Jabarkan Nota kaki dari Robert G. Ingersoll dalam bahasa melayu

Nathan G. Alexander,Race in a Godless World: Atheism, Race, and Civilization, 1850-1914. New York/Manchester: New York University Press/Manchester University Press, 2019.

Eric T. Brandt, Timothy Larsen, "The Old Atheism Revisited: Robert G. Ingersoll and the Bible," Journal of The Historical Society, vol. 11, no. 2 (2011), pp. 211–238.

Eugene V. Debs, "Recollections of Ingersoll," Pearson's Magazine, vol. 37, no. 4 (April 1917), pp. 302–307.

Susan Jacoby, The Great Agnostic: Robert Ingersoll and American Freethought. New Haven, CT: Yale University Press, 2013.

Orvin Larson, American Infidel: Robert G. Ingersoll a Biography. Citadel Press, 1962.

Susan Jacoby, Freethinkers: A History of American Secularism. Metropolitan Books, 2004.