Franz Exner (24.03.1849—15.02.1926) was an Austrian physicist and a member of the Austrian Academy of Sciences. He was born in Vienna. He graduated from the University of Vienna (1871). He was an assistant to A. Kundt at the universities of Würzburg and Strasbourg. From 1874 he worked at the University of Vienna (professor from 1879, rector in 1908—09, and director of the Physical Institute until 1920).
His work concerned optics, spectral analysis, molecular physics, calorimetry, electrochemistry and geophysics. He began the modern theoretical study of atmospheric electricity. In 1885 he established that the refractive index of a gas is related to its density of space filling. He studied Brownian motion. He proved that the square of the velocity of the particles in Brownian motion is proportional to the temperature. He investigated the diffusion of gases into a liquid.