On this day in 1752, the great mathematician Adrien-Marie Legendre was born. He was born to a rich family, which is more or less the way it goes. You see, if you were born poor, you were lucky to get to learn to read. If you look at the history of great thinkers, they mostly came from the middle of the income scale. The rich were too busy counting their money. They didn’t have to do anything, so they didn’t. And the poor were too busy not starving. So that left the children of the artisans and shopkeepers. But Legendre was a bit different.

But when revolution came to France, Legendre lost his fortune. But he wasn’t part of the useless rich, and so he survived. He was named one of the six members on the mathematics panel of the Institut National des Sciences et des Arts. And shortly before his death, he was made officer of the Légion d’Honneur.

What he is most well known for is one of the most powerful tools of mathematical physics: the Legendre transformation. As I wrote last year, “It allows you to transform a function from one set of variables to another. There are two classic examples of this. One is to transform the Lagrangian formulation of classical mechanics into the Hamiltonian formalism. The other is the transformation of thermodynamic internal energy—which we can’t measure—into enthalpy and other variables that we can measure.” It is a beautiful thing.

Happy birthday Adrien-Marie Legendre!