MLA

Gibbs, J. Willard (Josiah Willard), 1839-1903. Dwight, Timothy (1828-1916) - 2 autograph letters, signed, to Josiah Willard Gibbs, concerning his salary as professor at Yale. New Haven.. Box 2, folder 59. 1893 November 15, 1896 January 25. https://collections.library.yale.edu/catalog/2025171.

APA, 6th edition

Gibbs, J. Willard (Josiah Willard), 1839-1903. (["Box 2, folder 59"])(1893 November 15, 1896 January 25)[Dwight, Timothy (1828-1916) - 2 autograph letters, signed, to Josiah Willard Gibbs, concerning his salary as professor at Yale. New Haven.]. https://collections.library.yale.edu/catalog/2025171.