. The
old _Gainsway_ shook like this for eight days before they spotted the
tubes that were causing a four-cycle beat."

"Why can't we spot it right off?" Quill asked.

Mike got it then. Fitzhugh was listening in. Quill wanted Mike the Angel
to substantiate his own statements to the roboticist.

"There are sixteen generator tubes in the hull--two at each end of the
four diagonals of an imaginary cube surrounding the ship. At least two
of them are out of phase; that means that every one of them may have to
be balanced against every other one, and that would make a hundred and
twenty checks. It will take ten minutes if we hit it lucky and find the
bad tubes in the first two tries, and about twenty hours if we hit on
the last try.

"That, of course, is presuming that there are only two out. If there are
three...." He let it hang.

Mike grinned as Dr. Morris Fitzhugh's voice came over the intercom,
confirming his diagnosis of the situation.

"Isn't there any other way?" asked Fitzhugh worriedly. "Can't we stop
the ship and check them, so that we won't be subjected to this?"

"'Fraid not," answered Mike. "In the first place, cutting the external
field would be dangerous, if not deadly. The abrupt deceleration
wouldn't be good for us, even with the internal field operating. In the
second place, we couldn't check the field tubes if they weren't
operating. You can't tell a bad tube just by looking at it. They'd still
have to be balanced against each other, and that would take the same
amount of time as it is going to take anyway, and with the same effects
on the ship. I'm sorry, but we'll just have to put up with it."

"Well, for Heaven's sake do the best you can," Fitzhugh said in a
worried voice. "This beat is shaking Snookums' brain. God knows what
damage it may do unless it's stopped within a very few minutes!"

"I'll do the best I can," said Mike the Angel carefully. "So will every
man in my crew. But about all anyone can do is wish us luck and let us
work."

"Yes," said Dr. Fitzhugh slowly. "Yes. I understand. Thank you,
Commander."

Mike the Angel nodded curtly and went back to work.

Things weren't bad enough as they were. They had to get worse. The
_Brainchild_ had been built too fast, and in too unorthodox a manner.
The steady two-cycle throb did more damage than it would normally have
done aboard a non-experimental ship.

Twelve minutes after the throb started, a feeder valve in the
pre-induction ene