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Whewell, William (1832). First principles of mechanics, with historical and practical illustrations. Cambridge, England: Deighton. p. 35. OCLC13469803.
Slight, James; Burn, Robert Scott (1868). "Machines for the products of the soil". In Stephens, Henry (ed.). The Book of Farm Implements & Machines. Edinburgh: Blackwood. pp. 425–428. OCLC458892190.