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Perrin, Jean Baptiste

water existence rays physical

[peri] (1870–1942) French physical chemist: gave first definitive demonstration of the existence of atoms.

Perrin studied in Lyon and Paris, and in 1910 became professor of physical chemistry at the Sorbonne, but fled to America in 1941.

While studying for his doctorate, Perrin investigated cathode rays, showing them to be negatively charged and obtaining a rough value of their charge/mass ratio by measuring the negative charge required to stop them illuminating a fluorescent screen. His work showed that the rays are particles and not waves, and was soon to improve upon his results and show them to be electrons. Perrin is better known, however, for his classic studies of Brownian motion in 1908, in which he measured the distribution of particles of gamboge (a yellow gum resin from a Cambodian tree) suspended in water. His results confirmed a mathematical analysis of the problem by , and enabled Perrin to give accurate values for number and for the size of the water molecule. His work was widely accepted as final proof of the existence of atoms, and he was awarded the Nobel Prize for physics in 1926. He created several prestigious scientific institutions in France, including the CNRS (Centre National de la Recherche Scientifique).

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