--this isn't safe enough, even here.
In--in there!"

He pointed toward a vault-like door, leading to the subterranean steel
chambers where Herzog eventually counted on storing some hundreds of
thousands of tons of liquid oxygen--the reserve-chambers, impregnable to
lightning, fire, frost or storm, to man's attacks or nature's--the
chambers blasted from the living rock, deep as the Falls themselves,
vacuum-lined, wondrous achievement of the highest engineering skill the
world could boast.

"There! There!" repeated Flint, plucking at the dazed Waldron's sleeve.
"Tool-steel and concrete, twenty-five feet thick--and vacuum chambers
all about--_there_ we can hide! There's safety! Come, come quick!"

Staring, white-faced (he who had been so red!) and dumb, Waldron
yielded. Together, furtive as the criminals they were, these two
world-masters slunk toward the steel door, while without, their empire
was crashing down in smoke, and flame, and blood!

They had almost reached it when a smash of glass at the far end of the
laboratory whipped them round, in keener terror.

Staring, wild-eyed, they beheld the crouching figure of Herzog. Running,
even as he cringed, he had upset a glass retort, which had shattered on
the concrete floor. And as he ran, he screamed:

"_They're in! They're coming! Quick--the steel vaults! Let me in, there!
Let me in!_"

The coward was now a maniac with terror, his face perfectly white,
writhen with panic, and with staring eyes that gleamed horribly under
the greenish vacuum-lights.

"Back, you! Get out!" roared Waldron, raising a fist. "We--"

A sudden belch of flame, outside, split the night with terrible
virescence. The whole steel building trembled and swayed. Some of its
girders buckled; and the east wall, nearest the oxygen-tanks, caved
inward as a mass of many tons was hurled against it.

A stunning concussion flung all three men to the floor; and, as they
fell, a withering heat-wave quivered through the place.

"The oxygen-tanks!" gasped Flint. "They're blown up--they're
burning--God help us!"

Scorching, yet still eager to live, he crawled on hands and knees toward
the steel door. Waldron dragged himself along, half-dead with terror.
Now, dripping gouts of inextinguishable fire were raining on the roof of
the building. A whirlwind of flame was sweeping all its eastern side;
and a glare like that of Hell itself seared the eyes of the fugitives.

Quivering, trembling, slavering, the