Theodore Roosevelt (2015). “Theodore Roosevelt on Bravery: Lessons from the Most Courageous Leader of the Twentieth Century”, p.4, Skyhorse Publishing, Inc.
William Lyon Phelps (2016). “A Collection of Classic Essays by William Lyon Phelps - Including 'Happiness', 'Superstition', 'The Great American Game', and Many More”, p.83, Read Books Ltd
Theodore Roosevelt (2015). “Theodore Roosevelt on Bravery: Lessons from the Most Courageous Leader of the Twentieth Century”, p.4, Skyhorse Publishing, Inc.