The library also holds scattered correspondence from Russian/Soviet scientists, ca. 1900–1950, in its microfilm and manuscript collections; and a card index, the National Catalog of Sources, on physicists and astronomers, which might be useful in locating the papers of scientists who have had contacts with Russia/USSR. Restrictions: Individual oral history transcripts may have special restrictions; inquire at the library. Access to all manuscript materials and oral history interviews is restricted to persons who have completed an application for access which has been approved by Center staff.