Jeremy J. Siegel (1998). “Stocks for the Long Run: The Definitive Guide to Financial Market Returns and Long-term Investment Strategies”, McGraw-Hill Companies
John Adams, Charles Francis Adams (1850). “The Works of John Adams, Second President of the United States: Diary, with passages from an autobiography. Notes of debates in the Continental Congress, in 1775 and 1776. Autobiography”, p.79
Pope Benedict XVI's Letter to the Ecumenical Patriarch of Constantinople on the Occasion of the Seventh Symposium of the Religion, Science and the Environment Movement, w2.vatican.va. September 1, 2007.