Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Essays, second series”, p.128, Harvard University Press
"The complete works of Ralph Waldo Emerson: Nature addresses and lectures", Vol. 1, by Ralph Waldo Emerson, Ann Arbor, Michigan: University of Michigan Library, 2006.