Sophie Germainthe LabyrinthINTP

In February 1807, in Paris, Sophie Germain, 30, sat down to tell Carl Friedrich Gauss who she really was.

For more than two years the most admired mathematician in Germany had been writing to a gifted young Frenchman called Monsieur Le Blanc. The letters had been hers all along.

She was born on 1 April 1776 in the rue Saint-Denis, into a Paris merchant family. Women could not study at the new École Polytechnique, so she got hold of the lecture notes and sent the great Joseph-Louis Lagrange her work under a man's name: Le Blanc, a former student there.

On 21 November 1804, at 28, she used the name again in a first letter to Gauss, about the theory of numbers. He answered. To him, Monsieur Le Blanc was a promising colleague, and their letters went back and forth between Paris and Brunswick as one mathematician to another.

Labyrinths will see why the arrangement suited her. A letter can be drafted, checked and redrafted. It reaches the other person as pure argument, before anyone has looked at you.

Then, in late 1806, Napoleon's armies took Brunswick. Germain remembered Archimedes, the great geometer of Syracuse, killed by a soldier when his city fell. She asked General Joseph-Marie de Pernety, a friend of her family serving with the army, to make sure Gauss came to no harm.

Pernety sent an officer to find him. Gauss was safe, and puzzled. He did not know the general, and he had never heard of a Mademoiselle Germain.

So she wrote to explain, with great care. She was, she told him, “not as completely unknown to you as you might believe.” She had taken the name of Le Blanc, fearing “the ridicule attached to a female scientist.” She hoped the truth would not cost her the regard he had shown her under a borrowed name.

Gauss answered warmly. He praised the courage it takes to go deeply into a science so few people love.

Within two years, though, his letters stopped. His interests had moved away from numbers. She kept working. Twice she entered the Academy's contest on vibrating surfaces and fell short, and twice she went back to the equations. In January 1816, at her third attempt, she won the Paris Academy's prize for her theory of elastic surfaces, the first woman to win one. Around 1819 she wrote to Gauss again, with a bold plan of attack on Fermat's Last Theorem. No answer is known.

She died of breast cancer in Paris on 27 June 1831, at 55. She and Gauss never met.

For two years he read her mathematics and never knew her name. He learned it only because she had been afraid for his life.