Blaise Pascal

Blaise Pascal was born in Clermont-Ferrand in 1623 to a tax official who withdrew his son from formal schooling to tutor him at home. The experiment worked: by sixteen Pascal had written an essay on conic sections rigorous enough that Descartes refused to believe a teenager had produced it. By nineteen he had built a working mechanical calculator — the Pascaline — to help his father reconcile tax receipts. It was the first adding machine to reach commercial production.

His work on fluids followed in the 1640s, after Torricelli's mercury barometer reached France. Pascal sent his brother-in-law up the Puy-de-Dôme with a barometer and verified that the mercury column fell as altitude rose — direct evidence that the atmosphere has finite weight. From there he produced two treatises, published posthumously, that laid out what we now call Pascal's principle: a pressure applied to an enclosed fluid transmits undiminished to every point. The hydraulic press is a direct consequence.

After 1654 Pascal underwent a religious conversion and turned to theological writing, producing the Pensées and the Lettres provinciales. Parallel to this he co-founded probability theory with Fermat, working out the mathematics of fair stake division in games of chance. He died at thirty-nine, leaving behind a sprawl of work in geometry, hydrostatics, calculus, probability, and devotional philosophy.