Jean Baptiste Perrin

Jean Baptiste Perrin was born in France on 30 September 1870. He built his career studying something most scientists had taken for granted: whether matter was truly made of atoms, or if the atomic hypothesis was just a useful fiction. Focusing on Brownian motion — the jittery wandering of tiny particles suspended in liquid — he designed painstaking experiments on sedimentation equilibrium that matched Einstein's theoretical predictions with startling precision. That concordance settled the question: atoms existed, and you could measure their effects. The Nobel Prize in Physics followed in 1926…