The ArgumentThe societal context within which science is pursued generally acts as a productive force in the generation of knowledge. To analyze this action it is helpful to consider particular modes of mediation through which societal concerns are projected into the very local and esoteric concerns of a particular domain of research. One such mode of mediation occurs through material systems. Here I treat two such systems – the steam engine and the electric telegraph – in the natural philosophy of (...) William Thomson (Lord Kelvin).The steam engine illustratesconceptualmediation. It simultaneously instantiates “labor value” in political economy and “work” in engineering mechanics, thereby identifying the two concepts in the region of their common reference. The partial identification carries with it a structural analogy between a network of concepts from political economy and a similar network in natural philosophy, providing a potent heuristic for the reformulation and further development of dynamics.The electric telegraph illustratesmethodologicalmediation. It projects the interests of engineering and industry into the interests of electromagnetic theory and vice versa, thereby establishing, in Thomson's view, a Baconian unity of truth and utility. As the common reference of theory and practice, the telegraph locates the truth of theoretical knowledge in its utility and the utility of practical knowledge in its truth.These particular cases of conceptual and methodological mediation indicate how the local practices, concepts, and interests of a research specialty, or subculture, draw on and are adapted to those of the larger culture within which they develop. Thus the analysis of mediation leads to an ecological model of the social construction of scientific knowledge. (shrink)