is replied solemnly. "It is only during
the past generation we have learned of the completeness and awfulness
of their preparations. Your people can not combat their sound-ray.
With it they can remain outside the vision of those on the surface and
set the tall buildings of your cities in harmonic vibrations that will
bring them down in ruins about the ears of the populace."

* * * * *

"There'll be nothing left for them to take if they destroy all our
cities: nowhere for them to live. I don't get it."

"Only a few will be destroyed completely, to terrify the rest of the
inhabitants of your worlds. Others will be depopulated by means of
vibrations that will kill off the citizens without harming the cities
themselves--vibrations which are capable of blanketing a large area
and raising the body temperature of all living things therein to a
point where death will ensue in a very few minutes. Other vibrations
will paralyze all electrical equipment on the planet and make it
impossible for your ships of the air to set out to give battle, even
were they properly armed."

"Looks bad, Carr," said Mado glumly.

"It does that. We've got to go back and carry the warning."

"I fear it is too late," said Detis. "Much time will be needed in
which to develop a defense and surely it can not be done within the
three isini before they set forth--about four of your days."

"They leave that soon?" Carr was taken aback.

"Yes, with their one hundred and twenty vessels; forty to each of your
three planets; seventeen hundred men to a vessel."

Carr jumped to his feet. "By the heat devils of Mercury!" he roared,
"well go to their lousy little satellite and find a way to prevent
it!"

* * * * *

Ora gazed at his flushed face with unconcealed admiration.

"You're crazy!" exploded Mado. "What can we do with the _Nomad_?"

"Her D-ray can do plenty of damage."

"Yes, but they'd have us down before we could account for five of
their vessels. It's no use, I tell you."

But Carr was stubborn. "We'll pay them a call anyway. I'll bet we can
dope out some way of putting it over on them. Are you game?"

"Of course I'm game. I'll go anywhere you will. But it's a fool idea
just the same."

"Maybe so. Maybe not. Anyway--let's go."

"Just a moment, gentlemen," Detis interposed. "How about me?"

Carr stared at him and saw that his eyes shone with excitement. "Why,
I believe you