But when she hit the outer fringes of the ionosphere--that upper layer
of rarified protons, the rapidly moving current of high velocity ions
known as the plasmasphere--she bucked like a kicked horse. From deep
within her vitals, the throb began, a strumming, thrumming sound with a
somewhat higher note imposed upon it, making a sound like that of a bass
viol being plucked rapidly on its lowest string.

It was not the intensity of the ionosphere that cracked the drive of the
_Brainchild_; it was the duration. The layer of ionization was too
thick; the ship couldn't make it through the layer fast enough, in spite
of her high velocity.

A man can hold a red-hot bit of steel in his hand for a fraction of a
second without even feeling it. But if he has to hold a hot baked potato
for thirty seconds, he's likely to get a bad burn.

So it was with the _Brainchild_. The passage through Earth's ionosphere
during take-off had been measured in fractions of a second. The
_Brainchild_ had reacted, but the exposure to the field had been too
short to hurt her.

The ionosphere of Eisberg was much deeper and, although the intensity
was less, the duration was much longer.

The drumming increased as she fell, a low-frequency, high-energy sine
wave that shook the ship more violently than had the out-of-phase beat
that had pummeled the ship shortly after her take-off.

Dr. Morris Fitzhugh, the roboticist, screamed imprecations into the
intercom, but Captain Sir Henry Quill cut him off before anyone took
notice and let the scientist rave into a dead pickup.

"How's she coming?"

The voice came over the intercom to the Power Section, and Mike the
Angel knew that the question was meant for him.

"She'll make it, Captain," he said. "She'll make it. I designed this
thing for a 500 per cent overload. She'll make it."

"Good," said Black Bart, snapping off the intercom.

Mike exhaled gustily. His eyes were still on the needles that kept
creeping higher and higher along the calibrated periphery of the meters.
Many of them had long since passed the red lines that marked the
allowable overload point. Mike the Angel knew that those points had been
set low, but he also knew that they were approaching the real overload
point.

He took another deep breath and held it.

* * * * *

Point for point, the continent of Antarctica, Earth, is one of the most
deadly areas ever found on a planet that is supposedly non-