and we'll see if
the old puddle jumper will take off."

Dr. Bird ran to the propeller.

"Ready!" he cried.

"Contact!" snapped McCready.

The plane motor roared into life. The ship moved slowly forward as Dr.
Bird climbed on board. Toward the oncoming trucks they rushed across the
plain. A crash seemed imminent. In the nick of time McCready pulled back
on his joystick and the plane rose gracefully into the air, clearing the
leading truck by inches. The truck halted and hastily mounted a machine
gun.

"Too late!" laughed the lieutenant. "Now it's our turn for some fun."

He tapped the key of his radio transmitter. In a few seconds he received
an answer.

"They have reduced Fort Novadwinskaja," he reported to the rear cockpit,
"but they don't know what to fire at next. Their largest guns will reach
the factory easily. Shall I start some fireworks?"

"You may fire when ready, Gridly," chuckled Dr. Bird.

Again the lieutenant depressed his key. From their altitude of four
thousand feet, they could see the _Denver_. From its forward turret
came a puff of smoke. There were a few moments of pause and then a cloud
of black rose from the plain below them, half a mile from the factory.
McCready reported the position of the burst to the ship. A second shell
burst beyond the factory and the third just in front of it.

"It's a clear bracket," said McCready. "Now watch the gun. I'll give
them a salvo."

* * * * *

From the side of the _Denver_ came a cloud of black smoke as all of her
turret guns fired in unison. The aim was perfect. For a few moments all
was quiet and then the factory disappeared in a smother of bursting high
explosive shells.

Hardly had the shells landed than a terrific sheet of lightning ripped
across the sky. The thunderclap which seemed to come simultaneously,
rocked the plane like a feather. Sheet after sheet of lightning
illuminated the sky while the roar of thunder was continuous. Rain fell
in solid sheets. Even as they watched, it began to turn into snow. The
air grew bitterly cold.

"The solar magnet is wrecked," shouted the doctor, "and these storms are
the efforts of nature to return to normal."

"If they get any worse, we're doomed."

"But in a good cause."

Through the storm the plane raced. Suddenly the motor died with
sickening suddenness.

"Our haywire battery connections are gone," shouted McCready. "Say your
prayers."

The wind tossed the