they'll leave it at that? The men who know how to do it will
be scattered to a dozen or a hundred places, so they can't possibly
all be found, and they'll keep on secretly working until they've made
the beams and a protection against them and then something more deadly
still! We humans can't be conquered! We'll fight to the end of time!"

"But you yourself," said Jill desperately, "you said there couldn't be
a defense against the beam! You said it!"

"I was discouraged," he protested. "I wasn't thinking straight. Look!
With no equipment at all, I found out how to detect the stuff before
it was strong enough to paralyze us. You know that. The scientists
will have equipment and instruments, and now that they've got the beam
they'll be able to try things. They'll do better than I did. They can
try heterodyning the beam. They can try for interference effects. They
may find something to reflect it, or they can try refraction."

He paused anxiously. She sobbed, once. "But other weapons--"

"There may not be any. And there's bound to be some trick of
refraction that'll help. It thins out at the edges now. That's how we
get warning of it. It's refracted by ions in the air. That's why it
isn't a completely tight beam. Ions in the air act like drops of mist;
they refract sunshine and make rainbows after rain. And we got the
smell-effect first. That proves there's refraction."

He watched her face. She swallowed. What he'd said was largely without
meaning. Actually, it wasn't even right. The evidence so far was that
the nerves of smell were more sensitive than the optic nerves or the
auditory ones, while nerves to bundles of muscle were less sensitive
still. But Lockley wasn't concerned with accuracy just now. He wanted
to reassure Jill.

Then his eyes widened suddenly and he stared past her. He'd been
speaking feverishly out of emotion, while a part of his mind stood
aside and listened. And that detached part of his mind had heard him
say something worth noting.

He stood stock-still for seconds, staring blankly. Then he said very
quietly, "You made me think, then. I don't know why I didn't, before.
The terror beam does scatter a little, like a searchlight beam in thin
mist. It's scattered by ions, like light by mist-droplets. That's
right!"

He stopped, thinking ahead. Jill said challengingly, "Go on!" Again
what he'd said had little meaning to her, but she could see that he
believed it important.

"Why, a searchlight