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_.