Jean Baptiste Perrin
Perrin, Jean Baptiste (1870-1942) was a French physicist who won the 1926 Nobel Prize in physics for studying the discontinuous structure of matter and for devising an experiment that made it possible for the first time to measure the size of atoms.
Perrin was born on Sept. 30, 1870, in Lille, France, and received his degree from the Ecole Normal Superieure, Paris, in 1897. He then joined the physical chemistry staff of the Sorbonne, University of Paris, becoming full professor in 1910 and remaining there until 1940. He served as an officer in the Engineer Corps of the French Army in World War I (1914-1918). In 1940, Perrin fled to the United States when Germany invaded France during World War II (1939-1945).
In 1895, Perrin carried out an experiment that demonstrated that cathode rays consist of negatively charged particles. Cathode rays occur when electricity is passed through a vacuum in a glass tube. The negatively charged particles are now known as electrons.
Perrin then turned to the study of Brownian motion, a constant, random irregular motion often observed in very minute particles suspended in a liquid or gas. Brownian motion is caused by the impact of the surrounding molecules. Perrin studied the Brownian motion of suspended particles and provided proof for the existence of atoms. He determined a fairly accurate value for the Avogadro constant. This is usually written as a number, 6.02 X 10 to the power of 23. This number of particles of any substance is called one mole of the substance.
Perrin published his work in Les Atomes (Atoms, 1913), which sold 30,000 copies by 1936 and became a classic. Perrin established France's National Centre for Scientific Research and the Astrophysics Institute. He also established the Palace of Discovery for the 1937 International Exhibition in Paris.
Perrin was elected a Foreign Member of the Royal Society in 1918 and served as president of the French Academy of Sciences in 1938.
Perrin died in New York City on April 17, 1942. In 1948, his remains were transferred to France and placed in the Pantheon monument in Paris.