Gerda S. Norvig, William Blake (1993). “Dark Figures in the Desired Country: Blake's Illustrations to The Pilgrim's Progress”, p.45, Univ of California Press
William Blake, Robert N. Essick, Joseph Viscomi (1998). “Milton a Poem, and the Final Illuminated Works: The Ghost of Abel, On Homers Poetry, [and] On Virgil, Laocoön”, p.232, Princeton University Press