curving arc of speed showed that the big bulb was
under control. Over the ships it paused, to balance and swing, then shot
to the zenith as one of the great boats exploded in a cloud of vapor.

The following blast swept the airdrome. Planes yet on the ground went
like dry autumn leaves. The hangars were flattened.

Thurston cowered in awe. They were sheltered, he saw, by a slope of the
ground. No ridicule now for the bombs!

A second blast marked when the gas-cloud ignited. The billowing flames
were blue. They writhed in tortured convulsions through the air. Endless
explosions merged into one rumbling roar.

MacGregor had roused from his stupor; he raised to a sitting position.

"Hydrogen," he stated positively, and pointed where great volumes of
flame were sent whirling aloft. "It burns as it mixes with air." The
scientist was studying intently the mammoth reaction. "But the volume,"
he marveled, "the volume! From that small container! Impossible!"

"Impossible," the Secretary agreed, "but...." He pointed with his one
good arm toward the Pacific. Two great ships of steel, blackened and
battered in that fiery breath, tossed helplessly upon the pitching,
heaving sea. They furnished to the scientist's exclamation the only
adequate reply.

Each man stared aghast into the pallid faces of his companions. "I think
we have underestimated the opposition," said the Secretary of War
quietly. "Look--the fog is coming in, but it's too late to save them."

* * * * *

The big ships were vanishing in the oncoming fog. Whirls of vapor were
eddying toward them in the flame-blaster air. Above them the watchers
saw dimly the five gleaming bulbs. There were airplanes attacking: the
tapping of machine-gun fire came to them faintly.

Fast planes circled and swooped toward the enemy. An armada of big
planes drove in from beyond. Formations were blocking space above....
Every branch of the service was there, Thurston exulted, the army,
Marine Corps, the Navy. He gripped hard at the dry ground in a paralysis
of taut nerves. The battle was on, and in the balance hung the fate of
the world.

The fog drove in fast. Through straining eyes he tried in vain to
glimpse the drama spread above. The world grew dark and gray. He buried
his face in his hands.

And again came the thunder. The men on the ground forced their gaze to
the clouds, though they knew some fresh horror awaited.

The fog-clouds reflected