Claude-Louis Navier

Claude-Louis Navier was born in Dijon in 1785 and orphaned by fourteen, raised by his great-uncle Emiland Gauthey, the chief engineer of the Canal du Centre. The family craft was hydraulics — rivers, locks, barges — and the boy absorbed it as other boys absorbed Latin. He entered the École Polytechnique in 1802 and the École des Ponts et Chaussées in 1804, coming out at the very top of his cohort and stepping straight into a career as a state engineer.

His great paper of 1822, Mémoire sur les lois du mouvement des fluides, was an attempt to derive the equations of fluid motion from a molecular picture. He pictured a fluid as a lattice of point particles repelling one another, worked out the macroscopic stress tensor that their interactions would produce, and wrote down a partial differential equation for the velocity field that included — for the first time — a viscous term proportional to the Laplacian of the velocity. The molecular derivation was, in hindsight, wrong in its details: Stokes re-derived the same equation two decades later from a cleaner continuum argument. But the equation was Navier's first, and the name it now bears is just.

Navier's public fame, in his own lifetime, rested on the bridges. He built the Pont des Invalides in Paris (twice — the first version was demolished amid a political quarrel before it opened, a humiliation that broke his health), and his lecture notes at the Ponts et Chaussées became the standard text on the strength of materials across nineteenth-century Europe.