April 17, 1942 – Death of Jean Perrin, his discoveries resolved a century-long dispute

Perrin first suggested that negative charges are external to the nucleus. In 1895, he found that cathode rays deposit charge in an electroscope (an instrument that can read whether a body is electrically charged), with which he confirmed that they were negatively charged particles and published his findings at the Académie des Sciences. Joseph J. Thomson was interested in measuring the speed of these particles and that they would eventually be identified as electrons.

In 1905, Albert Einstein published his theoretical explanation of Brownian motion (random motion observed in particles found in a liquid or gas medium as a result of collisions with the molecules of said fluid) in terms of atoms, and Perrin made the experimental work to test and verify Einstein's predictions, thus resolving the century-long dispute over the atomic theory formulated by John Dalton.

In 1909, he published his research on the Brownian motion of particles in aqueous solution, indicating that this motion was a consequence of the incessant bombardment of the particles by water molecules and offering estimates of their size and the value of Avogadro's Number (number of particles). of molecules contained in a mole of gas under normal conditions) more exact than those that existed up to that moment. The results of his experiments were accepted as proof of the existence of molecules.

In 1919, he realized that the mass of one helium atom is less than that of four hydrogen atoms, and that Einstein's mass-energy equivalence implies that nuclear fusion could release enough energy to make stars shine for billions of years.

In 1926, he received the Nobel Prize in Physics for his work on the discontinuous structure of matter and for the discovery of sedimentation equilibrium.

In 1940, he moved to the United States where he headed the scientific department at the Free School of Higher Learning in New York.

If you want to know more about this scientist, click on the following link: Jean Baptiste Perrin