Jean Baptiste Perrin was a distinguished French physicist born on September 30, 1870, in Lille, France, who dedicated his career to establishing the physical reality of atoms and molecules. Educated at the École Normale Supérieure in Paris, he began his research career in 1894-1897 as an assistant in physics, focusing initially on cathode rays and X-rays. He received his doctorate in 1897 with a thesis on cathode and Röntgen rays and was appointed to a readership in physical chemistry at the Sorbonne, University of Paris. Over the course of his career, he became Professor of Physical Chemistry at the University of Paris, where he spent approximately thirty years conducting groundbreaking research. His early work established the negatively charged nature of cathode rays, resolving a fundamental debate in physics.
Perrin's most significant contribution came through his meticulous studies of Brownian motion, where he verified Albert Einstein's theoretical explanation of the random movement of particles suspended in liquids. By devising an ingenious system to observe and count gamboge particles at various depths in a liquid film only one twelve-hundredth of a millimeter deep, he demonstrated that particle concentration decreased exponentially with height in precise agreement with Einstein's mathematical predictions. This work provided the first conclusive experimental evidence for the existence of atoms and molecules, resolving a long-standing scientific debate against prominent skeptics like Ernst Mach and Wilhelm Ostwald. His research enabled the accurate calculation of Avogadro's number and the determination of molecular sizes, fundamentally transforming the understanding of matter's discontinuous structure. For this groundbreaking work, which confirmed the atomic nature of matter beyond reasonable doubt, Perrin was awarded the Nobel Prize in Physics in 1926.
Beyond his experimental work, Perrin profoundly influenced the institutional landscape of French science through his visionary leadership and socialist convictions. He was instrumental in founding major scientific institutions including the Centre National de la Recherche Scientifique (CNRS), the Palais de la Découverte science museum, and the Institut de Biologie Physico-Chimique, shaping France's scientific infrastructure for generations. As President of the Academie des sciences from 1938 and an outspoken antifascist, he championed scientific collaboration and accessibility until forced to flee France in 1940 due to political persecution. His influential book "Réalité moléculaire" (Molecular Reality) popularized the atomic theory and established his findings as universally accepted scientific truth. Perrin's legacy endures through the institutions he founded and his definitive contribution to establishing the physical reality of atoms, which remains a cornerstone of modern physics and chemistry.
