Chapter C: D E F G a B C' D' E' F' G' (5)

AIGUN ([=i]-g[u:]n'), a town of China, in Manchuria, on the Amur, with a good trade. Pop. 15,000.

AI'KIN, John, M.D., an English miscellaneous writer, born 1747, died 1822. He practised as physician at Chester, Warrington (where he taught physiology and chemistry at the Dissenters' Academy), and London; turned his attention to literature and published various works of a miscellaneous description, some in conjunction with his sister Mrs. Barbauld, including the popular _Evenings at Home_ (1792-5), written with the view of popularizing scientific subjects. His _General Biographical Dictionary_ (in 10 vols.) was begun in 1799 and finished in 1815. He was editor of the _Monthly Magazine_ from 1796 till 1807.

AI'KIN, Lucy, daughter of the preceding, was born in 1781, and died 1864. In 1810 she published _Poetical Epistles on Women_, which was followed by a number of books for the young and a novel _Lorimer_ (1814). In 1818 appeared her _Memoirs of the Court of Queen Elizabeth_, a very popular work. She afterwards produced similar works on the reigns of James I (1822) and Charles I (1833), and a _Life of Addison_ (1843). In 1824 she had published the literary remains and biography of her father. She carried on an interesting correspondence with Dr. Channing from 1826-42, which was published in 1874.

AIKMAN, William, an eminent Scottish portrait-painter, born in Forfarshire in 1682, died in 1731. He studied at Edinburgh and in Italy, visited Turkey, and spent the later portion of his life in London, where he enjoyed the friendship of most of the distinguished men of Queen Anne's time. The portrait of President Duncan Forbes (1685-1747) in the National Gallery is attributed to him.

AILAN'TO, or AILANTHUS (meaning tree of the gods), a tree, genus Ailantus, nat. ord. Simarubaceae. The _A. glandul[=o]sa_, a large and handsome tree, with pinnate leaves 1 or 2 feet long, is a native of China, but has been introduced into Europe and North America. A species of silk-worm, the ailanthus silk-worm (_Saturnia cynthia_), feeds on its leaves, and the material produced, though wanting the fineness and gloss of mulberry silk, is produced at less cost, and is more durable. The wood is hard, heavy, yellowish-white, and will take a fine polish. The tree has been in cultivation in England since 1751.

AILERON. See _Aeronautics_, _Aeroplane_.

AIL'RED (contracted form of ETHELRED), a religious and historical writer, supposed to have been born in 1097, but whether in Scotland or in England is not known, died 1166; abbot of Rievaulx, in the North Riding of Yorkshire. Wrote lives of Edward the Confessor and St. Margaret, Queen of Scotland, _Genealogy of the Kings of England_, _The Battle of the Standard_, &c.

AILSA CRAIG, a rocky islet in the Firth of Clyde, 10 miles from the coast of Ayr, of a conical form, 1097 feet high, and about 2 miles in circumference, precipitous on all sides except the north-east, where alone it is accessible, frequented by innumerable sea-fowl, including solan-geese, and covered with grass. On it is a lighthouse.

AILU'RUS. See _Panda_.

AIMARD ([=a]-m[:a]r), Gustave, French novelist, born 1818, died 1883. He lived for ten years among the Indians of North America, and wrote a number of stories dealing with Indian life, such as _Les Trappeurs de l'Arkansas_ (1858), _La Loi de Lynch_ (1859), _Les Nuits Mexicaines_ (1863), _Les Bohemes de la Mer_ (1865), which have been popular in English translations. His work is not unlike that of Fenimore Cooper.

AIN (a[n.]), a south-eastern frontier department of France, mountainous in the east (ridges of the Jura), flat or undulating in the west, divided into two nearly equal parts by the River Ain, a tributary of the Rhone; area, 2248 sq. miles; pop. (1921), 315,757. Capital, Bourg.

AINGER ([=a]n'j[.e]r), Rev. Alfred, born in 1837, died in 1904, was educated at King's College, London, and Trinity Hall, Cambridge, took orders after gaining his degree, and in 1866 was appointed reader of the Temple Church, London. He was made Master of the Temple in 1893, while holding also a canonry in Bristol Cathedral, to which he had been appointed in 1887. He was highly successful as a preacher, but is chiefly known by his literary labours, especially those connected with Lamb and Hood, whose works he edited. The volumes on Lamb and on Crabbe in the 'English Men of Letters' series are by him, and he wrote a memoir of Hood for his edition of the works. A volume of his sermons under the title of _The Gospel of Human Life_ was published after his death in 1904. Cf. Edith Sichel, _Life and Letters of Canon Ainger_.

AINMILLER ([=i]n'mil-er), Max Emanuel, a German artist who may be regarded as the restorer of the art of glass-painting, born 1807, died 1870. As inspector of the State institute of glass-painting at Munich he raised this art to a high degree of perfection by the new or improved processes introduced by him. Under his supervision this establishment (which afterwards became his own) produced a vast number of painted windows for ecclesiastical and other buildings, among the principal being a series of forty windows, containing a hundred historical and scriptural pictures, in Glasgow Cathedral. Some of his work is in St. Paul's Cathedral, and his finest productions are the windows in the Cathedrals of Cologne and Regensburg.

AINOS ([=i]'n[=o]z; that is, men), the native name of an uncivilized race of people inhabiting the Japanese island of Yesso, as also Sakhalien, and the Kurile Islands, and believed to be the aboriginal inhabitants of Japan. They do not average over 5 feet in height, but are strong and active. They are very hairy, wear matted beards, and have black hair which they allow to grow till it falls over their shoulders. Their complexion is dark brown, approaching to black. They support themselves by hunting and fishing. There are numerous legends relating to the Ainos. According to one of these, of Japanese origin, they descended from the constellation of the Bear, whilst another mentions as their ancestor a certain Okikurumi who came down from heaven. The Ainos call themselves Ainu Utara, and the Chinese refer to them as the Tungi (barbarians of the East). They are very superstitious, and worship a number of gods, such as the universal god (Opitta-Kamui), the sun (Tsup-Kamui), the bear (Isho-Kamui), &c. Cf. J. Batchelor, _The Ainu and their Folklore_.

AINSWORTH, Henry, a Puritan divine and scholar, born 1571, died 1622. He passed great part of his life in Amsterdam, being from 1610 pastor of a 'Brownist' church there (the Brownists being forerunners of the Independents). He was a voluminous writer, a controversialist and commentator, and a thorough Hebrew scholar.

AINSWORTH, Robert, born in Lancashire, 1660, earned his living by keeping a private school in or near London, and died there in 1743. Among other learned works he compiled the well-known _Latin and English Dictionary_, first published in 1736, which passed through many editions, but is now entirely superseded.

AINSWORTH, William Francis, an English physician, geologist, and traveller, born 1807. He was surgeon and geologist to the Euphrates expedition under Colonel Chesney, and published _Researches in Assyria, Babylonia, and Chaldaea_ (1838); _Travels in Asia Minor, Mesopotamia, and Armenia_ (1842); _Travels in the Track of the Ten Thousand Greeks_ (1844), &c. Died 1896.

AINSWORTH, William Harrison, an English novelist, born 1805, died 1882. He was the son of a Manchester solicitor and intended for the profession of law, but devoted himself to literature. He wrote _Rookwood_ (1834), _Jack Sheppard_, illustrated by Cruickshank (1839), and about forty other novels, including _Guy Fawkes_, _Tower of London_, _Windsor Castle_, _Lancashire Witches_, _Flitch of Bacon_, &c. His literary models were at first Sir Walter Scott and afterwards Victor Hugo's _Notre Dame de Paris_.

AIN-TAB ([.a]-in-t[:a]b'), a town of Northern Syria, 60 miles north of Aleppo; with manufactures of cottons, woollens, leather, &c., and an extensive trade. There is here an American Protestant mission. Pop. 45,000.

AINU. See _Ainos_.

AIR, the gaseous substance of which our atmosphere consists, being a mixture mainly of about 78 per cent by volume of nitrogen and 21 per cent of oxygen. The latter is absolutely essential to animal life, while the purpose chiefly served by the nitrogen appears to be to dilute the oxygen. Oxygen is more soluble in water than nitrogen, and hence the air dissolved in water contains about 10 per cent more oxygen than atmospheric air. The oxygen therefore available for those animals which breathe by gills is somewhat less diluted with nitrogen, but it is very much diluted with water. For the various properties and phenomena connected with air see such articles as _Atmosphere_, _Aeronautics_, _Air-pump_, _Barometer_, _Combustion_, _Respiration_, &c.

AIR, in music (in It. _aria_), a continuous melody, in which some lyric subject or passion is expressed. The lyric melody of a single voice, accompanied by instruments, is its proper form of composition. Thus we find it in the higher order of musical works; as in cantatas, oratorios, operas, and also independently in concertos.--_Air_ is also the name often given to the upper or most prominent part in a concerted piece, and is thus equivalent to _treble_, _soprano_, &c.

AIR, or ASBEN. See _Asben_.

AIRA. See _Hair-grass_.

AIR BEDS AND CUSHIONS, often used by the sick and invalids, are composed of india-rubber or of cloth made air-tight by a solution of india-rubber, and when required for use filled with air, which thus supplies the place of the usual stuffing materials. They tend to prevent bed-sores from continuous lying in one position. They are also cheap and easily transported, as the bed or cushion, when not in use, can be packed in small compass, to be again inflated with air when wanted.

AIR-BLADDER. See _Swimming-bladder_.

AIR-BRAKE, a brake operated by air pressure, usually applied to brake, simultaneously, all the wheels of a moving train. In the Westinghouse type, by means of an ingenious 'triple valve' carried one on each carriage, the train pipe is made to serve the dual purpose of supply and control. An air-pump on the engine compresses air into the main receiver, from which it flows through a reducing valve into the train pipe. The pressure, acting on the under side of the triple valve, moves the valve to its extreme position, thereby opening a passage to an auxiliary receiver on the carriage and also putting the brake cylinder into communication with the atmosphere. A spring in the brake cylinder keeps the brakes in the 'off' position.

To apply the brakes, the pressure is lowered in the train pipe. The air pressure in the auxiliary receiver reverses the triple valve, thus admitting air to the brake cylinder and closing the outlet to atmosphere.

To remove the brakes, air from the main receiver is passed into the train pipe, and the triple valve is restored to the 'off' position. See _Traction_.--BIBLIOGRAPHY: W. W. Wood, _Westinghouse Air-brake_; R. H. Blackhall, _Air-brake Catechism_.

AIR-CELLS, cavities in the cellular tissue of the stems and leaves of plants which contain air only, the juices of the plants being contained in separate vessels. They are largest and most numerous in aquatic plants, as in the _Vallisneria spir[=a]lis_ and the _Victoria regia_, the gigantic leaves of which latter are buoyed up on the surface of the water by their means.--The minute cells in the lungs of animals are also called air-cells. There are also air-cells in the bodies of birds. They are connected with the respiratory system, and are situated in the cavity of the thorax and abdomen, and sometimes extend into the bones. They are most fully developed in birds of powerful and rapid flight, such as the albatross.

AIRD, Thomas, a Scottish poet and miscellaneous writer, friend of Professor Wilson, De Quincey, and Carlyle, long editor of a newspaper in Dumfries; born 1802, died 1876. He wrote _The Devil's Dream on Mount Aksbeck_; _The Old Bachelor_, &c.

AIRDRIE, a municipal and parliamentary burgh of Scotland, in Lanarkshire, near the Monkland Canal, 11 miles east of Glasgow, in the centre of a rich mining district, with a large cotton-mill, foundries and machine shops, breweries, &c., and collieries and ironworks in its vicinity. Pop. 24,160.

AIR-ENGINE, an engine in which air heated, and so expanded, or compressed air is used as the motive power. A great many engines of the former kind have been invented, some of which have been found to work pretty well where no great power is required. They may be said to be essentially similar in construction to the steam-engine, though of course the expansibility of air by heat is small compared with the expansion that takes place when water is converted into steam. Engines working by compressed air have been found very useful in mining, tunnelling, &c., and the compressed air may be conveyed to its destination by means of pipes. In such cases the waste air serves for ventilation and for reducing the oppressive heat.

AIRE ([=a]r), a river of England, W. Riding of Yorkshire, rising to the south-east of Penyghent and flowing in a south-easterly direction to join the Ouse above Goole, having passed through Leeds on its way; length, 70 miles. It is navigable up to Leeds, and forms an important portion of the Aire and Calder Navigation system, which connects Goole, Hull, &c., with Liverpool. The Calder enters the Aire at Castleford. The district specially known as _Airedale_ is the valley of the Aire above Leeds.--A large breed of terrier, of which there are several varieties, is known as the _Airedale terrier_, a strongly-built animal, rather long in the legs, with a hard, close coat.

AIRE, a river of France, in the Argonne region, a tributary of the Aisne.

AIRE-SUR-L'ADOUR ([=a]r-s[.u]r-l[.a]-d[:o]r), a small but ancient town of France, department of Landes, the see of a bishop. Pop. 3000.

AIRE-SUR-LA-LYS ([=a]r-s[.u]r-l[.a]-l[=e]), an old fortified town of France, department of Pas de Calais, 10 miles south-east of St. Omer. Pop. 5000.

AIR-GUN, a gun from which the bullet is propelled by means of compressed air. Until about the middle of the nineteenth century air-guns were made with a metal reservoir in the butt; this reservoir was charged with air by means of a pump, and although one pumping put in enough air for six or seven shots, the process of loading was awkward and laborious. The well-known 'Gem' air-gun was worked by means of a spring, which compressed the air; the great defect of this gun was that the barrel was used as a cocking-lever, and so was apt to become bent and inaccurate. The 'Gem' was a smooth-bore gun, and early attempts at rifled air-guns failed, as the pellet was apt to stick in the barrel, owing to the low velocity not allowing it to take the grooves. The 'Quackenbush' air-gun made an attempt to get over this difficulty; its slugs were felted, and the felt took the rifling and greatly increased the accuracy of the weapon, but, of course, the ammunition was much more expensive than ordinary air-gun pellets. The B.S.A. air-rifle is an excellent weapon which has overcome all the early difficulties of construction. It has a fixed barrel, a separate cocking-lever, and a rotating breech-plug, and the muzzle velocity of its 16-grain pellet is 600 feet per second, which compares not unfavourably with the 1000 feet per second of the 40-grain bullet of a .22 long-rifle cartridge. An air-gun is a splendid weapon for practising markmanship, as it is almost noiseless, and as its ammunition costs little. It does not need to be elaborately cleaned, as a miniature rifle does; an occasional oiling is all that it requires to keep it in order, and with care it should fire an indefinite number of shots without losing its accuracy.

AIROLO ([.a]-i-r[=o]'l[=o]), a small town of Switzerland, canton Ticino, at the southern end of the St. Gothard Tunnel, and the first place on this route at which Italian is spoken. Pop. 2000.

AIR-PLANTS, or EPIPHYTES, are plants that grow upon other plants or trees, apparently without receiving any nutriment otherwise than from the air. The name is restricted to flowering plants (mosses or lichens being excluded) and is suitably applied to many species of orchids. The conditions necessary to the growth of such plants are excessive heat and moisture, and hence their chief localities are the damp and shady tropical forests of Africa, Asia, and America. They are particularly abundant in Java and tropical America.

AIR-PUMP, an apparatus by means of which air or other gas may be removed from or compressed into an enclosed space. It was invented by Otto von Guericke of Magdeburg about the year 1654, and described in 1657 by Gaspar Schott. An ordinary suction-pump for water is on the same principle as the air-pump; indeed, before water reaches the top of the pipe the air has been pumped out by the same machinery which pumps the water. An ordinary air-pump (see fig. 1) consists essentially of a cylinder or barrel with a piston and valves. The barrel is connected to the vessel from which the air is to be pumped. A is the vessel to be exhausted, C the air-pump cylinder, P the piston, VV valves in the piston, and O the connection to the vessel A. When the piston moves downwards from the position shown, it cuts off the connection with A by passing over O. The length L is made long enough so that O is kept covered up during the downstroke. The air filling the space D is compressed, and so lifts the valves VV and passes out through them. This goes on till the end of the downward stroke, when the volume is very small indeed. When the upward motion begins, the valves VV close, and the piston rises and creates a vacuum in D. When the piston rises sufficiently to uncover O (as in figure), air rushes from A into the highly-exhausted space D and fills it. The process is repeated indefinitely, and A is gradually exhausted.

Air-pumps for compressing air are constructed on the same principle, but the valves act the reverse way. The bicycle pump is a well-known example of this form of pump. In the Fleuss or Geryk pump greater efficiency is attained by having layers of oil in the barrel and above the piston. In nearly all pumps for producing the high vacua necessary, e.g. for the electric glow-lamp and the X-ray tube, mercury is employed. In one form, the Toepler pump, a reservoir containing mercury is connected by a flexible tube to the receiver. (See fig 2. T tube connecting pump to vessel to be exhausted; R, reservoir, raised above A to drive air in B and C through D and out into open air; R is then lowered, and B and C fill with air from receiver. Process then repeated.) By alternately lowering and raising the reservoir, gas is first withdrawn from the receiver and then expelled through D, which also acts as a barometer. The process is repeated until the desired degree of exhaustion is reached. In a second type, the Sprengel pump, a stream of mercury from a reservoir situated above the vessel to be exhausted falls in drops through a narrow vertical tube which communicates with the vessel. (See fig. 3. A, reservoir; B, tube leading to vessel to be exhausted; C, bubbles of air carried down by mercury.) The air is entrapped between the falling drops of mercury, and is carried down and expelled with it. In the filter-pump, water is used instead of mercury, the pump being connected to an ordinary water-tap.

A more recent form, the Gaede pump, is of the rotary type. (See fig. 4. C, iron case; G, glass front; P two-chamber porcelain drum rotated counter-clockwise about axle A. As mercury leaves chamber R, air enters from receiver by tube T and opening B. When B is immersed, mercury enters and air is driven into case C and removed through tube S.) A porcelain drum, divided into two cells, rotates within an air-tight case more than half filled with mercury. Each cell has an opening which, when above the mercury surface, places the cell in communication with the receiver. When the opening is immersed, the entrapped air passes by another channel into the outer case, from which it is removed by another less efficient pump. The pump will reduce the pressure within a 6-litre bulb from 10 millimetres to .00001 millimetre of mercury in fifteen minutes. Langmuir's pump employs the principle of the aspirator. A current of mercury vapour passes from a mercury boiler past a tube communicating with the apparatus to be exhausted, and sucks the air from it; the mercury is condensed in the upper part of the pump, returns by side tubes to the boiler and leaves the extracted air in this condenser. A less efficient pump is employed to remove the air from the mercury condenser as it accumulates. This pump is said to be simple and rapid in action, and capable of exhausting an 11-litre bulb from atmospheric pressure to .00001 millimetre in eighty seconds.

Air-pumps are largely used in steam engineering, both on land and at sea, to extract the air which enters the condenser with the steam (see _Condenser_). Several varieties of air-pumps are in use. 1. The ordinary piston-pump (fig. 1) in which the piston extracts air by first sucking it into the cylinder and then expelling it to the atmosphere. The opening leading to the condenser is closed during the stroke in which the air is expelled. Two or three cylinders are usually provided on each air-pump set, the former type being known as a 2-throw pump and the latter a 3-throw pump. One of the best-known makes is the _Edwards_ air-pump. Piston air-pumps are driven either by the main engine through a suitable mechanism, or by a separate electric motor. The amount of power required to drive them varies with the size of the set, and with large engines of over 10,000 h.p. it is about 1/2 per cent or less. Vacua as high as 29 inches (Bar. 30 inches) can be readily maintained on large plants by this type of pump, provided the condenser is suitably designed. In well-maintained plants bad vacua are commonly due to deficient air extraction, which may arise from the low-pressure air-piping not being air-tight, or from the air-pump being too small. 2. The water-ejector type uses the momentum of a jet of water to extract the air entrained with it. Well-known types of this plant are the ordinary barometric jet-condenser and the _Leblanc_ air-pump. In the latter type, a rotating wheel, which carries vanes, forcibly throws sheets of water into a pipe communicating with the condenser. The sheets of water lie across the pipe, and the space between them is filled up with air sucked from the condenser. This water, with the entrained air, is thrown out, against the atmospheric pressure, by the momentum imparted to the water sheets by the rotating wheel. Very high vacua can be obtained with the Leblanc pump, but the power required to drive it is more than is required with a 3-throw piston-pump. (Cp. Sprengel pump above). 3. A steam-ejector is also used, a jet of steam taking the place of the sheets of water in the Leblanc type. Parsons' _augmentor condenser_ works on this principle. A small jet of steam sucks the air from the main condenser and compresses it into a small so-called augmentor condenser. The pressure in this condenser is a little higher than the pressure in the main condenser, but it is sufficient to enable an ordinary 3-throw pump to be used efficiently. The steam used to extract the air is condensed in the augmentor condenser by cold water, and the interior of the augmentor condenser is connected to the inlet of an ordinary 3-throw pump. The 3-throw pump is called upon to deal with the air at a slightly higher pressure than the condenser pressure, and the vacuum in the main condenser is improved by the drop of pressure which exists between the augmentor condenser and the main condenser. In a well-designed plant, for instance, a 3-throw pump might be used to maintain a vacuum of 29 inches in the augmentor condenser, while the steam jet would provide another 1/2 inch of vacuum, giving 29-1/2 inches vacuum in the main condenser. The _pressure_ in the main condenser is thereby reduced from 1 inch Hg. to 1/2 inch Hg.; a reduction of _one-half_. (Cp. Langmuir's pump above--using a mercury-vapour jet instead of a steam jet.)--BIBLIOGRAPHY: S. P. Thompson, _The Development of the Mercurial Air-Pump_; E. Hausbrand, _Evaporating, Condensing, and Cooling Apparatus_.

AIR-RAIDS. Apart from various sporadic bomb-dropping attacks by the Italians in Tripoli in 1913, the first air-raid proper was made by a Zeppelin on Antwerp during the investiture of that city by the Germans in 1914. Later on this new method of warfare was developed to a considerable extent by both sides during the Great European War, both air-ships and aeroplanes being used. Air-craft for this purpose have been likened to long-range guns, with the advantage of greater precision, because the target is in view, and very much longer effective range--the Germans, for example, used to raid London, and on one occasion Edinburgh, from bases situated in North Germany and on the Schleswig coast. Air-raids are of great value in affecting the _moral_ of the enemy country by bringing home the effects of war in its most terrifying aspect to the civilian population at home, and thus causing the dislocation of traffic and diminishing the output of munitions. Their practical value is in attacking and destroying munition-factories, army head-quarters, naval bases, &c., in addition to such important work as the demolition of ammunition-dumps, and cutting lines of communication behind the front.

Various protective devices against raiding aircraft have been invented. Among these are high-angle guns, capable of throwing shells to a height of some 30,000 feet, though possibly the most effective defence is small high-speed aeroplanes armed with machine-guns and capable of reaching great heights in a short space of time. For use at night, kite-balloons (see _Balloons_) are sent up in clumps connected together by cables. From the cables is suspended a network of steel wires, which is invisible to the hostile air-craft, and in which they may become entangled and so brought down. These have been raised to a height of as much as 12,000 feet. For raiding purposes two types of aeroplane--in addition to air-ships--have been developed. 'Day bombers' carry out raids in daylight at heights of 12,000 to 20,000 feet on points from 50 to 100 miles behind the lines. 'Night-bombers' are slower machines which raid well into the enemy's territory--up to 200 or more miles--at heights varying from 8000 to 12,000 feet. It is usual for night-raids to be carried out by squadrons of machines flying in formation, each machine carrying about a ton of bombs (in 1918). Air-ships can carry 5-10 tons of bombs to places up to 1000 miles distant from their bases.

During the last months of the war, our Independent Air Force dropped 500 tons of bombs on German objectives, and this raiding over a wide area of industrial Germany played no small part in causing that loss of spirit among the enemy which led eventually to their request for an armistice, and their virtual capitulation.

AIR-SHIPS

AIR-SHIPS, lighter-than-air craft provided with means of propulsion and steering. The air-ship, unlike the aeroplane, is not dependent upon its engines for its power to remain in flight, but derives its sustentation from the hydrogen gas with which it is filled. Hydrogen, first weighed by Henry Cavendish in 1766, is the lightest gas known, being 14.47 times lighter than air. In the pure state it has a lifting force of 71.155 lb. per 1000 cu. feet, but for calculation purposes is usually assumed to contain 5 per cent of impurities, giving a 'lift' of approximately 68 lb. per 1000 cu. feet. Hydrogen is, when mixed with air, highly inflammable, and helium has therefore been suggested as a substitute. This has a lift, when pure, of about 65 lb. per 1000 cu. feet, but is only found in a few places in America and is therefore at present too expensive to be used in quantities. The lift of any given quantity of hydrogen depends upon the difference between its weight and that of an equal volume of air. As the amount, and therefore weight, of air contained in a given space varies with the barometric pressure and temperature, the lift of hydrogen given above varies also. These figures are based upon a temperature of 60deg F. and a barometric pressure of 30 inches. As an air-ship rises from the ground, the density, and therefore pressure, of the air decreases, which causes the hydrogen in the envelope to expand proportionately. Rise in temperature has the same effect. When an air-ship ascends, the gas therefore expands, and at a certain point would burst the envelope were valves not provided to allow some of the gas to escape. It is important to realize that as the expansion occurs at a rate corresponding to the decrease in density no alteration in lift occurs so long as gas is not lost through the valves. This would continue indefinitely if the gas-chamber were capable of stretching indefinitely, but with the cotton-fabric used in practice a height is reached when gas commences to escape from the automatic valves. From this moment the lift of the air-ship begins to decrease. At a certain point this decrease will have reached such a point that the air-ship is 'in equilibrium', i.e. she weighs precisely the same as the volume of air she displaces. This is known as the 'maximum height'. Up to 10,000 feet it is roughly true that 1/30 of the lift is lost per 1000 foot rise.

The simplest form of air-ship is the _non-rigid_, which consists of a rubberized cotton-fabric gas-container (the 'envelope'), from which the 'car', containing engines, crew, &c., is hung by flexible steel-wire ropes. To resist the bending moment introduced by the weight of the car, the envelope is inflated with hydrogen under pressure--usually about 25 mm. of water. So long as this pressure is greater than any local compression due to bending or loading in the fabric, the envelope will retain its shape. On coming down from a height, owing to the loss of gas, as already explained, the pressure will be reduced, and something must be done to restore it or the envelope will buckle. Fabric bags, known as 'ballonets', are therefore fitted inside the envelope, and as the air-ship descends air is forced into these bags, which supplies the lost pressure and maintains the shape of the envelope. The height to which a non-rigid air-ship can go, on returning from which the ballonets will be just full of air and the pressure the same as at starting, is known as the 'maximum ballonet height'. Ballonets are usually equivalent in volume to rather less than a quarter of the total volume of the air-ship--giving a maximum ballonet height of 6000 to 7000 feet. Usually from two to three ballonets are provided, according to the size of the air-ship. During the Great European War British non-rigid air-ships were constructed varying in size from a capacity of 70,000 cu. feet to 360,000 cu. feet. The former had one 75-h.p. engine, and the latter two of 375 h.p. each. Owing to difficulties in maintaining the shape and distributing the weight of the car over a long envelope, it is generally considered that 500,000 cu. feet probably represents the maximum size in which the non-rigid form of construction can be used. Above this size the _semi-rigid_ type is used. In this case the envelope remains as in the non-rigid, but a girder or 'keel' is introduced between the envelope and the car, the weight of which is therefore taken by the keel and thence distributed to the envelope instead of being taken direct from the envelope as in non-rigids. There has been little development of non-rigids in Great Britain. The most prominent types are the Italian 'Forlanini', 'Verduzzio', and military air-ships. The keel, in all these examples, is not a rigid girder in the vertical sense, as it consists of a number of sections connected together by links. It is designed to resist compression only so long as it is held straight by the pressure of the envelope, and is not capable of taking a bending moment. When a size of about 1,000,000-cu.-foot-hydrogen capacity is reached it becomes economical to use the _rigid_ method of construction. This is totally distinct from the other two types, as the non-rigid envelope is replaced by a rigid hull of sufficient strength to retain its shape without the assistance of any internal gas-pressure. The hull consists of a number of longitudinal members--usually built-up girders of 'duralumin', an aluminium alloy--connected together at distances of 25-30 feet by a number of 'transverse frames', or rings, forming bulkheads. The transverse frames are also of duralumin girders, and are braced by 'radical wires' running from the joints of these girders to a ring in the centre. Between each pair of these transverse frames is a gas-bag containing hydrogen. The gas-bags are made of rubberized cotton on to which is stuck 'gold-beater's skin', made from the lining of the intestines of an ox. This is done to prevent hydrogen leakage. This is necessary, as the fabric of the gas-bags of a rigid air-ship is lighter and contains less rubber than the envelope of a non-rigid.

A '[Delta]'-shaped keel runs along the interior of the ship, its weight being taken on the two bottom longitudinal girders. The chief function of the keel is to distribute the load of the various weights to the transverse frames of the air-ship. In it are slung the petrol-tanks, water-ballast tanks, bombs, &c., and living accommodation for the crew is also provided there. Along the bottom runs a walking-way from which access is gained to the cars and various parts of the air-ship. The cars containing the engines, wireless-cabin, and pilot's cabin are suspended from the transverse frames. Some of the cars, instead of being slung below the centre-line, are slung in pairs some little way up the side of the air-ship.

All air-ships are steered by means of rudders and, in the vertical sense, elevators, in precisely the same way as aeroplanes. Up to the end of 1919 speeds of 84 miles per hour had been reached and air-ships had climbed to 24,000 feet. The greatest distance covered in one flight was 4500 miles, while the longest time in the air was effected by R34 on her voyage to America, which occupied 108 hours--4 days 8 hours. Rigid air-ships of 2,750,000-cu.-foot capacity had been built with a length of nearly 300 feet and a gross lift of 60 tons. See also _Aeronautics_, _Balloons_.--BIBLIOGRAPHY: L. Sazerac de Forges, _La Conquete de l'Air_; Santos Dumont, _My Airships_; Hildebrandt, _Airships: Past and Present_; Major G. Whale, _British Airships: Past, Present, and Future_.

AIRY, Sir George Biddell, a distinguished English astronomer, was born at Alnwick, 27th July, 1801, and educated at Hereford, Colchester, and Trinity College, Cambridge, where he was senior wrangler in 1823. At Cambridge he was Lucasian professor of mathematics, and subsequently Plumian professor of astronomy and experimental philosophy, in the latter capacity having charge of the observatory. In 1835 he was appointed Astronomer Royal, and as such his superintendence of the observatory at Greenwich was able and successful. He resigned this post with a pension in 1881. His important achievement is the discovery of a new inequality in the motions of Venus and the earth. He wrote much and made numerous valuable investigations on subjects connected with astronomy, physics, and mathematics. Among separate works published by him may be mentioned _Popular Astronomy_, _On Sound and Atmospheric Vibrations_, _A Treatise on Magnetism_, _On the Undulatory Theory of Optics_, _On Gravitation_. He died 2nd Jan., 1892. He left an autobiography, published in 1896.

AISLE ([=i]l; from Lat. _ala_, a wing), in architecture, one of the lateral divisions of a church in the direction of its length, separated from the central portion or nave by piers or pillars. There may be one aisle or more on each side of the nave. The cathedrals at Chichester, Milan, and Amiens have five aisles, Antwerp and Paris seven, and that of Cordova nineteen aisles in all. The nave is sometimes called the central aisle. See _Cathedral_.

AISNE ([=a]n), a north-eastern frontier department of France; area, 2838 sq. miles. It is an undulating, well-cultivated, and well-wooded region, chiefly watered by the Oise in the north, its tributary the Aisne in the centre, and the Marne in the south. It contains the important towns of St. Quentin, Laon (the capital), Soissons, and Chateau Thierry. In the European War (1914-18) severe fighting took place on the Aisne, and a great battle was fought on 12th Sep., 1914. General Nivelle's offensive on the Aisne began in April, 1917. Pop. (1921), 421,575.

AIVA'LIK, or KIDONIA, a seaport of Asia Minor, on the Gulf of Adramyti, 66 miles north by west of Smyrna, carrying on an extensive commerce in olive-oil, soap, cotton, &c. Pop. 21,000.

AIX ([=a]ks), a town of Southern France, department Bouches-du-Rhone, on the River Arc, the seat of an archbishop. It is well built, has an old cathedral and other interesting buildings, including a university, a library (over 100,000 vols.), museum, &c.; manufactures cotton and woollen goods, oil, soap, hats, flour, &c.; warm springs, now less visited than formerly. Aix was founded in 123 B.C. by the Roman consul Gaius Sextius Calvinus, and from its mineral springs was called _Aquae Sextiae_ (Sextian Waters). Between this town and Arles, Marius gained his great victory over the Teutons, 102 B.C. In the Middle Ages the counts of Provence held their court here, to which the troubadours used to resort. Pop. 29,836.

AIX, or AIX-LES-BAINS ([=a]ks-l[=a]-ba[n.]), a finely-situated village of France, department of Savoie, 8 miles north of Chambery, on the side of a fertile valley, with much-frequented hot springs known to the Romans by the name of _Aquae Gratianae_, and with ruins of a Roman triumphal arch, and of a temple of Diana. Pop. 8900.

AIX-LA-CHAPELLE ([=a]ks-l[.a]-sh[.a]-pel; Ger. _Aachen_), a city of Rhenish Prussia, 38 miles west by south of Cologne, pleasantly situated in a fine vale watered by the Wurm, formerly surrounded by ramparts, now converted into pleasant promenades. It is well built, and though an ancient town has now quite a modern appearance. The most important building is the cathedral, the oldest portion of which, often called the nave, was erected in the time of Charles the Great (Charlemagne) as the palace chapel about 796. It is in the Byzantine style, and consists of an octagon, surrounded by a sixteen-sided gallery and surmounted by a cupola, in the middle being the tomb of Charlemagne. The adjoining Gothic choir, begun in 1353 and finished in 1413, forms the other chief division of the cathedral; it is lofty and of great elegance, and has fine painted windows. Another noteworthy building is the Rathaus (town hall), erected in the fourteenth century. Aix-la-Chapelle, with the adjoining Burtscheid, which may be considered a suburb, is a place of great commerce and manufacturing industry, the chief productions being woollen yarns and cloths, needles, machinery, cards (for the woollen manufacture), railway and other carriages, cigars, chemicals, silk goods, hosiery, glass, soap, &c. A considerable portion of its importance and prosperity arises from the influx of visitors to its sulphur and chalybeate springs and baths.--Aix-la-Chapelle was known to the Romans as _Aquisgranum_. It was the favourite residence of Charles the Great, who made it the capital of all his dominions north of the Alps, and who died here in 814. During the Middle Ages it was a free imperial city and very flourishing. Thirty-seven German emperors and eleven empresses have been crowned in it, and the imperial insignia were preserved here till 1795, when they were carried to Vienna. The town was in possession of France from 1794 to 1814. Pop. 156,143.--_Congress of Aix-la-Chapelle_, a congress held in 1818, by which the army of the allies in France was withdrawn after France had paid the contribution imposed at the peace of 1815, and by which independence was restored to France.--A _treaty_ of peace concluded at this city, 2nd May, 1668, as a result of the Triple Alliance, put an end to the war carried on against Spain by Louis XIV in 1667, after the death of his father-in-law, Philip IV, in support of his claims to a great part of the Spanish Netherlands, which he urged in the name of his queen, the infanta Maria Theresa. By this France obtained Lille, Charleroi, Douai, Tournai, Oudenarde, &c. The _second peace_ of Aix-la-Chapelle, 18th Oct., 1748, terminated the Austrian war of succession.

AJACCIO ([.a]-y[.a]ch'[=o]), the capital of Corsica, on the south-west coast of the island, on a tongue of land projecting into the Gulf of Ajaccio, the birthplace of Napoleon and the seat of a bishop, with coral and sardine fisheries, and a considerable trade. There are here a cathedral, a college with library and museum, marble statue of Napoleon, monument of the Bonaparte family, &c. Ajaccio is connected by railway with Bastia and other places, and is becoming a winter resort for people with weak lungs. Pop. 20,946.

AJAN'TA, a village and ravine of India, in the north-west of the Nizam's dominions, about 50 miles north-north-east of Aurangabad. The ravine, 4 miles N.W. of the village, is celebrated for its cave temples and monasteries, twenty-nine in number, excavated out of a wall of almost perpendicular rock about 250 feet high. They are all richly ornamented with sculpture, and covered with highly-finished paintings, representing subjects of almost all kinds. The oldest are assigned to about 200 B.C., the most modern to about A.D. 600, and they may be said to furnish a continuous record of Buddhist art during 800 years, the faith at the latter date being practically expelled from India.

A'JAX (Gr. _Aias_), the name of two Grecian chiefs who fought against Troy, the one being son of O[)i]leus, King of Locris, surnamed the Little, the other son of Telamon, the Great or Telamonian Ajax. The latter was from Salamis, and sailed with twelve ships to Troy, where he is represented by Homer as the boldest and handsomest of the Greeks, after Achilles. He had more than one combat with Hector, against whom he was well matched. On the death of Achilles, when his arms, which Ajax claimed, were awarded to Ulysses, he became insane and killed himself. This is the subject of Sophocles' tragedy _Ajax_. The other Ajax was hardly of less importance as a champion on the Greek side in the Trojan war. At the fall of Troy he entered the temple of Pallas Athena and seized Cassandra. He lost his life during his homeward voyage, either by shipwreck or by a flash of lightning sent by Athena, who was offended at the violation of her temple.

AJMERE, AJMIR, or AJMER, a British commissionership or province in India, Rajputana, divided into the two districts of Ajmere and Mairwara (or Merwara); area, 2711 sq. miles. The surface of the province, which is entirely surrounded by native States, is hilly in the north and west, where there is a branch of the Aravali range, but level in the south and east. The soil is partly fertile, but there are large barren sandy plains, and there are no rivers of any importance. There are a large number of tanks which collect the water of small streams, and are useful for irrigation. The province suffered severely from famine in 1899-1900, the population being reduced by 12 or 13 per cent. Pop. 501,395.--_Ajmere_, the capital, an ancient city, a favourite residence of the Mogul emperors, is 279 miles S.W. of Delhi, at the foot of Taragarh Hill (2853 feet), on which is a fort. It is surrounded by a wall, has well-built streets, and possesses a Government college, as also Mayo College for Rajput nobles, a Scottish mission, a mosque that forms one of the finest specimens of early Mahommedan architecture extant, and an old palace of Akbar, now the treasury. There is a trade in cotton, sugar, salt, &c., and the town is an important station on the Rajputana railway. Pop. 86,200.

AJOWAN' (_Ptych[=o]tis Ajowan_), an umbelliferous plant cultivated in India, Persia, and Egypt, the seeds of which are used in cookery and in medicine, having carminative properties. The seeds much resemble caraway seeds, have a strong smell of thyme, and are exported in some quantity to Europe as a source of _thymol_, now so well known.

AJU'GA, a genus of plants belonging to the labiate family. See _Bugle_.

AJ'UTAGE, a short tube of a tapering shape fitting into the side of a reservoir or vessel to regulate the discharge of water from it. Also, the nozzle of a tube for regulating the discharge of water to form a _jet d'eau_.

AKABAH', Gulf of, an arm of the Red Sea, on the east side of the Peninsula of Sinai, which separates it from the Gulf of Suez; nearly 100 miles long. The village of Akabah, at the northern extremity of the gulf, is supposed to be near the site of the _Ezion-geber_ of the Old Testament; and here also was Elath, long a place of note. Akabah still carries on a small trade. It was captured by the Arabs in 1917.

AKAGAMASEKI. Same as _Simonoseki_.

AKAROID RESIN, a resin obtained from some of the grass-trees of Australia, used in varnishes.

AKASSA, a seaport of Southern Nigeria, on a small island nearly opposite the chief mouth of the Niger. There are here engineering and other works, at which ships may be repaired, belonging to the Government.

AK'BAR (that is 'very great'), a Mogul emperor, the greatest Asiatic prince of modern times. He was born at Amerkote, in Sind, in 1542, succeeded his father, Humayun, a grandson of Sultan Baber, at the age of thirteen, and governed first under the guardianship of his minister, Beyram, but took the chief power into his own hands in 1560. He fought with distinguished valour against his foreign foes and rebellious subjects, conquering all his enemies, and extending the limits of the empire farther than they had ever been before, although on his accession they embraced only a small part of the former Mogul Empire. Although a Mohammedan by birth, he abandoned Islam and founded a new religion which he called 'Divine Faith' (_Diu-i-Olahi_). His contemporaries bestowed upon him the title of 'Guardian of Mankind'. He was also a generous patron of literature, and commissioned the Jesuit missionary, Jerome Xavier, to translate the four gospels into Persian. His government was remarkable for its mildness and tolerance towards all sects; he was indefatigable in his attention to the internal administration of his empire, and instituted inquiries into the population, character, and productions of each province. The result of his statistical labours, as well as a history of his reign, were collected by his minister, Abul Fazl, in a work called _Akbar-Nameh_ (Book of Akbar), the third part of which, entitled _Ayini-Akbari_ (Institutes of Akbar), was published in an English translation at Calcutta (1783-6, 3 vols.), and reprinted in London. He died in 1605. His mausoleum at Secundra, near Agra, is a fine example of Mohammedan architecture. Cf. V. A. Smith, _Akbar, The Great Mogul_.

AKEE' (_Blighia sap[)i]da_), a tree of the nat. ord. Sapindaceae, much esteemed for its fruit. The leaves are somewhat similar to those of the ash; the flowers are small and white, and produced in branched spikes. The fruit is lobed and ribbed, of a dull orange colour, and contains several large black seeds, embedded in a succulent and slightly bitter arillus of a pale straw colour, which is eaten when cooked. The akee is a native of Guinea, from whence it was carried to the West Indies by Captain Bligh in 1793.

A KEMPIS, Thomas. See _Thomas a Kempis_.

AKEN ([:a]'ken), a Prussian town, province of Saxony, on the left bank of the Elbe, with manufactures of tobacco, cloth, beetroot sugar, leather, &c. Pop. 7358.

A'KENSIDE, Mark, a poet and physician, born in 1721, at Newcastle-upon-Tyne, died in London in 1770. He was the son of a butcher, and was sent to the University of Edinburgh to qualify for the ministry, but chose the study of medicine instead. After three years' residence at Edinburgh he went to Leyden, and in 1744 became Doctor of Physic. In the same year he published the _Pleasures of Imagination_, which he is said to have written in Edinburgh, and which was translated into French by Baron d'Holbach (1769). In 1746 he wrote his much-praised _Hymn to the Naiads_. Having settled in London, he became a fellow of the Royal Society, and was admitted into the College of Physicians. In 1759 he was appointed first assistant and afterwards head physician to St. Thomas's Hospital. In his later days he wrote little poetry, but published several medical essays and observations. The place of Akenside as a poet is not very high, though Dr. Johnson praised the blank verse of his poems, and his somewhat cumbrous _Pleasures of Imagination_ was once considered one of the most pleasing didactic poems in our language.

AKERMANN', a fortified town and seaport in Bessarabia, near the mouth of the Dniester, with a good port. The vicinity produces quantities of salt, and also fine grapes from which excellent wine is made. A treaty was signed here, 6th Oct., 1826, between Russia and the Porte, by which Moldavia, Walachia, and Serbia were released from all but nominal dependence on Turkey. Pop. 40,000.

AKHALZIK, or ACHALZIK ([.a]-_h_[.a]l'tsik), a town of Russia in Asia, in the Trans-Caucasian government of Tiflis, 97 miles west of Tiflis, with a citadel. It was taken by the Russians in 1828. Pop. 15,977.

AK-HISSAR ('white castle'), a town in Asia Minor, 46 miles N.E. of Smyrna, occupying the site of the ancient Thyatira, relics of which city are here abundant. Here the Emperor Valens defeated the usurper Procopius in 366, and Murad defeated the Prince of Aidin in 1425. Pop. 20,000.

AKHTYRKA ([.a]_h_-tir'k[.a]), a cathedral town of the Ukraine, government of Kharkov, with a good trade and some manufactures. Pop. 31,918.

AKJERMANN ([.a]k-yer-m[.a]n'). Same as _Akermann_.

AKKAD, the northern portion of ancient Babylonia occupied by the earliest Semitic invaders when the southern portion was Sumer (or Sumeria) and occupied by non-Semites. There was also a city of the same name, the Biblical Accad (_Gen._ x), which was prominent before 2000 B.C. Its ruins were unearthed between 1917 and 1919. See _Babylonia_.

AKKAS, a dwarfish race of Central Africa, dwelling in scattered settlements to the north-west of Lake Albert Nyanza, about lat. 3deg N., lon. 29deg E. Their height averages about 4-1/2 feet; they are of a brownish or coffee colour; head large, jaws projecting (or prognathous), ears large, hands small. They are timid and suspicious, and live almost entirely by the chase, being exceedingly skilful with the bow and arrow. They were first seen by the traveller G. A. Schweinfurth in 1870.

AKMOLINSK', a Russian province in Central Asia, largely consisting of steppes and wastes; the chief rivers are the Ishim and Sari-Su; and it contains the larger part of Lake Balkash. Capital, Omsk. Area, about 225,070 sq. miles. Pop. 1,523,700.--_Akmolinsk_ is a place of some importance for its caravan trade. Pop. 11,000.

AKO'LA, a town of India, in Berar, the residence of the commissioner of Berar, on the River Morna, 150 miles W. by S. of Nagpur; with walls and a fort, and some trade in cotton. Pop. 29,289.

AK'RON, a town of the United States, in Ohio, 100 miles N.E. of Columbus, on an elevated site. Being furnished with ample water-power by the Little Cuyahoga, it possesses large flour-mills, woollen factories, manufactures of iron goods, &c. In the vicinity extensive beds of mineral paint are worked. Pop. (1920), 208,435.

AKSU' ('white water'), a town of Eastern or Chinese Turkestan, 300 miles from Kashgar, in the valley of the Aksu. It is an important centre of trade between Russia, China, and Tartary, and has manufactures of cotton cloth, leather, and metal goods. Formerly the residence of the kings of Kashgar and Yarkand. Pop. 30,000.

AKYAB', a seaport of Lower Burmah, capital of the province of Arracan, at the mouth of the River Kuladan or Akyab, of recent upgrowth, well built, possessing a good harbour, and carrying on an important trade, its chief exports being rice and petroleum. Pop. 35,680.

AL, the article in the Arabic language. It appears in English words derived from the Arabic, such as Algebra, Alchemy, Alcove.