Figure 22. — Peaucellier exact straight- 

 line linkage, 1873. From A. B. 

 Kempe, How to Draw a Straight Line 

 (London, 1877, p. 12). 



Figure 2 1 . — Top: Chebyshev straight- 

 line linkage, 1867; from A. B. Kempe, 

 How to Draw a Straight Line (London, 

 1877, p. 11). Bottom: Chebyshev- 

 Evans combination, 1867; from Oeuvres 

 de P. L. Tchebychef (St. Petersburg, 

 1907, vol. 2, p. 94). Points C, C, and 

 C" are fixed. A is the tracirig point. 



"the motion is of little or no practical use, for we can 

 scarcely imagine circumstances under which it would 

 be more advantageous to use such a complicated 

 system of levers, with so many joints to be lubricated 

 and so many pins to wear, than a solid guide of some 

 kind; but at the same time the arrangement is very 

 ingenious and in this respect reflects great credit on 

 its designer." '^ 



There is a persistent rumor that Professor Chebyshev 

 sought to demonstrate the impossibility of constructing 

 any linkage, regardless of the nuinber of links, that 



Figure 23. — Model of the Peaucellier 

 "Compas Compose," deposited in 

 Conservatoire National des Arts et 

 Metiers, Paris, 1875. Photo courtesy 

 of the Conservatoire. 



would generate a straight line; but I have found only 

 a dubious statement in the Grande Encyclopedie*" of the 

 late 19th century and a report of a conversation with 

 the Russian by an Englishman, James Sylvester, to 

 the effect that Chebyshev had "succeeded in proving 

 the nonexistence of a five-bar link-work capable of 

 producing a perfect parallel motion. . . ."" Regard- 

 less of what tradition may have to say about what 

 Chebyshev said, it is of course well known that 

 Captain Peaucellier was the man who finally syn- 

 thesized the exact straight-line mechanism that bears 

 his name. 



* Engineering, October 3, 1873, vol. 16, p. 284. 



*" La Grande Encyclopedic, Paris, 1886 ("Peaucellier"). 



^1 James Sylvester, "Recent Discoveries in Mechanical Con- 

 version of Motion," Notices of the Proceedings of the Royal Insti- 

 tution oj Great Britain, 1873-1875, vol. 7, p. 181. The fixed 

 link was not counted by Sylvester; in modern parlance this 

 would be a six-link mechanism. 



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BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



