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According to ancient and medieval science, aether ( ''aithēr''), also spelled æther or ether, also called quintessence, is the material that fills the region of the universe above the terrestrial sphere. The concept of aether was used in several theories to explain several natural phenomena, such as the traveling of light and gravity. In the late 19th century, physicists postulated that aether permeated all throughout space, providing a medium through which light could travel in a vacuum, but evidence for the presence of such a medium was not found in the Michelson–Morley experiment.〔Whittaker, Edmund Taylor (1910). ''A History of the theories of aether and electricity'' (1st ed.). Dublin: Longman, Green and Co.〕 ==Mythological origins== (詳細はHomeric Greek means "pure, fresh air" or "clear sky". In Greek mythology, it was thought to be the pure essence that the gods breathed, filling the space where they lived, analogous to the ''air'' breathed by mortals. It is also personified as a deity, Aether, the son of Erebus and Nyx in traditional Greek mythology. Aether is related to "to incinerate",〔Pokorny, Julius (1959). Indogermanisches etymologisches Wörterbuch, s.v. ''ai-dh-.''〕 and intransitive "to burn, to shine" (related is the name ''Aithiopes'' (Ethiopians; see Aethiopia), meaning "people with a burnt (black) visage").〔(Αἰθίοψ ) in Liddell, Scott, ''A Greek–English Lexicon'': "Αἰθίοψ , οπος, ὁ, fem. Αἰθιοπίς , ίδος, ἡ (Αἰθίοψ as fem., A.Fr.328, 329): pl. 'Αἰθιοπῆες' Il.1.423, whence nom. 'Αἰθιοπεύς' Call.Del.208: (αἴθω, ὄψ):— properly, Burnt-face, i.e. Ethiopian, negro, Hom., etc.; prov., Αἰθίοπα σμήχειν 'to wash a blackamoor white', Luc.Ind. 28." Cf. ''Etymologicum Genuinum'' s.v. , ''Etymologicum Gudianum'' s.v.v. . 〕 See also ''Empyrean''. ==Fifth element== In Plato's ''Timaeus'' (58d) speaking about air, Plato mentions that "there is the most translucent kind which is called by the name of aether (αίθηρ)".〔Plato, ''Timaeus'' (58d ).〕 but otherwise he adopted the classical system of four elements. Aristotle, who had been Plato's student at the Akademia, agreed on this point with his former mentor, emphasizing additionally that fire sometimes has been mistaken for aether. However, in his Book ''On the Heavens'' he introduced a new "first" element to the system of the classical elements of Ionian philosophy. He noted that the four terrestrial classical elements were subject to change and naturally moved linearly. The first element however, located in the celestial regions and heavenly bodies, moved circularly and had none of the qualities the terrestrial classical elements had. It was neither hot nor cold, neither wet nor dry. With this addition the system of elements was extended to five and later commentators started referring to the new first one as the fifth and also called it ''aether'', a word that Aristotle had not used.〔Hahm, David E., ''The Fifth Element in Aristotle's De Philosophia: A Critical Re-Examination'', The Journal of Hellenic Studies 102 (1982): 60-74.〕 Aether did not follow Aristotelian physics either. Aether was also incapable of motion of quality or motion of quantity. Aether was only capable of local motion. Aether naturally moved in circles, and had no contrary, or unnatural, motion.〔G. E. R. Lloyd), ''Aristotle: The Growth and Structure of his Thought'', Cambridge: Cambridge Univ. Pr., 1968, pp. 133-139, ISBN 0-521-09456-9.〕 Aristotle also noted that crystalline spheres made of aether held the celestial bodies. The idea of crystalline spheres and natural circular motion of aether led to Aristotle's explanation of the observed orbits of stars and planets in perfectly circular motion in crystalline aether. Medieval scholastic philosophers granted ''aether'' changes of density, in which the bodies of the planets were considered to be more dense than the medium which filled the rest of the universe. Robert Fludd stated that the aether was of the character that it was "subtler than light". Fludd cites the 3rd-century view of Plotinus, concerning the aether as penetrative and non-material.〔Robert Fludd, "Mosaical Philosophy". London, Humphrey Moseley, 1659. Pg 221.〕 See also Arche. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Aether (classical element)」の詳細全文を読む スポンサード リンク
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