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
were several cabins, including that of the engineer, the saloon, and
above them all a glass house in which stood the helmsman, who steered
the vessel by means of a powerful rudder. All these cabins were
lighted by port-holes filled with toughened glass, which has ten
times the resistance of ordinary glass. Beneath the hull was a system
of flexible springs to ease off the concussion when it became
advisable to land.

Engines of suspension and propulsion.--Above the deck rose
thirty-seven vertical axes, fifteen along each side, and seven, more
elevated, in the centre. The "Albatross" might be called a clipper
with thirty-seven masts. But these masts instead of sails bore each
two horizontal screws, not very large in spread or diameter, but
driven at prodigious speed. Each of these axes had its own movement
independent of the rest, and each alternate one spun round in a
different directi