. Bulletin. Science. (d) "Eccentric wheel" with internal driving wheel hung from working beam. Wheel B is pivoted at cen- ter of shaft Sun-and-planet gearing. This is the idea actually employed in Boulton and Watt engines. As the optional link JK held the gearwheel centers always equi- distant, the annular guide G M Figure 7.—James Watt's five alternative devices for the conversion of reciprocating motion to rotary motion in a steam engine. (British Patent 1306, October 25, 1781). From James P. Muirhead, The Origin and Progress of the Mechanical Inventiom of James Watt (London, 1
. Bulletin. Science. (d) "Eccentric wheel" with internal driving wheel hung from working beam. Wheel B is pivoted at cen- ter of shaft Sun-and-planet gearing. This is the idea actually employed in Boulton and Watt engines. As the optional link JK held the gearwheel centers always equi- distant, the annular guide G M Figure 7.—James Watt's five alternative devices for the conversion of reciprocating motion to rotary motion in a steam engine. (British Patent 1306, October 25, 1781). From James P. Muirhead, The Origin and Progress of the Mechanical Inventiom of James Watt (London, 1854, vol. 3, pis. 3-5, 7). hare," Watt wrote to his partner. "I have got a gUmpse of a method of causing the piston-rod to move up and down perpendicularly, by only fixing it to a piece of iron upon the beam, without chains, or perpendicular guides, or untowardly frictions, aich- heads, or other pieces of clumsiness .... I have only tried it in a slight model yet, so cannot build upon it, though I think it a very probable thing to succeed, and one of the most ingenious simple pieces of mechanism I have contrived . . ." '^ Watt's marvelously simple straight-line linkage was incorporated into a large beam engine almost imme- diately, and the usually pessimistic and reserved in- ventor was close to a state of elation when he told Boulton that the "new central perpendicular motion answers beyond expectation, and does not make the shadow of a ; ^' This linkage, which was in- cluded in an extensive patent of 1784, and two alterna- tive devices are illustrated here (fig. 9). One of the alternatives is a guided crosshead (fig. 9, top right). Brilliant as was the conception of this linkage, it was followed up by a synthesis that is very little short of incredible. In order to make the linkage attached to the beam of his engines more compact, Watt had IS Muirhead, op. cit. (footnote 3), vol. 2, pp. 191-192. " Ibid., p. 202. PAPER 27: KINEMATICS FROM
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