scure, ambiguous, and generally contradictory terms, to puzzle or exercise the wit in finding out its meaning; or an obscure discourse covering some common and well known thing under remote and uncommon terms. Many distinguished poets have written ænigmas in verse. In the East, they have been in vogue, both in ancient and modern times. Every nation has shown a fondness for them in the infancy of its cultivation. A great part of the Egyptian learning is said to have been comprised in ænigmas. In these, too, the ancient oracles often spoke. But the symbols of the ancient religions should not, as is often the case, be confounded with ænigmas. (See Hieroglyphics.) They were in vogue among the Jews.

EOLIAN HARP, or EOLUS' HARP, was introduced into England about the middle of the last century. It is generally a simple box of thin, fibrous wood (often of deal), to which are attached a number of fine catgut strings, sometimes as many as 15, of equal size and length, and consequently unisons, stretched on low bridges at each end. Its length is made to correspond with the size of the window or other aperture in which it is intended to be placed; its width is about five or six inches, its depth two or three. It must be placed with the strings uppermost, under which is a circular opening in the centre as in the belly of the guitar. When the wind blows athwart the strings, it produces the effect of a choir of music in the air, sweetly mingling all the harmonic notes, and swelling or diminishing the sounds according to the strength or weakness of the blast. A more recent Eolian harp, invented by Mr. Crossthwaite, has no sounding-board, but consists merely of a number of strings extended between two deal boards. The invention of the Eolian harp has been generally ascribed to father Kircher, but the fact is, that it was known and used at a much earlier date in the East, as Mr. Richardson has proved (Dissertation on the Manners and Customs of the East).

ÆOLIANS; a Greek tribe in Thessaly, who took their name from Æolus, son of Hellen, and grandson of Deucalion, spread themselves there, and established several small states. A portion of them went to Asia Minor, and possessed themselves of the ancient Troas, giving the territory the name of Æolis. While united in a confederacy, which held its yearly meetings, with much solemnity, at Cuma, they long continued free; afterwards, they came under

the dominion of the Lydians, then of the Persians. After they had thrown off the Persian yoke, with the help of Athens, they were again subdued by Darius Hystaspes, and, as the Greeks had afforded them repeated aid, the famous Persian war arose, B.C.500. They regained their liberty, but once more came under the Persian dominion, and so remained till the time of Alexander; and at length, after they had been freed by the Romans from the yoke of the Syrian kings, successors of Alexander in this portion of his vast em pire, they were totally subdued by Sylla, because they had assisted Mithridates. Their language, the Æolian dialect, was one of the three principal dialects of the Greek; their country was one of the most fertile in the world; agriculture and the raising of cattle were their chief occupations.

ÆOLIPILE; a spherical vessel of metal, with a pipe of small aperture, through which the vapor of heated water in the ball passes out with considerable noise. The ancient philosophers thought to explain by this experiment the origin of the winds. In Italy, it is said that the æolipile is used to remedy smoky chimneys.

ÆOLUS; in Homer, the son of Hippotas, and king of the island Lipara, to the north of Sicily. He is described as pious and just, hospitable to strangers, and the inventor of sails; having, moreover, foretold the course of the winds, with the utmost exactness, from his own observation, he was said to have the power of directing their course. His history was afterwards still more embellished with fiction; the poets made him a son of Jupiter or Neptune, and god of the winds. He is represented as an old man, with a long beard, holding a sceptre in his hand, sitting on a rock, or smiting the rock with his sceptre, at which signal the winds rush out. He is represented, also, standing in a grotto with a muscle in his mouth, and a pair of bellows under his feet.

ÆRA is used synonymously with epoch, or epocha, for a fixed point of time, from which any computation of it is made. Era is more correctly the range or circuit of years within certain points of time, and an epoch is one of those points itself. The word ara has been supposed to be derived from the abridgement, or initial letters, of Annus Erat Augusti, A.ER.A., a mode of computing time in Spain from the year of the conquest of that country by the Romans; and Vossius favors this opinion. Various

æras have been given by chronologists as aids in historical research; and it was a long time before all the Christian world agreed to compute time by the Christian æra. Mariana says that the Spanish æra ceased in the year of Christ 1383, under John I, king of Castile. It continued to be used somewhat longer in Portugal. We must subtract 38 from the number of a year of the Spanish æra to get that of the Christian. The Mahometan æra begins with the flight of the prophet, 16th July, 622. This is called the Hegira (q. v.) The ancient Roman æra began with the building of the city, 750 before Christ. The Jewish æra begins with the creation. AËRIAL PERSPECTIVE; that branch of the science of perspective, which treats of the relative diminution of the colors of bodies in proportion to their distance from the eye.

AERIANS; the followers of Aërius, an Arian monk and schismatic, who was exiled from Sebaste, in Armenia, because he denied the difference between the official power of a bishop and a presbyter, pronounced prayers and offerings in behalf of the dead to be ineffectual and injurious, rejected the ordinance of fasting, and declared the practice prevailing among Christians, of sacrificing a lamb on the passover, to be contrary to the spirit of their religion. Though guilty, in fact, only of opposing the abuses of the hierarchy, and the corruptions of superstition, the Aërians were condemned as heretics, and soon disappeared. The Protestants were accused of Aërianism by the Catholics, because they maintained propositions of a similar character.

AERODYNAMICS; a branch of aërology, or the higher mechanics, which treats of the powers and motion of elastic fluids. Aerodynamics are often explained in connexion with hydrodynamics, a branch of hydrology. (See Mechanics.)

AEROLITES; stones or masses that descend from the air. (See Meteoric Stones.) AËRONAUTICS; the art of sailing in or navigating the air. The idea of inventing a machine, which should enable us to rise into the air, appears to have occupied the human mind even in ancient times, but was never realized till the last century. Henry Cavendish, having discovered, about 1766, the great levity of inflammable air or hydrogen gas, Dr. Black, of Edinburgh, was led to the idea that a thin bladder, filled with this gas, must ascend into the air. Cavallo made the requisite experiments in 1782, and found that a bladder was too heavy, and paper

not air tight. Soap bubbles, on the contrary, which he filled with inflammable air, rose to the ceiling of the room, where they burst.-In the same year, the brothers Stephen and Joseph Montgolfier constructed a machine which ascended by its own power. In Nov. 1782, the elder Montgolfier succeeded, at Avignon, in causing a large bag of fine silk, in the shape of a parallelopiped, and containing 40 cubic feet, to mount rapidly upwards to the ceiling of a chamber, and afterwards, in a garden, to the height of 36 feet, by heating it in the inside with burning paper. The two brothers soon afterwards repeated the experiment at Annonay, where the parallelopiped ascended in the open air 70 feet. A larger machine, containing 650 cubic feet, rose with equal success. They now resolved to make the experiment on a large scale, and prepared a machine of linen, lined with paper, which was 117 feet in circumference, weighed 430 pounds, and carried more than 400 pounds of ballast. This they sent up, June 5, 1783, at Annonay. It rose in ten minutes to a height of 6000 feet, and fell 7668 feet from the place of ascension. The method used to cause it to ascend was, to kindle a straw fire under the aperture of the machine, in which they threw, from time to time, chopped wool. But, though the desired effect was produced, they had no clear nor correct idea of the cause. They did not attribute the ascension of the vessel to the rarefaction of the air enclosed in it by the operation of the heat, but to a peculiar gas, which they supposed to be developed by the burning of the straw and wool. The error of this opinion was not discovered till a later period.— These experiments roused the attention of all the philosophers of Paris. It occurred to some of them, that the same effect might be produced by inflammable air.

M. Charles, professor of natural philosophy, filled a ball of lutestring, 12 feet in diameter, and coated with a varnish of gum-elastic, with such gas. It weighed 25 pounds, rose 3123 feet in two minutes, disappeared in the clouds, and descended to the earth, after three quarters of an hour, at the village of Gonesse, about 15 miles from Paris. Thus we see two original kinds of balloons; those filled with heated air, and those filled with inflammable air.-Meantime, Montgolfier had gone to Paris, and found an assistant in Pilatre de Rozier, the superintendent of the royal museum. They completed, together, in Oct. 1783, a new machine,

74 feet in height and 48 in breadth, in which Rozier ventured for the first time to ascend, though only 50 feet. The balloon was from caution fastened by cords, and soon drawn down. Eventually, the machine, being suffered to move freely, took an oblique course, and at length sunk down, gradually about 100 feet from its starting place. By this the world was convinced that a balloon might, with proper management, carry a man through the air; and the first aerial expedition was determined on. Nov. 21, 1783, Pilatre de Rozier and the marquis d' Arlandes ascended from the castle la Muette, in the presence of an innumerable multitude, with a machine containing 6000 cubic feet. The balloon, after having attained a considerable height, came down, in 25 minutes, about 9000 yards from la Muette. But the daring aeronauts had been exposed to considerable danger. The balloon was agitated very violently several times; the fire had burnt holes in it; the place on which they stood was injured, and some cords broken. They perceived that it was necessary to descend without delay; but when they were on the surface of the earth, new difficulties presented themselves. The weak coal fire no longer supported the linen balloon, the whole of which fell into the flame. Rozier, who had not yet succeeded in descending, just escaped being burnt.-M. Charles, who had joined with M. Robert, soon after informed the public that they would ascend in a balloon filled with inflammable air. To defray the necessary expense of 10,000 livres, he opened a subscription. The balloon was spherical, 26 feet in diameter, and consisted of silk coated with a varnish of gum-elastic. The car for the aeronauts was attached to several cords, which were fastened to a net, drawn over the upper part of the balloon. A valve was constructed above, which could be opened from the car, by means of cords, and shut by a spring. This served to afford an outlet to the inflammable air, if they wished to descend, or found it necessary to diminish it. The filling lasted several days; and, Dec. 1, the voyage was commenced from the gardens of the Tuileries. The balloon quickly rose to a height of 1800 feet, and disappeared from the eyes of the spectators. The aeronauts diligently observed the barometer, which never stood at less than 26°, threw out gradually the ballast they had taken in to keep the balloon steady, and descended safely at Nesle. But as soon as Robert stepped out, and it

was thus lightened of 130 pounds, it rose again with great rapidity about 9000 feet. It expanded itself with such force, that it must have been torn to pieces, had not Charles, with much presence of mind, opened the valve to accommodate the quantity of gas to the rarity of the surrounding atmosphere. After the lapse of half an hour, the balloon sunk down on a plain, about three miles from the place of its second ascent.-These successful aërial voyages were soon followed by others. Blanchard had already ascended several times, when he determined to cross the channel between England and France, which is about 23 miles wide, in a balloon filled with inflammable air. He succeeded in this bold attempt, Jan. 7, 1785, accompanied by an American gentleman, Dr. Jeffries. About one o'clock, they left the English coast, and at half past two, were on the French. Pilatre de Rozier, mentioned before as the first aëronaut, attempted, June 14, 1785, in company with Mr. Romain, to pass from the French to the English side; but the attempt was unsuccessful, and the adventurers lost their lives. M. de Rozier had on this occasion united the two kinds of balloons; under one, filled with inflammable air, which did not alone possess sufficient elevating power, was a second, filled by means of a coal fire under it. Rozier had chosen this combination, hoping to unite the advantages of both kinds. By means of the lower balloon, he intended to rise and sink at pleasure, which is not possible with inflammable air; for a balloon filled with this, when once sunk to the earth, cannot rise again with the same weight, without being filled anew; while, on the contrary, by increasing or diminishing the fire under a balloon filled with heated air, it can be made to rise and fall alternately. But this experiment caused the death of the projectors. Probably the coals, which were only in a glowing state near the surface of the ground, were suddenly kindled to a light flame as the balloon rose, and set it on fire. The whole machine was soon in flames, and the two aeronauts were precipitated from on high. The condition of their mangled bodies confirms the conjecture that they were killed by the explosion of the gas.-This unhappy accident did not deter others; on the contrary, the experiments were by degrees repeated in other countries. However important this invention may be, it has as yet led to no considerable results. Its use has hitherto been confined to obser

vations in the upper regions of the atmosphere. But should we ever learn to guide the balloon at will, it might, perhaps, be employed for purposes of which we now have hardly an idea; possibly the plan of professor Robertson might be accomplished by the construction of a gigantic balloon, which would enable us to perform an aërial circumnavigation of the earth. During the French revolution, an aërostatic institution was founded at Meudon, not far from Paris, for the education of a corps of aëronauts, with the view of introducing balloons into armies as a means of reconnoitring the enemy. But this use of balloons was soon laid aside, for, like every other, it must be attended with great uncertainty, as long as the machine has to obey the wind. Among the French, Blanchard and Garnerin have undertaken the greatest number of aërial voyages; among the Germans, professor Jungius, in Berlin, in 1805 and 1806, made the first. Since that time, professor Reichard and his wife have become known by their aërial excursions. Even in Constantinople, such a voyage was performed, at the wish and expense of the sultan, by two Englishmen, Barly and Devigne. Blanchard has rendered an essential service to aeronauts by the invention of the parachute, which they can use, in case of necessity, to let themselves down without danger. Many attempts have been made to regulate the course of balloons, by means of oars, wings, &c., but hitherto with little

success.

AEROSTATION, or AEROSTATICS, is the science of weighing air, either by itself or with other substances. Since the invention of the balloon, this term has been sometimes applied to the art of managing balloons, which is more properly called aeronautics, (q. v.)

ESCHINES; a famous orator of Athens; born 393, died 323, B. C. Being the son of poor parents, he passed his youth among the lower classes, with whom he wandered about, partaking in their amusements, particularly in the festivals in honor of Bacchus. Encouraged by their applause, he became an actor, acquired the right of citizenship, engaged in politics, attended the lectures of Plato and Isocrates, and soon became the rival of Demosthenes, whom, however, he did not equal in power and energy, although he was distinguished by a happy choice of words, and by richness and perspicuity of ideas. He gradually lost the favor of the people, and fled to Rhodes and Samos, where he

gave instruction in rhetoric till his death. Three orations and twelve letters of his are extant. They are to be found in the collections of Aldus, Stephanus and Reiske, (3d and 4th vols.)

ESCHINES, the philosopher, a native of Athens, who, by way of distinction from the preceding, is called the Socratic, was a poor disciple of Socrates. We possess under his name three dialogues, "On Virtue," "On Riches," and "On Death," which, however, are not allowed by strict critics to be genuine. The best edition is that of I. F. Fischer, Leipsic, 1786.

ÆSCHYLUS; the father of ancient Greek tragedy; born in the 3d or 4th year of the 63d Olympiad (525 B. C.), at Eleusis, in Attica, of a noble family. Of the circumstances of his life we have but deficient and uncertain accounts. He fought in the battles of Marathon and Salamis, witnessed the destruction of the power of Darius and Xerxes, and wrote his tragedies under the proud feeling of a successful struggle for liberty. In these he first raised the tragical art from the rude beginnings of Thespis to a dignified character, so that he may be considered as its real creator. Tragedy sprang from his head in full armor (says A. W. Schlegel), like Pallas from the head of Jupiter. He clothed it with becoming dignity, and gave it an appropriate place of exhibition; he invented scenic pomp, and not only instructed the chorus in singing and dancing, but appeared himself in the character of a player. He first perfected the dialogue, and reduced the lyrical part of the tragedy, which still, however, occupies too much space in his plays. His characters are sketched with a few bold and strong features; his plots are extremely simple, but grand. His art knew nothing of intrigues and developements. All his poetry reveals a lofty and ardent mind. Not the softer emotions, but terror is his ruling characteristic. He holds up the head of Medusa to the overawed spectators. His manner of treating fate is terrible in the extreme; in all its gloomy majesty it hovers over mortals. The Cothurnus of Eschylus is of an iron weight; none but giant figures stride in it. It appears to have required an effort in him to represent mere men. He deals commonly with gods, especially the Titans, those elder deities, the symbols of the dark primitive powers of nature, long since cast down to Tartarus. In accordance with the grandeur of his figures, he endeavors to make their language gigantic

Thence arise harsh expressions, overloaded with epithets, and frequently, in his chorus, intricate constructions and great obscurity. In the daring grandeur of his images and expressions, he resembles Dante and Shakspeare. We have only 7 of his tragedies remaining: their whole number is stated to have been 70; according to some, 90; but among these, according to the testimony of the ancients, we have some of his principal works. They are, "The Prometheus Vinctus," "The Seven before Thebes," "The Persians," ""Agamemnon," "The Choëphore," "The Eumenides," and "The Suppliants." Disgusted at seeing inferior pieces preferred to his own, and particularly at the victory of the young Sophocles, or, according to the more probable account, compelled by an accusation of atheism, Eschylus left his native country, and went to Sicily, where be was received with great honors by king Hiero, and died 456 B. C., at the age of 70 years. The best editions of his works are, London, 1663 and 1664, folio, by Stanley; Hague, in 1745, 2 vols. quarto, by Paw; and Halle, 1809 to 1821, 5 vols. 3d edition by Schütz. Single plays have been published by Brunck, Herrmann, Blomfield, and others.

ESCULAPIUS; the god of medicine. Some writers call him a son of Apollo and Arsinoë, daughter of Leucippus; others, of Apollo and Coronis, daughter of Phlegyas. There are also different accounts of the wonders which befell his infancy. According to some, he was exposed by his mother, suckled by a goat, found by shepherds, and his divine nature recognised by a glittering halo round his head: according to others, Coronis having admitted the embraces of Ischys as well as those of Apollo, the latter, in a fit of anger (or Diana in his stead), killed Coronis, but saved the child from her womb. The last opinion was the most common, and was confirmed by the Pythian oracle. Apollo afterwards brought his son to Chiron, who instructed him in medicine and hunting. In the former he acquired a high degree of skill, so as to surpass even the fame of his teacher. He not only prevented the death of the living, but even recalled the dead to life. Jupiter, however, induced by the complaints of his brother Pluto, slew E. with a thunderbolt. After his death, he received divine honors. In particular, he was worshipped at Epidaurus in Peloponnesus, (see Argolis), where a temple with a grove was dedicated to him. From the

accurate register here kept of the most remarkable diseases and their remedies, the greatest physicians gathered experience and knowledge. Thence his worship spread over all Greece, and finally to Rome. After the plague had raged there for three years, ambassadors were sent to Esculapius at Epidaurus by the advice of the Delphian Apollo. They had hardly appeared before the god, when a serpent crept from beneath his image, and hastened directly to the Roman ship. This serpent, which was thought to be Esculapius himself, was carried with great solemnity to Rome, upon which the plague ceased. Esculapius had two sons, Machaon and Podalirius, who were called Asclepiades, and during the Trojan war made themselves famous as heroes and physicians. His daughters were Hygeia, Iaso, Panacea and Ægle, the first of whom was worshipped as the goddess of health. Esculapius is represented with a large beard, holding a knotty staff, round which was entwined a serpent, the symbol of convalescence. Near him stands the cock, the symbol of watchfulness. He is sometimes crowned with the laurel of Apollo. Sometimes his little son Telesphorus is represented beside him, with a cap upon his head, wrapped up in a cloak. Sometimes Esculapius is represented under the image of a serpent only.

Æsop; the oldest Greek fabulist. He is said to have been a native of Phrygia, and a slave, till he was set free by his last owner. He lived about the middle of the 6th century B. C. He inculcated rules of practical morality, drawn from the habits of the inferior creation, and thus spread his fame through Greece and all the neighboring countries. Croesus, king of Lydia, invited Æsop to his court, and kept him always about his person. Indeed, he was never absent, except during his journeys to Greece, Persia and Egypt. Croesus once sent him to Delphi to offer a sacrifice to Apollo; while engaged in this embassy, he wrote his fable of the Floating Log, which appeared terrible at a distance, but lost its terrors when approached. The priests of Delphi, applying the fable to themselves, resolved to take vengeance on the author, and plunged him from a precipice. Planudes, who wrote a miserable romance, of which he makes Esop the hero, describes him as excessively deformed and disagreeable in his appearance, and given to stuttering; but this account does not agree with what his contemporaries say of him.