Changing Faces: The Mistaken Portrait of Legendre

Adrien-Marie Legendre (1752–1833) made great contributions to analysis, number theory, celestial mechanics, and practical science. His name is attached to the Legendre differential equation, Legendre polynomials, the Legendre transformation, the Legendre symbol in number theory, the Legendre conditions in calculus of variations, the Legendre relation for elliptic integrals, the Legendre duplication formula for the gamma function, and the list goes on. He wrote important books on advanced calculus, number theory, and elliptic integrals. His textbook adaptation of Euclid’s geometry had a long life, was translated to many languages, and brought him popular fame. His work is honored today, yet curiously he was not so highly regarded during his lifetime and there was no publication of his collected works. Little is known of Legendre’s personal life and he remains a shadowy figure. For over a century one familiar portrait (Figure 1) has been displayed wherever Legendre’s work has been discussed in historical writing. It is included in books on history of mathematics such as Struik [14] and Eves [5]. It has been printed repeatedly to illustrate articles about Legendre, and it appears on many mathematical websites. Generations of mathematicians have known and recognized Legendre by that portrait. But the portrait has nothing to do with AdrienMarie Legendre. It is not his likeness. Instead it portrays a politician named Louis Legendre, an active participant in the French Revolution, no relation to the mathematician. This shocking and rather embarrassing revelation has emerged in the last few years, supported by strong evidence, as we will explain.