No one will deny the extraordinary interest and importance of this method which showed for the first time and in such minute detail the effects of the passage of ionizing radiations through a gas ... I am personally of the opinion that the researches of Mr Wilson in this field represent one of the most striking and important of the advances in atomic physics made in the last twenty years ... It may be argued that this new method of Mr Wilson's has in the main only confirmed the deductions of the properties of the radiations made by other more indirect methods. While this is of course in some respects true, I would emphasize the importance to science of the gain in confidence of the accuracy of these deductions that followed from the publication of his beautiful photographs. Ernest Rutherford, 1927

Rutherford refers here to the photography of particle tracks made visible as lines of condensation in the supersaturated water vapour of a cloud chamber. C. T. R. Wilson first saw and photographed tracks in March 1911. The cloud chamber had existed since 1895 when Wilson, pursuing his meteorological interests, developed the instrument to determine the process of droplet formation in clouds. Galison and Assmus have examined this early phase of the cloud chamber's existence, rightly concluding that, with the production of tracks and their photographic record, the instrument was radically transformed into a crucial tool of the particle physicist. This transformation was not immediate, however, and a genealogy of the apparatus cannot fully explain how this novel means to apprehend the existence and behaviour of hitherto invisible particles subsequently functioned within and contributed to the project of particle physics. My own focus is on the period immediately following Wilson's first publication of ray-track photographs. The central questions to be addressed are provided by Rutherford's comments above. In precisely what way did Wilson's work increase the confidence of scientists? How was his method more direct than others?