Materials, primarily from the period 1945-1964, including correspondence, classroom material, lectures, publications, research notes, newspaper articles, notes from graduate study and trips, a day book, an interview, and general miscellany. Most of the correspondents in this collection are eminent astronomers or laymen with a vital interest in astronomy; they include such people as Giorgio Abetti, Walter Baade, Philip C. Keenan, William W. Morgan, and Harcourt C. Vernon, as well as Sir Edmund Whittaker, F.J.M. Stratton, George Gamow, Harlow Shapley, and the families of the astronomically-minded Cleveland industrialists, Worcester Warner and Ambrose Swasey. There is correspondence and minutes relating to the American Astronomical Society, the Cleveland Museum of Natural History, the International Astronomical Union and other associations with which Nassau had relations. The main scientific interests documented are the use of the Schmidt-type telescope with optical refinements for the study of stellar spectra and the study of galactic structure, especially of the Milky Way and its evolution, by means of large, ongoing surveys of the stars, among which studies of stars discernible at either end of the spectrum play a large role. There is nothing from his early years nor about his family, except reminiscences in a 1961 interview conducted by Charles Weiner.