cage!"

The mighty walls of eight-foot metal shuddered and trembled. The UV
beams lashed out from the fort in quivering arcs now, they did not hold
their aim steady, and the magnetic shield that protected them from
atomic bombs was working and straining wildly. Eighteen great ships
quivered and tugged outside there now, straining with all their power to
remain in the same spot, as they passed on from one to another the
magnetic impulses that were now creating a titanic magnetic vortex about
the fort.

"The atostors will be exhausted in another fifteen minutes," the Chief
Technician roared into his transmitter. "Can the signals get through
those fields, Commander?"

"No, Mac. They've been stopped, Sparks tells me. We're here--and let's
hope we stay. What's happening?"

"They've got a revolving magnetic field out there that would spin a
minor planet. The whole blasted fort is acting like the squirrel cage in
an induction motor! They've made us the armature in a five hundred
million horsepower electric motor."

"They can't tear this place loose, can they?"

"I don't know--it was never--" The Chief stopped. Outside a terrific
roar and crash had built up. White darts of flame leapt a thousand feet
into the air, hurling terrific masses of shattered rock and soil.

"I was going to say," the Chief went on, "this place wasn't designed for
that sort of a strain. Our own magnetic field is supporting us now,
preventing their magnetic field from getting its teeth on metal. When
the strain comes--well, they're cutting loose our foundation with atomic
bombs!"

Five UV beams were combined on one interstellar ship. Instantly the
great machine retreated, and another dropped in to take its place while
the magnetic field spun on, uninterruptedly.

"Can they keep that up long?"

"God knows--but they have a hundred and more ships to send in when the
power of one gives out, remember."

"What's our reserve now?"

The Chief paused a moment to look at the meters. "Half what it was ten
minutes ago!"

Commander Wallace sent some other orders. Every torpedo tube of the
station suddenly belched forth deadly, fifteen-foot torpedoes, most of
them mud-torpedoes, torpedoes loaded with high explosive in the nose, a
delayed fuse, and a load of soft clinging mud in the rear. The mud would
flow down over the nose and offer a resistance foot-hold for the
explosive which empty space would not. Four hundred and three torpedoes,
equipped wit