Robert Green Ingersoll (1920). “Ingersoll: Fifty Great Selections, Lectures, Tributes, After Dinner Speeches and Essays, Carefully Selected from the Twelve Volume Dresden Edition of Colonel Ingersoll's Complete Works”
"Philosophy of Science", Volume 37 (p. 157), 1934; later quoted in Roger Gerhard Newton "The Truth of Science: Physical Theories and Reality" (p. 176), 1997.