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Ever since humans began trading with their neighbors, measurements have been necessary. When people turned from leading a nomadic life to settling in one place, measurement became important. Weights and measures were among the earliest tools invented by man. Primitive societies needed rudimentary measures for many tasks: constructing dwellings of an appropriate size and shape; fashioning clothing; or bartering food or raw materials. Today, measurements are required to meet higher accuracies in many fields due to our increasingly technological-oriented society.
Man understandably turned first to parts of his body and his natural surroundings for measuring instruments. Early Babylonian and Egyptian records and the Bible indicate that length was first measured with the forearm, hand, or finger and that time was measured by the periods of the sun, moon and other heavenly bodies. When it was necessary to compare the capacities of clay or metal containers, they were filled with plant seeds which were then counted to measure the volume. When means for weighing were invented, seeds and stones served as standards. For instance, the "carat," still used as a mass unit for gems, was derived from the carob seed.
As societies evolved, measurement units became more complex. The invention of numbering systems and the science of mathematics made it possible to create whole systems of measurement units suited to trade and commerce; land division; taxation; and scientific research. For these more sophisticated uses it was necessary not only to weigh and measure more complex things, it was also necessary to do it accurately time after time and in different places. However, with limited international exchange of goods and communication of ideas, it is not surprising that different systems for the same purpose developed and became established in different parts of the world, even in different parts of a single continent.
The measurement system in the United States today is nearly the same as that brought by the colonists from England. These measures had their origins in a variety of cultures including Babylonian, Egyptian, Roman, Anglo-Saxon and Norman-French. The ancient "digit," "palm," "span," and "cubit" units evolved into the "inch," "foot," and "yard." Roman contributions include the use of the number 12 as a base (our foot is divided into 12 inches) and words from which we derive many of our present measurement unit names. The "yard" as a measure of length can be traced back to the early Saxon kings. They wore a sash or girdle around the waist that could be removed and used as a convenient measuring device.
Standardization of the various units and their combinations into a loosely related system of measurement units sometimes occurred in fascinating ways. Tradition holds that King Henry I decreed that the yard should be the distance from the tip of his nose to the end of his thumb. The length of a furlong (or furrow-long) was established by early Tudor rulers as 220 yards. This led Queen Elizabeth I to declare, in the 16th century, that henceforth the traditional Roman mile of 5,000 feet would be replaced by one of 5,280 feet, making the mile exactly 8 furlongs and providing a convenient relationship between two previously ill-related measures. Thus, by the 18th century, England - through royal edicts, had achieved a greater degree of standardization than the continental countries. The English units were well suited to commerce and trade because they had been developed and refined to meet commercial needs. Through colonization and dominance of world commerce during the 17th, 18th and 19th centuries, the English system of measurement units was spread to and established in many parts of the world, including the American colonies.
Standards still differed to an extent undesirable for commerce among the 13 colonies. The need for greater uniformity led to clauses in the Articles of Confederation (ratified by the original colonies in 1781) and the Constitution of the United States (ratified in 1790) giving power to the Congress to fix uniform standards for weights and measures. Today, standards supplied to all the States by the National Institute of Standards and Technology assure uniformity throughout the country.
The need for a single worldwide coordinated measurement system was recognized over 300 years ago. Gabriel Mouton, Vicar of St. Paul in Lyons, proposed in 1670 a comprehensive decimal measurement system based on the length of one minute of arc of a great circle of the earth. In 1671, Jean Picard, a French astronomer, proposed the length of a pendulum beating seconds as the unit of length (such a pendulum would have been fairly easy to reproduce, thus facilitating the widespread distribution of uniform standards.) Other proposals were made, but over a century elapsed before any action was taken. In 1790 in the midst of the French Revolution, the National Assembly of France requested the French Academy of Sciences to "deduce an invariable standard for all the measures and all the weights." The Commission appointed by the Academy created a system that was both simple and scientific. The unit of length was to be a portion of the earth's circumference. Measures for capacity (volume) and mass were to be derived from the unit of length, thus relating the basic units of the system to each other and to nature. Furthermore, the larger and smaller version of each unit were to be created by multiplying or dividing the basic units by 10 and its powers. This feature provided a great convenience to users of the system, by eliminating the need for such calculations as dividing by 16 (to convert ounces to pounds) or by 12 (to convert inches to feet.) Similar calculations in the metric system could be performed simply by shifting the decimal point. Thus the metric system is a "base- 10" or "decimal" system.
The Commission assigned the name mètre - meter - to the unit of length. This name was derived from the Greek word metron, meaning "a measure." The physical standard representing the meter was to be constructed so that it would equal one ten-millionth of the distance from the north pole to the equator along the meridian of the earth running near Dunkirk in France and Barcelona in Spain. The metric unit of mass, called the "gram," was defined as the mass of one cubic centimeter (a cube that is 1/100 of a meter on each side) of water at its temperature of maximum density. The cubic decimeter (a cube 1/10 of a meter on each side) was chosen as the unit of fluid capacity. This measure was given the name "liter."
Although the metric system was not accepted with enthusiasm at first, adoption by other nations occurred steadily after France made its use compulsory in 1840. The standardized character and decimal features of the metric system made it well suited to scientific and engineering work. Consequently, it is not surprising that the rapid spread of the system coincided with an age of rapid technological development. In the United States, by Act of Congress in 1866, it was made "lawful throughout the United States of America to employ the weights and measures of the metric system in all contracts, dealings, or court proceedings."
By the late 1860's, even better metric standards were needed to keep pace with scientific advances. In 1875, an international treaty, the "Meter Convention," set up well-defined metric standards for length and mass, and established permanent machinery to recommend and adopt further refinements in the metric system. This treaty was signed by 17 countries, including the United States. As a result of the Treaty, metric standards were constructed and distributed to each nation that ratified the Convention. Since 1893, the internationally agreed-to metric standards have served as the fundamental measurement standards of the United States.
By 1900 a total of 35 nations, including the major nations of continental Europe and most of South America, had officially accepted the metric system. In 1971 the Secretary of Commerce, in transmitting to Congress the results of a 3-year study authorized by the Metric Study Act of 1968, recommended that the U.S. change to predominant use of the metric system through a coordinated national program. Congress responded by enacting the Metric Conversion Act of 1975. Section 5164 of Public Law 100-418, requires federal agencies to use the metric system by 1992.
The International Bureau of Weights and Measures located at Sevres, France, serves as a permanent secretariat for the Meter Convention, coordinating the exchange of information about the use and refinement of the metric system. As measurement science develops more precise and easily reproducible ways of defining the measurement units, the General Conference on Weights and Measures (the diplomatic organization made up of adherents to the Convention), meets periodically to ratify improvements in the system and the standards.