Chapter XII: Part 12

Entrenchments may be either hasty or deliberate. Hasty entrenchments are those made on the actual field of battle: by the attackers, to secure the ground won prior to another bound forward; by the defenders, to hold up the attack pending fresh dispositions of troops in rear. The amount of digging that can be done is necessarily small; existing cover must be utilized to the utmost. This may consist of ditches, hedges, sunken roads, railway embankments and cuttings, buildings, woods, shell-holes, &c. All of these are readily convertible into strong defences. The test of battle has proved, over and over again, that troops well trained in adapting natural cover to defence are very difficult to dislodge, once they have dug themselves in. Deliberate entrenchments are employed in the gradual building up of a trench system when once the opportunity of manoeuvre has ceased to exist; or in the preparation of a defensive position somewhat remote from the scene of active operations.

The following are the salient features in the design of modern entrenchments: (1) A parapet 18 inches high, and upwards of 5 feet thick, in front of every fire-trench. (2) Longitudinal division of every trench, either by projecting buttresses of earth or by bends, so that no straight portion exceeds 10 yards in length. The effect of this is to give protection against flanking or enfilade rifle-fire, and to localize the burst of shell. (3) A parapet on the rear side (parados), to shield the defenders from the back-blast of shell which burst beyond the trench. (4) Wide trenches (6 feet at the top), to minimize the risk of men getting buried during bombardment. (5) Accommodation, in dug-outs and other refuges, for a proportion of the troops.

Arms of precision have, during the past twenty years, compelled careful attention to the concealment of entrenchments. Although systems of trenches cannot now be hidden from the eye of the aeroplane-camera, yet the enemy can be kept in doubt, by correct design and careful siting of trenches, as to the strength in which the various portions of a position are held. It is for this reason that the deep fire-trench, with a low parapet in front, has been universally adopted, despite the obvious objection that minor undulations restrict the field of fire because the rifle is brought nearer to the ground. Earthworks on a sky-line, or those seen by the enemy against a distant background, violate the first principles of siting.

Modern entrenchments are arranged in depth. The 'lines' of Wellington's time have given place to a broad belt of mutually supporting defences, organized in three zones. These merge imperceptibly into one another, and each zone extends upwards of a mile from front to rear. The foremost fringe of the outpost zone is in contact with the enemy; it is the high-water mark on which the troops advancing during the last action have come to a standstill and dug themselves in. Very lightly manned, as befits an area where heavy shelling is rife, this zone, nevertheless, plays an important r[^o]le. It harbours the forward artillery observation posts, which control and direct the fire of the guns in rear. It furnishes a 'jumping-off' place for attacks. It takes the first shock of a hostile attack, and, although not strong enough to repulse a serious offensive, contributes to the enemy's ultimate defeat by depriving his onslaught of momentum. The battle zone is more elaborately organized, and capable of being very heavily manned. Within this area the defence intend to bring to a standstill the most determined offensive. It lies sufficiently far back from the fringe of the outpost zone to be reasonably immune from destructive bombardment. Lying still farther back is the third zone, which serves for the accommodation of reserves of troops, and is also prepared for defence, as a last resort, in case the enemy should penetrate the battle zone.

ENTREP[^O]T ([.a][n.]-tr-p[=o]; Fr.), a port where foreign merchandise which cannot enter the interior of a country is deposited in magazines under the surveillance of the custom-house officers till it is re-exported; also, any place where goods are sent to be distributed wherever customers are found.

ENTRE RIOS (en'tre r[=e]'os; 'between rivers'), a province of the Argentine Republic, lying between the Uruguay and the Paran['a]; area estimated at 29,240 sq. miles; pop. 425,370. The province is largely pastoral. Capital, Paran['a], with a pop. of 25,000

ENTRO'PION is the inversion or turning in of the eyelid. It may be congenital, or arise as the result of some inflammatory process or burn of the conjunctiva. Entropion affecting the lower lid appears also as the result of extreme photophobia (intolerance to light).

ENTROPY, a term introduced into physics by Clausius as the name of one of the two important thermodynamical properties of a substance which depend on its 'state'. Suppose we have 1 lb. of water at atmospheric pressure and 212deg F., say, and suppose we apply heat to the water and change it into 1 lb. of steam at 212deg F. The temperature does not change during this process, while the heat which must be added is the latent heat of the steam, namely, about 960 British Thermal Units. The increase of entropy from the first state to the second state is got by dividing the heat given to the substance, namely, 960 B.Th.U., by the absolute temperature at which that heat was given to the substance, namely, 461 + 212 = 673 degrees absolute, i.e. the increase of entropy is 960/673 = 1.43 units. If the temperature changes with the addition of heat, as it would usually do, we have to imagine the heat to be supplied in small quantities, and to take the average temperature of the body at which these tiny quantities of heat are supplied. The quotient heat / temperature is taken for each small quantity of heat, and the results are added together. The summation is defined as the increase in entropy between the initial and the final states.

In mathematical language the increase in entropy between state A and state B is given by ([phi]_B - [phi]_A) = Integral[dQ/T] from A to B, where [phi] stands for the entropy, Q for the heat received by the body, and T for the absolute temperature at which the heat is received. The importance of the entropy function, namely, the integral Integral[dQ/T], in thermodynamics is due to the fact that it is, like the internal energy of the substance, a function of the state of the substance only, and consequently in any temperature cyclic change in which the final state of the substance is the same as its initial state A, the total change, either of its internal energy or of its entropy, is zero. The fact that the total change in the internal energy of the substance is zero is practically equivalent to the _First Law of Thermodynamics_, while the fact that the total change of the entropy of the substance is zero is equivalent to the _Second Law of Thermodynamics_.--BIBLIOGRAPHY: J. H. Poynting and J. J. Thomson, _Textbook of Physics_ (vol. 3): _Heat._

EN'VELOPES, the paper covers that enclose letters or notes. They became common shortly after the introduction of the penny postage system; were at first made chiefly by hand, but are now not only shaped, but folded and gummed, by machinery.

ENVER PASHA, Turkish soldier and politician, born at Constantinople in 1879. He entered the Turkish army in 1896, and in 1905 took part in the Young Turk movement at Salonica. He joined the revolutionaries in 1908, was for a short time military attach['e] in Berlin, but in 1909 returned to Salonica, and assisted in the deposition of Sultan Abdul Hamid. He then took part in the Tripoli War and the second Balkan War, and recaptured Adrianople from the Bulgarians in July, 1913. After being Minister of War, Enver subsequently became one of the leaders of the Committee of Union and Progress. A staunch pro-German, he was to a great extent responsible for Turkey's entry into the European War as an ally of Germany. After the armistice of 1918, Enver Pasha fled to the Caucasus, and was active in inciting his countrymen to resist the terms of the Peace Treaty of 1920.

ENVIRONMENT, in biology, the surroundings of an organism, including non-living factors, such as climate and weather; and also other organisms. Plants and animals are more or less adapted to their surroundings, a good example being the mutual adaptations of flowers and insects, but there has been much controversy as to the way in which such adaptations have come about. Among all but unicellular organisms any individual consists of (1) a general body (_soma_), by which the life of the individual is maintained, and (2) germ cells, capable of becoming fresh individuals, and thus providing for the continuance of the species. According to a school of thought founded by some of the pre-Darwinian evolutionists, notably Buffon, Lamarck, and Treviranus, modifications of the soma (acquired characters) of an individual, brought about by the action of the environment (e.g. thickening of parts of the skin as the result of constant pressure), or by use and disuse (e.g. increased size of muscles; diminished wings of poultry), can be inherited, leading to increasing alteration capable of ending in the production of new species. Most living biologists, however, hold with Weismann that only _germinal variations_, i.e. variations in the substances of the germ-cells, are heritable. Much further research is necessary before it is possible to pronounce with certainty on many of the complex details involved in these theories. As to the part played by the environment, cases are known where this acts directly on the germ-cells, so as to influence their variation. But these are among some of the lower animals, in which the eggs develop outside the body of the parent, and we know hardly anything about the action of the environment on germs that develop internally. It has been suggested that modifications of the soma undoubtedly brought about by the influence of the surroundings may react upon the germ-cells and cause these to vary, but of this no proof has so far been forthcoming. Even if we admit that modifications of the soma are not inherited, they may nevertheless play a part in evolution by aiding the development of germinal variations that take the same direction. The whole subject is one of more than academic interest, especially in regard to the further evolution of human beings. Comparatively rapid advance, either in desirable or undesirable directions, would be possible if modifications acquired by the soma of an individual were capable of being inherited. So far as we know at present, acquired improvements in physique and mentality of individuals are not inherited by their offspring, which seems rather disappointing, but, on the other hand, undesirable modifications, including those due to disease, appear to be in the same case, and there is little reason to think that the children of parents possessing undesirable acquired characters are unduly handicapped from the very start. We must, of course, exclude cases of antenatal infection by the microbes of certain infectious or contagious diseases to which one or both parents have fallen victims, and also those of direct poisoning of germ-cells as the result of alcoholism.

EN'VOY, a person deputed by a Government to negotiate a treaty,or transact other business, with a foreign Government. We usually apply the word to a public minister sent for one particular purpose; hence an _envoy_ is distinguished from an _ambassador_, and is of inferior rank.

ENZYMES. See _Fermentation_, _Physiological Chemistry_.

E'OCENE, in geology, a term applied to the lower division of the Tertiary strata, from Gr. [=e][=o]s, dawn, and _kainos_, recent, because remains of existing organic species first occur here. The Eocene beds are arranged in two groups, termed the Lower and Upper Eocene; the strata formerly called Upper Eocene being now known as Oligocene. They consist of marls, limestones, clays, and sandstones, and are found in the Isle of Wight and in the south-east of England and north-west of France, in Central Europe, Western Asia, Northern Africa, and the Atlantic coast of North America.

['E]ON DE BEAUMONT. See _D'['E]on de Beaumont_.

E'OS, among the ancient Greeks the goddess of the dawn. See _Aurora_.

E[:O]TV[:O]S (eut'veush), Baron Joseph, a Hungarian statesman and author, born 1813, died 1871. He completed his studies at the University of Pesth in 1831. He had already, before leaving the university, produced three dramas--_The Critics_, _The Wedding_, and _Revenge_--the last a tragedy, all of which were well received. He became a friend of Kossuth, and distinguished himself as a journalist and orator of the popular party. In 1848, after the revolution of 15th March, he was appointed Minister of Public Instruction, resigned the same year, but was again appointed Minister of Public Instruction in 1867, and filled this office until his death. Among his works are the novels: _The Carthusian_, _The Village Notary_ (translated into English), and _Hungary in 1514_--giving vivid pictures of Hungarian life in modern and more remote epochs.

EOZO'IC ROCKS, the name given to the pre-Cambrian rocks, from their containing the first or earliest traces of life in the stratified systems.

EOZO'ON, a supposed gigantic fossil foraminifer found in the limestone of the pre-Cambrian rocks of Canada, whence the name _Eozo[:o]n canadense_. The structure, however, which is recognized also in Bavaria and in County Galway, has proved to be due to a zonal development of serpentine during metamorphism of the ancient limestones concerned. A similar structure occurs in limestone associated with the volcanic focus of Vesuvius.

EP'ACRIS, a genus of gamopetalous Dicotyledons, the typical genus of the nat. ord. Epacridaceae, distinguished by having a coloured calyx with many bracts, a tubular corolla with smooth limb, stamens affixed to the corolla, and a five-valved many-seeded capsule. The species are shrubby plants, with axillary, white, red, or purple flowers, generally in leafy spikes. Among those cultivated in Britain we may mention _E. grandifl[=o]ra_, which has flowers nearly an inch in length, of a brilliant reddish purple at the base and pure white at the apex. The order Epacridaceae consists of plants allied to the heaths, chiefly natives of Australia. The fruit of some species is eaten under the name of Australian cranberry, and they are cultivated in greenhouses for their flowers.

EP'ACT (Gr. _epaktos_, added), in chronology, the excess of the solar month above the lunar synodical month, and of the solar year above the lunar year of twelve synodical months. The epacts then are _annual_ and _menstrual_ or _monthly_. Suppose the new moon to be on the 1st of January: the month of January containing 31 days, and the lunar month only 29 days, 12 hours, 44 minutes, 3 seconds; the difference, 1 day, 11 hours, 15 minutes, 57 seconds, is the _menstrual epact_. The _annual epact_ is nearly 11 days; the solar year being 365 days, and the lunar year 354. The epacts were once of some importance in ecclesiastical chronology, being used for finding when Easter would fall.

EPAMINON'DAS, an ancient Greek statesman and general, who, for a short time, raised his country, Thebes, to the summit of power and prosperity. He was born about 418 B.C., and killed at the battle of Mantinea, 362 B.C. He took the leading part in the struggle during which Spartan supremacy in Greece was destroyed, and the supremacy of Thebes temporarily secured. Four times he successfully invaded the Peloponnesus at the head of the Thebans, but after his death Thebes soon sank to her former secondary condition. Throughout life Epaminondas was distinguished for the friendship subsisting between him and Pelopidas, with whom he served in the Spartan campaign, 385 B.C. His character is one of the finest recorded in Greek history. and his virtues have been praised by both Xenophon and Plutarch.

EPARCH (ep'[:a]rk), in Greece, the governor or prefect of a provincial division called an _eparchy_, a subdivision of a nomarchy or province of the kingdom. In Russia, an eparchy is the diocese or arch-diocese of a bishop or archbishop of the Greek Church.

EPAULEMENT (e-p[a:]l'ment: Fr. _['e]paule_, shoulder), in fortification, a term for the mass of earth or other material which protects the guns in a battery in front and on either flank.

EP'AULET, OR EP'AULETTE (Fr. _['e]paulette_, dim. of _['e]paule_, the shoulder), an ornamental shoulder-piece belonging to a military or other dress. Epaulettes were worn in the British army till 1855, and in the United States as late as 1872, and are still worn in the navy by all officers of and above the rank of lieutenant, and by some civil officers.

['E]P['E]E ([.e]-p[=a]), Charles Michel, Abb['e] de l', French philanthropist, born in 1712, died 1789. He had chosen the clerical profession, but had to leave the Church on account of Jansenist opinions. The great object of his life was the instruction of the deaf and dumb, upon whom he spent his whole income, besides what was contributed by benevolent patrons. In 1770 he founded at his own expense an institution for the deaf and dumb. He left several works on his method of instruction, one of these being _Institution des sourds et muets_ (1774).

['E]P['E]HY, a town of France, department of Somme, about 13 miles S.E. of Cambrai. It was the scene of fierce fighting during the European War, and was captured by the British in Sept., 1918.

EPEIRA (e-p[=i]'ra), a genus of spiders, comprising the largest and best-known British species. _E. diad[=e]ma_, the common garden spider, is a handsomely marked species, which constructs a beautifully symmetrical wheel-shaped web.

EPERIES (ep'er-y[=a]sh), a town of Czecho-Slovakia, formerly in Hungary, on the Tarcza, the seat of a Greek Catholic bishop. Pop. 16,323.

['E]PERNAY (ep-er-n[=a]; ancient SPARNACUM, and the Roman AQUAE PERENNES), a town of North-Eastern France, department of Marne, on the Marne, the central depot of the wine trade of Champagne. The vast wine-cellars of the town form a labyrinth of galleries cut in the tufa or calcareous soil of the district. ['E]pernay was occupied for a short time by the Germans at the beginning of the European War, and was one of the enemy's objectives in the second battle of the Marne (July, 1918). Pop. 21,811.

E'PHAH, or BATH, a Hebrew measure of capacity, containing, according to one estimate or calculation, 8.6696 gallons; according to another, only 4.4286 gallons.

EPHEDRA, the principal genus of the Gnetales family of Gymnosperms. The species are shrubby switch-plants, natives of the warm temperate zone, found especially on sandy soil. The ripe seeding cones have fleshy scales, and those of _E. distachya_ are eaten in South Russia.

EPHEM'ERA, the typical genus of the neuropterous insects constituting the family Ephemeridae, so named from the extreme shortness of their lives in the perfect state. They are known as _may-flies_ or _day-flies_, and are characterized by the slenderness of their bodies; the delicacy of their wings, which are erect and unequal, the anterior being much the larger; the rudimentary condition of the mouth; and the termination of the abdomen in three filiform appendages. In the state of larvae and pupae they are aquatic and exist for years. When ready for their final change, they creep out of the water, generally towards sunset of a fine summer evening, beginning to be seen generally in May. They shed their whole skin shortly after leaving the water, propagate their species, and die, taking no food in the perfect state. The may-fly is well known to anglers, who imitate it for bait.

EPHE'SIANS, THE EPISTLE TO THE, a canonical epistle addressed by the Apostle Paul to the Church which he had founded at Ephesus. It was written during his first captivity at Rome, immediately after he had written the _Epistle to the Colossians_ (A.D. 62); and was sent by the hands of Tychicus, who also bore the message to the Church at Colossae.

EPH'ESUS, an ancient Greek city of Lydia, in Asia Minor, one of the twelve Ionian cities, on the south side of the Caystrus, near its mouth. It was at one time the grand emporium of Western Asia, having a convenient and spacious harbour. The Apostle Paul visited Ephesus and established a Christian Church there, to which he dedicated one of his Epistles. It was famous for its temple of Artemis (Diana), called _Artemision_, the largest and most perfect model of Ionic architecture, and reckoned one of the seven wonders of the world. The first great temple, begun about 650 B.C. and finished after 120 years, was burnt by the notorious Herostratus in order to perpetuate his name, 356 B.C. (the night of Alexander the Great's birth). A second and more magnificent was then erected, which was burned by the Goths in A.D. 262. Some interesting remains have been discovered by excavation since 1896. Several Church councils were held here, especially the Third Ecumenical Council of 431, at which Nestorius was condemned. The site of the city is now desolate; near it is a poor village, Aiasoluk.

EPH'OD, a species of vestment worn by the Jewish high-priest over the second tunic. It consisted of two main pieces, one covering the back, the other the breast and upper part of the body, fastened together on the shoulders by two onyx stones set in gold, on each of which were engraved the names of six tribes according to their order. A girdle or band, of one piece with the ephod, fastened it to the body. Just above the girdle, in the middle of the ephod, and joined to it by little gold chains, rested the square breastplate with the Urim and Thummim. The ephod was originally intended to be worn by the high-priest exclusively, but a similar vestment of an inferior material seems to have been in common use in later times among the ordinary priests.

EPH'ORS, or EPH'ORI (Gr. _ephoroi_, overseers), magistrates common to many Dorian communities of ancient Greece, of whom the most celebrated were the Ephori of Sparta. They were five in number, were elected annually, and both the judicial authority and the executive power were almost entirely in their hands. Their power became an intolerable burden, especially to the kings, and in 225 B.C. Cleomenes III murdered the whole college and abolished the office.

E'PHRAEM SYRUS, that is, 'Ephraim the Syrian', writer of the Syrian Church, born at Nisibis, in Mesopotamia, about A.D. 306, died at Edessa in 373 or 378. He wrote several commentaries on Scripture, numerous homilies, and other works (as well as hymns), which have come down to us partly in Syriac, partly in Greek, Latin, and Armenian translations. They were edited by Assemani at Rome between 1732 and 1746, and by Overbeck at Oxford in 1865.

E'PHRAIM, the younger son of Joseph, and the founder of one of the twelve tribes of Israel. When the Israelites left Egypt, the Ephraimites numbered 40,500, and their possessions in the very centre of Palestine included most of what was afterwards called Samaria. Ephraim is also a town mentioned in _John_, xi, 54, and to which Jesus retired after His raising of Lazarus, when the Jewish authorities manifested their hostility against Him.

EP'IC, a poem of the narrative kind, dealing with a series of events or actions of permanent interest. Some authorities restrict the term to narrative poems written in a lofty style and describing the exploits of heroes. Others widen the definition so as to include not only long narrative poems of romantic or supernatural adventure, but also those of an historical, legendary, mock-heroic, or humorous character. Epic poetry is distinguished from drama in so far as the author frequently speaks in his own person as narrator; and from lyrical poetry by making the predominant feature the narration of action rather than the expression of emotion. Among the more famous epics of the world's literature may be noted: Homer's _Iliad_ and _Odyssey_, Virgil's _Aeneid_, the German _Nibelungenlied_, the Anglo-Saxon poem of _Beowulf_, the French _Song of Roland_, Dante's _Divina Commedia_, Tasso's _Gerusalemme Liberata_, Ariosto's _Orlando Furioso_, Milton's _Paradise Lost_, Spenser's _Faerie Queene_, Camoens' _Lusiads_ (Portuguese), and Firdusi's _Shah Namah_ (Persian). Hesiod's _Theogony_, the _Elder Edda_, the Finnish _Kalevala_, and the Indian _Mah[^a]bh[^a]rata_ may be described as collections of epic legends. The historical epic has an excellent representative in Barbour's _Bruce_; and specimens of the mock-heroic and humorous epic are found in _The Battle of the Frogs and Mice_, _Reynard the Fox_, Butler's _Hudibras_, and Pope's _Rape of the Lock_.--BIBLIOGRAPHY: Chassang and Marcou, _Les Chefs-d'oeuvre ['e]piques de tous les peuples_; W. M. Dixon, _English Epic and Heroic Poetry_; A. Lang, _Homer and the Epic_.

EPICHARMUS (ep-i-k[:a]r'mus), a Sicilian comic poet and philosopher of the Pythagorean school, born in the Island of Cos about 540 B.C., died 450 B.C. He removed to Syracuse, where at the court of Hieron he spent the remainder of his life. He is credited with the invention of written comedy, and Plato called him "a master of the comic type".

EPICTE'TUS, a Greek Stoic philosopher, born at Hierapolis, in Phrygia, about A.D. 60. He lived long at Rome, where, in his youth, he was a slave. Though nominally a Stoic, he was not interested in Stoicism as an intellectual system; he adopted its terminology and its moral doctrines, but in his discourses he appeared rather as a moral and religious teacher than as a philosopher. His doctrines approach more nearly to Christianity than those of any of the earlier Stoics, and although there is no trace in what is recorded of them of his having been directly acquainted with Christianity, it is at least probable that the ideas diffused by Christian teachers may have indirectly influenced them. The excellence of his system was universally acknowledged. When Domitian banished the philosophers from Rome (A.D. 94), Epictetus retired to Epirus, where he is supposed to have died. His disciple Arrian collected his opinions, which are preserved in two treatises called the _Discourses of Epictetus_, and the _Manual or Enchiridion_.

EPICU'RUS, a Greek philosopher, founder of the Epicurean school, was born in the Island of Samos 342 B.C., died at Athens 270 B.C. He settled at Athens 306 B.C., and purchased a garden in a favourable situation, where he established a philosophical school. Here he spent the remainder of his life, living in a simple manner and taking no part in public affairs. His pupils were numerous and enthusiastically devoted to him. His theory of the universe was based on the atomic theory of Democritus. The fundamental principle of his ethical system was that pleasure and pain are the chief good and evil, the attainment of the one and the avoidance of the other of which are to be regarded as the end of philosophy. The term 'Epicurean' has come to signify one who is indulging his sensual appetites without measure, but this is really due to a misapprehension of the meaning of the word pleasure as used by the philosopher. Epicurus himself was not an 'Epicurean' in this sense, for he endeavoured to give a moral tendency to this doctrine. He exalted the pure and noble enjoyments derived from virtue, to which he attributed an imperishable existence, as incalculably superior to the passing pleasures which disturb the peace of mind, the highest good, and are therefore detrimental to happiness. Peace of mind, based on meditation, he considered as the origin of all good. It is, however, easy to see that his use of the word 'pleasure' was calculated to produce the mischievous results with which Epicureanism has been charged. The philosophy of Epicurus has, therefore, been violently opposed and frequently misrepresented; but while it is not open to the charges of gross sensualism which have been brought against it, it cannot be considered as much better than a refinement of sensualism. In ancient times his philosophy appears to have been more popular in Greece than in Rome, although his disciples were numerous in both, and the Latin poem of Lucretius, _De Rerum Natura_, is a poetical exposition of his doctrines. Epicureanism was resuscitated in France by Pierre Gassendi, and its principles have been professed by De la Rochefoucauld, Rousseau, and Voltaire. Epicurus was a very voluminous writer, but few of his writings are extant, what we possess comprising only some fragments of a _Treatise on Nature_, two letters, and detached passages. Lucretius, Cicero, Pliny, and Diogenes Laertius are our chief authorities for his doctrines.--BIBLIOGRAPHY: Lange, _History of Materialism_; W. Wallace, _Epicureanism_; Guyau, _La Morale d'Epicure_; Taylor, _Epicurus_; W. Pater, _Marius the Epicurean_.

EP'ICYCLE, a conception of the ancient astronomy used to explain the irregular, and at times retrograde, motions of the planets. Corresponding to each planet there was supposed to be a circle called a _deferent_, which had the earth as its centre. Round this circle a point was imagined to revolve with uniform motion. That point formed the centre of a second and smaller circle, called an epicycle, and the actual planet was supposed to revolve with uniform motion round the circumference of the epicycle.

EPICY'CLOID, in geometry, a curve generated by a point on the circumference of a circle which rolls on the convex side of another fixed curve. The curve generated by rolling on the concave side is called a 'hypocycloid'. If the point is not on the circumference, the generated curves are called 'trochoids'.

EPICYCLOI'DAL WHEEL, a wheel or ring fixed to a framework, toothed on its inner side, and having in gear with it another toothed wheel of half the diameter of the first, fitted so as to revolve about the centre of the latter. It is used for converting circular into alternate motion, or alternate into circular. While the revolution of the smaller wheel is taking place, any point whatever on its circumference will describe a straight line, or will pass and repass through a diameter of the circle, once during each revolution. In practice, a piston-rod or other reciprocating part may be attached to any point on the circumference of the smaller wheel.

EPIDAU'RUS, a town and seaport of ancient Greece, situated in Argolis, in the Peloponnesus, particularly celebrated for its magnificent temple of Aesculapius, which stood on an eminence not far from the town. It had also temples of Artemis, Dionysus, Aphrodite, and Hera, and a splendid theatre still in fair preservation. The site is now occupied by the village _Epidavro_, where a congress met in 1822 and promulgated the 'Constitution of Epidaurus'.

EPIDEM'IC, or EPIDEMIC DISEASE (Gr. _epi_, upon, and _d[=e]mos_, people), signifies a disease which attacks a people, suddenly spreading from one to the other in all directions, prevailing a certain time and then dying away. It usually travels from place to place in the direction of the most-frequented lines of communication. The reason is that such diseases are commonly due to some infective material capable of being conveyed from one individual to another, and of being transported from place to place. In Britain smallpox and cholera are occasionally epidemic, whilst scarlet fever, measles, chickenpox, diphtheria, typhoid fever, &c., are almost invariably so. Certain diseases which appear to be more mental than physical sometimes occur so numerously as to assume an epidemic form, such as St. Vitus's dance, convulsionary diseases, or suicidal mania.

EPIDEN'DRUM (Gr. _epi_, upon, and _dendron_, a tree), a large genus of tropical American orchids, most of the species of which are epiphytic, growing on trees. The flowers are very handsome, and a large number of the species are in cultivation.

EPIDER'MIS, in anatomy, the cuticle or scarf-skin of the body; a thin membrane covering the true skin of animals, consisting of two layers, an inner or mucous layer, called the _rete mucosum_, composed of active cells containing granules of colouring matter, and an outer or horny layer, consisting of flattened scale-like cells, dry, inactive, and effete, which are constantly being shed in the form of dust. Both layers are destitute of blood-vessels or nerves.

_st_, Stomata.]

EPIDERMIS, in botany, the superficial layer of cells covering leaves and young stems. Its principal function is to restrict transpiration, for which purpose its outer wall is more or less cutinized, i.e. chemically modified so as to be very impervious to water and gases, especially the outermost part thereof, the so-called _cuticle_. Naturally both cuticle and epidermis as a whole are most strongly developed in drought-adapted plants or xerophytes (q.v.); and conversely the epidermis of submerged plants is not cutinized, nor is the superficial layer of ordinary roots. The epidermis frequently bears hairs of various kinds. Stems which undergo secondary growth in thickness soon cast off their epidermis, its r[^o]le being assumed by cork or bark. The water- and gas-proof covering provided by the epidermis is not continuous, but is interrupted by numerous minute pores or _stomata_, capable of opening and closing, through which accordingly a regulated interchange of gases takes place.

EP'IDOTE, a mineral of a green or grey colour, vitreous lustre, and partial transparency, a member of the garnet family. The primary form of the crystals is a right rhomboidal prism. The crystals occur in Norway, Siberia, Tyrol, and the United States.

EPIGAEA (-j[=e]'a), a genus of Ericaceous shrubs. _E. repens_, the trailing arbutus, is the May-flower of North America.

EPIGLOTTIS is a cartilaginous plate behind the tongue, which covers the glottis like a lid during the act of swallowing, and thus prevents foreign bodies from entering the larynx. In its ordinary position during respiration it is pointed upwards, but in the act of swallowing it is pressed downwards and backwards by the drawing up of the windpipe beneath the base of the tongue, and thus closes the entrance to the air-passages. See _Larynx_.

EP'IGRAM (Gr. _epi_, upon, _graphein_, to write), in a restricted sense, a short poem or piece in verse, which has only one subject, and finishes by a witty or ingenious turn of thought; in a general sense, a pointed or witty and antithetical saying. The term was originally given by the Greeks to a poetical inscription placed upon a tomb or public monument, and was afterwards extended to every little piece of verse expressing with precision a delicate or ingenious thought, as the pieces in the _Greek Anthology_. In Roman classical poetry the term was somewhat indiscriminately used, but the epigrams of Martial contain a great number with the modern epigrammatic character. Epigrams flourished in modern times after the Revival of Learning period, and all the Elizabethan versifiers tried their hand at them. Pope was a great master of the epigram, and the art was practised by Cl['e]ment Marot, Boileau, Voltaire, Schiller, Goethe, Byron, and Moore, and more recently by Sir William Watson.--Cf. Dodd, _Epigrammatists of Mediaeval and Modern Times_.

EPIGRAPHY, a term used both for the study of inscriptions as a whole, and for the science which deals with their classification and decipherment. The attention of the epigraphist is given to inscriptions upon stone, brick, metal, and other comparatively permanent material, as compared with writings upon parchment, papyrus, or paper; but he excludes inscriptions upon coins, which are in the department of the numismatist. The science of epigraphy is of immense importance for a knowledge of the past, the subject including inscriptions so far apart in point of time as Egyptian records of the days of Mena (4700 B.C.), and the Greek hexameters that commemorate the death in Westmorland of a young Syrian soldier in the army of Septimius Severus. Of still more recent date are the Runic inscriptions discovered in Greenland, which seem to place beyond a doubt the fact of Icelandic explorers having reached that country in the eleventh or twelfth century. The most important inscriptions are Egyptian, Cuneiform (Babylonian and Assyrian), Semitic, Greek, Latin, Indian, and Runic. The inscribed writings include epitaphs on the dead, records of important events, dedications of public buildings, with such comparatively private matters as receipts, contracts, and other business transactions. While inscriptions form a valuable source of knowledge, they cannot be accepted as invariably reliable. Reasons might in some cases exist for making a false or misleading record, as in the case of a eulogistic tombstone, while mistakes in spelling and other details may be due to a careless workman. The literature which deals with the science of epigraphy is very large.

R, Receptacle. K, Calyx. C, Corolla. A, Androecium. D, Disc. O, Ovule.]

EPIGYNOUS (e-pij'i-nus) FLOWERS, those in which the gynaecium is _inferior_, i.e. embedded in, and adherent to, the hollowed-out receptacle, so that the other parts of the flower appear to be inserted on the top of the ovary.

EP'ILEPSY (Gr. _epil[=e]psia_, literally, a seizure), a nervous disease, the falling-sickness, so called because the patient falls suddenly to the ground. It depends on various causes, often exceedingly complicated and incapable of being removed; hence it is often an incurable periodical disease, appearing in single paroxysms. In its fully developed form, convulsions, attended by complete unconsciousness, are the prominent feature. Among the different causes may be mentioned intense emotional disturbance in early childhood, injury to the brain or its coverings at birth or subsequently, or some irritation within the skull itself, such as tumours, &c., developing later in life. Epileptiform fits due to the last-mentioned cause differ from those of true epilepsy, and are known as _Jacksonian epilepsy_ (cf. Sir W. K. Gowers, _The Borderland of Epilepsy_). It is, for the most part, preceded by a tingling sensation, creeping up from the foot or hand to the breast and head, or some other premonitory symptom such as spectral illusions, headache, giddiness, confusion of thought, sense of fear, &c.; but sometimes there are no precursive symptoms. During the paroxysm all that is to be attended to is to prevent the patient from injuring himself; and this is to be accomplished by raising the head gently and loosening all tight parts of the dress. It is advisable to protect the tongue from being bitten by introducing a piece of india-rubber, cork, or soft wood between the teeth.

EPILO'BIUM, the willow-herbs, a genus of plants, nat. ord. Onagraceae. The species are herbs or under-shrubs with pink or purple, rarely yellow, flowers, solitary in the axils of the leaves or in terminal leafy spikes. The seeds are tipped with a pencil of silky hairs, and are contained in a long four-celled capsule. There are more than fifty species scattered over the arctic and temperate regions of the world, ten of them being natives of Britain.

EPIMEN'IDES (-d[=e]z), an ancient Greek philosopher and poet, born in Crete in the seventh century before Christ, he was held for an infallible prophet, and by some is reckoned among the seven wise men, instead of Periander. He is supposed to be the prophet referred to by St. Paul in _Titus_, i, 12: "One of themselves, even a prophet of their own, said, The Cretians are alway liars, evil beasts, slow bellies".

EPIMETHEUS (ep-i-m[=e]'th[=u]s), in Greek mythology, the son of Iapetus, brother of Prometheus, and husband of Pandora. Epimetheus may be translated 'afterthought', as Prometheus 'forethought'.

['E]PINAL, a town of Eastern France, capital of the department of the Vosges, on the Moselle. It is well built and has handsome quays, an ancient Gothic church, a communal college, a public library of 30,000 volumes, a museum, and extensive fortifications. The town was occupied by the Germans in the Franco-Prussian War of 1870, and since that time a modern fortress has been constructed. The manufactures consist of articles in metal, cottons, linens, woollens, earthenware, and leather. The famous paper-mills of Archettes are in the vicinity. Pop. 30,000.

['E]PINAY, Louise Florence P['e]tronille, Madame d', French authoress, born in 1726, died 1783. She became the wife of M. Delalive d'['E]pinay, who was collector-general of taxes. In 1748 she became acquainted with Rousseau, and gave him a cottage in which he passed many of his days. She was the author of _Les Conversations d'['E]milie_, a companion-volume to Rousseau's _['E]mile; Lettres [`a] mon Fils_; and _Mes Moments heureux_. She left interesting memoirs and correspondence.

EPIPHA'NIUS, ST., was born in Palestine about 310, died 403. About 367 he was consecrated Bishop of Salamis or Constantia, in Cyprus. A zealous denouncer of heresy, he combated the opinions of Arius and Origen. His work _Panarion_ gives the history, together with the refutation, of a great number of heresies. His festival is on the 12th of May.

EPIPH'ANY (Gr. _epiphaneia_, a manifestation or showing forth), a festival, otherwise called the _manifestation of Christ to the Gentiles_, observed on the 6th of January in honour of the adoration of our Saviour by the three Magi, or wise men, who came to adore him and bring him presents, led by the star. As a separate festival it dates from 813.

EP'IPHYTE (Gr. _epi_, on, _phyton_, a plant), a plant which grows and flourishes on the trunks and branches of trees, adhering to the bark, as a moss, lichen, fern, &c., but which does not, like a parasite, derive any nourishment from the plant on which it grows. Most orchids are epiphytes, and so are many Bromeliaceae and Cactaceae. Epiphytic Angiosperms are characteristic of humid tropical regions. Depending as they do entirely on atmospheric moisture, they show many curious adaptations, and are nearly always more or less xerophytic in structure.

EPI'RUS (Gr. _Epeiros_), a country of ancient Greece corresponding to Southern Albania and the north-western division of modern Greece. The most interesting locality in it was Dodona. The inhabitants were only in part Greeks. The Molossians at last acquired the ascendancy, and the kings of this tribe took the name of kings of Epirus. The most celebrated King of Epirus was Pyrrhus, who made war upon the Romans. Epirus became a Roman province in 168 B.C., and shared the fortunes of Rome till it was conquered by the Turks. The population is about 250,000. In Nov., 1914, Greece, with the consent of the Great Powers, occupied North Epirus, and formally took possession of it in March, 1916. By the end of 1920, however, the occupation had not yet been recognized.--Epirus is also the name of an administrative province of Greece, formed after the Balkan campaigns (1912-3) out of the territory acquired by the country.

EPISTEMOL'OGY (Gr. _epist[=e]m[=e]_, knowledge), that department of metaphysics which investigates and explains the doctrine or theory of knowing. It deals with the validity of knowledge rather than with the analysis of the knowing mind, and is thus distinguished from _psychology_. It is also distinguished from _ontology_, which investigates real existence or the theory of being.

EPIS'TOLAE OBSCURO'RUM VIRO'RUM (_Letters of Obscure Men_), the title of a collection of satirical letters which appeared in Germany in 1515, and professed to be the composition of certain ecclesiastics and professors in Cologne and other places. It is considered as one of the most masterly pieces of sarcasm in the history of literature, and its importance is enhanced by the effect it had in promoting the cause of the Reformation. The authorship of this satire has been a fertile subject of controversy, and is yet apparently far from being settled. It was ascribed to Reuchlin, and afterwards to Reuchlin, Erasmus, and Hutten. By a Papal bull the work was placed on the Index of forbidden books.

EP'ITAPH (Gr. _epi_, upon, and _taphos_, tomb), an inscription upon a tomb or monument in honour or memory of the dead. Epitaphs were in use both among the Greeks and Romans. The Greeks distinguished by epitaphs only their illustrious men. Among the Romans they became a family institution, and private names were regularly recorded upon tombstones. The same practice has generally prevailed in Christian countries. On Christian tombstones epitaphs usually give brief facts of the deceased's life, sometimes also the pious hopes of survivors in reference to the resurrection or other doctrines of the Christian faith, &c. Many so-called epitaphs are mere witty _jeux d'esprit_, which might be described as epigrams, and which were never intended seriously for monumental inscriptions. Dr. Johnson and William Wordsworth wrote essays on epitaphs.--Cf. Andrews, _Curious Epitaphs_.

EPITHALAMIUM (Gr. _epi_, on, and _thalamos_, a chamber), a nuptial song or poem in praise of a bride and bridegroom. Among the Greeks and Romans it was sung by young men and maids at the door of the bridal chamber of a newly-married couple. Epithalamia have been written by Spenser, Ben Jonson, and Donne.

EPITHE'LIUM, in anatomy, the cellular layer which lines the internal cavities and canals of the body, both closed and open, as the mouth, nose, respiratory organs, blood-vessels, &c., and which is analogous to the cuticle of the outer surface. There are several varieties of epithelium. The epithelium lining the blood-vessels is called sometimes _endothelium_.

EPIZO'A, a term applied to those parasitic animals which live upon the bodies of other animals, as lice, the itch-mite, &c.

EPIZO[:O]T'IC, or EPIZO[:O]TIC DISEASE, a disease that at some particular time and place attacks great numbers of the lower animals just as an epidemic attacks man. Pleuro-pneumonia is often an epizo[:o]tic, as is also the rinderpest.

EPOCH, or ERA, is a fixed point of time, commonly selected on account of some remarkable event by which it has been distinguished, and which is made the beginning or determining point of a particular year from which all other years, whether preceding or ensuing, are computed. The creation and the birth of Christ are the most important of the historical epochs. The creation has formed the foundation of various chronologies, the chief of which are: (1) The epoch adopted by Bossuet, Ussher, and other Catholic and Protestant divines, which places the creation in 4004 B.C. (2) The _Era of Constantinople_ (adopted by Russia), which places it in 5508 B.C. (3) The _Era of Antioch_, used till A.D. 284, placed the creation 5502 B.C. (4) The _Era of Alexandria_, which made the creation 5492 B.C. This is also the _Abyssinian Era_. (5) The _Jewish Era_, which places the creation in 3760 B.C. The Greeks computed their time by periods of four years, called _Olympiads_, from the occurrence every fourth year of the Olympic games. The first Olympiad, being the year in which Coroebus was victor in the Olympic games, was in the year 776 B.C. The Romans dated from the supposed era of the foundation of their city (Ab Urbe Condita, A.U.C.), the 21st of April, in the third year of the sixth Olympiad, or 753 B.C. (according to some authorities, 752 B.C.). The _Christian Era_, or mode of computing from the birth of Christ as a starting-point, was first introduced in the sixth century, and was generally adopted by the year 1000. This event is believed to have taken place earlier, perhaps by four years, than the received date. The Julian epoch, based on the coincidence of the solar, lunar, and indictional periods, is fixed at 4713 B.C., and is the only epoch established on an astronomical basis. The _Mohammedan Era_, or _Hej[)i]ra_, commences on 16th July, 622, and the years are computed by lunar months. The Chinese reckon their time by cycles of 60 years. Instead of numbering them as we do, they give a different name to every year in the cycle.

EPPING, a village of England, in Essex (giving name to a parliamentary division), 17 miles from London, in the midst of an ancient royal forest which one time covered nearly the whole of Essex. The unenclosed portion (5600 acres) was bought by the Corporation of London in 1882, and secured to the public as a free place of recreation. Pop. 4253.

EPSOM, a town in the county of Surrey, England, 15 miles S.W. of London, formerly celebrated for a mineral spring, from the water of which the well-known Epsom salts were manufactured. The principal attraction Epsom can now boast of is the grand race-meeting held on the Downs, the chief races being the Derby and Oaks. Epsom gives name to one of the seven parliamentary divisions of the county. Pop. 19,156.

EPSOM SALTS, sulphate of magnesium (MgSO_47H_2O), a cathartic salt which appears in capillary fibres or acicular crystals. It is found covering crevices of rocks, in mineral springs, &c.; but is commonly prepared by artificial processes from magnesian limestone by treating it with sulphuric acid, or by dissolving the mineral _kieserite_ (MgSO_4H_2O) in boiling water, allowing the insoluble matter to settle, and crystallizing out the Epsom salts from the clear solution. It is employed in medicine as a purgative, and in the arts. The name is derived from its having been first procured from the mineral waters at Epsom.

EPWORTH, a small town of N. Lincolnshire, 9 miles N. of Gainsborough, the birth-place of John Wesley, the founder of Methodism. Pop. 1836.

EQUATION, in algebra, a statement that two expressions have the same numerical value. An equation may be either identical or conditional. An example of an _identical equation_, or _identity_, is (x + y)(x - y) = x^2 - y^2. The left side here can be transformed into the right side, simply by applying the laws of algebra so as to carry out the operations indicated, without taking account in any way of the numerical values of x and y. An identical equation is, therefore, true for all values of the variables which appear in it. A _conditional_ equation is not true unless certain special values are assigned to the variables. Thus the equation 4x + 7 = 15 is not true for any value of x except 2. This value 2 is called a _root_, or _solution_, of the equation. An equation may have more than one root, e.g. x^2 + 6x = 7 has two roots, 1 and -7; and 2x^3 + 3x^2 = 2x + 3 has three roots, 1, -1, -3/2.

_Rational Integral Equations_ (_one Variable_).--The three equations just given are special cases of the class of rational integral algebraic equations. The general form of these is ax^n + bx^{n-1} + ... + kx + l = 0, where n is a positive integer, and a, b, ... k, l are given numbers. This equation is said to be of degree n. The branch of mathematics called the Theory of Equations is conventionally restricted to equations of this type. The fundamental result in this subject is that every rational integral equation has a root, a theorem which it is by no means easy to prove. It follows without difficulty that an equation of degree n has exactly n roots, real or imaginary. Two or more of the roots, however, may be equal to each other. To _solve_ an equation is to find its roots. The general equation of degree n can always be solved to any degree of approximation desired, when the numerical values of the coefficients a, b, ... are assigned. Graphical methods of solution are often the best (see _Graph_). When the coefficients a, b, ... are arbitrary, the general equation can be solved algebraically if n does not exceed 4, but not for greater values of n. It is not that the algebraical solution, or algebraic formula for the roots, when n is greater than 4, has not been discovered; it does not exist. This was proved more than a hundred years ago by Abel and Galois, two mathematicians of the highest distinction, who both died before they were thirty. For n = 2, the roots of the _quadratic_ equation ax^2 + bx + c = 0 are (-b +/- [sqrt]( b^2 - 4ac))/2a. For n = 3, the _cubic_ equation ax^3 + bx^2 + cx + d = 0 is reduced to the form z^3 + pz + q = 0 by putting x = z - b/3a ; the solution of z^3 + pz + q = 0 can be verified to be z = u - p/3u, where u is any one of the three cube roots of the quantity -1/2q + [sqrt](1/4q^2 + 1/27p^3). For n = 4, the _biquadratic_ equation is solved with the help of the solution of the cubic. The cubic was first solved by the Italian mathematician Tartaglia, who communicated the solution to Cardan, after binding him to keep it a secret. Cardan, however, gave the solution in his _Algebra_, published at N[:u]rnberg in 1545.

_Equations with more than one Variable._--A solution of an equation which contains more than one variable is a set of values of the variables making the equation true. Thus the equation x^2 - y^2 = 9 has solutions (x = 5, y = 4), (x = 3, y = 0), (x = 5, y = -4), and an unlimited number of others. When several variables occur, there are usually also several _simultaneous_ equations connecting them; a solution of these is a set of values of the variables making _all_ the equations true. When the number of equations is equal to the number of variables, there is in general a limited number of solutions of the system. Thus, e.g. the system of equations x^2 - y^2 = 9, 2x - y = 6 has two solutions (x = 3, y = 0) and (x = 5, y = 4), and no others. A useful rule is that the number of solutions of a system of this type is equal to the product of the degrees of the equations. Exceptions may arise when two solutions coalesce, or when infinite values of the variables occur.

Equations are of great importance in applied mathematics. The data of a problem generally lead to an equation, or a set of equations, among the quantities concerned. In practice a certain number of these quantities are known in any given case; the unknown quantities are then found by the solution of an equation or equations. Non-algebraic equations occur frequently--equations involving trigonometrical functions, for example. For a modern practical method of solving equations of many types, see _Nomography_.--BIBLIOGRAPHY: A. E. Layng, _Elementary Algebra_; C. Smith, _Algebra_. More advanced works are: G. Chrystal, _Algebra_; W. S. Burnside and A. W. Panton, _Theory of Equations_.

EQUATION, PERSONAL, the accustomed error, almost a constant quantity in the case of a practised observer, in timing a celestial phenomenon.