f dry land. We are
on the northern cap.

"We have the microphone turned way down. Let's step up the power a bit
and see if there are any sounds outside," said Arcot and walked over to
the power control switch. An instant later a low hum came from the
loudspeaker. There was a light breeze blowing. In the distance, forming
a dull background for the hum, there came a low rumbling that seemed
punctuated now and then by a greater sound.

"Must be a long way off," said Arcot, a puzzled frown on his face.
"Swing the ship around so we can see in what direction the sound is
loudest," he suggested.

Slowly Morey swung the ship around on its vertical axis. Without a
doubt, something off in the direction of the hills was making a
considerable noise.

"Arcot, if that's a fight between two animals--two of those giant
animals that you said might be here--I don't care to get near them!"
Fuller's narrowed eyes strove to penetrate the haze that screened the
low hills in the blue distance.

The microphone was shut off while the _Solarite_ shot swiftly forward
toward the source of the sound. Quickly the hills grew, the blue
mistiness disappearing, and the jagged mounds revealing themselves as
bleak harsh rock. As they drew nearer they saw beyond the hills,
intermittent flashes of brilliant light, heard shattering blasts of
sound.

"A thunderstorm!" Wade began, but Arcot interrupted.

"Not so fast, Wade--Fuller's animal _is_ there--the only animal in all
creation that can make a noise like that! Look through the
telescope--see those dots wheeling about there above the flashing
lights? The only animal that can make that racket is man! There are men
over there--and they aren't in a playful mood! Turn on the invisibility
while we can, Morey--and let's get nearer!"

"Look out--here we go!" Morey began to close a tiny switch set in one
side of the instrument panel--then, before the relay below could move,
he had flipped it back.

"Here, you take it, Arcot--you always think about two steps ahead of
me--you're quicker and know the machine better anyway."

Quickly the two men exchanged places.

"I don't know about that, Morey," said a voice from vacancy, for Arcot
had at once thrown the ship into invisibility. "The longer we're here,
the more mistakes I see we made in our calculations. I see what put me
off so badly on my estimate of the intelligence of life found here! The
sun gives it a double dose of heat--but also a double dose o