. Instead, each moment found him more
abject and more pitiable. Like an old woman he now wrung his hands and
groaned, hysterically; and now he paced the steel floor of the vault
that was destined to be his tomb; and now he stopped again and stared
about him with wild eyes.

On all sides, sheer up a hundred feet or more, the smooth steel sides of
the vast oxygen tank rose, studded with long lines of rivets.

Near the top a dark aperture showed where the six-inch pipe joined the
tank; the pipe destined to fill it, when Herzog's last process--never,
now, to be completed--should have been done.

The huge floor, 150 feet in diameter, sloped gently downward toward the
center; and here yawned another pipe, covered by a grating--the pipe to
drain the liquid oxygen out to the pumping station.

So deeply set in the rock of the Niagara cliff was this stupendous
tank, and so cunningly surrounded by vacuum-chambers, that now no
faintest sound of the Falls was audible. All that betrayed the nearness
of the cataract was a faint, incessant trembling of the metal walls, as
though the solid ribs of Earth herself were shuddering with the impact
of the plunge.

Old Flint surveyed this extraordinary chamber with mingled feelings. It
surely offered absolute protection, for the present--or seemed to--but
his distressed mind conjured alarming pictures of the future, in case no
rescue came. Death by starvation, thirst and madness loomed before him.
Nervously he recommenced his pacing. Another terribly serious factor was
to be considered. He had now been three hours without his dose of
morphia, and his nerves were calling, tugging insistently for it.

"Rotten luck," he grumbled, "that I've got none with me!" Even there, in
the imminent presence of disaster and death, his mind reverted to the
poison, more necessary to him than food.

Waldron now had grown fairly calm. He stood leaning against the steel
ladder, down which they had descended. Choosing a cigar, he proceeded to
light up.

"Might as well be comfortable while we wait," said he. "I only wish we
had a couple of chairs, down here. Oversight on our part that we didn't
have some steel ones put in, and a line of canned goods and a few quarts
of Scotch. The floor's a bit damp and cold to sit on, and I want a drink
damn bad!"

Flint swung about and faced him, pale and shaking, tortured with fear
and with longing for his dope.

"You--you don't think it _will_ be long, eh, do you?" h