E. M. Forster (2014). “Great Novels of E. M. Forster: Where Angels Fear to Tread, The Longest Journey, A Room with a View, Howards End”, p.482, Skyhorse Publishing, Inc.
Margaret Sanger, Michael W. Perry, H. G. Wells (2003). “The Pivot of Civilization in Historical Perspective: The Birth Control Classic”, p.40, Inkling Books
Adam Smith, Jean-Baptiste Say, J.R. McCulloch (2013). “History of Economic Theory: The Selected Writings of Adam Smith, Jean-Baptiste Say, and J.R. McCulloch”, p.133, Coventry House Publishing