SummaryThe complex relation between molecular ideas and hydrodynamics in midnineteenth-century British science is considered. This relation is presented in the historical literature, almost invariably, in terms of a complete antithesis which signified an ontological commitment on behalf of British scientists to the idea that matter was essentially continuous. However, the analysis will reveal that molecular ideas were scattered within the main body of hydrodynamics and that molecular discourse was intersecting hydrodynamical discussions at specific points. Questions of resistance and complex fluid (...) phenomena were inviting various molecular conceptualizations of fluid matter, although these never took the form of a complete mathematical theory. (shrink)