ABSTRACTThe torsion balance, an instrument that was first developed to demonstrate the high precision of physical science in the laboratory became a different sort of demonstration instrument in its brief vogue in the 1920s. This article considers intersecting stories of acquiring and testing the torsion balance as a field instrument in Canada, Britain and Australia. It examines the purchasing trip and fieldwork of A. H. Miller of the Dominion Observatory in 1928–1931, testing conducted by the British Geological Survey in 1926–1930, (...) and finally the Imperial Geophysical Experimental Survey of 1928–1930 in Australia. These different stories produce a kind of collective biography, illustrating well the variety of material and textual records that accrete around instruments, especially expensive ones. But the trials and travels of the torsion balance also point to large themes. By comparing the different ways an instrument becomes valuable, and to whom, these micro-histories reveal significant features of the developing identity of geophysics. They also show the interaction of different forms of scientific internationalism in the inter-war period. (shrink)

Summary Sydney Chapman is unanimously considered to have played a founding role in modern geomagnetism and to have opened up new lines of research in geophysics generally. Nevertheless, Chapman's conviction regarding the synthesis of the explanatory mechanisms of the atmosphere has gone practically unnoticed in the historiography of geophysics. This paper examines Chapman's contribution to ionospheric physics. It aims to understand Chapman's theory of ionospheric layer formation, and particularly its link to his theory of ozone formation. It deals first with (...) the traits which characterized Chapman's personality, as a way of explaining—and even perhaps justifying— his quest for the integration and synthesis of geophysical knowledge. It then analyses Chapman's model of ionospheric layers and his suggestions regarding its use as an operational tool (without ontological connotations), before continuing with his account of the formation of the ozone layer, which seemed to constitute the missing link for understanding ionosphere layer formation. The paper concludes with Chapman's attempt to reconcile geomagnetic and radio evidence. (shrink)

SUMMARYFaced with various anomalies related to nuclear physics in particular, in 1929 Niels Bohr suggested that energy might not be conserved in the atomic nucleus and the processes involving it. By this radical proposal he hoped not only to get rid of the anomalies but also saw a possibility to explain a puzzle in astrophysics, namely the energy generated by stars. Bohr repeated his suggestion of stellar energy arising ex nihilo on several occasions but without ever going into detail. In (...) fact, it is not very clear what he meant or how seriously he took the stellar energy hypothesis. This paper relates Bohr's comments to the period's attempts to find a mechanism for stellar energy and also to the role played by astrophysics at the Copenhagen institute. Moreover, it looks at how Bohr's hypothesis was received not only by physicists but also by astronomers. In this regard the disciplinary status of astrophysics and its contemporary relation to the new quantum mechanics is of relevance. It turns out that, with very few exceptions, the hypothesis was met with silence by astronomers and astrophysicists concerned with the problem of stellar energy production. And yet, for a brief period of time it did have an impact on how physicists thought about the interior of the stars. (shrink)