Felix Ehrenhaft’s measurement of the elementary electrical charge and other stories

AbstraktAt the beginning of the 20th century, Felix Ehrenhaft was an expert in ultramicroscopy as he investigated light scattering of metal colloids. Responding to the works of Einstein and Smoluchowski and others on the Brownian motion in liquids, Ehrenhaft demonstrated the Brownian motion also for gases using silver particles suspended in air. Using similar particles between the plates of a tiny capacitor, 1909 he published his first experimental results for the elementary electrical charge, which fitted quite well to other researcher’s results and methods. While Millikan with his oil drop experiment relied on the actual theories of the electron and won the Nobel prize 1923, Ehrenhaft – although knowing the current theoretical details – trusted in his extended experiments and postulated “subelectrons”. Some original parts of Ehrenhaft’s experiment for electrical charge measurement are still preserved at the University Vienna. As this experiment was permanently used for advanced lab courses until recent years, especially the housing of the capacitor was improved. So it was suitable for suspended particles as well as for the oil drop method. Ehrenhaft’s deviation from the mainstream of physics had consequences, although his house was open to many scientists and there were ties of friendship to Albert Einstein. Instead of getting head of the II. Physikalisches Institut 1920, Ehrenhaft got a small institute of his own, the III. Physikalische Institut, where he should not cause much harm. Having a letter of recommendation from Albert Einstein, 1933 he acquired the third largest magnet of the world in order to extend his studies of magnetophoresis and photophoresis. Unfortunately, in the same year his wife died and 1938 he was forced to emigrate. His magnet was brought to the Hafele-Kar near Innsbruck and was used for the studies of cosmic rays. 1964 this magnet was again installed at the University Vienna. 1946 Ehrenhaft returned to the University Vienna and got his old position. Six years later he died, however, his photophoresis formed the basis of modern aerosol physics at the University Vienna.
NameSachslehner, Franz
Veranstaltung2nd Int. Conference on the History of Physics
Art der VeranstaltungKonferenz
Keywords:103010 Geschichte der Physik
Keywords:1209 Experimentalphysik