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THE ENCYCLOPAEDIA BRITANNICA - ELEVENTH EDITION

THE ENCYCLOPAEDIA BRITANNICA

A DICTIONARY OF ARTS, SCIENCES, LITERATURE AND GENERAL INFORMATION

ELEVENTH EDITION

VOLUME II

ANDROS to AUSTRIA

A.B.R. - ALFRED BARTON RENDLE, F.R S F.L.S. D.Sc. Keeper of the Department of Botany, British Museum.

- ANGIOSPERMS

- ANGLO-SAXON CHRONICLE

- ANEURYSM

- ANGLI; ANGLO-SAXONS

- ANGLING

- ANGIOSPERMS .

- ANGORA

- ANHYDRITE

L.M.Br. - LOUIS MAURICE BRANDIN, M.A. Fielden Professor of French and of Romance Philology in the University of London.

- ANGLO-NORMAN LITERATURE

- ANIMAL-WORSHIP, ANIMISM

P.C.M. - PETER CHALMERS MITCHELL, F.R.S., F.Z.S., D.Sc., LL.D. Secretary to the Zoological Society of London from 1903. University Demonstrator in Comparative Anatomy and Assistant to Linacre Professor at Oxford, 1888-1891. Lecturer on Biology at Charing Cross Hospital, 1892-1894; at London Hospital, 1894. Examiner in Biology to the Royal College of Physicians, 1892-1896, 1901-1903. Examiner in Zoology to the University of London, 1903.

- ANIMAL

P.C.Y. - PHILIP CHESNEY YORKE, M.A. Magdalen College, Oxford.

- ANGLESEY, 1st EARL OF

- ANGLO-SAXON LAW

T.Ba. - SIR THOMAS BARCLAY, M.P.

- ANGARY

- ANGEL

W.H.Di. - WILLIAM HENRY DINES, F.R.S.

- ANEMOMETER

- ANGELICO, FRA

PRINCIPAL UNSIGNED ARTICLES

Anglican Communion. Angola.

THE ENCYCLOPAEDIA BRITANNICA

ELEVENTH EDITION

VOLUME II, PART I

ANDROS, or ANDRO, an island of the Greek archipelago, the most northerly of the Cyclades, 6 m. S.E. of Euboea, and about 2 m. N. of Tenos; it forms an eparchy in the modern kingdom of Greece. It is nearly 25 m. long, and its greatest breadth is 10 m. Its surface is for the most part mountainous, with many fruitful and well-watered valleys. Andros, the capital, on the east coast, contains about 2000 inhabitants. The ruins of Palaeopolis, the ancient capital, are on the west coast; the town possessed a famous temple, dedicated to Bacchus. The island has about 18,000 inhabitants.

ANEMOMETER , an instrument for measuring either the velocity or the pressure of the wind. Anemometers may be divided into two classes, those that measure the velocity, those that measure the pressure of the wind, but inasmuch as there is a close connexion between the pressure and the velocity, a suitable anemometer of either class will give information about both these quantities.

Velocity anemometers may again be subdivided into two classes, those which do not require a wind vane or weathercock, those which do. The Robinson anemometer, invented by Dr. Thomas Romney Robinson, of Armagh Observatory, is the best-known and most generally used instrument, and belongs to the first of these. It consists of four hemispherical cups, mounted one on each end of a pair of horizontal arms, which lie at right angles to each other and form a cross. A vertical axis round which the cups turn passes through the centre of the cross; a train of wheel-work counts up the number of turns which this axis makes, and from the number of turns made in any given time the velocity of the wind during that time is calculated. The cups are placed symmetrically on the end of the arms, and it is easy to see that the wind always has the hollow of one cup presented to it; the back of the cup on the opposite end of the cross also faces the wind, but the pressure on it is naturally less, and hence a continual rotation is produced; each cup in turn as it comes round providing the necessary force. The two great merits of this anemometer are its simplicity and the absence of a wind vane; on the other hand it is not well adapted to leaving a record on paper of the actual velocity at any definite instant, and hence it leaves a short but violent gust unrecorded. Unfortunately, when Dr. Robinson first designed his anemometer, he stated that no matter what the size of the cups or the length of the arms, the cups always moved with one-third of the velocity of the wind. This result was apparently confirmed by some independent experiments, but it is very far from the truth, for it is now known that the actual ratio, or factor as it is commonly called, of the velocity of the wind to that of the cups depends very largely on the dimensions of the cups and arms, and may have almost any value between two and a little over three. The result has been that wind velocities published in many official publications have often been in error by nearly 50%.

The other forms of velocity anemometer may be described as belonging to the windmill type. In the Robinson anemometer the axis of rotation is vertical, but with this subdivision the axis of rotation must be parallel to the direction of the wind and therefore horizontal. Furthermore, since the wind varies in direction and the axis has to follow its changes, a wind vane or some other contrivance to fulfil the same purpose must be employed. This type of instrument is very little used in England, but seems to be more in favour in France. In cases where the direction of the air motion is always the same, as in the ventilating shafts of mines and buildings for instance, these anemometers, known, however, as air meters, are employed, and give most satisfactory results.

Anemometers which measure the pressure may be divided into the plate and tube classes, but the former term must be taken as including a good many miscellaneous forms. The simplest type of this form consists of a flat plate, which is usually square or circular, while a wind vane keeps this exposed normally to the wind, and the pressure of the wind on its face is balanced by a spring. The distortion of the spring determines the actual force which the wind is exerting on the plate, and this is either read off on a suitable gauge, or leaves a record in the ordinary way by means of a pen writing on a sheet of paper moved by clockwork. Instruments of this kind have been in use for a long series of years, and have recorded pressures up to and even exceeding 60 lb per sq. ft., but it is now fairly certain that these high values are erroneous, and due, not to the wind, but to faulty design of the anemometer.

The fact is that the wind is continually varying in force, and while the ordinary pressure plate is admirably adapted for measuring the force of a steady and uniform wind, it is entirely unsuitable for following the rapid fluctuations of the natural wind. To make matters worse, the pen which records the motion of the plate is often connected with it by an extensive system of chains and levers. A violent gust strikes the plate, which is driven back and carried by its own momentum far past the position in which a steady wind of the same force would place it; by the time the motion has reached the pen it has been greatly exaggerated by the springiness of the connexion, and not only is the plate itself driven too far back, but also its position is wrongly recorded by the pen; the combined errors act the same way, and more than double the real maximum pressure may be indicated on the chart.

A modification of the ordinary pressure-plate has recently been designed. In this arrangement a catch is provided so that the plate being once driven back by the wind cannot return until released by hand; but the catch does not prevent the plate being driven back farther by a gust stronger than the last one that moved it. Examples of these plates are erected on the west coast of England, where in the winter fierce gales often occur; a pressure of 30 lb per sq. ft. has not been shown by them, and instances exceeding 20 lb are extremely rare.

Many other modifications have been used and suggested. Probably a sphere would prove most useful for a pressure anemometer, since owing to its symmetrical shape it would not require a weathercock. A small light sphere hanging from the end of 30 or 40 ft. of fine sewing cotton has been employed to measure the wind velocity passing over a kite, the tension of the cotton being recorded, and this plan has given satisfactory results.

Lind's anemometer, which consists simply of a U tube containing liquid with one end bent into a horizontal direction to face the wind, is perhaps the original form from which the tube class of instrument has sprung. If the wind blows into the mouth of a tube it causes an increase of pressure inside and also of course an equal increase in all closed vessels with which the mouth is in airtight communication. If it blows horizontally over the open end of a vertical tube it causes a decrease of pressure, but this fact is not of any practical use in anemometry, because the magnitude of the decrease depends on the wind striking the tube exactly at right angles to its axis, the most trifling departure from the true direction causing great variations in the magnitude. The pressure tube anemometer utilizes the increased pressure in the open mouth of a straight tube facing the wind, and the decrease of pressure caused inside when the wind blows over a ring of small holes drilled through the metal of a vertical tube which is closed at the upper end. The pressure differences on which the action depends are very small, and special means are required to register them, but in the ordinary form of recording anemometer , any wind capable of turning the vane which keeps the mouth of the tube facing the wind is capable of registration.

The great advantage of the tube anemometer lies in the fact that the exposed part can be mounted on a high pole, and requires no oiling or attention for years; and the registering part can be placed in any convenient position, no matter how far from the external part. Two connecting tubes are required. It might appear at first sight as though one connexion would serve, but the differences in pressure on which these instruments depend are so minute, that the pressure of the air in the room where the recording part is placed has to be considered. Thus if the instrument depends on the pressure or suction effect alone, and this pressure or suction is measured against the air pressure in an ordinary room, in which the doors and windows are carefully closed and a newspaper is then burnt up the chimney, an effect may be produced equal to a wind of 10 m. an hour; and the opening of a window in rough weather, or the opening of a door, may entirely alter the registration.

In the tube anemometer also it is really the pressure that is measured, although the scale is usually graduated as a velocity scale. In cases where the density of the air is not of average value, as on a high mountain, or with an exceptionally low barometer for example, an allowance must be made. Approximately 1-1/2% should be added to the velocity recorded by a tube anemometer for each 1000 ft. that it stands above sea-level.

ANENCLETUS, or ANACLETUS, second bishop of Rome. About the 4th century he is treated in the catalogues as two persons--Anacletus and Cletus. According to the catalogues he occupied the papal chair for twelve years .

ANEURYSM, or ANEURISM , a cavity or sac which communicates with the interior of an artery and contains blood. The walls of the cavity are formed either of the dilated artery or of the tissues around that vessel. The dilatation of the artery is due to a local weakness, the result of disease or injury. The commonest cause is chronic inflammation of the inner coats of the artery. The breaking of a bottle or glass in the hand is apt to cut through the outermost coat of the artery at the wrist and thus to cause a local weakening of the tube which is gradually followed by dilatation. Also when an artery is wounded and the wound in the skin and superficial structures heals, the blood may escape in to the tissues, displacing them, and by its pressure causing them to condense and form the sac-wall. The coats of an artery, when diseased, may be torn by a severe strain, the blood escaping into the condensed tissues which thus form the aneurysmal sac.

In the treatment of aneurysm the aim is generally to lower the blood pressure by absolute rest and moderated diet, but a cure is rarely effected except by operation, which, fortunately, is now resorted to more promptly and securely than was previously the case. Without trying the speculative and dangerous method of treatment by compression, or the application of an india rubber bandage, the surgeon now without loss of time cuts down upon the artery, and applies an aseptic ligature close above the dilatation. Experience has shown that this method possesses great advantages, and that it has none of the disadvantages which were formerly supposed to attend it. Saccular dilatations of arteries which are the result of cuts or other injuries are treated by tying the vessel above and below, and by dissecting out the aneurysm. Popliteal, carotid and other aneurysms, which are not of traumatic origin, are sometimes dealt with on this plan, which is the old "Method of Antyllus" with modern aseptic conditions. Speaking generally, if an aneurysm can be dealt with surgically the sooner that the artery is tied the better. Less heroic measures are too apt to prove painful, dangerous, ineffectual and disappointing. For anturysm in the chest or abdomen the treatment may be tried of injecting a pure solution of gelatine into the loose tissues of the armpit, so that the gelatine may find its way into the blood stream and increase the chance of curative coagulation in the distant aneurysmal sac.

ANFRACTUOSITY , twisting and turning, circuitousness; a word usually employed in the plural to denote winding channels such as occur in the depths of the sea, mountains, or the fissures separating the convolutions of the brain, or, by analogy, in the mind.

The seven angels of Ezekiel may be compared with the seven eyes of Yahweh in Zech. iii. 9, iv. 10. The latter have been connected by Ewald and others with the later doctrine of seven chief angels, parallel to and influenced by the Ameshaspentas , or seven great spirits of the Persian mythology, but the connexion is doubtful.

In the New Testament angels appear frequently as the ministers of God and the agents of revelation; and Our Lord speaks of angels as fulfilling such functions, implying in one saying that they neither marry nor are given in marriage. Naturally angels are most prominent in the Apocalypse. The New Testament takes little interest in the idea of the angelic hierarchy, but there are traces of the doctrine. The distinction of good and bad angels is recognized; we have names, Gabriel, and the evil angels Abaddon or Apollyon, Beelzebub. and Satan; ranks are implied, archangels, principalities and powers, thrones and dominions. Angels occur in groups of four or seven. In Rev. i.-iii. we meet with the "Angels" of the Seven Churches of Asia Minor. These are probably guardian angels, standing to the churches in the same relation that the "princes" in Daniel stand to the nations; practically the "angels" are personifications of the churches. A less likely view is that the "angels" are the human representatives of the churches, the bishops or chief presbyters. There seems, however, no parallel to such a use of "angel," and it is doubtful whether the monarchical government of churches was fully developed when the Apocalypse was written.

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