Yard

1 yard =
US customary/Imperial units
36 in 3 ft
SI units
0.9144 m

A yard (abbreviation: yd) is a unit of length in several different systems including English units, Imperial units and United States customary units. It is equal to 3 feet or 36 inches. Under an agreement in 1959 between Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States, the yard (known as the "international yard" in the United States) was legally defined to be exactly 0.9144 metres.[3] Prior to that date, the legal definition of the yard when expressed in terms of metric units varied slightly from country to country.

Contents

Equivalence to other units of length

1 international yard is equal to:

The early yard was divided by the binary method into two, four, eight and sixteen parts called the half-yard, span (unit), finger (unit) and nail (unit) respectively. Two yards are a fathom.

Historical origin

The yard derives its name from the word for a straight branch or rod,[4] although the precise origin of the measure is not definitely known. Some believe it derived from the double cubit, or that it originated from cubic measure, others from its near equivalents, like the length of a stride or pace. One postulate was that the yard was derived from the girth of a person's waist, while another claim held that the measure was invented by Henry I of England as being the distance between the tip of his nose and the end of his thumb.[5]

It was first defined in law by Edward I of England in 1305,[6][7][8] and again by Edward III of England in 1353.[9] Edward I's law stated "It is ordained that three grains of barley, dry and round, make an inch; 12 inches make a foot; 3 feet make an "ulna"; 5½ ulne make a perch; and 40 perches in length and 4 perches in breadth make an acre". It goes on to make reference to "the Iron Ulna of our Lord the King [that] contains 3 feet and no more".

Watson is of the opinion that the purpose of Edward I's legislation was to unify the measures of land and shorter units of length into a single system of measure, and that the words "3 feet and no more" were added to ensure the perch and chain were the same throughout the kingdom; the "iron ulna of ... the King" being nothing more that the mechanism by which this unification was achieved. He dismisses as "childish" the suggestion that the original yard was the length of the king's arm.[8]

In the mid-18th century Graham compared the standard yard of the Royal Society to other existing standards. These were a "long-disused" standard made in the time of Henry VIII, and a brass yard and a brass ell from the time of Queen Elizabeth and still in current use, held at the Exchequer; a brass yard and a brass ell at the Guildhall; and a brass yard presented to the Clock-Makers' Company by the Exchequer in 1671. The Exchequer yard was taken as "true"; the variation was found to be +1⁄20 to -1⁄15 of an inch, and an additional graduation for the Exchequer yard was made on the Royal Society's standard. In 1758 the legislature required the construction of a standard yard, which was made from the Royal Society's standard and was deposited with the clerk of the House of Commons; it was divided into feet, one of the feet into inches, and one of the inches into tenths. A copy of it, but with upright cheeks between which other measuring rods could be placed, was made for the Exchequer for commercial use.[10]

Following Royal Society investigations by John Playfair, Hyde Wollaston and John Warner in 1814 a committee of parliament proposed defining the standard yard based upon the length of a seconds pendulum. This was enacted in 1824.[11] This is 39.1392 inches, and can be derived from the number of beats (86,400) between two meridians of the sun. The temperature compensated pendulum was to be held in a vacuum at sea level in Greenwich, London to give the length of the standard yard. However, a new physical Imperial Standard Yard was authorised by the Weights and Measures Act 1878,[12] and was the legal standard in the United Kingdom until 1964. The "United Kingdom primary standard of the yard" (the old "Imperial Standard Yard") was measured as 0.914 396 9 metres in May 1963, one part in 300,000 shorter than the international yard that became the new legal standard, and was found to be shortening at a rate of about one part per million every 23 years.[13]

Current use

The yard is used as the standard unit of field-length measurement in American,[14] Canadian[15] and Association football,[16] in addition to Cricket[17] and Golf hole measurement for some countries.

There are corresponding units of area and volume: the square yard and cubic yard respectively. These are sometimes referred to simply as "yards" when no ambiguity is possible, for example an American or Canadian concrete mixer may be marked with a capacity of "11 yards" or "1.5 yards", where cubic yards are obviously referred to.

Yards are also used in road signs on roads in the United Kingdom[18] and the United States to specify short distances.

See also

References

  1. ^ Bennett, Keith (2004), Bucher, Jay L., ed., The Metrology Handbook, Milwaukee, WI: American Society for Quality Measurement, p. 8, ISBN 978-0-87389-620-7 .
  2. ^ Walford, Edward (1878), Old and New London, VI, http://www.british-history.ac.uk/report.aspx?compid=45276 .
  3. ^ a b A. V. Astin & H. Arnold Karo, (1959), Refinement of values for the yard and the pound, Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59-5442, Filed, June 30, 1959, 8:45 a.m.)
  4. ^ "yard2", A New Dictionary of English on Historical Principles, 10b, Oxford: University Press, 1928, pp. 16–17 .
  5. ^ Green, Judith A. (1986). The government of England under Henry I. Cambridge, England: Cambridge University Press. p. 106. ISBN 0-521-37586-X. 
  6. ^ 33 Edw. I, c. 6.
  7. ^ Bigg, P. H.; Anderton, Pamela (1963), "The Yard Unit of Length", Nature 200 (4908): 730–32, doi:10.1038/200730a0 
  8. ^ a b Watson, C. M. (1910), British Weights and Measures, London: John Murray, pp. 36–39, http://www.archive.org/details/britishweightsme00watsuoft .
  9. ^ 27 Edw. III, c. 10
  10. ^ Knight, Charles (1840). The Penny magazine of the Society for the Diffusion of Useful Knowledge, Volume 9. London: Society for the Diffusion of Useful Knowledge. http://books.google.com/books?id=-BHnAAAAMAAJ. 
  11. ^ 5 Geo 4 c.72: Levi, Leone (1866), "Standard Weights and Measures", Annals of British Legislation, 2 (2 ed.), London: Smith, Elder, pp. 420–421, OCLC 82207589 
  12. ^ Glazebrook, Richard (1922), "Measurement, Units of", Dictionary of Applied Physics, 1, pp. 580–88, http://www.archive.org/details/dictionaryofappl025484mbp .
  13. ^ Bigg, P. H.; Anderton, Pamela (1964), "The United Kingdom standards of the yard in terms of the metre", Br. J. Appl. Phys. 15 (3): 291, doi:10.1088/0508-3443/15/3/308 .
  14. ^ American Football pitch dimensions
  15. ^ Canadian Football Pitch dimensions
  16. ^ Association Football pitch dimensions
  17. ^ Cricket pitch dimensions
  18. ^ Driving Standards Agency (1999), The Highway Code, London: The Stationery Office, ISBN 0 11 551977 7, pp. 74–75