or
the rocket-ship. Thorn panted.

"He can't reach us with gas, now, and it looks like he doesn't dare
use a gun. They'd know he wasn't a Martian. At night he'll use that
helicopter, though. If we can only make those ships see us...."

* * * * *

They toiled on. The sun was already slanting down toward the western
sky. At four--by the sun--Thorn could point to a huge air-dreadnaught
hanging by lazily revolving gyros barely two miles away. He waved
wildly, frantically, but the big ship drifted on, unseeing. The
Fighting Force was no longer looking for Thorn and Sylva. They had
been carried into the rocket-ship fourteen hours and more before.
Sylva's screaming had been broadcast with the weird hoots and
whistles the United Nations believed to be the language of
inter-planetary invaders. The United Nations believed them dead. Now a
watch was being kept on the rocket-ship, to be sure, but it was
becoming a matter-of-fact sort of vigilance, pending the arrival of
the rest of the Fighting Force and the cracking of the dome of force
by the scientists who worked on it night and day.

On level ground, Thorn and Sylva would have reached the edge of the
dome in an hour. Here they had to climb up steep hillsides and down
precipitous slopes. Four times they halted to make frantic efforts to
attract the attention of some nearby ship.

It was six when they came upon the rim. There was no indication of its
existence save that three hundred yards from them boughs waved and
leaves quivered in a breeze. Inside the dome the air was utterly
still.

"There it is!" panted Thorn.

Wearied and worn out as they were, they hurried forward, and abruptly
there was something which impeded their movements. They could reach
their hands into the impalpable barrier. For one foot, two, or even
three. But an intolerable pressure thrust them back. Thorn seized a
sapling and ran at the barrier as if with a spear. It went five feet
into the invisible resistance and stopped, shot back out as if flung
back by a jet of compressed air.

"He told the truth," groaned Thorn. "We can't get out!"

* * * * *

Long shadows were already reaching out from the mountains. Darkness
began to creep upward among the valleys. Far, far away a compact dark
cloud appeared, a combat-squadron. It swept toward the dome and
dissociated into a myriad specks which were aircraft. The fliers
already swirling abou