Metric time

Metric time is the measure of time interval using the metric system, which defines the second as the base unit of time, and multiple and submultiple units formed with metric prefixes, such as kiloseconds and milliseconds. It does not define the time of day, as this is defined by various time scales, which may be based upon the metric definition of the second. Other units of time, the minute, hour, and day, are accepted for use with the modern metric system, but are not part of it.

Although part of the decimal metric system, the second derives its name from the sexagesimal system, which originated with the Sumerians and Babylonians, and divides a base unit into sixty minutes, minutes into sixty seconds, seconds into sixty tierces, etc. The word "minute" comes from the Latin pars minuta prima, meaning first small part, and "second" from pars minuta secunda or second small part. Angular measure also uses these sexagesimal units; in that field, it is the degree that is subdivided into minutes and seconds, while in time, it is the hour.

When the metric system was introduced in France in 1795, it included units for length, area, dry volume, liquid capacity, weight or mass, and even currency, but not for time. Decimal time of day had been introduced in France two years earlier, but was set aside at the same time the metric system was inaugurated, and did not follow the metric pattern of a base unit and prefixed units. James Clerk Maxwell and Elihu Thomson (through the British Association for the Advancement of Science - BAAS) introduced the Centimetre gram second system of units (cgs) in 1874, in order to derive electric and magnetic metric units, following the recommendation of Carl Friedrich Gauss in 1832.

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