The direct reading emission spectrometer was developed during the1940s. By substituting photo-multiplier tubes and electronics forphotographic film spectrograms, the interpretation of special lineswith a densitometer was avoided. Instead, the instrument providedthe desired information concerning percentage concentration ofelements of interest directly on a dial. Such instruments `de-skill' the job of making such measurements. They do this by encapsulatingin the instrument the skills previously employed by the analyst,by `skilling' the instrument. This paper presents a history of thedevelopment of the Dow Chemical/Baird Associates (...) direct reader. Thishistory is used to argue for a materialist conception of knowledge.The instrument is a material form of knowledge, knowledge of aspectsof spectroscopy, analytical spectrochemistry, electronics, instrumentdesign and construction, and metal production industry economics. (shrink)