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, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: English traits”, p.128, Harvard University Press
Ralph Waldo Emerson (1841). “The method of nature: An oration, delivered before the Society of the Adelphi, in Waterville College, in Maine, August 11, 1841”, p.7