The correspondence includes both incoming and outgoing and indicates the wide range of Chapman's personal and professional activities. The International Geophysical Year files reflect his role as head of the Special Committee and his involvement in all aspects of planning and implementing the IGY scientific and technical investigations. The lecture notes include his teaching lectures, primarily in geomagnetism, lectures delivered to professional organizations, and talks presented to community and civic organizations. Also included are a wide range of graphic materials, photographs, lantern slides, and diagrams used to illustrate his lectures. The book drafts are manuscripts in preparation of one unidentified book co-authored with Nagata; "Solar-Terrestrial Physics: an Account of the Wave and Particle Radiations from the Quiet and Active Sun, of the Consequent Terrestrial Phenomena" with Syun-Ichi Akasofu; and "The Mathematical Theory of Non-uniform Gases" with T. G. Cowling. The biographical materials include correspondence, honors and awards, and a copy of the festschrift presented on the occasion of his 80th birthday. The series of reprints is believed to include a copy of everything Chapman published as well as drafts of works never published, and works of interest by others, most notably by Julius Bartels and Carl Stormer. The scientific data consist primarily of barometric pressure readings from various observatories. Major topics include: auroras, barometric pressure, geomagnetism, history of physics, and the IGY. Major correspondents: Syun-Ichi Akasofu, Julius Bartels, Thomas George Cowling, Peter Calvin Kendall, James Van Allen, Ernest H. Vestine.