Nevertheless Robur had thought that the simpler his contrivance the
better. And the screws--the Saint Helices that had been thrown in
his teeth at the Weldon Institute--had sufficed for all the needs of
his flying machine. One series could hold it suspended in the air,
the other could drive it along under conditions that were marvelously
adapted for speed and safety.

If the ornithopter--striking like the wings of a bird--raised
itself by beating the air, the helicopter raised itself by striking
the air obliquely, with the fins of the screw as it mounted on an
inclined plane. These fins, or arms, are in reality wings, but wings
disposed as a helix instead of as a paddle wheel. The helix advances
in the direction of its axis. Is the axis vertical? Then it moves
vertically. Is the axis horizontal? Then it moves horizontally.

The whole of Robur's flying apparatus depended on these two
movements, as will be seen from the following detailed description,
which can be divided under three heads--the platform, the engines of
suspension and propulsion, and the machinery.

Platform.--This was a framework a hundred feet long and twelve wide,
a ship's deck in fact, with a projecting prow. Beneath was a hull
solidly built, enclosing the engines, stores, and provisions of all
sorts, including the watertanks. Round the deck a few light uprights
supported a wire trellis that did duty for bulwarks. On the deck were
three houses, whose compartments were used as cabins for the crew, or
as machine rooms. In the center house was the machine which drove the
suspensory helices, in that forward was the machine that drove the
bow screw, in that aft was the machine that drove the stern screw. In
the bow were the cook's galley and the crew's quarters; in the stern