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. The different parts of the engines and the
screws were made of gelatinized fiber, which combined in sufficient
degree flexibility with resistance. This material could be used in
every form. It was insoluble in most gases and liquids, acids or
essences, to say nothing of its insulating properties, and it proved
most valuable in the electric machinery of the "Albatross."

Robur, his mate Tom Turner, an engineer and two assistants, two
steersman and a cook--eight men all told--formed the crew of the
aeronef, and proved ample for all the maneuvers required in aerial
navigation. There were arms of the chase and of war; fishing
appliances; electric lights; instruments of observation, compasses,
and sextants for checking the course, thermometers for studying the
temperature, different barometers, some for estimating the heights
attained, others for indicating the variations of atmospheric
pressure; a storm-glass for forecasting tempests; a small library; a
portable printing press; a field-piece mounted on a pivot; breech
loading and throwing a three-inch shell; a supply of powder, bullets,
dynamite cartridges; a cooking-stove, warmed by currents from the
accumulators; a stock of preserves, meats and vegetables sufficient
to last for months. Such were the outfit and stores of the
aeronef--in addition to the famous trumpet.

There was besides a light india-rubber boat, insubmersible, which
could carry eight men on the surface of a river, a lake, or a calm
sea.

But were there any parachutes in case of accident? No. Robur did not
believe in accidents of that kind. The axes of the screws were
independent. The stoppage of a few would not affect the motion of the
others; and if only half were working, the "Albatross" could still
keep afloat in her natural element.

"And w