Marie Curie's letter to Eve Curie Labouisse (July 1929), as quoted in Eve Curie Labouisse "Madame Curie: A Biography" translated by Vincent Sheean (p. 341), 1937.
"Life Thoughts, Gathered from the Extemporaneous Discourses of Henry Ward Beecher, by One of His Congregation". Book edited by Edna Dean Proctor, 1859.