In this paper I investigate the prospects of integrated history and philosophy of science, by examining how philosophical issues concerning experimental practice and scientific realism can enrich the historical investigation of the careers of "hidden entities", entities that are not accessible to unmediated observation. Conversely, I suggest that the history of those entities has important lessons to teach to the philosophy of science. My overall aim is to illustrate the possibility of a fruitful two-way traffic between history and philosophy of science
