Furlong

In metrology, the furlong is a measure of length in imperial units and the "United States customary units" equal to one eighth of a mile, equal to 660 feet, 220 yards, 40 rods, 10 chains, or approximately 201 meters. Now, it is almost obsolete, except in horse racing, where in many countries it is the standard measure for track lengths.

In the United States, some states use the old definition for surveying purposes, leading to variations in furlong length of two parts per million, or about 0.4 millimeters (1⁄64 inch). This variation is too small to have practical consequences in many applications.

Using the international definition of the yard as exactly 0.9144 meters, a furlong is 201.168 meters and five furlongs is about 1 kilometer (1.00584 km exactly).

History

The name "furlong" derives from the Old English word "furth" (groove) and "lang" (long). Dated before, at least, the beginning of Anglo-Saxon times. Originally, it referred to the furrow length in one acre of an open plowed field (a communal medieval field, which was divided into strips). The furlong (meaning furrow length) was the distance that a team of oxen could plow without resting. This was standardized to be exactly 40 rods or 10 chains. The long furrow system arose because turning a team of oxen pulling a heavy plow was difficult. This offset the advantages of small furrow drainage and meant the furrows were made as long as possible. An acre is an area one furlong and one ridge (66 feet or 22 yards) wide. For this reason, the furlong was once called an 'acre length', although, in modern usage, an area of an acre can be any shape. The term furlong, or "shot", was also used to describe a grouping of adjacent stripes in an open field.

Among the early Anglo-Saxons, the "rod" it was the fundamental unit of land measurement.

At that time, the Saxons used the North German foot, which was about 10% longer than the 1959 International Agreement foot. When England switched to a smaller foot at the turn of the century XIII, the rods and furlongs remained unchanged, as property boundaries were already defined in rods and furlongs. The only thing that changed was the number of feet and yards in a rod or a furlong, and the number of square feet and square yards in an acre. The definitions went from the old to the new, like this:

The furlong was, historically, seen as being equivalent to the Roman furlong, which instead derived from the Greek system. For example, the King James Bible uses the term "furlong" instead of the Greek stadia, although more recent translations often use miles or kilometers in the main text and give the original numbers in footnotes.

In the Roman system:

A league was considered to be the distance a man could walk in an hour, and the mile (from "mille", meaning "thousand") consisted of 1,000 passus (steps, 5 feet, or double step).

After the fall of the Western Roman Empire, medieval Europe continued with the Roman system, which people proceeded to diversify, leading to serious complications in trade, taxation, etc. Around the year 1300, by royal decree; England standardized a long list of measures. Among the important units of distance and length, at that time, were the foot, the yard, the rod (or pole), the furlong, and the mile.

A description of 1675 states, "the measurer or measuring instrument of which the most usual has been the chain, and the common length for English measures four poles, as answering indifferently to the English mile and acre, 10 such chains in length making a furlong, and 10 simple square chains an acre, so that the square mile contains 640 square acres" -John Ogilby, Britannia, 1675

The official use of the furlong was abolished in the UK under the "Weights and Measures Act 1985", an act which also abolished the official use of several other, traditional units of measurement.

Use

In Myanmar, furlongs are currently used in conjunction with miles to indicate distances on highway signs. Mile posts on the Yangon-Mandalay Expressway use miles and furlongs.

In the rest of the world, the furlong has limited use, with the notable exception of horse racing in most English-speaking countries, including Canada and the United States. Distances for horse racing in Australia were converted to metric in 1972, but in the United Kingdom, Ireland, Canada, and the United States, races are still given in miles and furlongs. Also distances along English channels navigated by narrow boats are commonly expressed in miles and furlongs.

The city of Chicago street numbering system assigns a measurement of 800 address units to each mile, to keep up with the city system of eight blocks per mile. This means that each block in a typical Chicago neighborhood (in either north-south or east-west direction, but rarely both) is approximately one furlong in length. Salt Lake City blocks are also each one square furlong in the downtown area. The blocks become less regular in shape the further from the center, but the numbering system (800 units for each mile) remains the same throughout Sal Lake County. Blocks in central Logan, Utah and large sections of Phoenix, Arizona are similarly one square furlong in extent (eight to one mile, which explains the series of freeways that exist: 19th Ave, 27th, 35th, 43rd, 51st, 58th..). The city blocks in Melbourne's Hoddle Grid are also a furlong in length.

Much of Ontario, Canada, was originally surveyed on a ten-furlong grid, with major roads being sketched along grid lines. Now, those distances are shown on highway signs in kilometers, these major roads are almost exactly two kilometers apart. Exits on highways that run through Toronto, for example, are generally at two-kilometre intervals.

The furlong is also a base unit of the humorous "FFF system" Of units.

Length definition

The exact length of the furlong varies slightly between English-speaking countries. In Canada and the United Kingdom, which define the furlong in terms of the international yard of exactly 0.9144 metres, a furlong is 201.168m. Australia does not formally define the furlong, but does define the chain and link in terms of the international yardage.

In the United States, which defines the furlong, chain, rod, and link in terms of the "U.S. survey foot" of exactly 1200⁄3937 meters, a furlong is approximately 201.1684 m long. The United States does not formally define a "survey yard." The difference of approximately two parts per million between the US value and the "international" it is negligible for many practical measurements.

In October 2019, the "U.S. National Geodetic Survey" and the "National Institute of Standards and Technology" announced their joint attempt to retire the US survey foot, effective the end of 2022. The furlong on the "U.S. Customary units" it is since then defined based on the 1959 international foot, giving it the furlong length as exactly 201.168 meters in the United States, as well.

Equivalences

A furlong equals:

Eight furlongs equals one mile.