. "This is
on the level," he said, "not something you cooked up on the spur of the
moment?"

"It's on the level," said Paul. "You were right all along."

When he returned to his office an urgent message from Barker awaited
him. He hurried down to the testing laboratory, where the older man
greeted him in excitement and anxiety.

"It looks like we've got something by the tail and can't let go of it.
Come in and have a look."

Paul followed him and found Captain Harper in an observation room,
writhing on a cot in a storm of tears and emotional fury. He beat
against the walls and the floor with his fists as his sobbing continued
beyond control.

"What happened to him?" Paul demanded.

"We have three others in the same condition," said Barker. "We tried to
determine the effect of a pure feedback impulse, and fed it back to each
of them in amplified form as we found it on their charts. This is what
happened. I'm afraid we may have cost them their sanity, and we don't
know why."

"How could their own feedback do such a thing to them?" he asked in
wonder. "What part of the chart did you take it from?"

"We used the impulse that didn't get through, the one that was blocked
so that error resulted. Apparently this is the alternative to error." He
nodded toward the writhing, sobbing man. "Harper reached a point where
he _had_ to fail or else be subject to this psychic storm."

Paul ran his long, bony fingers through his hair. "This makes less sense
than ever! If that's true, then we've got to take back what we've told
Oglethorpe. His errorless man isn't possible, after all."

"I don't know." Barker shook his head thoughtfully. "Evidently the
production of error is a protection against the admission of this
intolerable feedback impulse. But the question remains: why is it
intolerable, and why does it become so after numerous other feedback
impulses have been passed?

"Yesterday we thought we had it all wrapped up. Now it's blown open
wider than ever before!"

* * * * *

Oglethorpe's public relations man prepared a statement to the effect
that further danger from pilot error in rocket ships and the second
Wheel could be considered as completely eliminated with the new training
processes that would make men incapable of technical errors.

Paul knew it was as ineffectual as the average Government release, but
he made no protest in his concern for Harper and the three other men. He
sign