From the Robin Catalogue:
L 409. Smithsonian Institution (Hodge, Karr, Langley, Rathbun, Walcott, Winlock). Forty-five letters to CSP, January 17, 1894-February 3, 1911; six letter drafts from CSP to S. P. Langley, May 20, 1901-June 1, 1908, and n.d. One letter (Langley) to Captain Davis, January 29, 1900. Miscellaneous materials: printed matter.
Partially published: HP 2:876-879 (“Peirce to Langley, c. May 20, 1900”)