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GP: Fachverband Geschichte der Physik

GP 3: Particles in Practice

GP 3.1: Vortrag

Dienstag, 17. März 2026, 11:00–11:30, KH 02.019

Particle Dance: On the Experimental Intertwining of Brownian Motion and Elementary Charge in the Early 20th Century — •Julia Bloemer — Europa-Universität Flensburg, Germany

The experiments with the oil-drop apparatus are celebrated for their precise determination of the elementary charge and are famously associated with the 1923 Nobel Prize in Physics awarded to Robert A. Millikan. Yet, the historical record reveals a much more complex picture. The same apparatus was simultaneously used by Millikan's doctoral student Harvey Fletcher to investigate another physical phenomenon, Brownian motion, and to determine a different constant, Avogadro's number. Brownian motion, the thermal and jittery movement of small particles, was treated as a disturbance in one line of inquiry -- elementary charge -- and became the very object of measurement in the other. This raises fundamental questions about experimental practice: How did taking Brownian motion into account change experimentation with the oil drop apparatus, as well as the subsequent data analysis and theoretical discussions? The results of this analysis will improve not only our understanding of a canonical experiment in the history of physics, but also of the process of control and stabilisation in experiments.

Keywords: History of Physics; elementary charge; Brownian Motion; experimental practice