French physicist Jean Baptiste Perrin (1870-1942) helped to prove that atoms and molecules exist, an achievement that earned him the 1926 Nobel Prize in physics.

Jean Baptiste Perrin was born in Lille, France, on September 30, 1870, and raised, along with two sisters, by his widowed mother. His father, an army officer, died of wounds he received during the Franco-Prussian War. The young Perrin attended local schools and graduated from the Lycée Janson-de-Sailly in Paris. After serving a year of compulsory military service, he entered the Ecole Normale Supérieure in 1891, where his interest in physics flowered and he made his first major discovery.

Between 1894 and 1897 Perrin was an assistant in physics at the Ecole Normale, during which time he studied cathode rays and X rays, the basis of his doctoral dissertation. At this time, scientists disagreed over the nature of cathode rays emitted by the negative electrode...