(d) 



"Eccentric wheel" with 

 internal driving wheel 

 hung from working beam. 

 Wheel B is pivoted at cen- 

 ter of shaft A. 



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 noise." ^' 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 THE TIME OF WATT 



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