Note 54 — PAPER 27

Ibid.,, pp. 6-7. I have not pursued the matter of cognate linkages (the Watt and Evans linkages are cognates) because the Roberts-Chebyshev theorem escaped my earlier search, as it had apparently escaped most others until 1958. See R. S. Hartenberg and J. Denavit, "The Fecund Four-Bar," Transactions of the Fifth Conference on Mechanisms, Cleveland, Penton Publishing Company, 1958, pp. 194-206, reprinted in Machine Design, April 16, 1959, vol. 31, pp. 149-152. See also A. E. R. de Jonge, "The Correlation of Hinged Four-Bar Straight-Line Motion Devices by Means of the Roberts Theorem and a New Proof of the Latter," Annals of the New York Academy of Sciences, March 18, 1960, vol. 84, art. 3, pp. 75-145 (published separately).