Based on a detailed analysis of Langevin's laboratory notebooks, this paper shows that his experimental work between 1896 and 1903 was not a sequence of disconnected research topics. The complex of instruments, formulas, and manual operations involved derived from a set of skills unique to Langevin. Significantly, Thomson, Rutherford, and Bloch had trouble reproducing the results Langevin obtained with the techniques he worked out in several laboratories and research schools in Paris and Cambridge. His experiences affected not only his apparatus and technique but also his research agenda, mode of argumentation, and professional strategies. These last included his importation of Cambridge ion physics into Paris, his fight for the acceptance of microphysics by his French colleagues, and his rise to a professorship at the Collèège de France.

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