers.

At two hours and a half Harper reached for a button and withdrew his
hand in abrupt hesitation. Then it darted out again and pressed
decisively. At three hours he was making two such hesitations every
cycle.

"Not so good," Barker commented. "Not for a man who battles himself the
way Harper does."

Nat Holt remained silent, watching critically the wavering dials and
graphs showing the engineer's physical condition and reaction.

At four and a half hours, Harper's hand reached for a lever in the
center of the board. But it didn't get m