ers in more recent publications,[124] and it is
likely that many more variations on this theme will appear.

[Footnote 122: Bottema, _op. cit._ (footnote 121).]

[Footnote 123: In 1851 Robert Willis had designed a coupler-point
path-generating machine (fig. 46) that could have been used to produce a
work similar to that of Hrones and Nelson.]

[Footnote 124: R. S. Hartenberg and J. Denavit, "Systematic Mechanism
Design," _Machine Design_, September 1954, vol. 26, pp. 167-175, and
October 1954, vol. 26, pp. 257-265; A. S. Hall, A. R. Holowenko, and H.
G. Laughlin, "Four-Bar Lever Crank Mechanism," _Design News_, September
15, 1957, vol. 12, pp. 130-139, October 1, 1957, vol. 12, pp. 145-154,
and October 15, 1957, vol. 12, pp. 132-141. For a nomographic approach,
with particular application to computers, see Antonin Svoboda,
_Computing Mechanisms and Linkages_, New York, 1948.]

[Illustration: Figure 45.--Paths of 11 points on the coupler
(horizontal) link are plotted through one cycle. Dashes indicate equal
time intervals. From John A. Hrones and G. L. Nelson, _Analysis of the
Four Bar Linkage_ (New York, 1951, p. 635).]

[Illustration: Figure 46.--Coupler-point path-generating machine for
four-bar linkage. This device, built by Professor Willis as a teaching
aid for demonstrating straight-line linkages, could have been adapted to
produce a plate like the one shown in figure 45. From Robert Willis, _A
System of Apparatus for the Use of Lecturers and Experimenters_ ...
(London 1851, pl. 3).]

Pursuit of solutions to the "complicated analytical theory" of linkages
was stimulated by publication of Ferdinand Freudenstein's "Analytical
Approach to the Design of Four-Link Mechanisms" in 1954,[125] and an
increasing interest in the problem is indicated by the extensive
literature that has appeared in the last five years.

[Footnote 125: _Transactions of the American Society of Mechanical
Engineers_, 1954, vol. 76, pp. 483-492. See also _Transactions of the
American Society of Mechanical Engineers_, 1955, vol. 77, pp. 853-861,
and 1956, vol. 78, pp. 779-787.]

The proper role of rational methods in the synthesis of mechanisms is
not yet clear. "While we may talk about kinematic synthesis," wrote two
of today's leaders in the field, "we are really talking about a hope for
the future rather than a great reality of the present."[126] When the
mental equipment and the enthusiasm of scholars who are devoting their
time to th