Figure 12. — Cartwright's geared straight-line 

 mechanism of about 1800, From Abraham 

 Rees, The Cyclopaedia (London, 181 g, "Steam 

 Engine," pi. 5). 



simple elements; arranging them into classes, and 

 comparing them together . . . ." 



Farey was of the opinion that while a mind like 

 Watt's could produce brilliant new ideas, still the 

 "common stock of ideas which are current amongst 

 cornmunities and professions, will generally prove 

 to be of a better quality than the average of those 

 new ideas, which can be produced by any individual 

 from the operation of his own mind, without assistance 

 from others." Farey concluded with the observation 

 that "the most useful additions to that common 



stock, usually proceed from the individuals who are 

 well acquainted with the whole series." '^ 



To Draw a Straight Line 



During most of the century after James Watt had 

 produced his parallel motion, the problem of devising 

 a linkage, one point of which would describe a 

 straight line, was one that tickled the fancies of 

 mathematicians, of ingenious mechanics, and of 

 gentlemanly dabblers in ideas. The quest for a 

 straight-line mechanism more accurate than that 

 of Watt far outlasted the pressing practical need 

 for such a device. Large metal planing machines 

 were well known by 1830, and by midcentury 

 crossheads and crosshead guides were used on both 

 sides of the Atlantic in engines with and without 

 working beams. 



By 1819 John Farey had observed quite accurately 



that, in England at least, many other schemes had 

 been tried and found wanting and that "no methods 

 have been found so good as the original engine; 

 and we accordingly find, that all the most established 

 and experienced manufacturers make engines which 

 are not altered in any great feature from Mr. Watt's 

 original engine . . . ." ^° 



Two mechanisms for producing a straight line 

 were introduced before the Boulton and Watt 

 monopoly ended in 1800. Perhaps the first was by 

 Edmund Cartwright (1743-1823), who is said to 

 have had the original idea for a power loom. This 

 geared device (fig. 12), was characterized patroniz- 

 ingly by a contemporary American editor as pos- 

 sessing "as much merit as can possibly be attributed 

 to a gentleman engaged in the pursuit of mechanical 

 studies for his own amusement." -'' Only a few small 

 engines were made under the patent.'* 



The properties of a hypocycloid were recognized 

 by James White, an English engineer, in his geared 

 design which employed a pivot located on the pitch 

 circle of a spur gear revolving inside an internal 

 gear. The diameter of the pitch circle of the spur 

 gear was one-half that of the internal gear, with the 



25 Farey, op. cit. (footnote 6), pp. 651, 652. 



26 In Rees, op. cit. (footnote 21), vol. 34 ("Steam Engine"). 

 John Farey was the writer of this article (see Farey, op. cit., p. 

 vi). 



2' Emporium 0} Arts and Sciences, December 1813, new ser., vol. 

 2, no. 1, p. 8L 

 2S Farey, op. cit. (footnote 6), p. 666. 



PAPER 27: KINEMATICS FROM THE TIME OF WATT 



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