. Bulletin. Science. Figure 15.—Oliver Evans' "Columbian" en- gine, 1813, showing the Evans, or "grass- hopper," straight-line linkage. From Emporium of Arts and Sciences (new ser., vol. 2, no. 3, April 1814, pi. opposite p. 380). engines.'^ The practical advantage of the Evans linkage, utilizing as it could a much lighter working beam than the Watt or Freemantle engines, would not escape Oliver Evans, and he was not a man of excessive modesty where his own inventions were concerned. Another four-bar straight-line linkage that became well known was attributed to Richard Rob
. Bulletin. Science. Figure 15.—Oliver Evans' "Columbian" en- gine, 1813, showing the Evans, or "grass- hopper," straight-line linkage. From Emporium of Arts and Sciences (new ser., vol. 2, no. 3, April 1814, pi. opposite p. 380). engines.'^ The practical advantage of the Evans linkage, utilizing as it could a much lighter working beam than the Watt or Freemantle engines, would not escape Oliver Evans, and he was not a man of excessive modesty where his own inventions were concerned. 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 ma- chines helped make the quest for straight-line linkages largely academic. I have not discovered what occa- sioned 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.'* The fact that the same linkage is shown in an engraving of 1769 (fig. 18) further confuses the issue.'^ The appearance in 1864 of Peaucellier's exact straight-line linkage went nearly unnoticed. A 33 Grevllle and Dorothy Bathe, Oliver Evans, Philadelphia, 19.'^5, pp. 88, 196, and passim. 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 loco- motive carriage, Roberts used Watt's "parallel motion" on a beam driven by a vertical cylinder. 3= This engraving appeared as plate 11 in Pierre Patte's 1769 work {op. cit. footnote 24). Patte stated that the machine de- picted in his plate 11 was invented by M. de Voglie and was actually used in Please n
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