ether again and set about the herculean task of making
the necessary repairs to the damaged mechanism in time to rescue
Joan before the twelve-hour limit should doom the girl to forever
remain an exile in that land of alien mystery beyond the atomic
barrier.

* * * * *

Their previous experiments with animals had proved that no living
creature from Earth could be brought back after it had been in Arret
over twelve hours. After that time the change in the atoms
constituting living tissues apparently became permanently Arretian,
for the Silver Belts returned without any trace of their original
wearers.

The necessary repairs to the damaged coils were of such an exacting
and intricate nature that any great speed was impossible. Hours
passed while the two men bent to their work with grim concentration.
Neither of them dared think too much of what nameless dangers might
be confronting Joan during those weary hours. Their actual knowledge
of Arret was so pitiably slight.

Some months ago, while they were experimenting upon apparatus for
reversing the electrical charges of an atom's electrons and protons,
they had first stumbled upon the incredible fact that such a place
as Arret really existed. They found that it was another world
occupying the same position in space as Earth, with the fundamental
difference in the two interwoven planes of existence lying in the
electrical make-up of the atoms that constituted matter in each
plane.

On Earth all atoms are composed of small heavy protons that are
always positive in charge, and larger lighter electrons that are
always negative. In Arret the protons were negative, and the
electrons positive. The result was two worlds occupying the same
space at the same time, yet with matter so essentially and
completely different that each world was intangible to the other.
They had named the unseen world Arret, the reverse of Terra.

Finding it impossible to work directly upon most forms of matter,
the experimenters had finally evolved a silver alloy that served as
a medium both for sending objects into Arret and then bringing
them back to Earth. By focussing the flame of the projection
apparatus upon a Silver Belt of this alloy, the electrical charges
of the Belt's atoms were reversed, automatically causing the Belt to
vanish from Earth and materialize in Arret. At the same time the
atoms of any object within the Belt's immediate radius were
similarly