re crystals of the
metals. If they can start a vibration in the crystals of the
metal--that's fatigue, metal fatigue enormously speeded. You know how a
quartz crystal oscillator in a radio-control apparatus will break, if
you work it on a very heavy load at the peak? They simply smash the
crystals of metal in the same way. Only they project their field."

"Then our toughest metals are useless? Can't something tough, rather
than hard, like copper or even silver for instance, stand it?"

"Calcium metal's the toughest going--and even that would break under the
beating those ships give it. The only way to withstand it is to have
such a mass of metal that the oscillations are damped out. But--"

The set tuned in on the IP station on Europa was speaking again. "The
ships are returning. There are one hundred and twenty-nine by accurate
count. Jorgsen reports that telescopic observation of the dead on the
fallen cruiser show them to be a _completely un-human race_! They are
of mottled coloring, predominately grayish brown. The ships are
returning. They have divided into ten groups, nine groups of two each,
and a main body of the rest of the fleet. The group of eighteen is
descending within range, and we are focusing our beams on them--"

Out by Europa, ten great UV beams were stabbing angrily toward ten great
interstellar ships. The metal of the hulls glowed brilliant, and
distorted slowly as the thick walls softened under the heat, and the air
behind pressed against it. Grimly the ten ships came on. Torpedoes were
being launched, and exploded, and now they had no effect, for the Mirans
within were protected.

The eighteen grouped ships separated, and arranged themselves in a
circle around the fort. Suddenly one staggered as a great puff of gas
shot out through the thin atmosphere of Europa to flare brilliantly in
the lash of the stabbing UV beam. Instantly the ship righted itself, and
labored upward. Another dropped to take its place--

And the great walls of the IP fort suddenly groaned and started in their
welded joints. The faint, whispering rustle of the crumbling beam was
murmuring through the station. Engineers shouted suddenly as meters
leapt the length of their scales, and the needles clicked softly on the
stop pins. A thin rustle came from the atostors grouped in the great
power room. "Spirits of Space--a revolving magnetic field!" roared the
Chief Technician. "They're making this whole blasted station a squirrel