Jean Baptiste Perrin Biography

World of Scientific Discovery on Jean Baptiste Perrin

Jean Baptiste Perrin was instrumental in proving the existence of the electron and, eventually, the atom. Born in 1870, Perrin was raised by his mother, his father having died shortly after the Franco-Prussian War. He was educated in Paris and received his doctorate from the Ecole Normale Superieure in 1897. Soon after he became a professor of Chemistry at the University of Paris, remaining there until the onset of World War II.

While still a student Perrin became interested in the study of cathode rays; in particular, he was curious as to the true nature of these rays. A controversy had swept Europe: some scientists believed the rays to be electromagnetic waves while others (such as Perrin) thought them to be tiny particles.

William Crookes, the foremost authority on cathode-ray tubes, had speculated that the rays were particles--a fourth state of matter yet undiscovered. Perrin designed his own cathode-ray tube equipped with a small metal cylinder; as the rays passed through the tube a portion were deflected onto the cylinder. At the end of the experiment a negative charge could be detected on the cylinder. Since this could not have been accomplished by electromagnetic waves, the experiment proved that the cylinder had been bombarded by negatively-charged particles. A few years later Joseph John Thomson determined the mass of these particles and introduced electrons to the world.

Perrin also conducted a series of atomic theory experiments the results of which were compiled in a 1909 publication. Perrin based his work upon the theories of Robert Brown who, in 1827, discovered that microscopic grains of pollen suspended in water moved rapidly and, apparently, randomly. Brown theorized that this motion came from the pollen being pushed around by moving water molecules, and this Brownian movement was thought by some to be a proof of the existence of atoms.

Perrin took Brown's work one step further. He assumed that the tiny pollen grains and the water in which they were suspended behaved like gas molecules; if this assumption were true then the laws that governed the motion of gases would also apply to water molecules. Through exhaustive research Perrin observed the motions of the pollen grains and, working backwards, eventually derived Avogadro's number--a mathematical constant essential to many gas laws. This seemed to indicate that Brownian movement was indeed caused by molecular collisions, and was regarded at the time as the final proof for the existence of the atom.

For this work Perrin received the 1926 Nobel Prize for physics. He held his position as professor of physical chemistry at the Sorbonne until 1940, when his anti-fascist views made it dangerous for him to remain. He fled to New York to escape the Germans, and died there in 1942.