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 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 direction from the others, so as to avoid any tendency to gyration.
Hence the screws as they rose on the vertical column of air retained their equilibrium by their horizontal resistance.
Consequently the apparatus was furnished with seventy-four suspensory screws, whose three branches were connected by a metallic circle which economized their motive force.
In front and behind, mounted on horizontal axes, were two propelling screws, each with four arms.
These screws were of much larger diameter than the suspensory ones, but could be worked at quite their speed.
In fact, the vessel combined the systems of Cossus, La Landelle, and Ponton d'Amecourt, as perfected by Robur.
But it was in the choice and application of his motive force that he could claim to be an inventor.
Machinery.--Robur had not availed himself of the vapor of water or other liquids, nor compressed air and other mechanical motion.
He employed electricity, that agent which one day will be the soul of the industrial world.
But he required no electro-motor to produce it. All he trusted to was piles and accumulators.
What were the elements of these piles, and what were the acids he used, Robur only knew.
And the construction of the accumulators was kept equally secret.
Of what were their positive and negative plates?
None can say.
The engineer took good care--and not unreasonably--to keep his secret unpatented.
One thing was unmistakable, and that was that the piles were of extraordinary strength; and the accumulators left those of Faure-Sellon-Volckmar very far behind in yielding currents whose amperes ran into figures up to then unknown.
Thus there was obtained a power to drive the screws and communicate a suspending and propelling force in excess of all his requirements under any circumstances.
But--it is as well to repeat it--this belonged entirely to Robur.
He kept it a close secret.
And, if the president and secretary of the Weldon Institute did not happen to discover it, it would probably be lost to humanity.
It need not be shown that the apparatus possessed sufficient stability. Its center of gravity proved that at once.
There was no danger of its making alarming angles with the horizontal, still less of its capsizing.
And now for the metal used by Robur in the construction of his aeronef--a name which can be exactly applied to the
"Albatross."
What was this material, so hard that the bowie-knife of Phil Evans could not scratch it, and Uncle Prudent could not explain its nature?
Simply paper!
For some years this fabrication had been making considerable progress.
Unsized paper, with the sheets impregnated with dextrin and starch and squeezed in hydraulic presses, will form a material as hard as steel.
There are made of it pulleys, rails, and wagon-wheels, much more solid than metal wheels, and far lighter.
And it was this lightness and solidity which Robur availed himself of in building his aerial locomotive.
Everything--framework, hull, houses, cabins-- were made of straw-paper turned hard as metal by compression, and - what was not to be despised in an apparatus flying at great heights-- incombustible.