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.28, Harvard University Press
John Adams, Charles Francis Adams (1854). “The Works of John Adams, Second President of the United States: With a Life of the Author, Notes and Illustrations”, p.158