"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."