For two centuries, the famous portrait of Legendre showed the wrong man
Textbooks, paintings and articles long illustrated the mathematician Adrien-Marie Legendre with a profile sketch labelled simply Legendre. In 2005 someone noticed it actually depicted Louis Legendre, an obscure politician born the same year. The only genuine likenesses turned out to be a caricature from 1820 and an image tied to the Eiffel Tower.
Legendre was born into a wealthy Paris family on 18 September 1752, studied at the Collège Mazarin and defended his thesis in 1770. A Berlin Academy prize in 1782, for a study of projectiles moving through resisting air, caught the eye of Lagrange. Later that decade he joined the Anglo-French Survey that used trigonometry to fix the distance between the Paris and Greenwich observatories, travelling to Dover and London in 1787 and calling on William Herschel, who had found Uranus.
The Revolution wiped out his fortune in 1793, the same year he married Marguerite-Claudine Couhin, who helped rebuild his affairs. He spent years examining artillery students and graduates of the École Polytechnique. His independence cost him: in 1824 his pension was cut off after he refused to vote for the government's candidate at the Institut National.
His best-selling work was a geometry textbook from 1794 that rearranged and streamlined Euclid and dominated classrooms for about a century. For researchers he left far more. In 1806, in an appendix to a book on comet orbits, he published the least squares method, now central to statistics and curve fitting, though Gauss had found it earlier. He introduced the gamma symbol, guessed the law of quadratic reciprocity that Gauss later proved, and in 1798 conjectured the prime number theorem, finally proved in 1896. His transformation links two formulations of classical mechanics and helps derive quantities in thermodynamics.
A drawn-out, painful illness ended his life in Paris on 9 January 1833. His widow kept his belongings as a memorial and, on her death in 1856, was buried beside him at Auteuil, leaving their country house to the village. Today his name is one of 72 engraved on the Eiffel Tower, and a lunar crater and an asteroid carry it as well.
Source: Adrien-Marie Legendre
