Julius Elster and Hans Geitel – Dioscuri of physics and pioneer investigators in atmospheric electricity

Abstract. Julius Elster and Hans Geitel contributed to the physics at the turn of the 19–20th century in many ways. We first summarize the life of these exceptional scientists. Then – owing to the topic of this journal – we focus on their atmospheric electricity research. With their experiments, careful evaluations and ingenious interpretation, Elster and Geitel made important contributions to precipitation electricity, the influence of solar radiation on the electric state of the atmosphere, the nature of charge carriers and the ionization of air by radioactivity. They proved their experimental skills by inventing new instruments with unprecedented accuracy and reliability. A very modern concept was their attitude to undertake long-term measurements at various locations. A section on their recognition in the physics community and their scientific distinctions concludes the paper.