Claude Adrien Helvétius (1777). “A Treatise on Man, His Intellectual Faculties and His Education: A Posthumous Work of M. Helvetius. Translated from the French, with Additional Notes, by W. Hooper, ...”, p.291
Theodore Roosevelt (2015). “Theodore Roosevelt on Bravery: Lessons from the Most Courageous Leader of the Twentieth Century”, p.36, Skyhorse Publishing, Inc.