peed of the shell was slackening!
The aperture containing the ionizing mechanism was still open; I
glanced within, The whirling ball of fire was not dimmed, but its
coruscations, instead of pouring down through the cylinder, swirled
and eddied and shot back as though trying to re-enter their source.
Rador nodded grimly.

"The Shadow takes its toll," he said.

We topped a rise--Larry gripped my arm.

"Look!" he cried, and pointed. Far, far behind us, so far that the
road was but a glistening thread, a score of shining points came
speeding.

"Lugur and his men," said Rador.

"Can't you step on her?" asked Larry.

"Step on her?" repeated the green dwarf, puzzled.

"Give her more speed; push her," explained O'Keefe.

Rador looked about him. The coppery ramparts were close, not more
than three or four miles distant; in front of us the plain lifted in a
long rolling swell, and up this the _corial_ essayed to go--with a
terrifying lessening of speed. Faintly behind us came shootings, and
we knew that Lugur drew close. Nor anywhere was there sign of Lakla
nor her frogmen.

Now we were half-way to the crest; the shell barely crawled and from
beneath it came a faint hissing; it quivered, and I knew that its base
was no longer held above the glassy surface but rested on it.

"One last chance!" exclaimed Rador. He pressed upon the control lever
and wrenched it from its socket. Instantly the sparkling ball
expanded, whirling with prodigious rapidity and sending a cascade of
coruscations into the cylinder. The shell rose; leaped through the
air; the dark crystal split into fragments; the fiery ball dulled;
died--but upon the impetus of that last thrust we reached the crest.
Poised there for a moment, I caught a glimpse of the road dropping
down the side of an enormous moss-covered, bowl-shaped valley whose
sharply curved sides ended abruptly at the base of the towering
barrier.

Then down the steep, powerless to guide or to check the shell, we
plunged in a meteor rush straight for the annihilating adamantine
breasts of the cliffs!

Now the quick thinking of Larry's air training came to our aid. As
the rampart reared close he threw himself upon Rador; hurled him and
himself against the side of the flying whorl. Under the shock the
finely balanced machine swerved from its course. It struck the soft,
low bank of the road, shot high in air, bounded on through the thick
carpeting, whirled like a dervish and fell upon