Two major questions motivate this study: How do new devices get taken up as experimental systems by scientists? How does the adoption of new instruments affect scientific knowledge? Many ramifications emerge from these two simple questions. Among these are historical questions about how, by whom, and why new instruments are introduced, or about how another, different set of instruments might be adopted given alternative social and cultural circumstances. Philosophical questions include the ways in which scientific understanding of the world depends on scientists' instruments and techniques. Sociological questions concern such issues as how the organization of work within disciplines and laboratories and other scientific institutions may depend on the equipment employed. All these questions are addressed in this book, which draws upon a range of archival sources as well as published scientific literature, through a detailed historical treatment of the electron microscope's introduction and early impact on the life sciences.