Meters - History & Definition

A meter is a unit of proper length. The word meter comes from the Greek word métron and was first used in 1675 by Italian scientist Tito Livio Burattini. In 1791 the French Academy of Sciences defined a meter as one ten-millionth of the length of the earth's meridian along a quadrant. However, in order to get an accurate measurement, The Bureau des Longitudes had to embark on a 9 year expedition to measure the length of the the meridian. When the mission was complete in 1799, the length was confirmed by constructing the platinum International Prototype Meter bar. This bar is stored at the Pavillon de Breteuil near Paris. It was later discovered that the Prototype Meter bar was 0.2 millimeters short due to researchers miscalculating the flattening of the earth, but this length still remained the standard for 75 years.

In 1875 the International Bureau of Weights and Measures (BIPM) was established. The BIPM ensures uniformity of the metric system of weights and measures among 51 nations around the world and maintains the accurate worldwide time of day. In 1889 the BIPM created a new prototype bar at the first General Conference on Weights and Measures. This new bar was made of 90% platinum and 10% iridium and the meter was measured at the melting point of ice. In 1927 the definition of the meter became even more precise by measuring it at 0 degrees Celsius. This standard for the length of a meter remained until 1960. On October 20, 1960, the International Prototype Meter bar was replaced with a new definition based upon a wavelength of krypton-86 radiation. This new definition was adopted as a means to eliminate any discrepancies in the measurement of a length of a meter. This measurement held steady until 1983 when the meter was revised to its present definition.

Today, the official measurement of the length of a meter, accepted and used by the International System of Units, is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. It is equivalent to approximately 39.375 inches. The meter is one of the 7 base units in the International System of Units from which all other units of measurement are derived. The term meter specifically refers to any instrument used to measure the magnitude of a quantity and is used in many applications in our everyday lives. For example, electrical energy usage is measured by the kilowatt-hour meter, our home audio systems measure volume with the volume-unit meter, and the ammeter is the basis to measure electric currents. Modern life is based upon the use of measurements and the meter is now accepted as the standard throughout most of the world.