Nine of these letters are addressed to Sir Alexander Dick of Edinburgh (1763-1768), and relate to Morgan's medical studies, his travels on the Continent, and the founding of the medical department of the College of Physicians. These are copies of originals in possession of Mrs. Dick Cunyngham, Prestonfield House, Edinburgh. In addition there are letters from Morgan to: Petrus Camper, William Smith, Samuel Vaughan, Jr.; and from Peter Collinson to Camper; Camper to Morgan; S. Vaughan Jr. to Camper; and an exchange between Christian F. Michaelis and Camper. These concern Morgan, with mentions of fossils (mastodon bones in America), natural history, comments on Franklin, Jefferson, and Angelica Kauffmann. These are from originals in the Petrus Camper Papers, on deposit (1976) at the University of Amsterdam Library.

Benjamin Silliman (1779-1864, APS 1805) was a scientist and educator. As a professor of chemistry at Yale University from 1802 to 1853, and pioneering teacher of chemistry, mineralogy and geology, Silliman was largely responsible for the conversion of Yale College to Yale University, with strong medical and scientific departments.

The largest portion of correspondence is with Charles Edwin Bessy on botanical matters, including botanical publications in the United States and Europe, and plants and shell specimens.