item has been sold.
perpetual calendar clock - Details:
The 14 day movement strikes the hours and half hours
on a bell with a Brocot dead beat escapement visible
through the upper dial and a compensated pendulum
of brass and steel peculiar to Ellicott's design.
The gilt engraved dial mask; the upper white enamel
dial with blue steel 'Breguet' style hands and Roman
chapter ring; the lower perpetual calendar showing:
day, date, month, equation of time, and moon phase.
The numbers on the calendar dial around the inner
circle indicate the difference between solar and mean
time, which shows the 'equation of time'. This allowed
people to set their clocks by using their sundials.
The movement signed 'Cromey, Bristol' and numbered
31945. The calendar movement numbered 31756. The case
is glazed on three sides and open to the front; multi-colored
gold ormolu on a white marble base; surmounted by
a 'ruffled pigeon'; numbered 39703.
William Cromey is listed in Britten’s as a clockmaker
and jeweler in Bristol, 1842.
Dimensions: Height 18" - width 10" at base
1752 British clockmaker John Ellicott developed a
temperature compensated pendulum which was used by
French clockmakers. The central rod is made of iron
while the two peripheral rods are made of brass, which
has a higher thermal expansion.
With a rise in temperature, the two brass rods expand
more and press down on the levers which press up on
the pins attached to the bob, raising the bob. This
compensates for the lengthening of the central rod,
keeping the bob at the same distance from the pendulum
pivot. Therefore the pendulum's period of swing stays
constant with changes in temperature.
images below to view large detailed photographs
of this clock
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