G. Stanley Hall (2013). “Adolescence - Its Psychology and Its Relations to Physiology, Anthropology, Sociology, Sex, Crime, and Religion (1931)”, p.12, Read Books Ltd
Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.24, St. Martin's Press
G. Stanley Hall (2013). “Adolescence - Its Psychology and Its Relations to Physiology, Anthropology, Sociology, Sex, Crime, and Religion (1931)”, p.365, Read Books Ltd