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A furlong is a measure of distance in imperial units and U.S. customary units equal to one-eighth of a mile, equivalent to 660 feet, 220 yards, 40 rods, or 10 chains. Using the international definition of the inch as exactly 25.4 millimetres, one furlong is 201.168 metres. However, the United States does not uniformly use this conversion ratio. Older ratios are in use for surveying purposes in some states, leading to variations in the length of the furlong of about two parts per million, or 0.4 millimetres ( inch). This variation is too small to have many practical consequences. Five furlongs are about 1.0 kilometre (1.00584 km is the exact value, according to the international conversion). ==History== The name ''furlong'' derives from the Old English words ' (furrow) and ' (long). Dating back at least to early Anglo-Saxon times, it originally referred to the length of the furrow in one acre of a ploughed open field (a medieval communal field which was divided into strips). The system of long furrows arose because turning a team of oxen pulling a heavy plough was difficult. This offset the drainage advantages of short furrows and meant furrows were made as long as possible. An acre is an area that is one furlong long and one chain (66 feet or 22 yards) wide. For this reason, the furlong was once also called an acre's length,〔 〕 though in modern usage an area of one acre can be of any shape. The term furlong, or shot, was also used to describe a grouping of adjacent strips within an open field. Among the early Anglo-Saxons, the rod was the fundamental unit of land measurement. A furlong was forty rods, an acre four by 40 rods, or four rods by one furlong. and thus 160 square rods. At the time, the Saxons used the North German foot, which was 10 percent longer than the foot of today. When England changed to the shorter foot in the late 13th century, rods and furlongs remained unchanged, since 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 definition of the rod went from 15 old feet to new feet, or from 5 old yards to new yards. The furlong went from 600 old feet to 660 new feet, or from 200 old yards to 220 new yards. The acre went from 36,000 old square feet to 43,560 new square feet, or from 4,000 old square yards to 4,840 new square yards. The furlong was historically viewed as being equivalent to the Roman stade (''stadium''), which in turn derived from the Greek system. For example, the King James Bible uses the term "furlong" in place of the Greek ''stadion'', although more recent translations often use miles or kilometres in the main text and give the original numbers in footnotes. In the Roman system, there were 625 feet to the ''stadium'', eight ''stadia'' to the mile, and three miles to the league. A league was considered to be the distance a man could walk in one hour, and the mile (from ''mille'', "meaning thousand") consisted of 1,000 ''passus'' (paces, five feet, or double-step). After the fall of the Roman Empire, medieval Europe continued with the Roman system, which the 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 the time were the foot, yard, rod(or pole), furlong, and the mile. The rod was defined as yards or feet, and the mile was eight furlongs, so the definition of the furlong became 40 rods and that of the mile became 5,280 feet (eight furlongs/mile times 40 rods/furlong times feet/rod). A description from 1675 states, "Dimensurator or Measuring Instrument whereof the mosts usual has been the Chain, and the common length for English Measures four Poles, as answering indifferently to the Englishs Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres." —John Ogilby, Britannia, 1675 The official use of the furlong was abolished in the United Kingdom under the Weights and Measures Act 1985, an act that also abolished the official use of many other traditional units of measurement. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「furlong」の詳細全文を読む スポンサード リンク
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