The Mendenhall Order marked a decision to change the fundamental standards of length and mass of the United States from the customary standards based on those of

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

to metric standards. It was issued on April 5, 1893, by

Thomas Corwin Mendenhall Thomas Corwin Mendenhall (October 4, 1841 – March 23, 1924) was an American autodidact physicist and meteorologist. He was the first professor hired at Ohio State University in 1873 and the superintendent of the U.S. Coast and Geodetic Surv ...

, superintendent of the U.S. Coast and Geodetic Survey, with the approval of the

United States Secretary of the Treasury The United States secretary of the treasury is the head of the United States Department of the Treasury, and is the chief financial officer of the federal government of the United States. The secretary of the treasury serves as the principal a ...

John Griffin Carlisle John Griffin Carlisle (September 5, 1834July 31, 1910) was an American politician from the commonwealth of Kentucky and was a member of the Democratic Party. He was elected to the United States House of Representatives seven times, first in 18 ...

. The order was issued as the Survey's ''Bulletin No. 26 – Fundamental Standards of Length and Mass''.

Standards before the order

In October 1834, the United Kingdom

Houses of Parliament The Palace of Westminster serves as the meeting place for both the House of Commons and the House of Lords, the two houses of the Parliament of the United Kingdom. Informally known as the Houses of Parliament, the Palace lies on the north ban ...

were destroyed in a

fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames ...

, and the British standards of length and mass were also destroyed. "When the new imperial standards to replace them were completed in 1855, two copies of the yard and one copy of the

avoirdupois The avoirdupois system (; abbreviated avdp.) is a measurement system of weights that uses pounds and ounces as units. It was first commonly used in the 13th century AD and was updated in 1959. In 1959, by international agreement, the defini ...

pound were presented to the United States". These were superior to the yard then in use, so one of them was adopted as the United States national standard yard. These yards were taken to England and re-compared with the imperial yard in 1876 and 1888. The pound provided by the United Kingdom agreed with the United States mint pound, which remained the national standard according to Barbrow and Judson. Hockert claims the UK pound replaced the mint pound. These were the fundamental standards for customary length and mass measurements in the United States, but the Office of Weights and Measures had other standards for metric measurements.

Official recognition of the metric system

The

Metric Act of 1866 The Metric Act of 1866, also known as the Kasson Act, is a piece of United States legislation that legally protected use of the metric system in commerce from lawsuit, and provided an official conversion table from U.S. customary units. Histo ...

was passed by Congress and allowed, but did not require, the use of the metric system. Included in the law was a table of conversion factors between the traditional and metric units. The U.S. Coast and Geodetic Survey Office of Weights and Measures had on hand a number of metric standards, and selected the iron Committee Meter and the platinum Arago Kilogram to be the national standards for metric measurement. The standard yard and pound previously mentioned continued to be the standards for customary measurements. A series of conferences in France between 1870 and 1875 led to the signing of the

Metre Convention The Metre Convention (french: link=no, Convention du Mètre), also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Braz ...

and to the permanent establishment of the

International Bureau of Weights and Measures The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organisation, through which its 59 member-states act together on measurement standards in four areas: chemistry ...

, abbreviated BIPM after the French name. The BIPM made meter and kilogram standards for all the countries that signed the treaty; the two meters and two kilograms allocated to the United States arrived in 1890, and were adopted as national standards.

Reasons for the change

The imperial standard yard of 1855 was found to be unstable and shortening by measurable amounts. Also, the mint pound was found to be “likewise unfit for use.” For several years before the Mendenhall order was actually issued, the Office of Weights and Measures was “practically forced” to use the metric standards because of their superior stability, and because they were better designed for carrying out precision comparisons. The Office found that the conversion tables in the 1866 law were satisfactory and used them to derive customary length and mass from the metric standards. The conversions were 1 yard = meter and 1 pound = kilogram. Therefore, the Mendenhall order amounted to a formal announcement of a change that had already occurred in practice. Another motivation for the order was that later that year, in August 1893, an

International Electrical Congress The International Electrical Congress was a series of international meetings, from 1881 - 1904, in the then new field of applied electricity. The first meeting was initiated by the French government, including official national representatives, lea ...

would be held in connection with the World's Fair in Chicago. Associated with the Congress would be a "Chamber of Delegates", officially organized for the purpose of coming to an international agreement on units of electrical quantities. As Mendenhall wrote,

Refinement of the conversions

The definitions of 1893 remained unchanged for 66 years, but increasing precision in measurements gradually made the differences in the standards in use in English-speaking countries important. By the

international yard and pound The international yard and pound are two units of measurement that were the subject of an agreement among representatives of six nations signed on 1 July 1959: the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa. T ...

agreement of July 1, 1959, Australia, Canada, New Zealand, South Africa, the United Kingdom, and the United States agreed that 1 yard = 0.9144 meter and that 1 avoirdupois pound = kilogram (but see

U.S. survey foot The foot ( feet), standard symbol: ft, is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, , is a customarily used alternative symbol. Since the International Yard and Po ...

Standards versus systems

Mendenhall ordered that the standards used for the most accurate length and mass comparison change from certain yard and pound objects to certain meter and kilogram objects, but did not require anyone outside of the Office of Weights and Measures to change from the customary units to the metric system.

References

* * Footnotes {{reflist, refs= {{cite web , title=Bronze Yard No. 11 , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=17 , archive-date=26 August 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19990826141236/http://museum.nist.gov/object.asp?ObjID=17 {{cite web , title=Imperial Avoirdupois Pound , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=19 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111114344/http://museum.nist.gov/object.asp?ObjID=19 Hockert, Carol. (21 July 2015).
Address to the National Conference on Weights and Measures to Commemorate Their 100th Meeting
. National Institute of Standards and Technology. {{cite web , title=Committee Meter , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=12 , archive-date=26 August 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19990826124504/http://museum.nist.gov/object.asp?ObjID=12 {{cite web , title=Arago Kilogram , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=20 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111114300/http://museum.nist.gov/object.asp?ObjID=20 {{cite web , title=National Prototype Meter No. 27 , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=37 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111111802/http://museum.nist.gov/object.asp?ObjID=37 {{cite web , title=Prototype Kilogram 20, replica , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=38 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111112604/http://museum.nist.gov/object.asp?ObjID=38 {{cite web , title=Fischer Transverse Invar Beam Comparator , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=54 , archive-date=12 April 2000 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/20000412110323/http://museum.nist.gov/object.asp?ObjID=54