f intra-atomic energy. Their vessels are not propelled as ours
are--they have so perfected that force that it acts upon every particle
of the structure and its contents...."

"How do you figure that?" blurted Seaton.

"Because of the acceleration they can stand. Nothing even semi-human,
and probably nothing living, could endure it otherwise. Right?"

"Yes--I never thought of that."

"Furthermore, they are far from home, for if they were from anywhere
nearby, the Osnomians would have known of them--particularly since it is
evident from the size of the vessel that it is not a recent development
with them, as it is with us. Since the green system is close to the
center of the Galaxy, it seems reasonable, as a working hypothesis, to
assume that they are from some system far from the center, perhaps close
to the outer edge. They are very evidently of a high degree of
intelligence. They are also highly treacherous and merciless...."

"Why?" asked Dorothy, who was listening eagerly.

"I deduce those characteristics from their unprovoked attack upon
peaceful ships, vastly smaller and supposedly of inferior armament; and
also from the nature of that attack. This vessel is probably a scout or
an exploring ship, since it seems to be alone. It is not altogether
beyond the bounds of reason to imagine it upon a voyage of discovery, in
search of new planets to be subjugated and colonized...."

"That's a sweet picture of our future neighbors--but I guess you're
hitting the old nail on the head, at that."

"If these deductions are anywhere nearly correct, they are terrible
neighbors. For my next point, are we justified in assuming that they do
or do not know about the zone of force?"

"That's a hard one. Knowing what they evidently do know, it's hard to
see how they could have missed it. And yet, if they had known about it
for a long time, wouldn't they be able to get through it? Of course it
may be a real and total barrier in the ether--in that case they'd know
that they couldn't do a thing as long as we keep it on. Take your
choice, but I believe that they know about it, and know more than we
do--that it is a total barrier set up in the ether."

"I agree with you, and we shall proceed upon that assumption. They know,
then, that neither they nor we can do anything as long as we maintain
the zone--that it is a stalemate. They also know that it takes an
enormous amount of power to keep the zone in place. Now we have gone as
fa