Correspondence, mainly relating to professional organizations and publications; manuscript material, scientific but also poetry and science fiction; course notes and lecture notes; technical notes and data; personal and biographical information including diaries (1948-1957, 1960, 1969-1979), notes and personal correspondence. The lecture notes were taken from courses taught by the physicist Paul Epstein at Caltech. These include higher dynamics, 1925; thermodynamics, 1925-1926; and quantum theory, 1926-1928. Also included is Richter's collection of science fiction publications (35 boxes) including numerous titles from 1926 through the early 1950s, such as Amazing Stories, Amazing Stories Quarterly, Astounding Science Fiction and Astounding Stories. Supplement includes diplomas, diary, memorabilia.