I was inspired to write Sophie’s Diary to honor Sophie Germain, to make her known to new generations of girls, and to promote her achievements. Knowing so little about her childhood, I wanted to present a perspective as to how the teenage Sophie must have learned mathematics on her own. Writing Sophie’s Diary became my way of bringing Sophie to life.

           What I wanted most of all was to put into context the environment surrounding the young Sophie Germain who, against all odds, became one of the greatest women mathematicians in history. Long ago, when I fist learned about Germain, I was immensely impressed by a woman, who not only lived during a time of great social turmoil but grew up in an era when women were not permitted in the universities. History records the achievements of other great female mathematicians who lived before and accomplished as much, but Sophie Germain did it alone. Hypathia had her father, Theon of Alexandria to teach her; Maria Agnessi had her Rampinelli and other instructors; and Emilie Chatelet had Maupertuis and Clairaut as her tutors of mathematics. Sophie Germain had no teacher.

Equally astonishing for me was to learn that Sophie Germain obtained lecture notes from professors at the École Polytechnique in 1794. According to her biography, she anonymously submitted her own analysis using a man’s name. This intrigued me more, as such daring act would be equivalent to acquiring notes and submitting homework for an advanced university mathematics course, without having attended high school. I wondered how she, as a teenager, could have taught herself mathematics during the siege of the French Revolution. At eighteen, Germain must have known enough mathematics to have the confidence to submit her work to not just any professor but one of the greatest mathematicians of the eighteenth century, Joseph Louis Lagrange.