"perpetual motion," in spite of an occasional dis- 

 claimer of such intent. 



Typical of many of these patented devices was a 

 linkage for "multiplying" the motion of a flywheel, 

 proposed in 1841 by Charles Johnson of Amity, Illi- 

 nois (fig. 37). "It is not pretended that there is any 

 actual gain of power," wrote Mr. Johnson; and prob- 

 ably he meant it. The avowed purpose of his linkage 

 was to increase the speed of a flywheel and thus 

 decrease its size.'"' 



An Englishman who a few years earlier had in- 

 vented a "new Motion" had claimed that his device 

 would supersede the "ordinary crank in steam en- 

 gines," the beam, parallel motion, and "external fly- 

 wheel," reduce friction, neutralize "all extra con- 

 tending power," and leave nothing for the piston to 

 do "but the work intended to be done." 



A correspondent of the Repertory of Patent Inventions 

 made short work of this device: "There is hardly one 

 assertion that can be supported by proof," he wrote, 

 "and most of them are palpable misstatements." The 

 writer attacked "the 'beetle impetus wheel,' which he 

 [the inventor] thinks us all so beetle-headed, as not to 

 perceive to be a flywheel," and concluded with the 

 statement: "In short the whole production evinces 

 gross ignorance either of machinery, if the patentee 

 really believed what he asserted, or of mankind, if he 

 did not." '"^ 



Although many of the mechanisms for which patents 

 were taken out were designed by persons who would 

 make no use of the principles involved even if such 

 principles could at that time have been clearly stated, 

 it is a regrettable fact that worthless mechanisms often 

 got as much space as sound ones in patent journals, 

 and objections such as the one above were infrequent. 

 The slanted information thus conveyed to the young 

 mechanician, who was just accumulating his first 

 kinematic repertory, was at times sadly misleading. 



From even this sketchy outline of the literature on 

 the subject, it should be fairly evident that there has 

 been available to the mechanician an enormous quan- 

 tity of information about mechanical linkages and 

 other devices. Whatever one may think of the quality 

 of the literature, it has undoubtedly had influence not 

 only in supplying designers with information but in 

 forming a tradition of how one ought to supply the 



Figure 37. — ^Johnson's "converting 

 motion," 1841. The linkage causes 

 the flywheel to make two revolutions 

 for each double-stroke of the engine 

 piston rod B. From U.S. Patent 2295, 

 October 1 1, 1841. 



background that will enable the mind to assemble and 

 synthesize the necessary mechanism for a given pur- 

 pose.'"^ 



Some of the mechanisms that have been given 

 names — such as the Watt straight-line linkage and 

 the Geneva stop — have appeared in textbook after 

 textbook. Their only excuse for being seems to be 

 that the authors must include them or risk censure by 

 colleagues. Such mechanisms are more interesting 

 to a reader, certainly, when he has some idea of 

 what the name has to do with the mechanism, and 

 who originated it. One such mechanism is the 

 drag link. 



After I had learned of the drag link (as most 

 American engineering students do), I wondered for 

 awhile, and eventually despaired of making any 

 sense out of the term. What, I wanted to know, was 

 being dragged? Recently, in Nicholson's Operative 

 Mechanic and British Machinist (1826), I ran across 

 the sketch reproduced here as figure 38. This figure, 

 explained Mr. Nicholson (in vol. 1, p. 32) "represents 

 the coupling link used by Messrs. Boulton and Watt 

 in their portable steam engines, a, a strong iron 

 pin, projecting from one of the arms of the fly-wheel 

 b; D, a crank connected with the shaft c; and e, a 

 link to couple the pin a and the crank d together, so 

 the motion may be communicated to the shaft c." 

 So the drag link was actually a link of a coupling. 

 Nothing could be more logical. A drag link mecha- 

 nism now makes sense to me. 

 Directly related to the drag link coupling were the 



i»3 U.S. Patent 2295, October 11, 1841. 



'"■I Repertory of Patent Inventions, ser. 3, October 1828, vol. 7, 

 pp. 196-200, and December 1828, vol. 7, pp. 357-361. 



'"* Some additional catalogs of "mechanical movements" are 

 listed in the selected references at the end of this paper. 



220 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



