The correspondence (1869-1883) is primarily routine business, i.e. navy orders and letters of recommendation, and also includes some personal letters. In addition, there are several notebooks and diaries, including notes from Pennsylvania Hospital clinical lectures, 1867-1869 (2 v.); diaries, 1865-1875 (7 v.); a volume of poetry; and general study notes. There is also early material (1745-1813) on the Cassin family, including a letter of indenture dated 1758.

These papers include correspondence from over 180 individuals, lecture notes and essays on mathematics, astronomy, and electricity, and his diaries from journeys through Germany (1798) and Switzerland (1802).

William Jacob Robbins (1890-1978, APS 1941) was a botanist and physiologist. From 1937 to 1957 he was director of the New York Botanical Garden. His research focused on culture methods of plants in relation to biochemistry and nutrition, especially on the synthetic abilities of fungi. His studies paralleled the scientific agenda of the Rockefeller Foundation, an agency with which he was closely associated for years as adviser and trustee. He was perhaps the most influential botanist in the National Academy of Sciences (NAS) during the early postwar era, and a principal participant in the plans for the global reconstruction of science. Robbins served as president of the American Philosophical Society from 1956 to 1959.