Part 29

EQUATION OF THE CENTRE, the difference between the actual heliocentric longitude of a planet revolving in an elliptic orbit and that which it would have at the same instant if it revolved in a circular orbit. It is zero at perihelion and aphelion.

EQUATION OF TIME, the difference between mean and apparent time, or the difference of time as given by a clock and as given by a sun-dial, arising chiefly from the varying velocity of the earth in its orbit and the eccentricity of the orbit. The sun and the clock agree four times in the year; the greatest difference between them at the beginning of November is fully sixteen minutes. See _Day_.

EQUA'TOR, that great circle of our globe every point of which is 90deg from the poles. All places which are on it have invariably equal days and nights. Our earth is divided by it into the northern and southern hemispheres. From this circle is reckoned the latitude of places both north and south. There is also a corresponding celestial equator in the plane of the terrestrial, an imaginary great circle in the heavens the plane of which is perpendicular to the axis of the earth. It is everywhere 90deg distant from the celestial poles, which coincide with the extremities of the earth's axis, supposed to be produced to meet the heavens. During his apparent yearly course the sun is twice in the celestial, that is, vertically over the terrestrial equator, on 21st March and 23rd September. Then the day and night are equal all over the earth, whence the name _equinox_.--The _magnetic equator_ is a line at every point of which the vertical component of the earth's magnetic force is zero; that is to say, a dipping needle carried along the magnetic equator remains horizontal. It is hence also called the _aclinic line_. It has a slightly devious course, but upon the whole keeps fairly near the geographical equator.

EQUATO'RIAL, an astronomical instrument contrived for the purpose of directing a telescope upon any celestial object, and of keeping the object in view for any length of time, notwithstanding the diurnal motion of the earth. For these purposes a principal axis resting on firm supports is mounted exactly parallel to the axis of the earth's rotation, and consequently pointing to the poles of the heavens, being fixed so as to turn on pivots at its extremities. To this there is attached a telescope moving on an axis of its own in such a way that it may either be exactly parallel to the other axis, or at any angle to it; when at right angles it points to the celestial equator. The two axes carry graduated circles, with the help of which, even during the day, the telescope can be pointed to any star whose declination and right ascension are known. By means of clockwork the instrument is given such a motion round its principal axis that the star is kept stationary in the field of view.

EQ'UERRY, in Britain, the name of certain officers of the royal household, in the department of the Master of the Horse, whose duties consist in attendance when the sovereign rides abroad. Equerries also form part of the establishments of the members of the royal family.

EQUESTRIAN ORDER, the order of 'Knights' in ancient Rome. The _equites_ or knights originally formed the cavalry of the army. They are said by Livy to have been instituted by Romulus, who selected 300 of them from the three principal tribes. About the time of the Gracchi (123 B.C.) the equites became a distinct order in the state, and the judges and the farmers of the revenue were selected from their ranks. They held their position in virtue of a certain property qualification, and towards the end of the Republic they possessed much influence in the state. They had particular seats assigned to them in the circus and theatre, and the insignia of their rank, in addition to a horse, were a gold ring and a robe with a narrow purple border (the _clavus angustus_). Under the later emperors the order grew less influential, and finally disappeared.

EQ'UIDAE, the horse family, a division of the odd-toed (perissodactyle) Ungulates or hoofed mammals. There is but one existing genus, Equus, distinguished by the possession of a mane; hard pads (callosities) on the inner side of each fore-limb (and sometimes of the hind-limb); a single functional digit (the third or middle one) terminating in a large curved hoof; a simple stomach; 44 teeth, including 12 incisors with pitted crowns, 4 canines (tushes) reduced in the female, and 28 grinding teeth with broad crowns, except the first (wolf tooth), which is rudimentary. The forms included are horses, asses, and zebras; the first being distinguished from the others by the presence of callosities ('chestnuts') on the hind-limbs as well as the fore. The domesticated horse (_E. caballus_) has a large flat tail abundantly hair-clad, and is not known with certainty in the wild state, though possibly the tarpan of South Russia (Tartary) may represent the original stock. Another candidate for this honour is the small wild species (_E. przewalskii_) native to the deserts of Central Asia. The domestic ass (_E. asinus_) is related to a number of wild species, such as the onager (_E. onager_) of South Asia, the kiang (_E. hemionus_) of Tibet, and two African species (_E. africanus_ and _E. somalicus_). The striped zebras are purely African, and four species are generally recognized--the common or mountain zebra (_E. zebra_), Burchell's zebra (_E. burchelli_), Grevy's zebra (_E. grevyi_), and the quagga (_E. quagga_). The geological record enables us to derive horses from a small plantigrade five-toed form (Phenacodus), by gradual increase in size, complication of teeth, loss of digits, and elongation of limbs, to the unguligrade condition.

EQUILIB'RIUM, in statics, the condition when a body is acted on by two or more forces which balance one another. The body may be either at rest or moving with uniform speed in a straight line. In the first case, when the body, being slightly moved out of any position, always tends to return to its position, that position is said to be one of _stable equilibrium_; when the body, after a slight displacement, tends to move away from its previous position, the body is in _unstable equilibrium_. If, after displacement, the body tends to remain at rest, its state is one of _neutral equilibrium_.

EQUINOC'TIAL, in astronomy, the circle in the heavens otherwise known as the celestial equator. When the sun is on the equator, there is equal length of day and night over all the earth: hence the name _equinoctial_.--_Equinoctial gales_, storms which have been supposed to take place about the time of the sun's crossing the equator, that is, at the vernal and autumnal equinoxes, in March and September.--_Equinoctial points_ are the two points wherein the celestial equator and ecliptic intersect each other; the one, the first point of Aries, is called the _vernal_ point; and the other, in Libra, the _autumnal_ point. These points move backward or westward at the rate of 50" of arc in a year. This is called the precession of the equinoxes.

EQ'UINOX, one of the equinoctial points. The term is also applied to the dates at which the sun passes through them, viz. 21st March and 23rd September, when day and night are of equal length all over the world. See _Day_; _Earth_; _Equinoctial_; _Seasons_.

EQUISETALES, a group of Pteridophytes, represented at the present day only by the genus Equisetum (q.v.). It was much more prominent in the Carboniferous flora, in which large woody horse-tails (Calamites) played an important part.

EQUISE'TUM, a genus of vascular cryptogamous plants with hollow jointed stems, type of the group Equisetales, growing in wet places, and popularly called _horse-tails_.

EQ'UITY (Lat. _aequus_, fair, equal), in English law, the system of supplemental law administered in certain courts, founded upon defined rules, recorded precedents, and established principles, the judges, however, liberally expounding and developing them to meet new exigencies. While it aims at assisting the defects of the common law, by extending relief to those rights of property which the strict law does not recognize, and by giving more ample and distributive redress than the ordinary tribunals afford, equity by no means either controls, mitigates, or supersedes the common law, but rather guides itself by its analogies, and does not assume any power to subvert its doctrines. The Court of Chancery was formerly in England the especial court of equity, but large powers were by the Judicature Act of 1873 given to all the divisions of the Supreme Court to administer equity, although many matters of equitable jurisdiction are still left to the chancery division in the first instance.--BIBLIOGRAPHY: F. T. White and O. O. Tudor, _Leading Cases in Equity_; C. Thwaites, _Student's Guide to Equity_.

EQUITY OF REDEMPTION, in law, the advantage allowed to a mortgager of a reasonable time to redeem an estate mortgaged, when it is of greater value than the sum for which it is mortgaged.

EQUIV'ALENT, in chemistry, the number of parts by weight of an element which will combine with or displace 8 parts by weight of oxygen or 1.008 parts by weight of hydrogen.

ERANTHIS. See _Winter Aconite_.

['E]RARD, S['e]bastien, a celebrated musical-instrument maker, born at Strasbourg in 1752, died 1831. He went to Paris at the age of eighteen, and in concert with his brother, Jean Baptiste, produced pianofortes superior to any that had previously been made in France. He afterwards established a manufactory in London, and made considerable improvements in the mechanism of the harp.

ERASIS'TRATUS, an ancient Greek physician and anatomist, said to have been a grandson of Aristotle. He lived in the third century before the Christian era, and was court physician of Seleucus Nicator, King of Syria. He was the first who systematically dissected the human body, and his description of the brain and nerves is much more exact than any given by his predecessors. He classified the nerves into nerves of sensation and of locomotion, and, it is said, almost stumbled upon the discovery of the circulation of the blood. Of his works only the titles and some fragments remain.

ERAS'MUS, Desiderius, a Dutch scholar, one of the greatest of the Renaissance and Reformation period, born at Rotterdam in 1467, died in 1536. His original name was Gerard, but this he changed according to a fashion of the time. After the death of his parents, whom he lost in his fourteenth year, his guardians compelled him to enter a monastery; and at the age of seventeen he assumed the monastic habit. The Bishop of Cambrai delivered him from this constraint. In 1492 he travelled to Paris to perfect himself in theology and literature. He became the instructor of several rich Englishmen (from one of whom--Lord Mountjoy--he received a pension for life), and accompanied them to England in 1497, where he was graciously received by the king. Returning soon after to the Continent, he took his doctor's degree, was relieved from his monastic vows by dispensation from the Pope, and published several of his works. In 1510 he returned to England, wrote his _Praise of Folly_ while residing with Sir Thomas More, and was appointed Lady Margaret professor of divinity and Greek lecturer at Cambridge. In 1514 he returned to the Continent and lived chiefly at Basel, where he died. To extensive learning Erasmus joined a refined taste and a delicate wit, and rendered great and lasting service to the cause of reviving scholarship. Although Erasmus took no direct part in the Reformation, and was reproached by Luther for lukewarmness, he attacked the disorders of monasticism and superstition, and everywhere promoted the cause of truth. A humanist rather than a reformer or a theologian, he waged war upon ignorance and superstition. He edited various classics, the first edition of the Greek Testament from MSS. (with Latin translation), &c., but his best-known books are the _Encomium Moriae_ (Praise of Folly) and his _Colloquies_. His letters are very valuable in reference to the history of that period.--BIBLIOGRAPHY: S. Knight, _Life of Erasmus_; C. Butler, _Life of Erasmus_; E. F. H. Capey, _Life of Erasmus_; P. S. Allen, _The Age of Erasmus_.

ERAS'TUS (Gr. _erastos_, lovely, translation of Ger. _Lieber_), the learned name of Thomas Lieber, a Swiss physician, who maintained the opinions from which the well-known epithet of _Erastian_, as now used, is derived. He was born at Baden in 1523, and died at Basel 1584. He was successively professor of medicine at Heidelberg, and of ethics at Basel. In his writings he maintained the complete subordination of the ecclesiastical to the secular power; and denied to the Church the right to exclude any one from Church ordinances, or to inflict excommunication.

ER'ATO, in Greek mythology, one of the nine Muses, whose name signifies loving or lovely. She presided over lyric and especially amatory poetry, and is generally represented crowned with roses and myrtle, and with the lyre in the left hand and the plectrum in the right in the act of playing.

ERATOS'THENES, an ancient Greek astronomer, born at Cyrene, in Africa, 276 B.C., died about 194 B.C. He was librarian at Alexandria, and gained his greatest renown by his investigations of the size of the earth. He rendered much service to the science of astronomy, and first observed the obliquity of the ecliptic. Of the writings attributed to him one only remains complete--_Katasterismoi_--which treats of the constellations.

ER'BIUM, a rare metal found along with yttrium, terbium, and other rare elements in some rare minerals. Its properties are but little known. It was discovered by Mosander in 1843.

ERCILLA Y ZUNIGA (er-thil'y[.a] [=e] th[:o]-ny[=e]'g[.a]), Don Alonso de, Spanish soldier and poet, born 1533, died 1595. He became page to the Infant Don Philip, accompanied him on his travels, and in 1554 went with him to England, on the occasion of his marriage with Queen Mary. After this he fought against the Araucanians of South America (Chile), and his epic _La Araucana_ is based on the events of this war. It is written in excellent Spanish, and occupies an honourable position in the national literature. The first fifteen cantos were published in 1569, and the continuations, thirty-seven cantos, appeared in 1578 and 1589.

ERCKMANN-CHATRIAN (sh[.a]t-ri-[:a][n.]), the joint name of two French-Alsatian writers of fiction. ['E]mile Erckmann, born at Pfalzburg 1822, studied law at Paris, and died in 1899. Alexandre Chatrian, born near Pfalzburg in 1826, died in 1890, was for some time teacher in the Pfalzburg College. They formed a literary partnership in 1847, but it was not till the appearance of _L'Illustre Docteur Math['e]us_ in 1859 that success attended them. Among their most popular books are: _L'Ami Fritz_, _Madame Th['e]r[`e]se_, _Histoire d'un Conscrit de 1813_, _L'Histoire d'un Paysan_, and _Waterloo_, most of which have been translated into English. Their drama _Le Juif Polonais_ was made famous by Sir Henry Irving under the name of _The Bells_.

ERDMANN, Johann Eduard, German philosopher, born 1805, died 1892. He studied theology at Dorpat and Berlin; in 1829 became a clergyman, but in 1832 returned to Berlin and took his degree in philosophy. In 1836 he became professor extraordinary of philosophy at Halle, being appointed ordinary professor in 1839. He wrote numerous philosophical works, mostly characterized by Hegelian tendencies, including: _Body and Soul_, _Nature and Creation_, _Outlines of Psychology_, _Outlines of Logic and Metaphysics_, _Psychological Letters_, and _Belief and Knowledge_. His greatest work is his _Outlines of the History of Philosophy_, which has been translated into English (3 vols., 1889).

ER'EBUS, in Greek mythology, the son of Chaos and Darkness, and father of Aether and Hemera (day). The name Erebus was also given to the infernal regions.

ER'EBUS, MOUNT, a volcano of the antarctic regions in S. Victoria Land; height, 12,400 feet; discovered by Ross, 1841.

ERECHTHEUS (e-rek'th[=u]s), in Greek mythology, a mythical king of Athens to whom a fine temple, the _Erechth[=e]um_, was built on the Acropolis. In some representations of him he is depicted as half snake, so that he was one of the autochthones, the earth-born ancestors of the Athenians.

ERECTION, LORDS OF, in Scots history, those private owners into whose hands the ecclesiastical estates belonging to the clergy had passed during the religious changes of the Reformation period.

ER'FURT (Lat. _Erfordia_, ford of Erpe, its legendary founder), an important town in the Prussian province of Saxony, on the River Gera, formerly a fortress with two citadels, now given up as such. It has a fine cathedral dating from the thirteenth century and several handsome Gothic churches. The university, founded in 1378 and suppressed in 1816, was long an important institution. There is still an academy of science and a library with 60,000 volumes. The monastery (now an orphanage) was the residence of Luther from 1501 to 1508. Erfurt is a busy industrial town and is in a very flourishing condition. The industries are varied, including clothing, machinery, leather, shoes, ironmongery, and chemicals. Flower-growing is extensively carried on in the neighbourhood, plants and seed being produced for sale in great quantities. Pop. 123,550.

ER'GOT, the altered grain of rye and other grasses caused by the attack of an ascomycetous fungus called _Claviceps purpurea_. The grain is replaced by a dense fungoid tissue (sclerotium) largely charged with an oily fluid. In its perfect state this germinates and produces the Claviceps fructification. When diseased rye of this kind is eaten in food for some time, it sometimes causes death by a kind of mortification called dry gangrene. Ergot is used in obstetric practice to promote the contraction of the uterus.

ERICA (e-r[=i]'ka), the heaths, a large genus of branched rigid shrubs, type of the nat. ord. Ericaceae, most of which are natives of South Africa, a few being found in Europe and Asia. The leaves are narrow and rigid; the flowers are globose or tubular, and four-lobed. Five species are found in Britain.

ERICACEAE, a nat. ord. of gamopetalous Dicotyledons. Representative genera: Calluna, Erica, Rhododendron.

ERICHSEN (er'ik-sen), Sir John Eric, surgeon, born 1818, died in 1890. He was the son of a Copenhagen merchant, but spent nearly all his life in England. He studied at University College, London, became a member of the Royal College of Surgeons in 1839, a fellow in 1845, and in 1850 professor of surgery and hospital surgeon at University College. In 1865 he succeeded Quain as professor of clinical surgery in the same college, but retired in 1875. Appointed president of University College in 1887, he also held that post till his death. He was chief surgeon extraordinary to Queen Victoria, and in 1895 was made a baronet. His most important work was his _Science and Art of Surgery_ (1853), which has gone through many editions, and has been translated into several languages. He also published a volume on _Concussion of the Spine_ (1875).

ER'ICSSON, John, engineer, born in Sweden 1803, died in 1889. He served for a time in the Swedish army; removed to London in 1826, and to New York in 1839. He is identified with numerous inventions and improvements in steam machinery and its applications. His chief inventions are his caloric engine, the screw propeller (1836), which has revolutionized navigation, and his turret-ships, the first of which, the _Monitor_, distinguished itself in the American Civil War, and inaugurated a new era in naval warfare. He afterwards devoted himself to studies of the earth's motion and the intensity of solar heat.

ERIDANUS, the River Eridanus (modern Po), one of the constellations of the ancient astronomy, in which Ptolemy catalogued thirty-four stars. Appropriately to its name, it covers a large expanse of the heavens, its northern portion, just to south-west of Orion, reaching the celestial equator. The part visible in our latitudes does not contain bright stars, but at the southern extremity is the first-magnitude Achernar, a conspicuous object to southern observers.

ERIE ([=e]'ri), one of the great chain of North American lakes, between Lakes Huron and Ontario, about 265 miles long, 63-1/2 miles broad at its centre, from 40 to 60 fathoms deep at the deepest part; area, 6900 sq. miles. The whole of its southern shore is within the territory of the United States, and its northern within that of Canada. It receives the waters of the upper lakes by Detroit River at its south-western extremity, and discharges its waters into Lake Ontario by the Niagara River at its north-east end. The Welland Canal enables vessels to pass from it to Lake Ontario. It is shallow compared with the other lakes of the series, and is subject to violent storms. The principal harbours are those on the United States side--Buffalo, Erie, and Cleveland.

ERIE, a city, Pennsylvania, United States, an important railway and commercial centre on the southern shore of Lake Erie. There are numerous ironworks (including foundries, rolling-mills, and blast-furnaces), petroleum refineries, breweries, tanneries, and wood-working factories. The harbour is one of the best on the lake. Pop. 76,600.

ERIE CANAL, the largest in the United States, serving to connect the great lakes with the sea. It begins at Buffalo on Lake Erie, and extends to the Hudson at Albany. It is 363 miles long; has in all 72 locks; a surface width 70 feet, bottom width 42 feet, and depth 7 feet. It is carried over several large streams on stone aqueducts; cost nearly L2,000,000, and was opened in 1825. The navigation is free.

ERIGENA (e-rij'e-na), Joannes Scotus (_Scotus_, Scot, and _Erigena_, Irish-born), an eminent mediaeval scholar and metaphysician, probably born of Scotch parentage in Ireland about 800-810, died in France about 875. He spent a great part of his life at the court of Charles the Bald of France, and was placed at the head of the school of the palace. The king further imposed upon him the double task of translating into Latin the Greek works of the pseudo Dionysius the Areopagite, and of composing a treatise against Godeschale on _Predestination and Free-will_. This treatise, and another, _De Divisione Naturae_, contained many views in opposition to the teachings of the Church. They were condemned by the Councils of Valencia in 855 and of Langres in 859, and Pope Nicholas I demanded the immediate disgrace of the culprit. His subsequent history is not known.--Cf. Gardner, _Studies in John the Scot_.

ERIN'NA, a Greek poetess who lived about 600 B.C. She is said to have been an intimate friend of Sappho, and died at the age of eighteen. She acquired a high reputation for poetry, and her chief work was called _Elakat[=e]_ (The Distaff), of which nothing has come down to us. An epitaph or two which are still extant, and believed by some to be hers, are by others deemed spurious.

ERIODEN'DRON, the wool tree, a genus of plants, nat. ord. Malvaceae (mallows). There are eight species natives of America, but one belongs to Asia and Africa. The species are noble plants, growing from 50 to 100 feet high, having palmate leaves, and red or white flowers. The woolly coat of the seeds of some of the species is used in different countries for stuffing cushions and similar purposes.

ERIS, in Greek mythology, the goddess of discord, the sister of Ares, and, according to Hesiod, daughter of Nyx (night). Not being invited to the marriage of Peleus, she revenged herself by means of the _apple of discord_.

ER'ITH, a town of England, in Kent, on the Thames, about 14 miles east of London, a pleasant summer resort. Pop. 27,755.