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Air is often seen as a universal power or pure substance. Its fundamental importance to life can be seen in words such as ''aspire'', ''inspire'', ''perspire'' and ''spirit'', all derived from the Latin ''spirare''. ==Greek and Roman tradition== Air is one of the four classical elements in ancient Greek philosophy and science. According to Plato, it is associated with the octahedron; air is considered to be both hot and wet. The ancient Greeks used two words for air: ''aer'' meant the dim lower atmosphere, and ''aether'' meant the bright upper atmosphere above the clouds.〔W. K. C. Guthrie, ''A History of Greek Philosophy'', vol. 1, pp. 466, 470–71.〕 Plato, for instance writes that "So it is with air: there is the brightest variety which we call ''aether'', the muddiest which we call mist and darkness, and other kinds for which we have no name...."〔Plato, ''Timaeus'', ch. 27, p. 83.〕 Among the early Greek Pre-Socratic philosophers, Anaximenes (mid-6th century BCE) named air as the ''arche''.〔Guthrie, ''History of Greek Philosophy'', vol. 1, pp. 115–16, 120–32; Jonathan Barnes, ''Early Greek Philosophy'', pp. 77–80.〕 A similar belief was attributed by some ancient sources to Diogenes Apolloniates (late 5th century BCE), who also linked air with intelligence and soul (''psyche''), but other sources claim that his ''arche'' was a substance between air and fire.〔Guthrie, vol. 2, pp. 362–81; Barnes, pp. 289–94.〕 Aristophanes parodied such teachings in his play ''The Clouds'' by putting a prayer to air in the mouth of Socrates. Air was one of many ''archai'' proposed by the Pre-socratics, most of whom tried to reduce all things to a single substance. However, Empedocles of Acragas (c. 495-c. 435 BCE) selected four ''archai'' for his four roots: Air, fire, water, and earth. Ancient and modern opinions differ as to whether he identified air by the divine name Hera, Aidoneus or even Zeus. Empedocles’ roots became the four classical elements of Greek philosophy.〔Guthrie, vol. 2, pp. 138–46. Guthrie suggests that Hera is the safest identification for air.〕 Plato (427–347 BCE) took over the four elements of Empedocles. In the ''Timaeus'', his major cosmological dialogue, the Platonic solid associated with air is the octahedron which is formed from eight equilateral triangles. This places air between fire and water which Plato regarded as appropriate because it is intermediate in its mobility, sharpness, and ability to penetrate. He also said of air that its minuscule components are so smooth that one can barely feel them.〔Plato, ''Timaeus'', chap. 22–23; Gregory Vlastos, ''Plato’s Universe'', pp. 66–82.〕 Plato's student Aristotle (384–322 BCE) developed a different explanation for the elements based on pairs of qualities. The four elements were arranged concentrically around the center of the universe to form the sublunary sphere. According to Aristotle, air is both hot and wet and occupies a place between fire and water among the elemental spheres. Aristotle definitively separated air from aether. For him, aether was an unchanging, almost divine substance that was found only in the heavens, where it formed celestial spheres.〔G. E. R. Lloyd, ''Aristotle'', chapters 7–8.〕 In ancient Greek medicine, each of the four humours became associated with an element. Blood was the humor identified with air, since both were hot and wet. Other things associated with air and blood in ancient and medieval medicine included the season of spring, since it increased the qualities of heat and moisture; the sanguine temperament (of a person dominated by the blood humour); hermaphrodite (combining the masculine quality of heat with the feminine quality of moisture); and the northern point of the compass.〔Londa Schiebinger, p. 162.〕 The alchemical symbol for air is an upward-pointing triangle, bisected by a horizontal line. 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「Air (classical element)」の詳細全文を読む スポンサード リンク
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