Jean Baptiste Perrin was instrumental in proving the existence of the electron and, eventually, the atom. Born in 1870, Perrin was raised by his mother, his father having died shortly after the Franco-Prussian War. He was educated in Paris and received his doctorate from the Ecole Normale Superieure in 1897. Soon after he became a professor of Chemistry at the University of Paris, remaining there until the onset of World War II.

While still a student Perrin became interested in the study of cathode rays; in particular, he was curious as to the true nature of these rays. A controversy had swept Europe: some scientists believed the rays to be electromagnetic waves while others (such as Perrin) thought them to be tiny particles.

William Crookes, the foremost authority on cathode-ray tubes, had speculated that the rays were particles--a fourth state of matter yet undiscovered. Perrin designed his own cathode-ray tube...