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Kennedy, _The Mechanics of Machinery_, ed. 3, London, 1898, pp. vii, x.] [Footnote 87: Siegfried Heinrich Aronhold, "Outline of Kinematic Geometry," _Verein zur Befoerderung des Gewerbefleisses in Preussen_, 1872, vol. 51, pp. 129-155. Kennedy's theorem is on pp. 137-138.] [Illustration: Figure 32.--Robert Henry Smith (1852-1916), originator of velocity and acceleration polygons for kinematic analysis. Photo courtesy the Librarian, Birmingham Reference Library, England.] Kennedy, after locating instant centers, determined velocities by calculation and accelerations by graphical differentiation of velocities, and he noted in his preface that he had been unable, for a variety of reasons, to make use in his book of Smith's recent work. Professor Kennedy at least was aware of Smith's surprisingly advanced ideas, which seem to have been generally ignored by Americans and Englishmen alike. Professor Smith, in a paper before the Royal Society of Edinburgh in 1885, stated clearly the ideas and methods for construction of velocity and acceleration diagrams of linkages.[88] For the first time, velocity and acceleration "images" of links (fig. 33) were presented. It is unfortunate that Smith's ideas were permitted to languish for so long a time. [Footnote 88: Robert H. Smith, "A New Graphic Analysis of the Kinematics of Mechanisms," _Transactions of the Royal Society of Edinburgh_, 1882-1885, vol. 32, pp. 507-517, and pl. 82. Smith used this paper as the basis for a chapter in his _Graphics or the Art of Calculating by Drawing Lines_, London, 1889, pp. 144-162. In a footnote of his paper, Smith credited Fleeming Jenkin (1833-1885) with suggesting the term "image." After discarding as "practically useless" Kennedy's graphical differentiation, Smith complained that he had "failed to find any practical use" for Reuleaux's "method of centroids, more properly called axoids." Such statements were not calculated to encourage Kennedy and Reuleaux to advertise Smith's fame; however, I found no indication that either one took offense at the criticism. Smith's velocity and acceleration diagrams were included (apparently embalmed, so far as American engineers were concerned) in _Encyclopaedia Britannica_, ed. 11, 1910, vol. 17, pp. 1008-1009.] [Illustration: Figure 33.--Smith's velocity image (the two figures at top), and his velocity, mechanism, and acceleration diagrams, 1885. The image of link BACD is shown as figure _bacd_.
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