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Metric time

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Not to be confused withDecimal time.
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Metric timeis the measure of time intervals using themetric system.The modernSIsystem defines thesecondas thebase unitof time, and forms multiples and submultiples withmetric prefixessuch as kiloseconds and milliseconds. Other units of time –minute,hour,andday– areaccepted for use with SI,but are not part of it. Metric time is a measure of time intervals, whiledecimal timeis a means of recordingtime of day.

History[edit]

The second derives its name from thesexagesimalsystem, which originated with theSumeriansandBabylonians.This system divides a base unit into sixty minutes, each minute into sixty seconds, and each second into sixtytierces.The word "minute" comes from the Latinpars minuta prima,meaning "first small part", and "second" frompars minuta secundaor "second small part".Angular measurealso uses sexagesimal units; there, it is thedegreethat is subdivided into minutes and seconds, while in time, it is the hour.

In 1790, French diplomatCharles Maurice de Talleyrand-Périgordproposed that the fundamental unit of length for the metric system should be the length of apendulumwith a one-second period, measured at sea level on the 45th parallel (50 grades in the new angular measures), thus basing the metric system on the value of the second. A Commission of Weights and Measures was formed within the French Academy of Sciences to develop the system. The commission rejected the seconds-pendulum definition of themetrethe following year because the second of time was an arbitrary period equal to 1/86,400 day, rather than a decimal fraction of a natural unit. Instead, the metre would be defined as a decimal fraction of the length of theParis Meridianbetween theequatorand theNorth Pole.[1][2][3][4][5]

The commission initially proposed the decimal time units later enacted as part of the newRepublican calendar.In January, 1791,Jean-Charles de Bordacommissioned Louis Berthoud to manufacture a decimal chronometer displaying these units. On March 28, 1794, the commission's president,Joseph Louis Lagrange,proposed using the day (Frenchjour) as the base unit of time, with divisionsdéci-jourandcenti-jour,and suggested representing 4déci-joursand 5centi-joursas "4,5", "4/5", or just "45".[6]The final system, as introduced in 1795, included units for length, area, dry volume, liquid capacity, weight or mass, and currency, but not time.Decimal time of dayhad been introduced in France two years earlier, but mandatory use was suspended at the same time the metric system was inaugurated, and did not follow the metric pattern of a base unit and prefixed units.

Base units equivalent to decimal divisions of the day, such as 1/10, 1/100, 1/1,000, or 1/100,000 day, or other divisions of the day, such as 1/20 or 1/40 day, have also been proposed, with various names. Such alternative units did not gain any notable acceptance. In China, during theSong Dynasty,a day was divided into smaller units, calledkè(Khắc). Onekèwas usually defined as1⁄100of a day until 1628, though there were short periods before then where days had 96, 108 or 120kè.[7]A kè is about 14.4 minutes, or 14 minutes 24 seconds. In the 19th century, Joseph Charles François de Rey-Pailhade endorsed Lagrange’s proposal of usingcentijours,but abbreviatedcé,and divided into 10decicés,100centicés,1,000millicés,[8]and 10,000dimicés.[9][10]

James Clerk MaxwellandElihu Thomson(through theBritish Association for the Advancement of Science,or BAAS) introduced theCentimetre gram second system of unitsin 1874 to derive electric and magnetic metric units, following the recommendation ofCarl Friedrich Gaussin 1832.

In 1897, theCommission de décimalisation du tempswas created by the FrenchBureau of Longitude,with the mathematicianHenri Poincaréas secretary. The commission proposed making the standardhourthe base unit of metric time, but the proposal did not gain acceptance and was eventually abandoned.[11]

When the modernSIsystem was defined at the 10thGeneral Conference on Weights and Measures(CGPM) in 1954, the ephemeris second (1/86400 of a mean solar day) was made one of the system's base units. Because the Earth's rotation is slowly decelerating at an irregular rate and was thus unsuitable as a reference point for precise measurements, the SI second was later redefined more precisely as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of theground stateof thecaesium-133 atom. The international standardatomic clocksuse caesium-133 measurements as their main benchmark.

In computing[edit]

In computing, at least internally, metric time gained widespread use for ease of computation.Unix timegives date and time as the number of seconds since January 1, 1970, and Microsoft'sNTFSFILETIME as multiples of 100 ns since January 1, 1601.VAX/VMSuses the number of 100 ns since November 17, 1858, andRISC OSthe number of centiseconds since January 1, 1900.Microsoft Exceluses number of days (with decimals,floating point) since January 1, 1900.

All these systems present time for the user using traditional units. None of these systems is strictly linear, as they each have discontinuities atleap seconds.

Prefixes[edit]

Metric prefixes for subdivisions of a second are commonly used in science and technology. Milliseconds and microseconds are particularly common. Prefixes for multiples of a second are rarely used:

Multiple Name of unit Seconds In common units
101 decasecond 10 0.17 minutes
102 hectosecond 100 1.67 minutes (or 1 minute 40 seconds)
103 kilosecond 1000 16.7 minutes (or 16 minutes and 40 seconds)
106 megasecond 1000000 11.6 days (or 11 days, 13 hours, 46 minutes and 40 seconds)
109 gigasecond 1000000000 31.7 years (or 31 years, 252 days, 1 hour, 46 minutes, 40 seconds, assuming that there are 7 leap years in the interval)

See also[edit]

References[edit]

  1. ^Alder, Ken (2002).The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World.New York: Free Press. pp. 291–323.ISBN978-0-7432-1675-3.
  2. ^Schwartz, Randy K. (September 2008)."The Birth of the Meter"(PDF).The Mathematical Association of America.Retrieved4 April2023.
  3. ^Commission des poids et mesures (1793). Haüy, René-Just (ed.).Instruction abrégée sur les mesures déduites de la grandeur de la Terre, uniformes pour toute la République, et sur les calculs relatifs à leur division décimale; par la Commission temporaire des poids & mesures républicaines, en exécution des décrets de la Convention nationale. Édition originale(in French). France: de l'imprimerie nationale exécutive du Louvre (A Paris).
  4. ^Frangsmyr, Tore; Heilbron, J. L.; Rider, Robin E. (1990).The Quantifying Spirit in the 18th Century.Berkeley: University of California Press.
  5. ^de Borda, Jean-Charles; de Condorcet, Nicolas (1791).Rapport sur le choix d'une unité de mesure(in French). Paris: L'IMPRIMERIE NATIONALE.OL25945285M.
  6. ^Procès-verbaux du Comité d'instruction publique de la Convention nationale.1897. p. 605.
  7. ^Sôma, Mitsuru; Kawabata, Kin-aki; Tanikawa, Kiyotaka (2004-10-25)."Units of Time in Ancient China and Japan".Publications of the Astronomical Society of Japan.56(5): 887–904.Bibcode:2004PASJ...56..887S.doi:10.1093/pasj/56.5.887.ISSN0004-6264.
  8. ^Histoire d'heure - Fractionnement du tempsArchived2015-05-22 at theWayback Machine
  9. ^"AJB, Volume 9, 1907".1908.
  10. ^"Report of the Sixth International Geographical Congress: Held in London, 1895".1896.
  11. ^"Einstein's Clocks, Poincare's Maps: empires of time By Peter Louis Galison".

External links[edit]

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