MLA

Palmquist, Peter E. (1936-2003). "Stereoscopic Slides." Harper's New Monthly Magazine. Box 33, folder 106. 1860 October. https://collections.library.yale.edu/catalog/33292666.

APA, 6th edition

Palmquist, Peter E. (1936-2003). (["Box 33, folder 106"])(1860 October)["Stereoscopic Slides." Harper's New Monthly Magazine]. https://collections.library.yale.edu/catalog/33292666.