In 1909, Jean Perrin proved that atoms exist by calculating Avogadro's number using three different methods, all involving liquid phase systems. First, he used a gamboge soap-like emulsion, second by doing experimental work on Brownian motion, and third by confirming Einstein’s theory of particle rotation in the liquid phase.
In 1926, Perrin won the Nobel Prize in physics for proving, conclusively, the reality of the “atomistic description” of nature — a recognition often said to mark the final and formal acceptance of Leucippus’ c.450BC atomic theory by science "officially".
Quotes | On
The following are quotes on Perrin:
- “Jean and Francis Perrin held similar political and philosophical ideas. Both were socialists and atheists. Like many nineteenth century French men of science, Jean Perrin viewed science almost as a religion.”
- — Mario Berberan-Santos (2001), “Pioneering Contributions of Jean and Francis Perrin to Molecular Luminescence” (pg. 17) 
Quotes | By
The following are quotes by Perrin:
- “Molecules and atoms are lifeless beings that never evolve.”
- — Jean Perrin (1903), Treatise on Physical Chemistry (pg. #)
- Valeur, Bernard; Brochon, Jean-Claude. (2001). New Trends in Fluorescence Spectroscopy: Applications to Chemical and Life Sciences (§2: “Pioneering Contributions of Jean and Francis Perrin to Molecular Luminescence”, pgs. 7-34, atheists, pg. 17). Springer, 2012.
- (a) Perrin, Jean. (1903). Treatise on Physical Chemistry (Traite de Chimie Physique: Les Principes) (pgs. 177, 179-80). Paris.
(b) Kragh, Helge and Weininger, Stephen J. (1996). “Sooner Science than Confusion: the Tortuous Entry of Entropy into Chemist” (Jst), Historical Studies in the Physical and Biological Sciences, 27(1): 91-130.
- White, Harvey. (c.1950). “Jean Perrin’s Cathode Ray Tube, J.J. Thomson’s Experiment, Millikan’s Oil Drop Experient” (YT), 16mm Educational Films, 2020.
- Jean Perrin – Hmolpedia 2020.