de Borda, Jean-Charles
Born Dax, (Landes), France, 4 May 1733
Died Paris, France, 19 February 1799
Jean-Charles de Borda was a positional astronomer, instrument designer, and one of the founders of the metric system. Borda was born in a noble family, son of Jean-Antoine de Borda and Jeanne-Marie Thérèse de Lacroix. He began his education at the Jesuit school La Flèche, and later entered the light cavalry and then the Academy of Engineers of Mézières. His scientific curiosity made him eligible for the Paris Academy of Sciences in 1756. Borda’s first publications in the annals of the academy deal with a subject not directly related to astronomy: the resistance of fluids. In 1769, due to Aymar Joseph de Roquefeuil’s insistence, the Marine Academy was created, and Borda was elected a member and professor of mathematics. There, he developed a great deal of his astronomical knowledge.
In 1771, Borda embarked on the frigate La Flore, destined for America. He was accompanied by the astronomer Alexandre Pingré , with the goal to study the behavior of chronometers and to determine their utility when using the lunar-distances method to determine longitude at sea. The simplified method, which Borda tested on this trip and was published in two volumes with tables in 1778, became common practice in the French navy. Simplified versions of the method were also published in the Connaissance des tempsin the years 1779, 1780, and 1787.
Borda specialized in positional astronomy to be used in navigation and astronomical instrumentation, and in this field he accomplished his best work. Other trips to America and Africa sealed his fame as a sailor and as an educated scientist. He was named captain, and was captured during combat by the British in 1782 and in 1784. With his health too weak for life at sea, Borda was named superintendent of construction of the school of naval engineers. In 1795, at its creation, he was also selected a member of the Bureau of Longitudes.
From 1778 Borda perfected an instrument adumbrated by Tobias Mayer in 1752, which he named the “repeating circle” or “astronomical circle.” Borda’s circle competed with the traditional quadrant used for astronomical measurements both at sea and on land, and its superiority was manifested in the operation of the geodesic union of the observatories in Greenwich and Paris, which took place in 1787. Under his direction, the artist E. Lenoir made a great number of instruments of various dimensions. In 1801, the Spanish astronomer and mariner José de Mendoza introduced new improvements that led to the instrument’s definitive shape for use in navigation and in terrestrial operations. Borda also calculated, in subsequent years, numerous trigonometric sexagesimal and centesimal tables for better use of the instrument.
As an expert observer and a careful experimenter, Borda’s name was associated from the very beginning with the activity that would be the most important of his later years: the work on the basis of a new system of weights and measures promoted by revolutionary France. It was his initiative, on record in the Procès verbaux de l'Académie des sciences, to create a commission that drew up the definitive project. Indeed, on 16 February 1791, the academy selected him along with Pierre de Laplace , J. A. Condorcet, Joseph Lagrange , and Gaspard Monge to propose a new model of measurements founded on the length of a terrestrial meridian. The report on 19 March 1791 constituted without a doubt the origin of the decimal metric system, which became the international system of weights and measures. In his work to define the metric system, Borda displayed an unwearied activity up until his death. He was in charge along with C. A. de Coulomb of measuring the length of the pendulum that marked seconds at the 45° parallel. Borda verified the rules used to measure the geodesic bases and to determine the model kilogram. He supervised the construction of repeating circles, which Jean Delambre and Pierre Méchain used in their measurements.
On 5 July 1795, Borda presented his Rapport sur la vérification du mètre qui doit server d'étalon pour la fabrication des unités républicaines, which introduced the provisional meter, and was part of all the commissions that determined the definitive meter. In the middle of these efforts to officially approve this new measurement, Borda died.
Translated by Claudia Netz.
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