her you would have observed a craft not unlike, in
shape, the German Zeppelins. But it differed from those war balloons in
several important particulars.

Tom's craft was about six hundred feet long, and the diameter of the
gas bag, amidships, was sixty feet, slightly larger than the largest
Zeppelin. Below the bag, which, as I have explained, was made up of a
number of gas-tight compartments, hung from wire cables three cabins.
The forward one was a sort of pilot-house, containing various
instruments for navigating the ship of the air, observation rooms,
gauges for calculating firing ranges, and the steering apparatus.

Amidships, suspended below the great bag, were the living and sleeping
quarters, where food was cooked and served and where those who operated
the craft could spend their leisure time. Extra supplies were also
stored there.

At the stern of the big bag was the motor-room, where gas was generated
to fill the balloon compartments when necessary, where the gasoline and
electrical apparatus were installed, and where the real motive power of
the craft was located. Here, also, was carried the large quantity of
gasoline and oil needed for a long voyage. The Mars could carry
sufficient fuel to last for over a week, provided no accidents occurred.

There was also an arrangement in the motor compartment, so that the
ship could be steered and operated from there. This was in case the
forward pilot-house should be shot away by an enemy. And, also, in the
motor compartment were the sleeping quarters for the crew.

All three suspended cabins were connected by a long covered runway, so
that one could pass from the pilot-house to the motor-room and back
again through the amidship cabin.

At the extreme end of the big bag were the various rudders and planes,
designed to keep the craft on a level keel, automatically, and to
enable it to make headway against a strong wind. The motive power
consisted of three double-bladed wooden propellers, which could be
operated together or independently. A powerful gasoline engine was the
chief motive power, though there was an auxiliary storage battery,
which would operate an electrical motor and send the ship along for
more than twenty-four hours in case of accident to the gasoline engine.

There were many other pieces of apparatus aboard, some not completely
installed, the uses of which I shall mention from time to time, as the
story progresses. The gas-generating machine w