Thurston, Herbert (1907). Angelus. Vol. 1. New York: Robert Appleton Company. Retrieved April 27, 2020. This article incorporates text from this source, which is in the public domain.
Herbert Thurston, voce Angelus, in Charles George Herbermann (a cura di), Catholic Encyclopedia, Robert Appleton Company, New York , vol. I, 1907, p. 486.