Figure lO. — Watt's "parallel motion." En- 

 gine's working beam is pivoted at A. Pivot F 

 is attached to the engine frame. From 

 Dyonysius Lardner, The Steam Engine (Phila- 

 delphia, 1852), pi. 5 (American ed. 5 from 

 London ed. 5). 



I am more proud of the parallel motion than of 

 any other mechanical invention I have ever made."^^ 



The Watt four-bar linkage was employed 75 years 

 after its inception by the American Charles B. 

 Richards when, in 1861, he designed his first high- 

 speed engine indicator (fig. 11). Introduced into 

 England the following year, the Richards Indicator 

 was an immediate success, and ixiany thousands 

 were sold over the next 20 or 30 years.^^ 



In considering the order of synthetic abihty required 

 to design the straight-line linkage and to combine 

 it with a pantograph, it should be kept in mind 

 that this was the first one of a long line of such 

 mechanisms.-* Once the idea was abroad, it was only 

 to be expected that many variations and alternative 

 solutions should appear. One wonders, however, 



what direction the subsequent work would have 

 taken if Watt had not so clearly pointed the way. 



In 1827 John Farey, in his exhaustive study of 

 the steam engine, wrote perhaps the best contem- 

 porary view of Watt's work. Farey as a young man 

 had several tiraes talked with the aging Watt, and 

 he had reflected upon the nature of the intellect that 

 had caused Watt to be recognized as a genius, even 

 within his own lifetime. In attempting to explain 

 Watt's genius, Farey set down some observations 

 that are pertinent not only to kinematic synthesis 

 but to the currently fashionable term "creativity." 



In Farcy's opinion Watt's inventive faculty was 



Figure 1 1 . — Richards high-speed engine indi- 

 cator of 1 86 1, showing application of the Watt 

 straight-hne linkage. {USNM 307515; Smith- 

 sonian photo 46570). 



in the direction of its length; and contrivances, by which such 

 alternate rectilinear motions are converted into continuous 

 rotatory ones, or vice versa . . . ." Robert Willis in his Principles 

 of Mechanism (London, 1841, p. 399) described parallel motion 

 as "a term somewhat aukwardly applied to a combination of 

 jointed rods, the purpose of which is to cause a point to describe 

 a straight line . . . ." A. B. Kempe in How to Draw a Straight 

 Line (London, 1877, p. 49) wrote: "I have been more than 

 once asked to get rid of the objectionable term 'parallel motion.' 

 I do not know how it came to be employed, and it certainly 

 does not express what is intended. The expression, however, 

 has now become crystallised, and I for one cannot undertake 

 to find a solvent." 



22 Muirhead, op. cit. (footnote 3), vol. 3, note on p. 89. 



23 Charles T. Porter, Engineering Reminiscences, New York, 1908, 

 pp. 58-59, 90. 



far superior to that of any of his contemporaries; 

 but his many and various ideas would have been of 

 little use if he had not possessed a very high order 

 of judgment, that "faculty of distinguishing between 

 ideas; decomposing compound ideas into more 



21 At least one earlier straight-line linkage, an arrangement 

 later ascribed to Richard Roberts, had been depicted before 

 Watt's patent (Pierre Patte, Memoirs sur les objets les plus im- 

 portans de I' architecture, Paris, 1769, p. 229 and pi. 11). However, 

 this linkage (reproduced here in figure 18) had no detectable 

 influence on Watt or on subsequent practice. 



198 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



