Adam Smith (2007). “The Wealth of Nations: An Inquiry Into the Nature and Causes of the Wealth of Nations: With an introduction by Jonathan B. Wight, University of Richmond”, p.62, Harriman House Limited
Charles Babbage's remarks in November 1839, recalling events in 1821; as quoted in Harry Wilmot Buxton and Anthony Hyman "Memoir of the Life and Labours of the Late Charles Babbage", 1988.