About one unknown K. N. Leontiev's autograph

The article contains information about a copy of the print of "Byzantism and Slavism" by K. N. Leontiev from the third issue of "Readings at the Imperial Society of Russian History and Antiquities at Moscow University" published in 1876. The book was found in a Moscow antique store, and contained the author's manuscript to the director of the Moscow Main Archive of the Ministry of Foreign Affairs, F. A. Bühler. The relations of K. N. Leontiev with F. A. Bühler are considered. A special handwritten proofreading is provided, made by one of the author's close friends and has differences from all known publications of this work. This copy is important for the study of the bibliography of K. N. Leontiev, as well as for clarifying the text of "Byzantism and Slavism".