source, but not until after Boulton and Watt had 

 spent considerable effort and money on it.-^ 



In 1777 a speaker before the Royal Society in 

 London observed that in order to obtain rotary out- 

 put from a reciprocating steam engine, a crank 

 "naturally occurs in theory," but that in fact the crank 

 is impractical because of the irregular rate of going of 

 the engine and its variable length of stroke. He said 

 that on the first variation of length of stroke the 

 machine would be "either broken to pieces, or turned 

 back.'"' John Smeaton, in the front rank of English 

 steam engineers of his time, was asked in 1781 by His 

 Majesty's Victualling-Office for his opinion as to 

 whether a steam-powered grain mill ought to be 

 driven by a crank or by a waterwheel supplied by a 

 pump. Smeaton's conclusion was that the crank was 

 quite unsuited to a machine in which regularity of 

 operation was a factor. "I apprehend," he wrote, 

 "that no motion communicated from the recipro- 

 cating beam of a fire engine can ever act perfectly 

 equal and steady in producing a circular motion, 

 like the regular efflux of water in turning a water- 

 wheel." He recommended, incidentally, that a 

 Boulton and Watt steam engine be used to pump 

 water to supply the waterwheel.'' Smeaton had 

 thought of a flywheel, but he reasoned that a flywheel 

 large enough to .smooth out the halting, jerky opera- 

 tion of the steam engines that he had observed would 

 be more of an encumbrance than a pump, reservoir, 

 and waterwheel.* 



The simplicity of the eventual solution of the prob- 

 lem was not clear to Watt at this time. He was not, 

 as tradition has it, blocked merely by the existence of 

 a patent for a simple crank and thus forced to invent 

 some other device as a substitute. 



Matthew Wasl^rough, of Bristol, the engineer coni- 

 monly credited with the crank patent, made no 

 mention of a crank in his patent specification, but 

 rather intended to make use of "racks with teeth," or 

 "one or more pullies, wheels, segments of wheels, to 



* Henry W. Dickinson and Rhys Jenkins, James Watt and 

 the Steam Engine, Oxford, Clarendon Press, 1927, pp. 146-148, 

 pis. 14, 31. This work presents a full and knowledgeable dis- 

 cussion, based on primary material, of the development of 

 Watt's many contributions to mechanical technology. It 

 is ably summarized in Dickinson, op. cit. (footnote 2). 



" John Farey, A Treatise on the Steam Engine, London, 1 827, 

 pp. 408-409. 



' Reports of the Late John Smeaton, F.R.S., London, 1812, vol. 

 2, pp. 378-380. 



* Farey, op. cit. (footnote 6), p. 409. 



which are fastened rotchets and clicks or palls. . . ." 

 He did, however, propose to "add a fly or flys, in 

 order to render the motion more re,gular and uni- 

 form." Unfortunately for us, he submitted no draw- 

 ings with his patent specification.^ 



James Pickard, of Birmingham, like Boulton, a 

 buttonmaker, in 1780 patented a counterweighted 

 crank device (fig. 6) that was expected to remove the 

 objection to a crank, which operated with changing 

 leverage and thus irregular power. In figure 6, the 

 counterweighted wheel, revolving twice for each 

 revolution of the crank (a), would allow the counter- 

 weight to descend while the crank passed the dead- 

 center position and would be raised while the crank 

 had maximum leverage. No mention of a flywheel 

 was made in this patent.'" 



Wasbrough, finding that his "rotchets and clicks" 

 did not serve, actually used, in 1780, a crank with a 

 flywheel. Watt was aware of this, but he remained 

 unconvinced of the superiority of the crank over 

 other devices and did not immediately appreciate the 

 regulating ability of a flywheel.'' In April 1781 Watt 

 wrote to Boulton, who was then out of town: "I know 

 from experiment that the other contrivance, which 

 you saw me try, performs at least as well, and has in 

 fact many advantages over the crank." '^ The "other 

 contrivance" probably was his swash wheel which he 

 built and which appeared on his next important 

 patent specification (fig. 7a). Also in this patent 

 were four other devices, one of which was easily 

 recognizable as a crank, and two of which were 

 eccentrics (fig. 7a, b). The fourth device was the 

 well-known sun-and- planet gearing (fig. 7e).'^ In 

 spite of the similarity of the simple crank to the several 

 variations devised by Watt, this patent drew no fire 

 from Wasbrough or Pickard, perhaps because no 

 reasonable person would contend that the crank itself 

 was a patentable feature, or perhaps because the 

 similarity was not at that time so obvious. However, 

 Watt steered clear of directly discernible application 

 of cranks because he preferred to avoid a suit that 

 might overthrow his or other patents. For example, 

 if the Wasbrough and Pickard patents had been 

 voided, they would have become public property; 



British Patent 1213, March 10, 1779. 

 i» British Patent 1263, August 23, 1780. 



11 Dickinson and Jenkins, op. cit. (footnote 5), pp. 150, 154. 



12 Ibid., p. 154. 



1' William Murdock, at this time a Boulton and Watt erector, 

 may have suggested this arrangement. Ibid., p. 56. 



192 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



