This essay details a public display of four steam engine models assembled in a Leiden orphanage courtyard in 1777. By examining the multiple purposes to which these engines were and could be put, alongside the various interests, goals and interpretations of their inventors, instructors and audience, the notion of a clear division between public and private as well as scientific research and popularization is questioned. In its place, the essay ends with a generalized image of modern science, its practitioners, users and audiences seen as a complex terrain in which relations and divisions are constantly asserted, contested and renegotiated.