= Jean Perrin
{c}
{title2=1870–1942}
{wiki}
= Jean Baptiste Perrin
{c}
{synonym}
<Jean Perrin> tested the molecular interpretation of <Brownian motion> by counting suspended particles at different heights in an <emulsion>. Their equilibrium <number density> decreases with height as $n(z)\propto e^{-m_{\mathrm{eff}}gz/(k_BT)}$, where the effective <mass> includes the correction for <buoyancy>. A <microscope> thus connects a visible spatial distribution with the microscopic <Boltzmann constant>. Comparing such measurements with particle size and temperature supplied independent estimates of the <Avogadro constant>, turning the molecular hypothesis into a quantitative experimental question.<Les Atomes by Jean Baptiste Perrin/III. Mouvement brownien - Émulsions>[Sections 61–64, particle counting and height-dependent equilibrium concentration; modern notation]{ref}
Physics (also physical chemistry).https://www.cnrseditions.fr/auteur/jean-perrin/[Independent professional profile]{ref}
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{title=Portrait of <Jean Perrin>}
{description=Agence de presse Meurisse / Bibliothèque nationale de France; existing Commons crop. https://commons.wikimedia.org/wiki/File:Jean_Perrin.jpg[Commons PD-old/life-plus-70 claim in the country of origin, with a request for a separate US tag. No universal rights claim.], via Wikimedia Commons.}
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