Chapter M: M. J. SUTHERLAND, D.Sc., F.I.C (13)

DYNAM'ICS is the science which deals with the laws of force in their relation to matter at rest or in motion, and as such it is differentiated from _kinematics_, which considers motion mathematically, and apart from the forces producing it. Dynamics is divided into two great branches: _statics_, which treats of solid bodies at rest under the action of forces; and _kinetics_, which treats of the action of forces in producing motion in solid bodies. Formerly the latter alone was called dynamics, and to this, in conjunction with statics, the general name _mechanics_ was given. In the wide sense dynamics includes also hydrodynamics. It is to Newton that we owe the clear statement of the three primary laws of force on which the science of dynamics is based. These are: (1) that every body remains in a state of rest, or of uniform motion along a straight line, unless it is compelled by force to change that state; (2) that rate of change of momentum is in proportion to the force employed, and occurs along the straight line in which the force acts; (3) that, as the result of every action, there is always an equal and opposite reaction. These laws, which were formulated from experiment, involve the conception of force as a primary influence or action expressed in terms of space, time, and matter. Now, in dealing with the laws of force, a standard of measurement is required which shall be applicable to all forces at all times, and we therefore require to begin by establishing units of space, time, and mass. There are two systems of units in use, the one British, the other French. In the British system the foot is taken as the unit of length, and the second as the unit of time. In the French the centimetre is the unit of length, the second the unit of time; the unit velocity in the one case being that of one foot per second, in the other one centimetre per second. The British unit of mass is the pound (the mass of a certain lump of platinum deposited in the Exchequer Office, London); the French the gramme; and accordingly the French units of space, mass, and time are commonly known as the C.G.S. (centimetre, gramme, second) units. As the weight of a pound (or a gramme) is not the same at all parts of the earth's surface, it cannot give us of itself an absolute or dynamical unit of force, that is, an invariable unit; but taking it in conjunction with unit time and unit velocity, we do obtain such a unit. Two absolute units of force are in common use in dynamics, the _poundal_ and the _dyne_, the latter being the absolute unit in the C.G.S. system. The former is _that force which, acting on the mass of one pound for one second, generates in that mass a velocity of one foot per second_. The latter is _that force which, acting on the mass of one gramme for one second, generates in that mass a velocity of one centimetre per second_. It is important in dynamics to distinguish between _mass_ and _weight_. The _mass_ of one pound is the quantity of matter equal to a certain standard quantity (a certain lump of metal) and is quite independent of force. The _weight_ of one pound is the force with which the mass of one pound is attracted to the earth's surface by the force of gravity. Another important term is _momentum_: the momentum of a body in motion at any instant is the product of the mass of the body and the velocity at that instant. See _Couple_; _Elasticity_; _Energy_; _Force_; _Hydrodynamics_; _Kinematics_; _Kinetics_; _Statics_; _Thermodynamics_; _Waves_.--BIBLIOGRAPHY: Kelvin and Tait, _Natural Philosophy_; A. Gray, _Dynamics_; P. G. Tait, _Dynamics_; S. L. Loney, _Mechanics and Hydrostatics for Beginners_.

DYN'AMITE. See _Explosives_.

DY'NAMO. See _Generator_.

DYNAMOM'ETER, an apparatus for measuring the power or rate of working of a machine. There are two types, the transmission dynamometer, which measures the power of the machine without sensibly diminishing it; and the absorption dynamometer, which measures the power by using it all. The instrument is generally employed to determine the horse-power transmitted by a shaft or by belting.--Cf. Aspinall Parr's _Electrical Engineering Testing_.

DYRRHACHIUM. See _Durazzo_.

DY'SART, a royal and municipal burgh of Scotland, in Fife, on the Firth of Forth. It is an old place, and is a member of the Kirkcaldy district of parliamentary burghs. Pop. of royal burgh, 4197.

DYS'ENTERY is a disease of an acute type, due to the action of a bacillus, characterized by pain and frequent passage of blood and mucus. Owing to improved sanitation, dysentery has become less frequent. In temperate countries sporadic cases occur from time to time, and occasional epidemics break out, but in the tropics widespread epidemics occur, and the disease is a serious menace. It is a very frequent camp disease, and has been the scourge of all armies in tropical and semi-tropical regions. The bacilli are widely spread by the faeces of infected persons, and usually the infection takes place by the mouth. The onset is rapid, and marked by fever, pain in the abdomen, and frequent stools. At first mucus only is seen in the stools, but soon blood appears. In very acute cases the patient is seriously ill in forty-eight hours, and may die on the third or fourth day. Moderate cases may go on for several weeks, with resulting convalescence. Some cases become chronic in type, and a person may have chronic dysentery for years. Bismuth in large doses is given, and morphia is a most useful drug to relieve the pain and quieten the bowel. Normal saline solution is given by rectum after the acute stage, whenever possible. Chronic dysentery requires dietetic treatment for the persistent dyspepsia and irritability of the bowel. Amoebic dysentery, due to the _Amoeba dysenteriae_, is a distinct disease.

DYS'ODILE, a yellowish or greenish foliated carbonaceous substance found in Sicily originally, and derived from the decay of minute organisms. When ignited, it burns and emits a very unpleasant smell.

DYSON, Sir Frank Watson, F.R.S., LL.D.(Edin.), British astronomer, born at Ashby 8th Jan., 1868, the son of a Baptist minister. Educated at Bradford Grammar School and Trinity College, Cambridge, he became chief assistant at the Royal Observatory, Greenwich, in 1894, and secretary of the Royal Astronomical Society in 1899. Astronomer Royal for Scotland in 1905, he was appointed Astronomer Royal for England in 1910. He was knighted in 1915.

DYSPEP'SIA, or GASTRITIS, may be either acute or chronic. _Acute dyspepsia_ may follow when more food is taken than the stomach can digest, or when unsuitable articles are taken. The symptoms are headache, depression, nausea, vomiting, with pain, varying from a feeling of discomfort in the abdomen to marked tenderness. The tongue is furred, and usually there is diarrhoea, while in the more severe attacks the onset is marked by chill and a rise of temperature. An attack may last from one day to four days. Treatment for mild cases is simply a dose of castor-oil (children) or blue pill (adults), but in severe cases vomiting should be promoted by warm water, or the stomach tube if necessary, and a dose of calomel (3 grains), followed by salts, should be given. Absolute rest to the stomach is necessary, and only small quantities of water allowed. Repeated attacks lead to the establishment of the chronic form. _Chronic dyspepsia_ is a condition of disturbed digestion due to the prolonged use of unsuitable, or improperly prepared, foods. Hot cakes, excess of tea, coffee, or alcohol, rapid and irregular meals are all common causes. It may also arise in the course of diseases like anaemia, chronic tuberculosis, gout, Bright's disease, chronic heart disease, cirrhosis, and in diseases of the stomach itself, as cancer, gastric ulcer, and gastric dilatation. The most common symptoms are a feeling of oppression after food, tenderness over the stomach, headache, nausea, flatulence, constipation, and occasionally vomiting. Treatment consists of dietetic measures, regulated exercises, change of air and surroundings, and avoidance of depression. Milk should be used freely, and in severe cases should be given alone till improvement sets in. Fats and greasy dishes should be avoided. Fruits are sometimes well borne, and at other times the reverse. Drugs do not play so important a r[^o]le, but bitter tonics, like nux vomica, quassia, gentian, &c., are the best. Constipation should be treated when necessary.

DYSPHO'NIA is difficulty in speaking, and is the result of some forms of laryngitis. The condition is aggravated by attempts to use the voice, and complete rest is necessary to bring about an early and satisfactory recovery. Tonics, moderate exercise, and a holiday hasten recovery.

DYSPNOEA (dis-pn[=e]'a) is difficult or laboured breathing. It is a symptom of diseases of the heart or lungs, and is produced by any condition which interferes with normal respiration. It is sometimes present in nervous disturbances.

DZE'REN, or DZE'RON, the Chinese antelope, a remarkably swift species of antelope (_Procapra guttur[=o]sa_) inhabiting the dry arid deserts of Central Asia, Tibet, China, and Southern Siberia. It is nearly 4-1/2 feet in length, and 2-1/2 feet high at the shoulder.

DZIG'GETAI, or KIANG (_Equus hemi[)o]nus_), a species of wild ass native to Central Asia, allied both to the horse and ass. Its head is large like that of the ass, but in form resembles that of the horse. The ears also resemble those of the horse. It runs with a rapidity exceeding that of the best Arabian horses.

DZOUNGARIA, or SUNGARIA, a Chinese territory in Central Asia, stretching from about 43deg to 48deg N. lat. and from about 82deg to 86deg E. long. It has an area of 147,950 sq. miles, and pop. 600,000. It is administratively connected with Kuldja, and since the surrender of Kuldja by the Russians in 1880 is again under Chinese rule. Dzoungaria, once the centre of an independent empire, was first conquered by the Chinese in 1757.

* * * * *

E

E, the second vowel and the fifth letter of the English alphabet. It occurs more frequently in English words than any other letter of the alphabet. Its long or natural sound in English coincides with the sound of _i_ in the Italian and French languages, as in _here_, _mere_, _me_. It has also another principal sound, a short one, heard in _met_, _men_. It has besides a sound like _a_ in _bare_, as in _there_, _where_, &c., and the obscure sound which is heard in _her_. As a final letter in English it is generally silent, but it serves to indicate that the preceding vowel is to have its long sound, as in _mane_, _cane_, _plume_. When two _e_'s come together the sound is generally the same as that of the single _e_ long, as in _deem_, _esteem_, _need_ (compare, however, _pre-exist_, &c.).

E, in music, is the third note or degree of the diatonic scale, answering to the _mi_ of the Italians and French.

EADIE ([=e]'di), John, D.D., a Scottish preacher and theologian, born 1810, died 1876. He was educated at Glasgow University, and entered the ministry of the Secession Church, becoming in 1843 professor of biblical literature in the Divinity Hall of the Church, a post which he continued to hold after the Secession body was merged in the United Presbyterian Church (in 1847). Among his works are _Biblical Cyclopaedia_; _Analytical Concordance to the Scriptures_; _Ecclesiastical Cyclopaedia_; _Commentary on the Greek Text of Ephesians_, and similar works on _Colossians_, _Philippians_, and _Galatians_; and _The English Bible_. He was one of the scholars engaged on the Revised Version of the New Testament.

EAD'MER, an English monk, the friend and biographer of St. Anselm. In 1120 he was chosen Bishop of St. Andrews; but as the Scottish king refused to recognize the right of the Archbishop of Canterbury to consecrate him, he returned to England and died a simple monk about 1124. Besides the life of St. Anselm, Eadmer wrote lives of St. Wilfrid, St. Dunstan, St. Odo, and other English saints, as well as a valuable history (_Historiae Novorum_) of events in England and the English Church from 1066 to 1122.

la mogilnik_)]

tus vocifer_)]

EAGLE (Lat. _aquila_, Fr. _aigle_), the general name of raptorial birds that form a group or sub-family (Aquil[=i]nae) of the great family Falconidae, which includes the eagles, falcons, and hawks. The eagle is popularly regarded as the noblest and most courageous of the rapacious birds. It soars to a greater height than any other European bird, from which circumstance the ancients considered it as the bird or messenger of Jove. The genus Aqu[)i]la, which includes the most typical eagles, is distinguished by its long and powerful bill, the curve commencing at the cere, by its wings reaching to the tip of the tail, and by its tarsi being feathered to the toes. The imperial eagle (_A. mogilnik_) of Central Europe, North-East Africa, India, and China is probably the species to which the popular belief in the courage, strength, and nobleness of eagles is to be traced. _A. chrysaetus_, the golden eagle, is the chief British species. It measures over 6 feet from tip to tip of the expanded wings, and 3 feet from the beak to the end of the tail. The adults have the body brownish, becoming darker with age; the feathers of the head and neck pointed, and of a golden-red hue. This species is found all over the northern hemisphere. It was once common in the Highlands of Scotland, but is now becoming rare. The Kirghis and other tribes of Central Asia use the golden eagle to kill antelopes, foxes, and even wolves. Another British eagle is the erne or sea-eagle (_Haliaetus albicilla_) found near the sea-coast or lakes, and feeding largely on fish. The general colour is greyish-brown, the head pale-coloured, the tail white. The bald eagle (_Haliaetus leucoceph[)a]lus_), found in North America and North-East Asia, is the symbol of the United States, though Franklin deplores the selection on account of his mean and dishonest habit of robbing the industrious osprey of the fish caught by him. Like all members of the genus, his diet is less restricted than that of the true eagles; and he even takes carrion. See also _Harpy Eagle_.

EAGLE, as a symbol. The eagle first appears as a war standard amongst the Persians, through whom it reached the Egyptians. As the standard of the Roman armies it was first used by Marius, and afterwards took the place of all the other emblems at the head of the legions. It was first made of wood, then of silver, and finally, under Caesar and his successors, of gold. In the Mediaeval Ages the eagle became the heraldic emblem of the Holy Roman Empire, and was made double-headed in the fourteenth century. When the Holy Roman Empire fell to pieces in 1806, the double-headed eagle was retained by Austria. The double-headed eagle was assumed by Tsar Ivan III in 1472, and became the national military symbol of Russia; the single-headed eagle was assumed by the modern German Empire in 1871, and by the United States of America. The American eagle stands with outspread wings guarding a shield, with the motto _E pluribus unum_. The eagle was also the badge of several orders, the chief of which were the order of the _Black Eagle_, founded by the Elector of Brandenburg in 1701, and the highest order in Prussia; the order of the _Red Eagle_, also a Prussian order, and founded in 1705; and the Russian order of the _White Eagle_, originally Polish, and instituted in 1325.

EAGLE, a gold coin in the United States of the value of ten dollars, or L2 sterling, first coined in 1795. There are also half-eagles, quarter-eagles, and double-eagles.

EAGLE-HAWK, a name sometimes applied to small South American eagles (genus Morphnus), with short wings and long legs.

EAGLEHAWK, a gold-mining town in Victoria, Australia, 4 miles from Bendigo. Pop. 8130.

EAGLE-OWL, a name for several large horned owls, such as _Bubo ignavus_ (the great horned owl), little inferior in size to the golden eagle, found in many parts of Europe and sometimes in Britain. An allied species, the Virginian horned owl (_B. virginianus_), is common in the United States.

EALING, a municipal and parliamentary borough of Middlesex, the former a few miles west of London. Pop. 61,222.

P, Concha. E.C., External canal. D, Drum. H, Hammer. A, Anvil. E, Eustachian tube. S. Stirrup, S.C, Semicircular canals. C, Cochlea. Arrows denote the direction of vibration.]

EAR, the organ of hearing. In the higher vertebrates it is divided into the outer, middle, and inner ear. The external ear, which is a cartilaginous funnel for collecting the sound waves and directing them inwards, is composed of the _concha_, or projecting part, and of the _auditory canal_, which extends from the _concha_ to the membrane of the _tympanum_ or _drum_. This membrane is a partition stretched obliquely across the bottom of the auditory canal, which it separates from the middle ear or tympanum; it is semi-transparent and very delicate. It vibrates with the waves of sound which strike against it, and transmits the vibrations to certain little bones of the cavity of the tympanum. These bones, which have been named respectively the hammer (_malleus_), the anvil (_incus_), and the stirrup (_stapes_), transmit the vibrations to the internal ear, forming a chain communicating at one end with the membrane just mentioned, and at the other with the inner ear. The internal ear consists of a complicated system of tubes known as the _membranous labyrinth_, containing fluid in which waves are set up by the vibrations transmitted to it by the little bones from the drum membrane. The lower part of the labyrinth is coiled like a snail shell, and is called the _cochlea_. It is the real organ of hearing. The upper part consists of three _semicircular canals_, the function of which is to record the position and movements of the body in space. The middle ear communicates with the pharynx by the Eustachian tube, through which air from the mouth may be introduced into the tympanic cavity, so as to permit vibrations of the drum membrane. In the external auditory canal of the ear is produced the cerumen or ear-wax. The cut shows P the concha, E.C. the external canal, D the drum membrane partly removed, S the stirrup, A the anvil and H the hammer, the small bones communicating with the drum and vestibule, C cochlea, S.C semicircular canals, E Eustachian tube.--Cf. Sir Thomas Wrightson, _An Enquiry into the Analytical Mechanism of the Internal Ear_.

EAR-COCKLE, a disease in wheat caused by the presence in the grain of worms belonging to the genus Vibrio. It is called in some parts of England _purples_.

EARL (A.Sax. _eorl_; Dan. _jarl_), a degree of the British nobility between marquess and viscount, the title of highest antiquity in England. The title was made hereditary by William the Conqueror, and for a time was used interchangeably with that of _count_, the corresponding title on the Continent. The wife of an earl is still called a _countess_. The earl was the highest in rank of the nobility until Edward III created a duke in 1357, and Richard II a marquess in 1385. The first earl of England is the Earl of Arundel. An earl's coronet is composed of eight pearls raised upon points, with small leaves between, above the rim. See _Peer_.

EARLE, John, English bishop and writer, born about 1601, died 1665. He was educated at Oxford, and, after writing some short poems, gave to the world anonymously in 1628 _Microcosmographie, or a Piece of the World discovered in Essays and Characters_--a work full of wit, humour, and admirable character-painting. He was tutor to Charles II, accompanied him during his exile, and was held by him in the highest esteem. In 1662 he was consecrated Bishop of Worcester, and next year was translated to Salisbury.

EARLE, Rev. John, Anglo-Saxon scholar, was born in 1824, and died in 1903. He studied at Oriel College, Oxford, where he obtained first-class honours in classics, and was elected a fellow (1848). In the following year he took orders, and was appointed for five years university professor of Anglo-Saxon. In 1857 he became rector of Swanswick, near Bath, and in 1871, a prebendary of Wells. The five years' rule having been rescinded, he was re-elected professor of Anglo-Saxon at Oxford in 1876, and continued to hold the position, together with the rectory of Swanswick, until his death. Among his contributions to the study of Anglo-Saxon and modern English are the following: _Two Saxon Chronicles Parallel_ (1865); _The Philology of the English Tongue_ (1871); _A Book for the Beginner in Anglo-Saxon_ (1877); _English Plant Names from the Tenth to the Fifteenth Century_ (1880); _Anglo-Saxon Literature_ (1884), a very useful and informing little manual; _Handbook to the Land Charters and other Saxonic Documents_ (1888); _English Prose: its Elements, History, and Usage_ (1890); _The Deeds of Beowulf_ (1892), a translation of the well-known Anglo-Saxon epic; _The Psalter of 1539_ (1894); and _A Simple Grammar of English now in Use_ (1898). He also wrote a book on _Bath, Ancient and Modern_ (1864).

EARLESTOWN, a town of Lancashire, England, 14 miles east of Liverpool. There are here engineering-works, sugar-works, and other establishments. Pop. 9020.

EARL-MARSHAL, a great officer of England, who had, anciently, several courts under his jurisdiction, as the court of chivalry and the court of honour. He is the head of the College of Arms (Heralds' College), grants armorial bearings, and determines all claims in connection with them. Since 1672 the office is hereditary in the family of Howard (Dukes of Norfolk). There was also an earl-marshal of Scotland, the office being hereditary in the Keith family until 1716, when it was abolished.

EARLOM, Richard, English mezzotinto engraver, born 1743, died 1822. His engravings from Reynolds, Hogarth, Van Huysum, &c., and from Claude's _Liber Veritatis_, are exceptionally fine, and are standard works in their department.

EARLSTON (originally ERCILDOUN), a village of Scotland in Berwickshire. Near it are the ruins of the ancient tower, which belonged to the famous Thomas the Rhymer. Pop. 1749.

Peterborough Cathedral. Part of the West Front Lincoln Cathedral. Early English Pillars in the Eastern Transept]

EARLY ENGLISH ARCHITECTURE, the first of the Pointed or Gothic styles of architecture that prevailed in England. It succeeded the Norman in the reign of Richard I (1189), and continued to the end of the reign of Henry II in 1272, a period of 123 years, when it gradually merged into the Decorated style. One of the leading peculiarities in this style is the form of the windows, which are narrow in proportion to their height, and terminate in a pointed arch, resembling the blade of a lancet (and therefore often called the _Lancet_ style). Throughout the early period of the style they are very plain, particularly in small churches; but in cathedrals and other large buildings the windows, frequently combined two or more together, are carried to a great height, are richly and deeply moulded, and the jambs ornamented with slender shafts. On the eastern and western fronts of small churches the windows are often combined in this manner, with a circular window above and a richly moulded door below; but in large buildings there is often more than one range of windows, and the combinations are very various. Though separated on the outside, these lancets are in the interior combined into one design, thus giving the first idea of a compound window. The doorways are in general pointed, and in rich buildings sometimes double; they are usually moulded, and enriched with the tooth-ornament. The buttresses are often very bold and prominent, and are frequently carried up to the top of the building with but little diminution, and terminate in acutely pointed pediments, which, when raised above the parapet, produce in some degree the effect of pinnacles. In this style, likewise, flying-buttresses were first introduced (see _Buttresses_), and the buttresses themselves much increased in projection owing to the comparative lightness of the walls, which required some counter-support to resist the outward pressure of the vaulting. The roof in the Early English style appears always to have been high pitched, and the towers surmounted by lofty pointed spires, as at Salisbury Cathedral. In the interior the arches are usually lancet-shaped, and the pillars often reduced to very slender proportions. As if to give still greater lightness of appearance, they are frequently made up of a centre pillar, surrounded by slight detached shafts, only connected with the pillar by their capitals and bases, and bands of metal placed at intervals. These shafts are generally of Purbeck marble, the pillar itself being of stone, and from their extreme slenderness they sometimes appear as if quite inadequate to support the weight above them. The earliest example of Early English architecture is the choir of Canterbury, followed by the choir of Lincoln Cathedral, but some of the best examples are to be seen in Salisbury Cathedral. The architects of this style carried their ideas of lightness to the utmost limits of prudence, and their successors have been afraid to imitate their example. The abacus of the capitals is generally made up of two bold round mouldings, with a deep hollow between. The foliage is peculiar, generally very gracefully drawn, and thrown into elegant curves; it is usually termed _stiff-leaved_, from the circumstance of its rising with a stiff stem from the neck-mould of the capital. The trefoil is commonly imitated, and is very characteristic of the style. The mouldings of this style have great boldness, and produce a striking effect of light and shade. They consist chiefly of rounds separated by deep hollows, in which a peculiar ornament, called the _dog's-tooth_, is used, whenever ornament can be introduced. This ornament is as characteristic of the Early English as the zigzag is of the Norman. See _Dog's-tooth_.--Cf. F. Bond, _An Introduction to English Church Architecture, from the 11th to the 16th Century_.

EARNEST, in law, any sum paid in advance, to bind parties to the performance of a verbal agreement, or something given by a buyer to a seller as a pledge of adherence to a bargain. The party is then obliged to abide by his bargain, and is not discharged upon forfeiting his earnest. In England the general view is that the sum paid as earnest, however small, is part of the price.

EAR-RING, an ornament for the ear, consisting of a ring or hook passing through the lobe, with a pendant of diamonds, pearls, or other jewels frequently attached. Ear-rings were commonly worn amongst the Oriental nations, and by both sexes, especially in Babylonia and Assyria, from the earliest times. Amongst the Greeks and Romans the wearing of ear-rings was usually confined to women. In England the Romanized Britons and the Anglo-Saxons wore them, but the fashion declined in the tenth century, and was again introduced in the sixteenth century, in Queen Elizabeth's time.

EARSDON, an urban district or town of England, South Northumberland, several miles north-west of Tynemouth, with productive collieries. Pop. 10,568.

EARTH, the planet which we inhabit, a nearly spherical body which every twenty-four hours rotates from west to east round an imaginary line called its axis--this axis having as its extremities the north and south poles--while in the course of a year it completes a revolution round the sun. To an observer whose view is not obstructed, the visible part of the earth appears as a circular and horizontal expanse, on the circumference of which the heavens appear to rest. Accordingly, in remote antiquity, the earth was regarded as a flat, circular body, floating on the waters. But even in antiquity the spherical form of the earth began to be suspected. It is only on this supposition that we can explain how the horizon of vision grows wider and wider the higher the position we choose, how the tops of towers and mountains at a distance become visible before the bases, how the hull of a ship first disappears as she sails away, and how, as we go from the poles towards the equator, new stars become visible. Besides these proofs there are many others, such as the circular contour of the earth's shadow seen on the moon during an eclipse. The mere fact that the earth can be circumnavigated does not, as is sometimes assumed, prove it to be globular. But its surface, land and ocean, has been almost all explored and accurately mapped, and the relative distances and directions found to obtain between the places on its surface are consistent only with its possessing such a shape.

The earth is not, however, an exact sphere, but is very slightly flattened at the poles, so as to have the form known as an _oblate spheroid_. In this way the _polar diameter_, or diameter from pole to pole, is shorter than the diameter at right angles to this--the _equatorial diameter_. The most accurate measurements make the polar diameter almost 27 miles less than the equatorial, the equatorial diameter being found to be 7926.7 miles, and the polar 7900 miles. The earth is regarded as divided into two halves--the northern and the southern hemisphere--by the _equator_, an imaginary line going right round it midway between the poles. In order to indicate with precision the position of places on the earth additional circles are imagined to be traced upon the surface in such a manner that those of the one set all pass through both poles, while those of the other are drawn parallel to the equator. The former are called _meridians_, the latter _parallels of latitude_, and by reference to them we can state the latitude and longitude, and thus the exact position, of any place.

Many experiments by various methods have been made in order to determine the average density of the earth, and the total quantity of matter it contains. Amongst these methods may be mentioned: (1) that of measuring the deflection of a plumb-line due to a mountain's attraction, and thereby comparing the mass of the earth with that of the mountain; (2) that founded on the difference of oscillation period of a pendulum when placed at the summit of a mountain and when at the sea-level; (3) by the determination of the difference of gravity at the top and the bottom of a deep mine, by pendulum experiments; (4) Cavendish's experiment with the torsion balance, which attempts to compare the attractive force of two large lead balls upon two small lead balls with that exercised by the earth. From these and other experiments it has been calculated that the mean density of the earth is to that of water as about 5-1/2 to 1.

The earth, in common with the other planets, moves round the sun, completing its revolution in about 365 days and 6 hours. The orbit of the earth is an ellipse, with the sun in one of its foci. Hence the earth is not equally distant from the sun throughout the year; it is over 3,000,000 miles nearer at one time than another, its least distance (_perihelion_ distance), according to recent calculations, being about 91,340,000 miles; its greatest (_aphelion_ distance), 94,450,000; and the mean distance, 92,897,000 miles. From this it may be calculated that the velocity of the earth in its orbit is about 18-1/2 miles a second. About 3rd Jan. the earth is nearest the sun, and about 4th July farthest from it. This position of matters, which is subject to slow alteration in the course of ages, at present tends to moderate the seasonal variations in the northern hemisphere, and to intensify them in the southern. The passage of the earth round its orbit causes the sun to appear as if it described an annual circuit of the heavens; and hence it is that at one time of the year one group of stars is seen in the neighbourhood of the sun near sunrise or sunset, and at another time another group. This apparent path of the sun is the _ecliptic_, and corresponds with what would be the path of the earth as seen from the sun; and the groups of stars through which the sun successively passes form the _zodiac_.

The earth's daily motion about its own axis takes place in twenty-three hours, fifty-six minutes, and four seconds of mean time. This diurnal revolution is the occasion of the alternation of day and night. As the axis on which the earth performs its diurnal rotation is inclined towards the plane of its path about the sun at an angle of 66-1/2deg, and the angle between the plane of the ecliptic and the plane of the earth's equator is therefore 23-1/2deg, the sun ascends in the heavens, as seen from our northern latitudes, from 21st March to 21st June (the summer _solstice_), to about 23-1/2deg above the celestial equator, and descends again towards the equator from 21st June to 23rd Sept.; it then sinks till 22nd Dec. (the winter _solstice_), when it is about 23-1/2deg below the equator, and returns again to the equator by 21st March. This arrangement is the cause of the seasons, and the inequality of day and night attending them. For all places removed from the equator, day and night are equal only twice in the year (at the _equinoxes_). At the summer solstice in the northern hemisphere the north pole of the earth is turned towards the sun, and the south pole away from it, and for places within 23-1/2deg of the former there is a period of longer or shorter duration during which the sun is continually above the horizon throughout the twenty-four hours of each day, while round the latter there is an equal extent of surface within which the sun for similar periods is below the horizon. (See _Day_.) The reverse state of matters occurs at the winter solstice. The circles bounding these regions are called respectively the _arctic_ and the _antarctic_ circle, and the regions themselves the _polar_ or _frigid zones_. Throughout a region extending to 23-1/2deg on each side of the equator the sun is directly overhead at any place twice in the year. The circles which bound this region are called the _tropics_, that in the northern hemisphere being the tropic of _Cancer_, that in the southern the tropic of _Capricorn_, while the region between is the _torrid zone_. The regions between the tropics and the polar circles are respectively the _north_ and _south temperate zones_.

From the evidence furnished by volcanoes, hot springs, sinking of mines, &c., it is known that the earth has a high internal temperature. Taking the average of the various observed rates of increase this temperature seems to increase 1deg F. for every 60 feet of descent. Assuming this to continue, the rocks at a depth of 2 miles would be as hot as boiling water, and at a depth of 50 miles the heat would be such as at the surface would melt every known solid. This being so, various theories as to the internal condition of the earth have been proposed: (1) that a thin envelope or crust surrounds a molten interior. It can be shown, however, that as tides must be produced in such a molten mass the cool outer crust would be unable to withstand the enormous force of these unless it were about 2000 miles thick. (2) That the interior is solid, with spaces here and there filled with liquid or gaseous material. This theory assumes that there are within the earth enormous cavities filled with molten rock, which escapes, when local pressure is removed, in the form of volcanic outbursts. (3) That the earth consists of a thin crust, a large solid nucleus, and a liquid film between the nucleus and the crust. (4) That the earth is solid to the centre, but any part may become liquid if local pressure is removed. On this theory it is supposed that if water should percolate to liquefied rocks, it would be converted into steam, and produce the various volcanic phenomena.

The question of the constitution of the earth's interior has in recent years been much investigated by means of seismographic records. These appear to indicate that there are three distinct divisions. The outer crust has a thickness of from 20 to 40 miles. It possesses a high power of resistance to all kinds of stress. Beneath it is a large shell possessing a density and elasticity resembling fine steel. This shell has a high rigidity against changing forces of shorter duration, like tidal action, but in its outer parts at least yields in time to unvarying long-continued stress. The third or innermost division of the earth is probably molten, as it can transmit compressional waves, but yielding immediately to distortional or twisting forces, is unable to transmit distortional waves. This innermost portion appears to be a sphere of radius approximately one-half that of the earth as a whole. The transition between the crust and intermediate shell is abrupt, but that between the latter and the central portion is more gradual.

The earth (like the other planets) is believed to have condensed and solidified from a gaseous or nebular condition, and to have once had a far higher temperature than now. If such were the case, the outer surface, losing heat by radiation, would be the first part to cool quickly; while the interior, losing its heat by conduction, would not cool so rapidly, and, therefore, would naturally have a higher temperature than the portion at the surface. This is what all observations indicate the condition of the earth to be, and the shape of the earth also indicates that it must once have been in a fluid state. Calculations have been made of the time which has elapsed since solidification commenced, the estimates being in general of the order of hundreds of millions of years. See _Nebular Hypothesis_.

Another feature that the earth as a whole presents is its magnetism. When a magnetic needle is balanced on a point, it remains at rest in one position only, pointing then nearly due north and south. This can be explained only on the supposition that the earth acts as a great magnet. It has, in fact, two poles--a north and a south magnetic pole--which are not very far from the geographical poles. The magnetic equator, where the vertical force is zero and the dipping needle takes a horizontal position, does not diverge greatly from the geographical equator. The earth acts upon all magnets as they act upon each other, and it is for this reason that they point north and south.

The surface of the earth contains over 196,000,000 sq. miles, of which about two-sevenths is dry land, the remaining five-sevenths being water. The land is arranged into masses of irregular shape and size, the greatest connected mass being in the eastern hemisphere. The chief masses receive the name of continents, detached masses of smaller size being islands. The surface of the land is variously diversified, exhibiting mountains, valleys, plains, plateaus, deserts, &c. The water area of the earth is divided into oceans, seas, bays, gulfs, &c., while rivers and lakes may be regarded as features of the land surface. The great phenomena of the oceans are currents and tides. The population of the whole earth is estimated at from 1600 to 1700 millions. The earth is attended by the moon as a subordinate or secondary planet. See also such articles as _Climate_, _Currents_, _Ocean_, _Earthquake_, and _Seasons_.--BIBLIOGRAPHY: A. von Humboldt, _Cosmos_; E. Reclus, _The Earth and its Inhabitants_; T. G. Bonney, _The Story of our Planet_; T. M. Reade, _The Evolution of Earth Structure_; _Theory of Geomorphic Changes_; A. T. Swaine, _The Earth: its Genesis and Evolution, considered in the Light of the most Recent Scientific Research_.

EARTHENWARE, a name applied to the commoner sorts of pottery-ware. The older kinds of earthenware, such as Majolica, Delft-ware, Faience, and Palissy-ware, are not only glazed, but are besides elaborately coloured and enamelled and ornamented with raised figures of various kinds. See _Pottery_.

EARTH-HOUSES, a name generally given throughout Scotland to underground buildings, also known as 'Picts' houses' or 'Picts' dwellings'. The earth-house in its simplest form consists of a single irregular-shaped chamber, formed of unhewn stones, the side walls gradually converging towards the top until they can be roofed by stones of 4 or 5 feet in width, all covered in by a mound of earth rising slightly above the level of the adjacent ground. In the more advanced form of these structures two or three chambers are found. Earth-houses are frequent in the north-east of Scotland, occasionally thirty or forty being found in the same locality. Querns, bones, deers' horns, earthen vessels, cups and implements of bone, stone celts, bronze swords, and the like, are occasionally found in connection with them. Very similar structures, known as beehive-houses, occur also in Ireland and Cornwall.

EARTH-NUT, the _Conopodium denudatum_, an umbelliferous plant common in woods and fields in Britain. The leaves are ternately divided, and the small white flowers are in terminal umbels. The tuber or nut is about 4 or 6 inches below the surface, at the termination of a long slender root. It is brown, the size of a chestnut, of a sweetish farinaceous nature, resembling in taste the common chestnut. Swine are very fond of the nuts, and fatten rapidly where they are abundant. The name is frequently applied to _Carum Bulbocast[)a]num_, which has a similar tuber. See _Ground-nut_.

EARTHQUAKE, a shaking of the earth's surface, propagated from place to place by a wave motion. It may vary in intensity from the slightest perceptible tremor to a violent shock which bursts open chasms and changes the appearance of the ground. Earthquakes originate in the crust of the earth, generally at only a very few miles depth, and probably never lower than about 30 miles. The point of origin is called the centre or seismic focus, and the place on the surface vertically over it the epicentre. It is rather difficult to tell the depth of the focus. Mallet estimated this by projecting backward the direction of travel of the wave at different points, as judged from the inclinations of the rents in buildings, &c., assumed to be at right angles to the line of propagation. The accuracy of this method has been improved by substituting evidence of direction as given by seismographs. The focus of an earthquake is often submarine, and subsequent to the shock transmitted through the solid earth a great sea-wave may invade the land and produce far more disastrous effects.

In some cases an earthquake may be caused by a fall of rock in some subterranean cavity. This gives only a minor and local shock. The vast majority of earthquakes are certainly _tectonic_, originating from the snapping of strata under great strain, or the further slipping of portions of the earth's crust along previously existing fault planes. Such dislocations probably arise sometimes from the variations of weight supported by the earth's crust in neighbouring regions, due to the transport by rivers of material, which they erode at one place and deposit at another. A further cause is the contraction undergone by the earth in its secular cooling. There are also earthquakes of _volcanic_ origin, accompanying eruptions, but these are not usually of any great violence, nor do they involve any large area. The coasts of the Pacific Ocean--American, Asiatic, and East Indian--are much visited by earthquakes, in especial the Japanese Islands. The other band of greatest frequency has a direction outlined by the Azores, Alps, Mediterranean, and the Caucasus and Himalaya Mountains. It may be noted that all the regions specially affected are distinguished by steep gradients of the earth's surface.

AB, Surface of earth. F, Focus. E, Epicentre. 1-4, Successive positions of earthquake wave. S, S, Cracked walls; the cracks being at right angles to CF and DF give some indication of the depth of focus.]

In recent years much information has been obtained by the investigation of earthquakes by various kinds of seismograph. One single instrument at a particular station, e.g. a Milne seismograph, will enable the distance of the epicentre to be calculated. From the results of three stations, the precise locality can practically always be told. With additional or particular forms of instruments, this may even be possible by means of the records at one station. Earthquake waves are found to consist of distinctly defined types. The first to arrive are the preliminary tremors or first-phase waves, then the second-phase waves, next the third-phase or large waves, and lastly the concluding waves, consisting largely of 'echoes' or reflected vibrations. The speed of the preliminary tremors is found to be only about 2 miles per second for very short distances, but for a quadrant of the earth's surface they travel at an average of about 7 miles per second, a speed which is only slightly exceeded for still greater distances. The second-phase waves travel with a little under two-thirds of these velocities. These two classes of wave have been proved to travel through the earth, approximately along chords, but with the path slightly bent, convex towards the earth's centre. The first-phase waves are longitudinal, or waves of compression; the second-phase are transverse, or waves of distortion. The greater speed for greater distances is due to the track being more through the earth's interior and less through its outer portions, as the interior transmits wave-motion much more rapidly than the crust. The rigidity at some depth from the surface has been shown to be of the same order of magnitude as the rigidity of steel. The third-phase waves are of much longer vibration period and wide amplitude, and have been compared to a groundswell on the sea. Their time of passage from the epicentre to any place is proportional to the distance measured round the earth's surface, and it is clear that they travel on the surface, and not through the interior. Their speed is nearly 2 miles per second. The difference in time between the arrival of the preliminary tremors at any station and the arrival of the second-phase waves, or between the second-phase and third-phase waves, enables the distance of the epicentre to be easily found, as these differences, of course, become greater with increasing distance.

The number of earthquakes has been found to be enormously greater than was at one time supposed; in fact, small tremors are occurring daily in one part or another of the earth. Great and destructive shocks are generally preceded by minor shocks in the same district, and they are always followed for months afterwards by a series of gradually lessening after-shocks. Among the most remarkable earthquakes of modern times were those which destroyed Lima in 1746, and Lisbon in 1755; more recently destructive earthquakes visited Calabria in 1857, Peru and Ecuador in 1868, the Island of Ischia in 1884, Japan in 1896, North India and Calabria in 1905, San Francisco in 1906, Messina and Reggio in 1908. One of the greatest earthquakes of recent times was that which visited the provinces of Kansu and Shensi in North-West China, on 16th Dec., 1920. (See _Seismograph_.)--BIBLIOGRAPHY: J. Milne, _Earthquakes and other Earth-Movements_; C. Davison, _A Study of Recent Earthquakes_; C. G. Knott, _The Physics of Earthquake Phenomena_.

EARTHS, a term applied in geology to certain loosely aggregated siliceous and aluminous materials, the detritus of pre-existing rocks. In chemistry the term earth is given to certain metallic oxides, such as the 'alkaline earths' lime, baryta, and strontia; also to alumina and a series known as the 'rare earths'. The earths were regarded as simple bodies until Sir H. Davy proved them to be compounds of oxygen with metals.

EARTH-SHINE, in astronomy, a name given to the faint light visible on the part of the moon not directly illuminated by the sun, due to the illumination of that portion by the sunlight which the earth reflects on her. It is most conspicuous when the illuminated part of the disc is small, as soon after new moon. This phenomenon is popularly described as 'the old moon in the new moon's arms'.

EARTH-TONGUE. See _Geoglossum_.

EARTHWORKS (in fortification) are military works formed chiefly of earth and designed either as permanent or temporary defences. They are cheaper, more easily repaired, and expose their defenders to less risk from broken stone than stone-works. See _Entrenchments_.

EARTHWORM, the name applied to segmented worms (Annelids) that burrow in the soil, and belong to the ord. Oligochaeta, a subdivision of the bristle-worms (Chaetopoda). They have a long, cylindrical body, divided by transverse furrows into numerous rings. The mouth is destitute of jaws, and they have no eyes, tentacles, or other head appendages. They are hermaphrodite. The commonest British forms are chiefly species of Lumbricus and Allolobophora. They feed on earth and various kinds of animal and vegetable matter, and move by the contractions of successive parts of the body aided by a double row of bristles. They are of great service to the agriculturist by loosening the soil and increasing its depth. This is chiefly the result of their mode of nourishment, since they deposit the soil they have swallowed, after digestion, in heaps called _worm castings_ which bring up rich fine soil to the surface, gradually covering the upper layer sometimes to the extent of several inches.

EAR-TRUMPET, an artificial instrument for aiding the collection of the vibrations or waves of sound, and carrying them in an intensified form to the internal parts of the ear. They are generally made of tin, vulcanite, or gutta-percha, and are of various forms. A small kind known as ear-cornets or acoustic auricles, attached to the ear by a spring, is sometimes used in slight cases of deafness.

la auricularia_). Male and female]

EARWIG (_Forfic[)u]la_), a common orthopterous insect whose name is derived from its supposed habit of insinuating itself into the ears of persons. This is practically impossible, yet the notion is widely spread, as appears from the names given to the earwig in different languages, as in Fr. _perceoreille_ (pierce-ear), in Ger. _ohrenh[:o]hler_ (ear-borer). Much damage is sustained by gardeners from the depredations of these insects among fruit and tender vegetables, which constitute their proper food. The earwig is about three-quarters of an inch in length, having the wings folded under very short and truncate elytra or wing-cases, and the extremity of the abdomen armed with a horny forceps.

EASEMENT, in law, a right or privilege which one proprietor may have to use the land of another in connection with the needs of his own land, as the use of a way, a water-course, &c. The right to an easement may be acquired either by grant or by uninterrupted enjoyment for a period of years.

EAST, one of the four cardinal points, being the point in the heavens where the sun is seen to rise at the equinox, or the corresponding point on the earth; that point of the horizon lying on the right hand when one's face is turned towards the north pole. By _the East_, in an indefinite sense, is often meant Syria, Arabia, Persia, India, and the eastern part of the world generally.

EASTBOURNE, a municipal borough and flourishing watering-place of England, county of Sussex, on the English Channel, near Beachy Head; also a parliamentary division of Sussex. The town is handsomely built, having fine parades and well-planted walks and drives. Pop. 52,544.

EAST CAPE, the most easterly point of Asia, projecting into Behring's Strait nearly opposite Cape Prince of Wales in Alaska.

EASTER, the festival commemorating the resurrection of Christ, observed in the Roman Catholic, the Greek, Anglican, Lutheran, and other branches of the Christian Church. By the first Christians it was considered to continue the feast of the _passover_, at which the paschal lamb, a type of Christ, was sacrificed. Hence its name in Greek (_pascha_), French (_p[^a]ques_), and other Romance languages is taken from the Hebrew _pesach_, passover. The English name, according to the Venerable Bede, comes from the Anglo-Saxon _Eostre_ (from Teutonic _Austr[=o]_), a goddess of light or spring, whose festival was celebrated in April. There was long a dispute in the Christian Church as to the proper time for holding Easter, the Christians of the East celebrating it on the same day as that on which the Jewish passover fell, that is, the 14th of Nisan (hence they were called _quarto decimani_), while the majority of the Church celebrated it on the Sunday next after this day. The controversy was decided by the Council of Nice (Nicaea) in 325, which settled that it was to be reckoned as at present, namely, that Easter is the first Sunday after the full moon which happens upon or next after the 21st of March; and if the full moon happens on a Sunday, Easter-day is the Sunday after, but, properly speaking, for the 'full moon' in the above the 'fourteenth day of the moon' should be substituted.--Cf. Sir J. G. Frazer, _The Golden Bough_.

EASTER DUES, or OFFERINGS, in the Church of England, certain dues paid to the parochial clergy by the parishioners at Easter as a compensation for the tithe for personal labour.

EASTER EGGS. The egg was anciently a symbol of the mother goddess and of birth: the sun emerged from the cosmic egg. The Saxon goddess Easter was a life-giver. On Easter Day, the day of Christ's resurrection, eggs (Pasche eggs) were dyed in symbolic colours, and boiled hard to be rolled or used in egg-breaking contests. The Jews have eggs at the Passover Feast.