AbstractThe 1830s and 1840s witnessed a European movement to accumulate data about the terrestrial environment, enterprises including the German and British geomagnetic crusades. This movement was not limited to geomagnetic studies but notably included an important meteorological component. By focusing on observation practices in sedentary and expeditionary contexts, this paper shows how the developing fields of geomagnetism and meteorology were then intimately interlinked. It analyses the circulation and cross-connections of the practices and discourses shared by these two research fields. Departing from a Humboldtian historiography, the paper especially stresses the role of Adolphe Quetelet, director of the Brussels Observatory, whose importance in the development of the earth sciences has until now been largely neglected. It reassesses the involvement of the French scientific community in the British and German geomagnetic crusades, moving beyond the well-known account of Arago's opposition to these undertakings. It is hoped thereby to contribute to a better historical understanding of the renewal of the earth sciences in the second quarter of the nineteenth century.