The 'copter went up the long, sloping, bulldozed snow-ramp. Soames
checked his radio contact. He nodded. The engines hummed and roared and
bellowed, and the ship lifted deliberately and floated away over the
icy waste.

The little helicopter was very much alone above a landscape which had
never known a growing thing.

Soames kept in radar contact and when he was ready he told the base,
"I'm going down now, hunting crevasses."

He let the 'copter descend. The waste was featureless, then and for a
seemingly interminable time afterward. Then his estimated position
matched the site of the static-earth-shock-concussion-wave-occurrence.
There seemed nothing about this part of the snow-desert which was
different from any other part. No. Over to the left. A wind-pattern
showed in the snow. It was already being blown away; its edges dulled.
But it was rather far from a probable thing. There were
lines--hollows--where gusts had blown at the snow's surface. They were
spiral lines, tending toward a center. They had not the faintest
resemblance to the crater of an explosion which might have made an
earth-shock.

Soames took a camera out of its place in the 'copter. Gail stared down.

"I've seen something like that," she said puzzledly. "Not a picture.
Certainly not a snow-field. I think it looks like a diagram of some
sort."

"Try a storm-wind diagram," said Soames drily. "The way a cyclone ought
to look from directly overhead. The meteorology boys will break down and
cry when they see this picture!"

He took pictures. The shadows of the wind-made indentations would come
out clearly in the film.

"Unless," said Soames, "unless somebody got a snap of a whirlwind
touching a snow-field and bouncing up again, this will be a photographic
first. It's not an explosion-pattern, you'll notice. Wind and snow
weren't thrown away from the center. They were drawn toward it.
Momentarily. It's an explosion inside out, an implosion-pattern to be
more exact."

"I don't understand," said Gail.

"An explosion," said Soames grimly, "is a bursting-out of a suddenly
present mass of gas. An implosion is a bursting-in of a suddenly present
vacuum. Set off a firecracker and you have an explosion. Break an
electric bulb and you have an implosion. That pattern behind us is an
implosion-pattern."

"But how could such a thing be?"

"If we knew," said Soames wrily, "maybe we'd be running away. Maybe we
should."

The 'copter droned on and on an