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mile: Definition from Answers.com

A mile is a unit of length, usually used to measure distance, in a number of different systems, including Imperial units, United States customary units and Norwegian/Swedish mil. Its size can vary from system to system, but in each is between one and ten kilometers. In contemporary English contexts mile refers to either:

the statute mile of 5,280 feet (1,609.344 m exactly), or 63,360 inches
the international nautical mile of exactly 1,852 meters (about 6,076 feet).

There have been several abbreviations for mile (with and without trailing period): mi, ml, m, M. In the United States, the National Institute of Standards and Technology now uses and recommends mi, but in everyday usage (at least in the U. S.) miles per hour is almost always abbreviated as mph or m.p.h. (rather than mi/h).

Historical definitions

A unit of distance called a mile was first used by the Romans and denoted a distance of 1,000 paces (one pace is two steps, 1,000 paces being, in Latin, mille passus) or 5,000 Roman feet, and corresponded to about 1,480 meters, or 1,618 modern yards.^[1]

The current definition of a mile as 5,280 feet (as opposed to 5,000) dates to the 13th century, and was confirmed by statute in the reign of Queen Elizabeth I; the change was needed to accommodate the rod which (as opposed to the mile) was a measure ensconced in legal documents (see the discussion about furlongs).

Types of mile

In modern usage, various distances are referred to as miles.

Statute miles

The Statute Mile is the distance typically meant when the word mile is used without other qualifying words (e.g. Nautical Mile, see below).

It originates from a Statute of the English parliament in 1592 during the reign of Elizabeth I. This defined the Statute Mile as 5,280 feet or 1,760 yards; or 63,360 inches. The reason for these rather irregular numbers is that 5,280 feet is made up of eight furlongs (the length generally that a furrow was ploughed before the horses were turned, furlong = furrow-long). In turn a furlong is ten chains (a surveyor's chain, used as such until laser range finders took over); a chain is 22 yards and a yard is three feet, making up 5,280 ft. Twenty-two yards is also the length of a cricket pitch, a game originating in England and played today particularly in countries that were once part of the British Empire.

Before the statute of the English parliament, there was confusion on the length of the "mile". The Irish mile was 2,240 yards (6,720 ft) and the Scottish mile was the length of the Royal Mile in Edinburgh, from the Castle to the Palace of Holyroodhouse, and was 1,976 yards (5928 ft). In England the Roman mile of 5,000 feet was often used, a length not divisible without fractions into furlongs or yards (5,000 ft = 1,666⅔ yards). For other "miles" see the list below. In the late 1500s, accurate ground mapping was becoming commonly available, such as Christopher Saxton's maps of the English Counties. Therefore, a standard mile became more important than before, hence the Parliamentary Statute. It may also have been related to the potential for taxation, for which a standard measure across the country would be required to prevent regional arguments about length and area.

The United States has two definitions of 'mile'
- The US statute mile is defined as 5,280 survey feet and is therefore 1,609.34722 metres.
- The US term 'international mile' is 5,280 'international feet' and is 1,609.344 metres.
The U.S. survey mile is based on an inch defined by 1 metre = 39.37 inches exactly. It is equal to 5,280 U.S. survey feet, 6,336/3,937 km or approximately 1,609.347 metres. One international mile is equal to 0.999 998 survey miles. The survey mile is used by the United States Public Land Survey System.

The United Kingdom definition is 1,609.344 metres and is contained in The Units of Measurement Regulations 1995.^[2]

Nautical miles

On the utility of the nautical mile
Each circle shown is a great circle – the analog of a line in spherical trigonometry – and hence the shortest path connecting two points on the globular surface.

The nautical mile was originally defined as one minute of arc along a meridian (or in some instances any great circle) of the Earth. Although this distance varies depending on the latitude of the meridian (or great circle) where it is used, on average it is about 6,076 feet (about 1852 m or 1.15 statute miles).

The nautical mile per hour is known as the knot.

Navigators use dividers to step off the distance between two points on the map, then place the open dividers against the minutes-of-latitude scale at the edge of the map, and read off the distance in Nautical Miles. Since it is now known that the Earth is an ellipsoid (spheroid), not a sphere, the distance of Nautical Miles derived from this method varies from the equator to the poles. For instance, using the WGS84 Ellipsoid, the commonly accepted Earth model for many purposes today, one minute of latitude at the WGS84 equator is 6,087 feet and at the poles is 6,067 feet.

In the United States of America, the nautical mile was defined in the nineteenth century as 6,080.2 feet (1,853.249 m), whereas in the United Kingdom the Admiralty Nautical Mile was defined as 6,080 feet (1,853.184 m) and was approximately one minute of latitude in the latitudes of the south of the UK. Other nations had different definitions of the nautical mile, but it is now internationally defined to be exactly 1,852 metres.

The nautical mile is almost universally used for navigation in aviation, maritime, and nautical roles because of its relationship with degrees and minutes of latitude and the ability to use the latitude scale of a map for distance measuring.

An alternative term - sea mile - is still used for the distance of one minute of latitude.^{[citation needed]}

Other miles

The Roman mile (Latin mille passus, plural milia passuum), equalled 1,000 double paces (passus, plural passūs) of five Roman feet (pēs, plural pedēs) each. Its length was 5,000 Roman feet, approximately 1500 m.
The Danish mile (Danish mil) was equal to 7,532 metres (or 24,000 Danish feet or 12,000 alen).
The Data mile is used in radar-related subjects and is equal to 6,000 feet (1.8288 kilometres).
The Dutch mile (the "Hollandic" mile) was nearly the 19th part of a degree (~5.8 kilometres).
The Dutch mile (or "Netherlandic" mile) was exactly one kilometre in the Dutch Metric System 1820-1870.
The German mile was reckoned to be the 15th part of a degree (and thus about four nautical miles in length or 6.4 kilometres).
The Irish mile was equal to 2,240 yards (2,048.256 m).
The Italian mile also called the Roman mile (~1.52 kilometres or 0.944 statute miles) was a thousand paces of five Roman feet each (the Roman foot being one fifth of an inch less than the London foot).
The term metric mile is used in sports such as athletics (track and field) and speedskating to denote a distance of 1.5 kilometres. In United States high school competition the term is sometimes used for a race of 1.6 kilometres.
The Norwegian/Swedish mil (the Swedish mile, currently used in Norway and Sweden) has been defined as ten kilometres from 1 January 1889, when a metric system was introduced in Sweden. The pre-metric mil (in earlier times rast, lit. rest, pause) was about 11.3 kilometres in Norway (see Long Mile below) and 10,688.54 metres in Sweden, representing a suitable distance between rests when walking. In informal and non-precise situations involving longer distances of several kilometres, the mil is, as a rule, used instead of the kilometre. It is also used commonly for measuring vehicle fuel consumption; litres per mil means litres consumed per ten kilometres.^[3]
The Polish mile was nearly equal to the Dutch mile.
The Scottish mile was equal to 1,976.5 yards (1,807.3116 m).
The long mile, traditionally used by the Norwegians, Swedes and Hungarians, was about a German mile and a half or around eleven kilometres.
The Finnish corresponding unit, virsta, was 1,068.8 m. Ten virsta made one peninkulma (literally "hound's hearing", a distance a dog's bark can be heard in still air), 10.688 km. Today peninkulma refers to ten kilometres in Finnish colloquial usage (compare mil in Norwegian and Swedish usage).
The swimmer's mile is 1,500 meters or 30 laps in a 25 meter pool. This (roughly) converts to 1650 yards in a 25 yard pool (33 laps), the standard distance for intercollegiate competition in the United States.
A country mile is used colloquially to denote a very long distance.
The radar mile is a unit of time, equal to the time required for a radar pulse to travel a distance of two miles (one mile each way). Thus, the radar statute mile is 10.8 μs and the radar nautical mile is 12.4 μs.^[4]

References

'Of Divers Measures', in Laurence Echard, 1741, The Gazetteer's or Newsman's Interpreter, London: Ballard et al. (first published 1703)

^ Smith, Dictionary of Greek and Roman Antiquities, page 762
^ [1]
^ [2]
^ A Dictionary of Units

External links

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