Sophie Germain Wrote to Gauss as a Man for Three Years

In 1789, the 13-year-old Sophie Germain worked her way through her family's library to Étienne Bézout's Traité d'Arithmétique and a Latin account of Archimedes's death — killed at Syracuse, the legend went, while concentrating on a geometry problem. She decided to become a mathematician. Her parents disapproved. She studied past midnight in an unheated bedroom anyway; her mother eventually relented.

The École Polytechnique opened in Paris in 1794, when Germain was 18, and refused to admit women. Germain obtained the lecture notes through a former student — Antoine-Auguste Le Blanc, who had withdrawn — and began submitting solutions to Joseph-Louis Lagrange's analysis class under his name. When Lagrange asked to meet "M. Le Blanc," Germain told him the truth. He kept teaching her.

Years later, after working through Carl Friedrich Gauss's Disquisitiones Arithmeticae, she wrote to the author. The first letter, dated November 21, 1804, was signed M. Le Blanc. So were the letters that followed for the next three years, including her early work on Fermat's Last Theorem, where she proved a partial result that bears her name today: Sophie Germain's theorem.

Her cover broke in 1806. Napoleon's army was advancing on Braunschweig, where Gauss lived. Germain remembered Archimedes and feared Gauss might meet the same fate. She contacted a French general her family knew and asked him to look after Gauss. He did. When Gauss asked who had sent him, the answer was: a Sophie Germain.

Gauss wrote to her astonished. "How to describe to you my admiration and astonishment at seeing my esteemed correspondent M. Le Blanc metamorphose himself into this illustrious personage." She wrote as M. Germain after that.