Carlo Croce, Cogorno, Italy. 2003. 12"h x 8.5"w
x 8.5"d, without dome. 15"h x 11"diameter with dome. Custom design,
completely hand made. Dead bead verge - crown wheel escapement, one-half seconds pendulum.
Click on the picture to go to a page for
more detail. Click here for photos
of the clocks' construction.
This design is a closely based upon that originally made by John Joseph Merlin in 1776.
It is regarded as the first true skeleton clock made in England and remains one of quite
igneous and original design. During the period of 1820 - 1850 a few fine makers such as Condliff and the partnerships of Strutt and Wigston, and Parker
and Pace produced some beautiful quality and highly ingenious clocks, but only in limited
numbers. By the mid nineteenth century the production of skeleton clocks had increased
dramatically, roughly matching the rapidly increasing industrial wealth of the country,
and it was at this stage that their manufacture was largely taken over by a few
specialized firms such as Smith of Clerkenwell and Evans of Handsworth.1
Merlin was principal mechanic to James Cox, the celebrated maker of of automata and
musical clocks. In 1773 Merlin left Cox and established his own museum of automata known
as Merlin's Necromantic Cave. His main field of activity was in the design of mechanized
musical instruments. He was also the inventor of the roller skate. He used the skates in a
demonstration where, as described by the source footnoted below: 'supplied with a pair of
these and a violin he mixed in the motley group of one of the celebrated Mrs. Corneily's
masquerades at Carlisle House, Soho Square; when, not having provided the means of
retarding his velocity, or commanding its direction, he impelled himself against a mirror
of more than five hundred pounds value, dashed it into atoms, broke his instrument to
pieces, and wounded himself severely'.2 The
shock of this incident appears to have made Merlin give up his desires to to set this
invention before the public, and it was left to the Americans to reintroduce the roller
skate under that name in the early 1870s.2
Unfortunately, like Congreves' rolling ball clock; while
an ingenious design and interesting to look at, it is a poor time keeper and difficult to
keep running. The verge escape wheel has 60 teeth and is used to indicate the seconds.
Normally a verge has an odd number of teeth so the resting or dead faces of the verge are
staggered on on either side of its' axis. The center wheel has 60 teeth and drives
directly the vertical escapement pinion which is a worm gear. It is here that the clock
exhibits it main problem in reliability. A worm driving a toothed wheel provides a
reliable, low torque input. However, in reverse, a high torque from the toothed wheel to
the worm is required. While this works well in the fly fans of a music box or clock fly
fans which do not involve static friction (see Rahmer),
this is wholly unsuitable to drive a pendulum! A pendulum involves a process of starts and
stops entailing greater frictional forces known as static vs. moving friction.
The profile of a normal toothed wheel driving against a worm gear results in a very small
area representing the edge of the tooth driving the worm. This creates a great deal of
pressure in a tiny area resulting in high friction. A helical gear instead of a
conventional 60 toothed wheel would have solved this problem, but this was prior to
Charles McDowalls' helical geared skeleton clocks of the 1830s.
It is doubtful that Merlin's original clock ran for any length of time before
lubrication failure due to the problems discussed and the deficiencies of the oils
available in those days, caused it to stop. A modern, synthetic, high pressure automotive
grease applied to the worm gear is used to overcome this problem. Even so, wear is
apparent on the edges of the main toothed center wheel.
1. Roberts, Derek, British Skeleton Clocks, Suffolk, England 1987
2. Busby, T., Concert Room and Orchestra Anecdotes,
London, England 1825