Letter from [Ivan Ivanovich] Yastrebtzov, June 21, 1829 (St. Petersbourg [St. Petersburg]), Box: 24, Folder: 61. Letters, literary manuscripts, and personal papers of the Porter family, MS 28. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/467306 Accessed January 02, 2025.