Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Nature, addresses, and lectures”, p.53, Harvard University Press
Arthur Penrhyn Stanley (1864). “A Reasonable, Holy, and Living Sacrifice: A Sermon Preached in Westminster Abbey, on January 10, 1864, Being the Day Following His Installation”, p.18