hundred feet and longer.
And every one of them conformed to the rule perfectly!

Only around the base of the city there seemed to be a slight deviation.
Where the invisible cone should have touched the ground, there was a
series of low buildings made of some dark metal, and all about them the
ground appeared scarred and churned.

"They certainly seem to have some kind of ray screen over that city,"
Morey commented. "Just look at that perfect cone effect and those low
buildings are undoubtedly the projectors."

Arcot had brought the ship to a halt as he came through the pass in the
mountain. The shining hull was in the cleft of the gorge, and was, no
doubt, quite hard to see from the city.

Suddenly, a vagrant ray of the brilliant sun reached down through a
break in the overcast of clouds and touched the shining hull of the
_Ancient Mariner_ with a finger of gold. Instantly, the ship shone like
the polished mirror of a heliograph.

Almost immediately, a low sound came from the distant city. It was a
pulsing drone that came through the microphone in a weird cadence; a
low, beating drone, like some wild music. Louder and stronger it grew,
rising in pitch slowly, then it suddenly ended in a burst of rising
sound--a terrific whoop of alarm.

As if by magic, every ship in the air above the city shot downward,
dropping suddenly out of sight. In seconds, the air was cleared.

"It seems they've spotted us," said Arcot in a voice he tried to make
nonchalant.

A fleet of great, long ships was suddenly rising from the neighborhood
of the central building, the tallest of the group. They went in a
compact wedge formation and shot swiftly down along the wall of the
invisible cone until they were directly over the low building nearest
the _Ancient Mariner._ There was a sudden shimmer in the air. In an
instant, the ships were through and heading toward the _Ancient Mariner_
at a tremendous rate.

They shot forward with an acceleration that was astonishing to the men
in the spaceship. In perfect formation, they darted toward the lone,
shining ship from far-off Earth!

XIV

The four earthmen watched the fleet of alien ships roar through the air
toward them.

"Now how shall we signal them?" asked Morey, also trying to be
nonchalant, and failing as badly as Arcot had.

"Don't try the light beam method," cautioned Arcot. The last time they
had tried to use a light beam signal was when they first contacted the
Nigra