Scottish professor of medical jurisprudence at the University of Edinburgh from 1832, who was editor of the eighth edition of Encyclopædia Britannica.

Traill graduated from the University of Edinburgh (1802) and for 30 years practiced medicine in Liverpool, where he helped to found, and was secretary of, the Literary and Philosophical Society and also devoted time to establishing the Royal Institution and the Mechanics Institution. On his return to Edinburgh he was chosen by Britannica proprietor Adam Black to edit the eighth edition. The first volume appeared just before Traill became president (December 1852) of the Edinburgh Royal College of Physicians. Traill's articles for Britannica included, among other contributions, “Medical Jurisprudence” and “Light and Heat.”