Jean Perrin
(born Sept. 30, 1870,
Lille
, France?died April 17, 1942,
New York
, N.Y., U.S.) was a French physicist who, in his studies of the Brownian motion of minute particles suspended in liquids,
verified
Albert Einstein’s
explanation of this phenomenon and thereby confirmed the atomic nature of matter. For this achievement he was honoured with the
Nobel Prize
for Physics in 1926.
Educated at the Ecole Normale Superieure,
Paris
, Perrin joined the faculty of the
University of Paris
(1898) where he became professor of
physical chemistry
(1910?40). In 1895 he established that cathode rays are negatively charged particles (electrons). His attempt to determine the mass of these particles was soon anticipated by the work of
J.J. Thomson
.
Britannica Quiz
Faces of Science
About 1908 Perrin began to study
Brownian motion
, the erratic
movement
of particles suspended in a
liquid
. Einstein’s mathematical analysis (1905) of this phenomenon suggested that the particles were being jostled by the randomly moving water molecules around them. Using the newly developed
ultramicroscope
, Perrin carefully observed the manner of sedimentation of these particles and provided experimental confirmation of Einstein’s equations. His observations also enabled him to estimate the size of water molecules and atoms as well as their quantity in a given value. This was the first time the size of atoms and molecules could be reliably calculated from actual visual observations. Perrin’s work helped raise atoms from the status of useful
hypothetical
objects to observable entities whose reality could no longer be denied.