This collection includes correspondence, articles, newsclippings, photographs, and recordings, concerning Menzel's documentation of UFOs as natural phenomena explainable in scientific terms. One can find material on the National Investigation Committee on Aerial Phenomena, Project Blue Book, the Velikovsky controversy, and a card file of meteor activity, 1946-1961.

The manuscripts of father William Mitchell and daughter Maria Mitchell are not easily separated, and are treated here together. The collection includes William Mitchell's autobiography, his memoir of Judge Walter Folger of Nantucket, astronomical and meteorological observations, lectures, family and other correspondence.