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Myria- (symbol my) is a now obsolete decimal metric prefix denoting a factor of 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.
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.
- 29th Congress of the United States, Session 1 (1866-05-13). "H.R. 596, An Act to authorize the use of the metric system of weights and measures". Archived from the original on 2013-05-10. Retrieved 2015-10-12.
- Brewster, David (1830). "Measures". The Edinburgh Encyclopædia. 13. Edinburgh, UK: William Blackwood, John Waugh, John Murray, Baldwin & Cradock, J. M. Richardson. p. 494. Retrieved 2015-10-09.
- Brewster, David (1832). "Measures". The Edinburgh Encyclopædia. 12 (1st American ed.). Joseph and Edward Parker. p. 572. Retrieved 2015-10-09.
- Lange, Norbert Adolph; Forker, Gordon M. (1956) . Handbook of Chemistry (9 ed.). Sandusky, Ohio, USA: Handbook Publishers, Inc.
- Lange, Norbert Adolph (1973) . Dean, John Aurie, ed. Lange's Handbook of Chemistry (11 ed.). New York, USA: McGraw-Hill Book Company. pp. 3–16. ISBN 0-07-016190-9. Retrieved 2016-08-28.
Prefixes for Naming Multiples and Submultiples of Units: […] The prefix "myria" is sometimes used for 104 and "lakh" for 105.
- Cardarelli, François (2012) . Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins. Translated by Shields, M. J. (reworked ed.). Springer Science & Business Media. p. 17. ISBN 978-1-4471-0003-4. Retrieved 2016-08-24.
- "La Loi Du 18 Germinal An 3 - Décision de tracer le mètre, unité fondamentale, sur une règle de platine. Nomenclature des "mesures républicaines". Reprise de la triangulation" (in French). histoire.du.metre.free.fr. Retrieved 2015-10-12.
- Wallis, John (1685). A Proposal about Printing a Treatise of Algebra, Historical and Practical. University of Oxford, UK: John Davis. p. 16. Retrieved 2017-01-21.
And yet if this Number be not thought large enough, let all these (saith he) be called the First Period; and this Unit, an Unit of the first Numbers of the second Period; and (after so many places more) an Unit of the first Numbers (or Classis) of the third Period; and so onward to a Myriad of Myriads of such Periods: The last Unit of which, that is, one Myriad of Myriads, of the Myrio-myresimal Classes, of such Myrio-myresimal Period, answers (in our Notation) to 1 followed by 8, 0000, 0000, 0000, 0000, Ciphers: That is, 1 with Eight Myriads of Myriads of Myriads of Myriads of Ciphers.
- Cooley, Le Roy Clark (1889). The New Text-book of Chemistry: For Use in High Schools and Academies.
10 kiloliters = 1 myrioliter
- The West American Scientist. 1895.
The myriogram equals 22.046 lbs. avoirdupois.
- Dingler, Johann Gottfried (1823). Polytechnisches Journal (in German). 11. Stuttgart, Germany: J.W. Gotta'schen Buchhandlung. Retrieved 2015-10-09.
- Appell, Wolfgang (2009-09-16) . "Königreich Frankreich" [Kingdom of France]. Amtliche Maßeinheiten in Europa 1842 [Official units of measure in Europe 1842] (in German). Archived from the original on 2011-10-05. Retrieved 2011-02-10 (Website based on Alte Meß- und Währungssysteme aus dem deutschen Sprachgebiet, ISBN 3-7686-1036-5.)
- Benoît, Jean-René (1905). "Annex 1". In Comité International des Poids et Mesures. Procès-Verbaux des Séances (PDF) (in French). 3 (2 ed.). Paris, France: Gauthier-Villars, imprimeur-libraire du Bureau des Longitudes, de l'École Polytechnique. p. 176. Retrieved 2015-10-12.
- Comité International des Poids et Mesures (1935). "Procès-Verbaux des Séances" (in French). 17 (2 ed.). Paris, France: Gauthier-Villars, imprimeur-libraire du Bureau des Longitudes, de l'École Polytechnique: 76.
- Roberts, Richard W. (1975-06-01). Metric System of Weights and Measures - Guidelines for Use. USA: Director of the National Bureau of Standards. Federal Register FR Doc.75-15798 (1975-06-18).
Accordingly, the following units and terms listed in the table of metric units in section 2 of the act of July 28, 1866, that legalized the metric system of weights and measures in the United States, are no longer accepted for use in the United States: myriameter, stere, millier or tonneau, quintal, myriagram, kilo (for kilogram).
- Judson, Lewis V. (1976-10-01) . "Appendix 7". In Barbrow, Louis E. Weights and Measures Standards of the United States, a brief history (PDF). Derived from a prior work by Louis A. Fisher (1905). USA: US Department of Commerce, National Bureau of Standards. p. 33. LCCN 76-600055. NBS Special Publication 447; NIST SP 447; 003-003-01654-3. Retrieved 2015-10-12.
- Danloux-Dumesnils, Maurice (1969). The metric system: a critical study of its principles and practice. The Athlone Press. p. 34. Retrieved 2015-10-09. (a translation of the French original Esprit et bon usage du systeme metrique, 1965)