In the
early 19th century, an Englishman named Sir William Congreve invented an
unusual clock that kept time using balls rolling down an incline. At that time,
most clocks kept time through the regular swinging of a pendulum.
The
Congreve rolling ball clock consists of a brass plate with a zigzag path carved
on it. A small brass ball rolls down the carved track, and when it reaches the
end of the track, the ball hits a lever and a spring raises the end of the
plate, reversing the tilt of the plate and sending the ball rolling back the
other way. The lever also advances the clock hands by the same amount of time
the ball takes to run down the tracks. In most designs this is 15 seconds, but
in some larger clocks it can be as long as one minute.
While
Congreve is often credited with the invention of the rolling ball clock, it
wasn’t an original design. Such clocks had been made previously by the French
inventor Nicolas Grollier de Servière and the German clockmaker Johann Sayller,
both in the 17th century. Some sources maintain that Congreve was unaware of
the existence of these designs, but according to Mark Frank, who runs a website
devoted historical timepieces, Congreve “may have assimilated some of the
details from a clock made by Johann Sayller”, especially since both designs
employed a zigzag track. Grollier's rolling ball clock, on the other hand, had
a straight track.
One
way Congreve’s design differs from Sayller’s is that the latter used a number
of balls and a fixed table rather than the single ball and tilting table
employed by Congreve. Congreve attempted to make an “extreme detached
escapement”, as he described in his patent. In reality, the clock’s accuracy
was vulnerable to many external factors.
Sayller's
rolling ball clock built in 1626. Photo credit:
www.my-time-machines.net
Setting
up the clock required extreme precision. The staff at the Buckingham Palace,
who were tasked with keeping time with a rolling ball clock, described it in
1837 as the “most complicated and troublesome machine.”
The
assistant conservator of technology at the National Museum of Scotland, Darren
Cox, wrestled with one clock for two months with little success.
”The
clock and the tilting table (front and back) need to be totally level. I have
found that, even with the temporary cover I have made for it to keep the dust
out, the metal ball needs to be polished at least once every two weeks to
remove debris,” he explains.
"However,
the biggest task in getting this clock to work was adjusting all the levers and
the table that had been bent and twisted previously. It takes very little to
stop the ball from rolling and if it doesn’t roll fast enough it will not be
able to unlock the train of wheels and lift the table.”
Dust
was the biggest problem. The time taken by the ball to roll down the inclined
track varied greatly depending on the cleanliness of the track and the ball. In
addition, the metal expands or contracts with changes in temperature, altering
the length of the track and size of the ball.
Darren
Cox found the clock would lose or gain as much as 45 minutes a day.
While
the Congreve rolling ball clock was a notoriously poor timekeepers, they are
undeniably beautiful and fascinating to watch.
Rolling ball clock at the British Museum.
Rolling ball clock at the National Museum of
Scotland.
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