Svante Arrhenius, cosmical physicist and auroral theorist

Abstract. Many scientists in the fin de siècle era saw a need to coordinate and unify the increasing amount of data relating the physical conditions of the Earth and the Sun; or more generally to establish a synthetic perspective that covered the earth sciences in relation to the new astrophysical sciences. Promoted under the label "cosmical physics'', the unifying solar–terrestrial perspective was in vogue for a decade or two. Perhaps more than any other scientist in the period, the versatile Swedish chemist and physicist Svante Arrhenius represented the aims of cosmical physics. A central problem in the new and ambitious research programme was to understand the origin and nature of the aurora, and to relate it to other celestial phenomena such as the solar corona and the tails of comets. In 1900 Arrhenius proposed a unified explanation of these and other phenomena based on the Sun's radiation pressure. The theory was widely discussed, praised as well as criticized. Arrhenius was not only a key scientist in the short-lived tradition of cosmical physics, but also influential as a popular writer and powerful member of the Nobel Committee for Physics. His work illustrates an approach to the earth and space sciences characteristic of the fin de siècle period.