PIO XI (1857-1939). Saint Charles Borromee et les exercises de Saint Ignace. Paris: Spes, 1930. With signed autograph letter on Leonardo da Vinci and the Codex Atlanticus. Interesting specimen, enriched by an autograph letter signed by Achille Ratti, future Pope Pius XI, then prefect of the Ambrosian Library, in which the future pontiff addresses historical-artistic issues related to Leonardo da Vinci and the Codex Atlanticus. Data Milano, Biblioteca Ambrosiana, 22 February 1913, the letter responds punctually to the questions of an unidentified scholar about the illustrations of a manuscript, discussing its colors, figures, style and quality of the execution and comparing them directly with the Leonardo drawings preserved in the Codex Atlanticus. The letter thus constitutes an interesting testimony of the activity of Ratti as librarian and scholar before the election to the pontificate: Prefect of the Ambrosian since 1907, he would become pope under the name of Pius XI in 1922. Of particular interest is his direct involvement in the study and consultation of the Codex Atlanticus, one of the greatest nuclei of manuscripts and drawings of Leonardo preserved at the Ambrosian Library. 8vo (180 × 110 mm). With an autograph letter signed by A. Ratti, Prefect of Milan, dated, Biblioteca Ambrosiana, February 22, 1913, linked in the volume. Coeva bonding with leather back. Origin: ex libris Haldenwac. (1)