Theodore Dunham, Jr, (1897-1984) was an American astronomer, physicist, and physician. Throughout his career, Dr. Dunham pioneered research on interstellar cosmic rays, the development of telescopes, stellar spectrophotometry, the study of interstellar material and the spectrophotometry of cells. The Theodore Dunham , Jr. Papers (1921-1984) contain professional correspondence, research notes, published and unpublished works by Dunham and others, detailed photographs and oversize sketches of astronomical observations, administrative details of the Mount Desert Island Astronomical Association and of a career-long association with the Fund for Astrophysical Research. Includes some medical research, but primarily contains his astrophysical research conducted at Mount Wilson Observatory, California and Mount Stromlo Observatory, Australia.