A masterful treatment of quantum theory, this classic work develops the subject's most important concepts from experimental evidence and from theory related to the wave nature of free particles. The first half concerns the classical mechanics of point particles, and the second focuses on extensions of quantum theory relevant to problems of atomic and molecular structure. "One of the best expositions of quantum theory." - American Scientist. AUTHOR: Rotterdam native H. A. Kramers (1894 1954) studied under Niels Bohr in Copenhagen during World War I and received his Ph.D. from Leiden after the war. He taught at Copenhagen, Utrecht, and the Delft University of Technology.