The first years of this century witnessed the final rejection of determinism in physical theory; there is no more compelling example of this than the synthesis forged in the early 1920s between theories of matter and theories of light. The insight of Louis de Broglie that led to the most complete formulation of wave–particle dualism was the last act in a series of preliminary attempts by physicists to resolve paradoxes that had arisen in theories of radiation following the discovery of x-rays. Historians have not directed sufficient attention either to radiation theory or to experimental studies of recent physics. In the case at hand, significant empirical data were recognized to challenge classical radiation theory long before the theory was successfully modified to agree with them. The gradual recognition, based on these experimental results, that internal consistency is unattainable by electromechanical interpretations of radiation forms the subject of this book.

This study grew out of concerns first raised while I was a student of physics. The inadequacy of most textbook discussions of historical and epistemological issues led me back to the original papers and then to the literature on history of science. I was fortunate to be introduced to the latter by John Heilbron, whose critical approach and demand for clarity in expression showed how insight can be won in historical analysis of scientific thought.