The upper hull was one hundred feet long and twenty feet in diameter at the widest part.  It tapered to points at either end.  It was attached to the lower hull by strong braces, at either end, while from the center there extended a pipe which connected with the lower section.  This pipe was intended to convey the lifting gas to the part which corresponded to the bag of the balloon, save that it was of metal instead of silk, or rubber as is usual.

There were two reasons for this.  One was that it would not be liable to puncture, particularly in the proposed underground trip, and the other was that it did not have to be so large as a cloth bag would have had to be.  It was also a permanent part of the ship, and on a voyage where part of the time the travelers would be in the air and part on the water, and when the change from one to the other would have to be made quickly, this was necessary.  It would have taken too long to raise the ship in the air had a cloth bag been used to contain the gas.

The lower hull or main part of the craft was one hundred and fifty feet long, and forty feet through at the largest part, in the centre.

It was divided into four sections.  The forward one contained the sleeping quarters of Professor Henderson and his crew.  There was a small stateroom for each one.  Above was a conning or observation tower, reached by a small flight of steps.  From this tower the ship could be steered, stopped and started, as could also be done from the engine room, which was in the after part of the hull.

As in the Porpoise and Monarch, electricity formed the motive power and was also used for many other purposes on board.  Engines operated by gas produced the current which heated, lighted and moved the ship, as well as played a part in producing the wonderful gas.

The ship moved forward or backward by means of a novel arrangement.  This was by the power of compressed air.  From either end of the lower hull there projected a short pipe working in a ball and socket joint, so it could be turned in any direction.  By means of strong pumps a current of compressed air could be sent out from either pipe.  Thus when floating above the earth the ship was forced forward by the blast of air rushing from the pipe at the stern.  It was the same principle as that on which a sky rocket is shot heavenward, save that gases produced by the burning of powder in the pasteboard rocket form its moving impulse.

In the case of the Flying Mermaid, it could be made to move backward by sending the air out of the forward tube.  Thus, when in the water, the compressed air rushing from the pipe struck the fluid and forced the ship forward or backward as was desired.  It floated on the surface, the deck being about three feet out of water, while the aluminum gas bag was overhead.

The engine room was a marvel of machine construction.  It contained pumps for air and water, motors, dynamos, gas engines, and a maze of wheels and levers.  Yet everything was very compact and no room was wasted.