over a comparatively short space, as in quarries, excavations for canals, docks, &c.; in the construction of bridges, in shipbuilding, &c. Besides being employed in such works—not to mention the coaling of a battleship at sea from a coal transport standing by—elevated ropeways miles in length have also been constructed between places where no roads exist, or where road carriage is much more expensive. The greatest aerial line yet in existence is in the Argentine Republic, being built to connect a mining locality in the Andes, about 15,000 feet above sea-level, with a station on the Northern Railway 11,500 feet lower down and about 22 miles off, the line running across deep chasms and hollows, and being in places supported on iron towers 130 feet high. The wire rope is said to have a length of 87 miles.
Aë′rians, the followers of Aërius of Pontus, who in the fourth century originated a small heretical sect, objecting to the established feast-days, fasts or abstinences, the distinction between bishops and presbyters, prayers for the dead, &c.
Aerodynam′ics, a branch of physical science which treats of the properties and motions of elastic fluids (air, gases), and of the appliances by which these are exemplified. This subject is often explained in connection with hydrodynamics. See also Meteorology.
Aeröe, or Arröe (är′eu-e), an island of Denmark, in the Little Belt, 15 miles long by 5 broad, with 12,000 inhabitants. Though hilly, it is very fertile.
A′erolite, a meteoric stone, meteorite, or shooting-star. See Meteoric Stones.
Aeronau′tics, the art or science of navigating the air, including Aviation (see Aeroplane and Sea-planes) and Aerostation (see Balloons and Air-ships). From the days of the mythical exploit of Dædalus and Icarus, students of 'experimental philosophy', or scientists, of all ages, turned their thoughts and inventive genius to the evolution of a machine by means of which man could fly. Most of the early schemes of which any details have survived were based upon the observation of birds and embodied the flapping of wings affixed to the arms or legs. Among the very early experimenters may be mentioned the monk Oliver of Malmesbury (A.D. 1050), de Pérouse (1420), who is said to have succeeded in flying over Lake Trasimene, and the great Leonardo da Vinci. All these produced designs for what are known as Ornithopters, or flapping-wing machines. There was, however, another school which believed in the future of machines which would be themselves lighter than air. The idea in the minds of the experimenters of this school was in the early days the replacing of the air in brass globes by a vacuum. If the brass were thin enough it was believed that the globe would then be sufficiently light to rise. It was, however, not realized that under such circumstances the globe would inevitably collapse under the pressure of the atmosphere with no corresponding internal pressure to withstand it. Among this 'lighter-than-air' school of experimenters were the famous Roger Bacon (twelfth century), Robert Hooke of the Royal Society (1644), and Francesco de Lana, a Jesuit priest (1660). It was this school which ultimately achieved success by providing the first machine of any sort to leave the ground and rise into the air. On 5th June, 1783, the first balloon ascended from the village of Annonay in France. It owed its inception to the genius of two brothers, paper-makers by trade, named Etienne and Joseph Montgolfier. Struck by the sight of smoke ascending from a chimney, after many failures with flapping-wing models, they conceived the idea of filling a receptacle with smoke and seeing if it would rise. They built a balloon or 'globe' of paper and canvas, and lit a fire of wood and straw below the aperture in it. The balloon gradually filled and rose into the air to a height reported to be 6000 feet, though this is probably an exaggeration. It remained in the air for ten minutes and landed 1½ miles away. This was the forerunner of the
'Montgolfières', or hot-air balloons, which are a feature of fêtes and Guy Fawkes' Day celebrations. It was followed by the sending up of a 'Montgolfière' from Versailles on 18th Sept. of the same year, carrying a basket containing a sheep, a cock, and a duck. The first human beings to make an ascent were Pilâtre de Rozier and the Marquis d'Arlande, who went away from Paris on 21st Nov., 1783. They passed right over Paris, and were in the air for twenty-five minutes, during which time they replenished the fire suspended in a brazier below the neck of the balloon.
The real genesis of the balloon, or air-ship as we know it to-day, was due to the discovery of hydrogen as the lightest gas, which discovery was made in 1766 by an English chemist, Henry Cavendish. Various people claim the credit of having been the first to call attention to the possibilities of this gas for aerial navigation. In 1781 Dr. Joseph Black of Edinburgh suggested to his pupils that a thin bladder filled with 'the inflammable gas' (hydrogen) would rise into the air, but it appears doubtful whether he ever actually made the experiment. Tiberius Cavallo the same year, before the Royal Society, demonstrated that soap-bubbles filled with hydrogen would rise and float in the air. The honour of building the first hydrogen balloon belongs, however, to three Frenchmen—the brothers Robert, and Charles, a physicist. They sent up a hydrogen-filled balloon of varnished silk from the Champ de Mars, Paris, on 7th Aug., 1783. One of the Roberts and Charles themselves made the second human ascent in their balloon—the first in a hydrogen balloon as opposed to a Montgolfière (as above)—on 1st Dec. the same year. In 1784 the same Frenchmen constructed the first 'air-ship' or navigable balloon to the order of the Duc de Chartres (Philippe Egalité). The gas container of this was elongated in form, and it could be propelled to some small extent by means of oars, and steered by a rudder. In the same year a French military officer, named Meusnier, produced a completely detailed design for an air-ship. This embodied the first suggestion of screw-propellers, to be worked by man-power, and also provided for a 'ballonet' into which air could be driven to replace hydrogen lost owing to expansion during the ascent. Meusnier's design was the genesis of the modern non-rigid air-ship, all the essential features remaining. This air-ship was, however, never built.
