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 this conclusion, he was able to assimilate the physical theory of Heraclitus, as is explained in the Hypotyposes of Sextus Empiricus. For admitting that contraries co-exist for the perceiving subject, he was able to assert the co-existence of contrary qualities in the same object. Having thus disposed of the ideas of truth and causality, he proceeds to undermine the ethical criterion, and denies that any man can aim at Good, Pleasure or Happiness as an absolute, concrete ideal. All actions are product of pleasure and pain, good and evil. The end of ethical endeavour is the conclusion that all endeavour is vain and illogical. The main tendency of this destructive scepticism is essentially the same from its first crystallization by Aenesidemus down to the most advanced sceptics of to-day (see ). For the immediate successors of Aenesidemus see,. See also and. Of the  nothing remains; we have, however, an analysis in the Myriobiblion of Photius.

AEOLIAN HARP (Fr. harpe éolienne; Ger. Äolsharfe, Windharfe; Ital. arpa d’ Eolo), a stringed musical instrument, whose name is derived from Aeolus, god of the wind. The aeolian harp consists of a sound-box about 3 ft. long, 5 in. wide, and 3 in. deep, made of thin deal, or preferably of pine, and having beech ends to hold the tuning-pins and hitch-pins. A dozen or less catgut strings of different thickness, but tuned in exact unison, and left rather slack, are attached to the pins, and stretched over two narrow bridges of hard wood, one at each end of the sound-board, which is generally provided with two rose sound-holes. To ensure a proper passage for the wind, another pine board is placed over the strings, resting on pegs at the ends of the sound-board, or on a continuation of the ends raised from 1 to 3 in. above the strings. Kaufmann of Dresden and Heinrich Christoph Koch, who improved the aeolian harp, introduced this contrivance, which was called by them Windfang and Windflügel; the upper board was prolonged beyond the sound-box in the shape of a funnel, in order to direct the current of air on to the strings. The aeolian harp is placed across a window so that the wind blows obliquely across the strings, causing them to vibrate in aliquot parts, i.e. (the fundamental note not being heard) the half or octave, the third or interval of the twelfth, the second Octave, and the third above it, in fact the upper partials of the strings in regular succession. With the increased pressure of the wind, the dissonances of the 11th and 13th overtones are heard in shrill discords, only to give place to beautiful harmonies as the force of the wind abates. The principle of the natural vibration of strings by the pressure of the wind was recognized in ancient times; King David, we hear from the Rabbinic records, used to hang his kinnor (kithara) over his bed at night, when it sounded in the midnight breeze. The same is related of St Dunstan of Canterbury, who was in consequence charged with sorcery. The Chinese at the present day fly kites of various sizes, having strings stretched across apertures in the paper, which produces the effect of an aerial chorus.

AEOLIS, an ancient district of Asia Minor, colonized at a very early date by Aeolian Greeks. The name was applied to the coast from the river Hermus to the promontory of Lectum, i.e. between Ionia to S. and Troas to N. The Aeolians founded twelve cities on the mainland, including Cyme, and numerous towns in Mytilene: they were said also to have settled in the Troad and even within the Hellespont.

AEOLUS, in Greek mythology, according to Homer the son of Hippotes, god and father of the winds, and ruler of the island of Aeolia. In the Odyssey (x. 1) he entertains Odysseus, gives him a favourable wind to help him on his journey, and a bag in which the unfavourable winds have been confined. Out of curiosity. or with the idea that it contains valuable treasures, Odysseus’ companions open the bag; the winds escape and drive them back to the island, whence Aeolus dismisses them with bitter reproaches. According to Virgil, Aeolus dwells on one of the Aeolian islands to the north of Sicily, Lipara or Strongyle (Stromboli), where he keeps the winds imprisoned in a vast cavern (Virgil, Aen. i. 52). Another genealogy makes him the son of Poseidon and Arne, granddaughter of Hippotes, and a descendant of Aeolus, king of Magnesia in Thessaly, the mythical ancestor of the tribe of the Aeolians (Diodorus iv. 67).

AEON, a term often used in Greek ( ) to denote an indefinite or infinite duration of time; and hence, by metonymy, a being that exists for ever. In the latter sense it was chiefly used by the Gnostic sects to denote those eternal beings or manifestations which emanated from the one incomprehensible and ineffable God. (See .)

AEPINUS, FRANZ ULRICH THEODOR (1724–1802), German natural philosopher, was born at Rostock in Saxony on the 13th of December 1724. He was descended from John Aepinus (1499–1553), the first to adopt the Greek form ( ) of the family name Hugk or Huck, and a leading theologian and controversialist at the time of the Reformation. After studying medicine for a time, Franz Aepinus devoted himself to the physical and mathematical sciences, in which he soon gained such distinction that he was admitted a member of the Berlin academy of sciences. In 1757 he settled in St Petersburg as member of the imperial academy of sciences and professor of physics, and remained there till his retirement in 1798. The rest of his life was spent at Dorpat, where he died on the 10th of August 1802. He enjoyed the special favour of the empress Catherine II., who appointed him tutor to her son Paul, and endeavoured, without success, to establish normal schools throughout the empire under his direction. Aepinus is best known by his researches, theoretical and experimental, in electricity and magnetism, and his principal work, Tentamen Theoriae Electricitatis et Magnetismi, published at St Petersburg in 1759, was the first systematic and successful attempt to apply mathematical reasoning to these subjects. He also published a treatise, in 1761, De distributione caloris per tellurem, and he was the author of memoirs on different subjects in astronomy, mechanics, optics and pure mathematics, contained in the journals of the learned societies of St Petersburg and Berlin. His discussion of the effects of parallax in the transit of a planet over the sun’s disc excited great interest, having appeared (in 1764) between the dates of the two transits of Venus that took place in the 18th century.

AEQUI, an ancient people of Italy, whose name occurs constantly in Livy’s first decade as hostile to Rome in the first three Centuries of the city’s existence. They occupied the upper reaches of the valleys of the Anio, Tolenus and Himella; the last two being mountain streams running northward to join the Nar. Their chief centre is said to have been taken by the Romans about 484 (Diodorus xi. 40) and again about ninety years later (id. xiv. 106), but they were not finally subdued till the end of the second Samnite war (Livy ix. 45, x. 1; Diod. xx. 101), when they seem to have received a limited form of franchise (Cic. Off. i. 11, 35). All we know of their subsequent political condition is that after the Social war the folk of Cliternia and Nersae appear united in a res publica Aequiculorum, which was a municipium of the ordinary type (C.I.L. ix. p. 388). The Latin colonies of Alba Fucens (304 ) and Carsioli (298 ) must have spread the use of Latin (or what passed as such) all over the district; through it by the chief (and for some time the only) route (Via Valeria) to Luceria and the south.

Of the language spoken by the Aequi before the Roman conquest we have no record; but since the (q.v.), who lived farther east, spoke in the 3rd century  a dialect closely akin to Latin, and since the  (q.v.), their neighbours to the south-west, did the same, we have no ground for separating any of these tribes from the Latian group (see ). If we could be certain of the origin of the q in their name and of the relation between its shorter and its longer form (note that the i