The faceless mathematician – 04/04/2023 – Marcelo Viana

Adrien-Marie Legendre (1752–1833) is one of the great French mathematicians. His works deal with different areas of mathematics, and concepts with his name populate the mathematics books of our days. He was knighted by Napoleon and is one of 72 scientists whose names are inscribed on the Eiffel Tower.

However, little is known about his life. The family was wealthy, but the assets were confiscated at the height of the French Revolution, in the same year, 1793, that the revolutionary government closed the Academy of Sciences, its source of income. The only good thing about that year was his marriage to Marguerite-Claudine Couhin, his lifelong companion.

Until 2005, only one portrait of Legendre was known, regularly used in mathematics history books and which is spread on the internet. It was in that year that two students at the University of Strasbourg discovered that this portrait was also used to represent another person, the revolutionary politician Louis Legendre (1752–1797), who had the same surname.

The ensuing investigation showed that the image was part of a collection of lithographs of celebrities published in 1833 by the artist François-Séraphin Delpech and which arguably depicts the politician, not the mathematician. Suddenly Adrien-Marie has no face!

How could such a mistake have happened and been perpetuated for more than a century? The first misattribution of the portrait would have happened in a book about the work of scientists published by Alphonse Rebière, in 1900. By that time both Legendres, the mathematician and the politician, and all the people who knew them in life had already died.

The most ironic thing is that, although they were not related, despite the same last name, their lives were connected: Louis played a key role in the closure of academies and scientific societies, which condemned Adrien-Marie to poverty. To give an idea of ​​the character, it is enough to mention that Louis Legendre was the author of the proposal that, in addition to being guillotined, King Louis 16 had his body quartered in 84 parts, so that each department of France could receive a piece…

Another turnaround occurred in 2007, when the mathematician Gérard Michon discovered, in the Library of the Institute of France –an institution created by Napoleon in 1803 to replace the then-defunct Academy of Sciences–, a collection of watercolors by the painter Julien-Léopold Boilly that represented members of the Institute.

One of them features caricatures of Legendre, with a severe expression, and his colleague Joseph Fourier, with a good-natured smile. It’s a bit of an odd image, one that doesn’t match Legendre’s personality description by his contemporaries, but it’s the only one we have of him.

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