Metre

Article

July 6, 2022

The metre, symbol m (without abbreviation), is the International System (SI) unit of length. It is one of its seven base units, from which derived units (the SI units of all other physical quantities) are constructed. First unit of measurement of the initial metric system, the meter (from the Greek μέτρον / metron, "measurement") was first defined as the 10,000,000th part of a half terrestrial meridian, then as the length of a meter international standard, then as a multiple of a certain wavelength and finally, since 1983, as "the length of the path traveled by light in vacuum for a duration of one 299,792,458th of a second".

History

The first appearance of the meter dates from 1650 as the length of a pendulum beating the second, the idea of ​​a "universal measure", that is to say a "metro cattolico" (according to the Italian Tito Livio Burattini), from which comes the word meter. Since that date, it will always keep this order of magnitude in its multiple definitions. “We set the unit of measurement at the ten-millionth part of a quarter of the meridian and we call it meter”. On July 11, 1792, in their report to the Academy of Sciences on the nomenclature of linear and surface measurements, Borda, Lagrange, Condorcet and Laplace defined for the first time what would become almost a century later the unit of international reference measurement of lengths. The word "meter" had already been used in the French language for more than a century in compound words such as thermometer (1624, Leurechon) or barometer (1666).

Revolutionary laws and decrees

On March 19, 1791, the Royal Academy of Sciences adopted the report of a commission composed of Condorcet, Borda, Laplace and Monge and which recommended choosing, as the basis of the new universal system of weights and measures, the ten-millionth part of the quadrant of the terrestrial meridian passing through Paris. On March 26, 1791, the National Assembly, at the request of Talleyrand and in view of the report of the Academy of Sciences, had voted to carry out the measurement of an arc of meridian from Dunkirk to Barcelona to give an objective basis to the new unit of measure. Delambre and Méchain are in charge of the precise measurement of the meridian arc from Dunkirk to Barcelona. The triangulation takes place from June 1792 to the end of 1798, with 115 triangles and two bases: that of Melun, and that of Perpignan. Angles are measured with Borda's repeating circle method. The operations were not yet completed until in 1793, a first provisional meter had to be adopted. Based on calculations of the meridian by Nicolas-Louis de Lacaille in 1758 and with a length of 3 feet 11 lines 44 hundredths, or 443.44 lines of the toise of Paris, this provisional meter was proposed in January 1793 by Borda, Lagrange , Condorcet and Laplace and adopted by decree on August 1, 1793 by the Convention. With the law of 18 germinal year III (April 7, 1795), the Convention instituted the decimal metric system and continued the measurements of the terrestrial meridian which had been interrupted at the end of 1793 by the Committee of Public Safety. On 4 Messidor Year VII (June 22, 1799), the prototype of the definitive meter, in platinum, in accordance with the new calculations of the meridian, was presented to the Council of Five Hundred and the Council of Elders by a delegation and then deposited in the National Archives. The law of 19 Frimaire Year VIII (December 10, 1799) enacted at the beginning of the Consulate, establishes the definitive meter. The provisional meter fixed in the laws of August 1, 1793 and 18 germinal year III is revoked. It is replaced by the definitive meter, whose length fixed by the measurements of the meridian by Delambre and Méchain is 3 feet 11 lines 296 thousandths.

Adoption of the meter

In 1801, the Helvetic Republic, at the instigation