Henry, Robert, and William Tytler. “A Letter from the Late Dr Henry, Author of the History of Great Britain, to William Tytler, Esq., With Answer”. Archaeologia Scotica 1 (November 30, 1793): 538-540. Accessed September 25, 2020. http://journals.socantscot.org/index.php/arch-scot/article/view/353.