Jacques Français (mathematician)

Jacques Frédéric Français (born June 20, 1775 in Saverne , † March 9, 1833 in Metz ) was a French mathematician.

He was the son of a retailer in Saverne. His brother François Français was also a mathematician. Jacques Français attended the College in Strasbourg and volunteered for the army in the Revolutionary Wars in 1793 and joined the pioneers in 1794. From 1797 he studied at the École Polytechnique and from 1798 at the École du Génie (the school for military engineers). In 1801 he went as a lieutenant in the Napoleonic army with his expedition to Egypt. On his return he was stationed in Toulon and became captain of the sappers. In November 1802 he became deputy commander of the staff headquarters of the engineer corps there. He took part in the sea battles at Cape Finisterre and Trafalgar . In 1807 he was stationed in Strasbourg under Étienne Louis Malus , at whose suggestion he again dealt with mathematics (more precisely analytical geometry) (he had already published a mathematical treatise in 1800). From 1810 he commanded the École d'Application in Metz and became professor of military art there in 1811.

After the death of his brother François Français, who was also a mathematician, he found a letter from Adrien-Marie Legendre in his estate , referring to the geometric representation of complex numbers by Jean-Robert Argand (without giving his name). Argand had published a book about it in private print in 1806, but it went virtually unnoticed, apart from Legendre. In 1813 he published these results in the widely read Annales de Mathématiques ( Annales de Gergonne ) and asked the unknown author to report, which Argand did soon after. This publication led to the knowledge of the geometric interpretation of complex numbers as two-dimensional vectors in broader circles (a publication on this by the Dane Caspar Wessel in 1799 had largely gone unnoticed). There was a discussion in the Annales in which François and Argand defended the geometric interpretation against François-Joseph Servois , who only wanted complex numbers to be treated algebraically.

After that, he seems to have given up mathematics.

Web links

• John J. O'Connor, Edmund F. Robertson :  Jacques.html Jacques Français (mathematician). In: MacTutor History of Mathematics archive .