(Philadelphia, 1826, vol. I, pl. 5).]

Directly related to the drag link coupling were the patents of John
Oldham (1779-1840), an Irish engineer who is remembered mainly for the
coupling that bears his name (fig. 39). His three patents, which were
for various forms of steamboat feathering paddle wheels, involved
linkages kinematically similar to the drag link coupling, although it is
quite unlikely that Oldham recognized the similarity. However, for his
well-known coupling, which employs an inversion of the elliptical
trammel mechanism, I have found no evidence of a patent. Probably it was
part of the machinery that he designed for the Bank of Ireland's
printing house, of which Oldham was manager for many years. "Mr. Oldham
and his beautiful system" were brought to the Bank of England in 1836,
where Oldham remained until his death in 1840.[106]

[Footnote 106: Oldham's paddle-wheel patents were British Patents 4169
(October 10, 1817), 4429 (January 15, 1820), and 5445 (February 1,
1827). Robert Willis (_op. cit._ footnote 21, p. 167) noticed the
existence of the coupling. Drawings or descriptions of the banknote
machinery apparently have not been published though they probably still
exist in the banks' archives. The quotation is from Frederick G. Hall,
_The Bank of Ireland 1783-1946_, Dublin, 1949. John Francis in his
_History of the Bank of England_ (London, 1848, vol. 2, p. 232) wrote:
"The new machinery for printing the notes, which was introduced by Mr.
Oldham ... is well worthy of a visit, but would be uninteresting to
delineate."]

[Illustration: Figure 39.--_Top_, Original Oldham coupling built before
1840, using a cross (instead of a center disk), as sketched by Robert
Willis in personal copy of his _Principles of Mechanism_ (London, 1841,
p. 167). _Bottom_, Oldham coupling as illustrated in Alexander B. W.
Kennedy, _Kinematics of Machinery_, a translation of Franz Reuleaux'
_Theoretische Kinematik_ (London, 1876, pp. 315-316).]

The Geneva stop mechanism (fig. 40) was properly described by Willis as
a device to permit less than a full revolution of the star wheel and
thus to prevent overwinding of a watch spring. It was called Geneva stop
because it was used in Geneva watches. The Geneva wheel mechanism, which
permits full rotation of the star wheel and which is frequently used
for intermittent drives, was improperly called a Geneva stop in a
recent textbook probably because the logical origin of the term h