JENIGM A AERONAUTICS. 



45 



Gnossus, who flourished a little later than Cicero, 

 snd taught scepticism, in Alexandria, to a greater 

 ext* nt than had been done before. He placed truth 

 in the general agreement of men as to the impres- 

 sions produced by external objects. 



.^ENIGMA ; a proposition put in obscure, ambigu- 

 ous, 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 jenigmas 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 cul- 

 tivation. A great part of the Egyptian learning is 

 said to have been comprised in asnigmas. In these, 

 Too, the ancient oracles often spoke. But the sym- 

 bols of the ancient religions should not, as is often 

 the case, be confounded with senigmas. (See Hiero- 

 glyphics.) They were in vogue among the Jews. 



^EOLIAN HARP, or .^EoMJs HARP, was introduced 

 into England about the middle of the last century. It 

 is generallya simple box of tin, 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 corres- 

 pond 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 tliree. 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 swell- 

 ing 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). 



JEoiJANs; a Greek tribe in Thessaly, who took 

 their name from ^Eolus, 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 JEolis. While 

 united in a confederacy, which held its yearly meet- 

 ings, with much solemnity, at Cuma, they long con- 

 tinued free ; afterwards, they came under the domi- 

 nion 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 Hys- 

 taspes, 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 tune 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 

 empire, they were totally subdued by Sylla, because 

 they had assisted Mithridates. Their language, the 

 .iKolian dialect, was one of the three principal dia- 

 lects of the Greek ; their country was one of the 

 most fertile in the world ; agriculture and the raising 

 of cattle were their chief occupations. 



dBoLiPiLE; a spherical vessel of metal, with a 

 pipe of small aperture, through which the vapour 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 aeolipile is used to remedy smoky 

 chimneys. , 



JJoLirs ; 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, fore 

 told die course of the winds, with the utmost exact- 

 ness, 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 scep- 

 tre, at which signal the winds rush out. He is re- 

 presented, also, standing in a grotto with a muscle in 

 his mouth, and a pair of bellows under his feet. 



/ERA is used synonymously with epoch or epoc/ia, 

 (q. v.) for a fixed point of time, from which any com- 

 putation of it is made. JEra 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 

 eera has been supposed to be derived from the abridg- 

 ment, or initial letters, of Annus Era Augusti, 

 A.E.R.A., a mode of computing time in Spain from 

 the year of the conquest of that country by the 

 Romans ; and Vossius favours this opinion. Various 

 feras 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 aera. Mariana says that the Spanish 

 aera ceased in the year of Christ 1383, under John 

 I., king of Castile. It continued to be used some- 

 what longer in Portugal. We must subtract 38 from 

 the number of a year of the Spanish aera to get that 

 of the Christian. The Mahommedan aera begins with 

 the flight of the prophet, 16th July, 622. This is 

 called the Hegira (q. v.) The ancient Roman aera 

 began with the building of the city, 750 before Christ. 

 The Jewish aera begins with the creation. 



AERIAL PERSPECTIVE ; that branch of the science 

 of perspective which treats of the relative diminution 

 of the colours of bodies hi proportion to their dis- 

 tance from the eye. 



AERIANS ; the followers of Aerius, 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, pro- 

 nounced 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 

 Aerians were condemned as heretics, and soon dis- 

 appeared. The protestants were accused of Aeri- 

 anism by the catholics, because they maintained 

 propositions of a similar character. 



AERODYNAMICS ; a branch of aerology, 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. 



AEROLITES ^stones or masses that descend from 

 the air. See Meteoric Stones. 



AERONAUTICS ; 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 until the last century. Henry 

 Cavendish, having discovered, about 1766, the groat 

 levity of inflammable ah* or hydrogen gas, Dr Black, 

 of Edinburgh, was led to the idea that a thin blad- 

 der, filled with this gas, must ascend into the air. 



