"The Metropolis and Modern Life" by Georg Simmel (1903), translated by Kurt Wolff in "The Sociology of Georg Simmel" edited by D. Weinstein, New York: Free Press, (p. 422), 1950.
Thomas Troward (2013). “The Edinburgh Lectures on Mental Science: Spirit and Matter, Subjective and Objective Mind, Power of Subconscious Mind (New Thought Edition - Secret Library)”, p.22, Lulu Press, Inc