Henry James (2015). “The Portrait of a Lady (Unabridged): From the famous author of the realism movement, known for The Turn of The Screw, The Wings of the Dove, The American, The Bostonian, The Ambassadors, What Maisie Knew…”, p.38, e-artnow
Richard P. Feynman, Robert B. Leighton, Matthew Sands (2015). “The Feynman Lectures on Physics, Vol. I: The New Millennium Edition: Mainly Mechanics, Radiation, and Heat”, p.119, Basic Books