These original contributions by philosophers and historians of science discuss a range of issues pertaining to the testing of hypotheses in modern physics by observation and experiment. Chapters by Lawrence Sklar, Dudley Shapere, Richard Boyd, R. C. Jeffrey, Peter Achinstein, and Ronald Laymon explore general philosophical themes with applications to modern physics and astrophysics. The themes include the nature of the hypothetico-deductive method, the concept of observation and the validity of the theoretical-observation distinction, the probabilistic basis of confirmation, and the testing of idealizations and approximations. The remaining four chapters focus on the history of particular twentieth-century experiments, the instruments and techniques utilized, and the hypotheses they were designed to test. Peter Galison reviews the development of the bubble chamber; Roger Stuewer recounts a sharp dispute between physicists in Cambridge and Vienna over the interpretation of artificial disintegration experiments; John Rigden provides a history of the magnetic resonance method; and Geoffrey Joseph suggests a statistical interpretation of quantum mechanics that can be used to interpret the Stern-Gerlach and double-slit experiments. This book inaugurates the series, Studies from the Johns Hopkins Center for the History and Philosophy of Science, directed by Peter Achinstein and Owen Hannaway. A Bradford Book.