Swing Time

Marine clock circa 1750 by Pierre de Rivaz.

For centuries, pendulum clocks were the world's most precise timekeeping devices and widely used until the invention of the quartz clock in 1927.  The most accurate, called astronomical regulators, were used in observatories for celestial navigation and astronomy.  The Royal Society of London had five longcase (aka grandfather) clocks built for expeditions.  Captain Cook took one on his first voyage, and two on each of his other two voyages.

The Wells Cathedral clock was built in 1392, and has been in continual use
ever since.  In the 1600s a pendulum replaced the foliot balance and anchor
escapement.  It is the second oldest surviving clock in England (first is in
Salisbury Cathedral).  Image courtesy the Science Museum

The first person to conceive of the idea of using a swinging weight to control the speed of a clock was Galileo.  He was blind in 1637; his son Vincenzio and his pupil Viviani helped him develop his idea, but not successfully.  Drawing on Galileo's work, the Dutch scientist Christiaan Huygens built a working model in 1656, and patented it the following year.

Drawing of a pendulum clock from 1659, that
was designed by Galileo in 1641.  Since Galileo
was blind by then it was most likely drawn by
his student, Viviani.  Image courtesy of Wikipedia.

Until Huygen's invention, most mechanical clocks used a foliot balance and a verge escapement to keep a clock ticking at a steady rate.  These clocks gained or lost up to fifteen minutes a day.  Huygen's clock could run for three hours with a one second error.  Before the pendulum clock, very few clocks were reliable enough to merit a minute hand.  Huygen's had not only a minute hand, but a second hand as well, only he wasn't sure where to put them.  On his pendulum clock, the minute hand had its own small dial near the bottom of the face.  The hour hand was short, and shared a dial with the longer second hand.

A 1647 clock by Salomon Coster.  Image courtesy of here.

The first clocks made to Huygen's design, and under his supervision, were by clockmaker Salomon Coster in 1657.  As news spread of this new design, Ahasuerus Fromanteel, from a London family of clockmakers, sent his son, Johannes, or John, to work with Coster.  When John returned to London he helped his father build them.  The Fromanteels improved on the design and constantly added new features.  Their basic design was used in table and longcase clocks in the 17th and 18th centuries.

Contract between Salomon Coster and Johannes (John) Fromanteel.  It was
notarized by Josue de Putter in the Hague.  Signed when Fromanteel was 18,
in September of 1657.  Image courtesy the Science Museum.

In 1666, Huygen published Horologium Oscillatorium, while director of the Académie des Sciences in Paris.  This classic text gives a complete mathematical explanation and description of the pendulum.  In 1675, he built the first working chronometer using a balance wheel and spring instead of a pendulum.  Balance wheels and springs were used in most watches until the quartz crystal oscillator was invented.

Rare lantern clock by Fromanteel.
Image courtesy of www.brianloomes.com.

Even though Huygen's clock was the best at keeping accurate time, he continued perfecting it.  Since he knew that the swing of a pendulum was not constant, he calculated the motion mathematically.  He discovered by 1659 that a long pendulum worked better than a short one, and spent years producing different mechanisms to regulate the speed.  One invention was a pendulum that swung in circles, which produced a clock without a ticking sound.

The second pendulum clock built by
Huygens in 1673.  Image courtesy of Wikipedia.

It was found that when a steel pendulum is heated by one degree, it will lose a half second daily.  In 1721, the first pendulum clock with temperature compensation was made.  It had a container of mercury at the bottom of the steel rod.  If the temperature increased, the mercury would expand quicker than the steel, which kept the center of mass in the same place.  Eventually pendulum rods were made of metals that didn't expand.

A precision astronomical
mercury pendulum clock,
1887.  Image courtesy of Wikipedia.

Changes in air pressure also affect pendulums, so complicated systems were made to compensate in the 19th century.  Once pendulum clocks were made to be wound electrically, they could be sealed and the pressure was unvaried.  The most accurately produced pendulum clock was invented in 1921, called the Shortt-Synchronome Free pendulum clock.  It had an error rate of about one second per year.

A Shortt-Synchronome free pendulum clock, courtesy of Wikipedia.

Pendulum clocks did more than keep time, they were objects of status.  Their case styles changed to reflect whatever style of furniture was popular at the time they were made.  They have a solid place in timekeeping history, although now they are kept for their value as antiques and decorative items.

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