[Illustration: Figure 27.--Gaspard Monge (1746-1818), professor of mathematics at the Ecole Polytechnique from 1794 and founder of the academic discipline of machine kinematics, From _Livre du Centenaire, 1794-1894, Ecole Polytechnique_ (Paris, 1895, vol. 1, frontispiece).] Enthusiastic as Kempe was, however, he injected an apologetic note in his lecture. "That these results are valuable cannot I think be doubted," he said, "though it may well be that their great beauty has led some to attribute to them an importance which they do not really possess...." He went on to say that 50 years earlier, before the great improvements in the production of true plane surfaces, the straight-line mechanisms would have been more important than in 1876, but he added that "linkages have not at present, I think, been sufficiently put before the mechanician to enable us to say what value should really be set upon them."[54] [Footnote 54: _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).] It was during this same summer of 1876, at the Loan Exhibition of Scientific Apparatus in the South Kensington Museum, that the work of Franz Reuleaux, which was to have an important and lasting influence on kinematics everywhere, was first introduced to English engineers. Some 300 beautifully constructed teaching aids, known as the Berlin kinematic models, were loaned to the exhibition by the Royal Industrial School in Berlin, of which Reuleaux was the director. These models were used by Prof. Alexander B. W. Kennedy of University College, London, to help explain Reuleaux's new and revolutionary theory of machines.[55] [Footnote 55: Alexander B. W. Kennedy, "The Berlin Kinematic Models," _Engineering_, September 15, 1876, vol. 22, pp. 239-240.] Scholars and Machines