Ernest Freeberg, The Age of Edison: Electric Light and the Invention of Modern America (New York: Penguin Books, 2013), 76–80.

John McCusker, ed., "Colonial Statistics", Governance and International Relations, vol. 5 of Historical Statistics of the United States: Millennial Edition, ed. Susan B. Carter et al. (New York: Cambridge University Press, 2006), 627; Richard Sutch, ed., "National Income and Product", Economic Structure and Performance, vol. 3 of Historical Statistics of the United States: Millennial Edition, 3.