remarked
Jack. "There's enough ice under us to supply the whole United States."

"It is getting colder!" exclaimed the inventor as he glanced at an
instrument near him. "It is fifteen below zero now!"

In truth the _Monarch_ was far to the north. She had gone faster than
the inventor calculated. A glance downward showed that all traces of
civilization had been left behind.

There was nothing to be seen but snow and ice, ice and snow, piled in
fantastic heaps,--mountains, ridges, hills and valleys.

The professor hastily made a few calculations.

"I believe we are somewhere over Greenland or Baffin Bay, but whether we
are over the land or sea I cannot tell. At any rate we are still going
north," and he glanced at the compass.

They were about to retrace their steps to the dining cabin, when there
was a sudden settling of the _Monarch_. It seemed to be plunging
downward.

"What's the matter?" cried Jack.

The inventor hurried to the engine room. A glance at the registering
needle of the instrument for telling the height attained, showed that
the ship was sinking fifty feet a minute.

"Some conglomerous contraption has disproportionated herself," cried
Washington. "What shall I do, Perfessor?"

"Start the gas generator at full speed!" cried the inventor. "Heat the
vapor before it goes to the bag! The cold has contracted the gas in the
holder above so that it will no longer support us! Work quick,
Washington!"

Washington sprang to set the gas machine in operation. He seemed to be
having trouble with it.

"She won't work!" he called. "She's busted!"

Faster and faster the airship continued to sink. The inventor hurried to
Washington's help, but it seemed that nothing could be done. On board
the _Monarch_ there was deadly fear in every heart.

"I can't keep her afloat!" the professor groaned.

Down and down went the craft. The inventor and Washington were working
furiously. The boys, old Andy and Tom and Bill hurried to the engine
room.

Then came a sudden jolt. The airship had struck the ice!

"Shut off the engines!" cried the professor. "Stop everything or we'll
go to smash! We must set to work to repair the gas machine and raise the
ship."

The _Monarch_ had settled down on a vast ice plane. So gently had the
ship sunk through the air that she had suffered no injury. She rested on
an even keel and there was still enough lifting power in the gas
contained in the bag to keep that afloat, so that the