Millimeters, Inches, Feet, MilesDate: 07/10/2003 at 19:23:10 From: Erik Subject: Metric to English/British conversion The question is rather elementary, but one for which I haven't found a satisfactory answer. The conversions given for millimeters to inches is 25.4, and for feet to miles is 5280. Are these numbers exact? Are there exactly 160934400 millimeters in 100 miles? Date: 07/10/2003 at 22:48:40 From: Doctor Peterson Subject: Re: Metric to English/British conversion Hi, Erik. Surprisingly, these two conversions are both exact. For details on the current definition of the inch, see A Tale of Two Feet OR The Case of The Double Standard - T. J. Keefe http://physics.ccri.cc.ri.us/keefe/twofeet.htm The US Metric Law of 1866 said that one meter was equal to 39.37 inches, exactly. In 1959, the relationship between inches and centimeters was redefined to be that one inch is equal to 2.54 centimeters, exactly. Maps produced by the US Coast and Geodetic Survey continued to use the old standard. To clarify which foot you are talking about, the old foot, derived from 1 meter = 39.37 inches (exactly), is referred to as the "US survey foot". The new foot, derived from 1 inch = 2.54 cm (exactly), is referred to as the "international foot". Of course, this is the American definition; I don't know whether the British inch is defined the same way. See also Inch - Eric Weisstein's World of Physics http://scienceworld.wolfram.com/physics/Inch.html An nonmetric unit of length, originally defined as the lengths of three "average size" barleycorns laid end-to-end, but now more rationally defined as 2.54 cm. An older definition no longer used was 1 meter = 39.37 inches, giving 2.54000508 cm/inch. The number of feet in a mile has always been a whole number, though not always the same one. According to How Many? A Dictionary of Units of Measurement - Russ Rowlett http://www.unc.edu/~rowlett/units/ The word comes from the Latin word for 1000, mille, because originally a mile was the distance a Roman legion could march in 1000 paces (or 2000 steps, a pace being the distance between successive falls of the same foot). There is some uncertainty about the length of the Roman mile. Based on the Roman foot of 29.6 centimeters and assuming a standard pace of 5 Roman feet, the Roman mile would have been 1480 meters (4856 feet); however, the measured distance between surviving milestones of Roman roads is often closer to 1520 meters or 5000 feet. In any case, miles of similar lengths were used throughout Western Europe. In medieval Britain, several mile units were used, including a mile of 5000 feet (1524 meters), the modern mile defined as 8 furlongs (1609 meters), and a longer mile similar to the French mille (1949 meters), plus the Scottish mile (1814 meters) and the Irish mile (2048 meters). In 1592 the British Parliament settled the question by defining the statute mile to be 8 furlongs, 80 chains, 320 rods, 1760 yards or 5280 feet. The statute mile is exactly 1609.344 meters. If you have any further questions, feel free to write back. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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