To all four of us, Carsten was the best possible friend and colleague. To Finn, he was a fellow student in the history of science for several years at the Niels Bohr Institute; to Relge, he was a welcome resource for personal and intellectual interac tion in an otherwise less than fertile environment for the history of science; Roger was Carsten's friend and advisor, not least in the development of the dissertation on which the present book is based; and as director of the Niels Bohr Archive, Erik was his main advisor in his historical work. Because he was the person closest to Carsten's work on his Ph. D. dissertation on the history of beta decay, on which the present book is based, it is only fitting that Erik stands as single author of the words in Carsten's memory at the very beginning of this book. Before his untimely death shortly after the completion of the Ph. D. disser tation, Carsten had himself plans to develop the dissertation into a book. Being a true perfectionist, he wanted to rework the manuscript substantively, especially with regard to relating it to the broader discussion among historians of science."

In 1920s, a long-lasting controversy on the interpretation of nuclear beta spectrum arose between Lise Meitner and Charles Drummond Ellis. This controversy, and the reactions from the contending parties when it was settled, reflect clearly the difference between the scientific communities in Berlin and Cambridge at that time. The Meitner-Ellis controversy ended in 1929, and it left an anomaly that attracted leading theoretical physicists. A new dispute, this time between Niels Bohr and Wolfgang Pauli, broke out. It concerned the explanation of the continuity of the primary beta particles and dominated the discussions for the next five years. Pauli argued for a new particle, and Bohr for a new theory; both suggestions were radical steps, but they reflected two different ways of doing physics.