Completely non-mathematical, yet wholly faithful to the basic concepts of quantum mechanics, this book tells the fascinating story of the most thoroughgoing revolution in physics since Newton. In the first year of the twentieth century, a professor of theoretical physics in Berlin, Max Planck, suggested that light was not absorbed smoothly, but rather in small bundles or quanta. Five years later, a Swiss patent clerk, Albert Einstein, proposed that the radiation itself must exist as quanta. Thus was born a new age in physics the age of the quantum in which some of the most basic assumptions of classical physics were swept away, and a magnificent new theoretical structure created. This new physics was steeped in higher mathematics. Its concepts were often in contradiction with common sense. It rapidly became increasingly abstract and complex, to such an extent that even those well versed in classical physics were often unable to follow its labyrinthine turns and twists. How then could the layman understand it? This book answers that question. By means of analogies, examples, and imaginative insights, it acquaints the layman with the historical development and basic meaning of such momentous theories and discoveries as Bohr's energy levels of the atom, Pauli's exclusion principle, de Broglie's wave theory, Bohr's correspondence principle. Schroedinger's wave equation, Heinsenberg's uncertainty principle, Dirac's fundamental laws of quantum mechanics, Sommerfeld's fine structure theory, Feynman's world lines, electron spin, invariance, the quantum number, and numerous other concepts that so drastically changed our notion of the universe. A long postscript, written especially for this edition, brings the reader abreast of events to 1958. Of the books attempting an account of the history and contents of modern atomic physics which have come to my attention, this is the best. The captivating beauty of its prose, the ingenuity of its organization and the peculiar adequacy of its analogies entitle a reviewer of this book to such luxurious praise. Henry Margenau, Professor of Physics, Yale University.