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.9, Harvard University Press
Ralph Waldo Emerson (2010). “Essays and English Traits by Ralph Waldo Emerson: The Five Foot Shelf of Classics, Vol. V (in 51 Volumes)”, p.285, Cosimo, Inc.