John Neagle was among the better known portrait painters in Philadelphia during the first half of the nineteenth century and was the husband of Thomas Sully's niece, Mary C. Sully. The Neagle Papers is a small assemblage of personal correspondence, documents, and notes assembled by Neagle during his career. The letters are primarily of a personal nature, but along with the five bound volumes, offer insight into Neagle's study of painting and the techniques he employed. Included among the bound volumes are recipes for varnish, megellup, and drying oils and notes on watercolor painting.

Though the Miscellaneous Manuscripts collection is composed of items that do not fall readily into any other existing collection, the two dominant intellectual areas represented in the collection are Early American History and History of Science.