myrio-

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.

In 1685 John Wallis proposed the usage of myrio.
Also, in 19th century English it was sometimes spelled myrio, in line with a puristic opinion by Thomas Young.

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. (Website based on ''Alte Meß- und Währungssysteme aus dem deutschen Sprachgebiet'', .) 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)
*hebdo-
* Obsolete metric prefix

References

{{Reflist, refs=
{{cite book , title=A Proposal about Printing a Treatise of Algebra, Historical and Practical , author-first=John , author-last=Wallis , author-link=John Wallis , publisher=John Davis , location=University of Oxford, UK , date=1685 , page=16 , url=https://books.google.com/books?id=TXpmAAAAcAAJ , access-date=2017-01-21 , quote=And yet if this Number be not thought large enough, let all these (saith he) be called the ''First Period''; and this ''Unit'', a Unit of the first Numbers of the second Period; and (after so many places more) a 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.
{{cite book , date=1889 , author-first=Le Roy Clark , author-last=Cooley , title=The New Text-book of Chemistry: For Use in High Schools and Academies , publisher=Ivison, Blakeman, Taylor& Company , url=https://archive.org/details/newtextbookchem01coolgoog , quote=10 kiloliters = 1 myrioliter
{{cite book , date=1895 , title=The West American Scientist , quote=The myriogram equals 22.046 lbs. avoirdupois.

Greek words and phrases
Metric prefixes
Decimal prefixes