s were concerned.

[Footnote 33: Greville and Dorothy Bathe, _Oliver Evans_, Philadelphia,
1935, pp. 88, 196, and _passim_.]

Another four-bar straight-line linkage that became well known was
attributed to Richard Roberts of Manchester (1789-1864), who around 1820
had built one of the first metal planing machines, which machines helped
make the quest for straight-line linkages largely academic. I have not
discovered what occasioned the introduction of the Roberts linkage, but
it dated from before 1841. Although Roberts patented many complex
textile machines, an inspection of all of his patent drawings has failed
to provide proof that he was the inventor of the Roberts linkage.[34]
The fact that the same linkage is shown in an engraving of 1769 (fig.
18) further confuses the issue.[35]

[Footnote 34: Robert Willis (_op. cit._ [Footnote 21] p. 411) credited
Richard Roberts with the linkage. Roberts' 15 British patent drawings
exhibit complex applications of cams, levers, guided rods, cords, and so
forth, but no straight-line mechanism. In his patent no. 6258 of April
13, 1832, for a steam engine and locomotive carriage, Roberts used
Watt's "parallel motion" on a beam driven by a vertical cylinder.]

[Footnote 35: This engraving appeared as plate 11 in Pierre Patte's 1769
work (_op. cit._ footnote 24). Patte stated that the machine depicted in
his plate 11 was invented by M. de Voglie and was actually used in
1756.]

[Illustration: Figure 17.--Straight-line linkage (before 1841)
attributed to Richard Roberts by Robert Willis. From A. B. Kempe, _How
to Draw a Straight Line_ (London, 1877, p. 10).]

[Illustration: Figure 18.--Machine for sawing off pilings under water,
about 1760, designed by De Voglie. The Roberts linkage operates the bar
(_Q_ in detailed sketch) at the rear of the machine below the operators.
The significance of the linkage apparently was not generally recognized.
A similar machine depicted in Diderot's _Encyclopedie_, published
several years later, did not employ the straight-line linkage. From
Pierre Patte, _Memoirs sur les objets plus importants de l'architecture_
(Paris, 1769, pl. 11).]

The appearance in 1864 of Peaucellier's exact straight-line linkage went
nearly unnoticed. A decade later, when news of its invention crossed
the Channel to England, this linkage excited a flurry of interest, and
variations of it occupied mathematical minds for several years. For at
least 10 years before and 20