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Myria- is a now obsolete decimal metric prefix equal to 104 (ten thousand). It originates from the Greek μύριοι (''mýrioi'') (myriad). The prefix was part of the original metric system adopted by France in 1795, but was not adopted when the SI prefixes were internationally adopted by the 11th CGPM conference in 1960. Based on a proposal of Thomas Young, some early 19th century publications used ''myrio-'' as a synonym for ''myria-''.〔〔 The ''myriametre'' (10 km) is occasionally encountered in 19th-century train tariffs, or in some classifications of wavelengths as the adjective ''myriametric''. The French ''mesures usuelles'' (1812-1839) did not include any units of length greater than the ''toise'', but the ''myriametre'' remained in use throughout this period. In Sweden and Norway, the ''myriametre'' is still common in everyday use. In these countries this unit is called ''mil''. Of units customarily used in trade in France, the ''myriagramme'' (10 kg) was the metric replacement for an avoirdupois unit, the ''quartier'' (25 pounds). Isaac Asimov's novel ''Foundation and Empire'' still mentioned the ''myriaton'' in 1952. The myria’s symbol of ''my'' ultimately led to its demise. In 1905 the Comité International des Poids et Mesures (CIPM) assigned it the symbol ''M'', wishing to use only single-letter symbols. This meant that myriameter, for example, was abbreviated Mm. But in the first part of the twentieth century, electrical engineers began to use capital M for the prefix mega-, as in megawatt and megohm. This usage became so widely and firmly adopted that in 1935 the CIPM adopted the prefix “mega-” with “M” as its symbol, dropping the myria- entirely. In 1975, the United States, having previously authorized use of the myriameter and myriagram in 1866, declared the terms no longer acceptable. ==See also== *Myriagon *Myriapoda *dimi- (aka decimilli-, a former French metric prefix denoting the inverse (10-4) of the myria- prefix up to 1961〔 (a translation of the French original ''Esprit et bon usage du systeme metrique'', 1965)〕 *Obsolete metric prefix 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「Myria-」の詳細全文を読む スポンサード リンク
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