compressed-air system, as well as the lighting-plant of the air-liner.

As the two men entered the engine-room, the Master nodded to
Auchincloss. He stood a moment gazing at the brightly flecked metal of
the engines, the gleaming walls--hollow and filled with noninflammable
helium gas of great lifting power--the men on watch over all this
splendid mechanism. Then he passed between engines No. 4 and No. 5,
toward the aft wall of the compartment.

Four doors opened in the bulkhead, there. Two communicated with
storerooms, one opened into the passage that led to the aft
observation pit, the fourth gave access to the sick-bay. This door the
Master slid back. Followed by the major he passed through.

A small but fully equipped hospital met their eyes. Cots,
operating-table, instrument-cases, sterilizers, everything was
complete. Immaculate cleanliness reigned. On two of the cots, men were
lying.

Beyond, Captain Alden--still fully dressed--was sitting on a white
metal chair. The captain's face was still concealed by the celluloid
mask, but a profound pallor was visible on the lower portion of his
right cheek and along his left jaw. The set of that jaw showed an
invincible obstinacy that bespoke rebellion.

Dr. Lombardo, a dark-skinned Florentine, who had been talking with
Captain Alden, turned at the Master's entrance into the sick-bay.
Already Lombardo had put on a white linen jacket. Though he had not
yet had time to change his trousers, he nevertheless presented a
semi-professional air as he advanced to meet the newcomers.