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Grandfather Clocks

grandfather clock
noun

floor clock, antique grandfather clock, tallcase clock or longcase clock
synonym

A grandfather clock is simply, a pendulum clock enclosed in a tall, freestanding, narrow cabinet (usually 6 to 8 feet tall, with ornate carvings about the top and around the clock face).

pendulum
noun

A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices, especially clocks.  Also referred to as a simple pendulum.

Below we have constructed a horology timeline, depicting the theory, invention and production of the pendulum clock.  Because the pendulum clock is the “heart” of any grandfather clock, we feel this information is quite essential and very interesting.

1602, November 29th
Galilei Galileo writes in a letter that pendulums of the same length swing with the same time no matter what the amplitude (the extent of a vibratory movement, measured from the mean position to an extreme), the first written evidence of this concept.

1641
The son of Galileo, Vincenzo Galilei, builds a clock with a pendulum, a device based on his father's earlier concept.

1656
Christiaan Huygens develops a form of pendulum clock based on the cycloid. The cycloid is a curve that, when used to control a pendulum, precisely adjusts the beat (coinciding with amplitude changes) so that it remains constant.  Despite the theoretical advantages of using a cycloid as a control, simpler forms of the pendulum clock will prove to be more practical.

1657
Dutch clockmaker Salomon Coster, in The Hague (the de facto capital of the Netherlands), begins to construct a series of spring-driven clocks that use a pendulum instead of a foliot balance (balance wheel) to regulate the time.  These clocks are thought to be an outgrowth of the work of Christiaan Huygens the previous year.

1670
William Clement, the English horologist, invents the recoil, or anchor escapement, which controls the amplitude of a pendulum.  His theory was; a smaller arc makes for a more accurate clock.  Clement's escapement becomes the standard used in household clocks, such as the "grandfather" clocks of the English and Americans and the mantel clocks of the French.  He also invents the minute hand.

1671
In London, William Clement begins production of the clocks with the new "anchor" or "recoil" escapement, a substantial improvement over the norm because it interferes less with the motion of the pendulum.

1673
Christiaan Huygens's “Horologium Oscillatorium Sive de Motu Pendulorum” ("The Oscillation of Pendulums") is the first fundamental work on scientific and practical mechanics, discussing the mathematics and theory of time-keeping devices.  In it, Huygens calculates the equivalent pendulum length and the laws of centripetal force.  He proposes a form of pendulum clock based on the cycloid, a curve that, when used to control a pendulum, precisely adjusts the beat (coinciding with amplitude changes) so that it remains constant.  This turns out to be a clumsy adaptation and proves that his previous pendulum clocks were more accurate and efficient.

1675
Huygens develops the balance wheel and spring assembly (still found in some of today's wristwatches).  This improvement allowed portable 17th century watches to remain accurate up to +/- 10 minutes a day.

1714
John Harrison constructs his marine chronometer Number Four.  His chronometer contained a spring and balance wheel escapement that won the British government's 1714 prize (worth more than $10,000,000 in today's currency) for a means of determining longitude to within one-half a degree.

1721
George Graham improves the pendulum clock's accuracy to 1 second per day, by compensating for changes in the pendulum's length due to temperature variations. John Harrison, a carpenter and self-taught horologist, refined Graham's temperature-compensation techniques and developed new methods for reducing friction.

1761
With John Harrison's marine chronometer Number Four aboard and his son William Harrison to take the readings, the HMS Deptford sails off toward the West Indies to test whether Harrison's method can be used to find the longitude at sea.  It kept time on board a rolling ship to about one-fifth of a second a day, nearly as well as a pendulum clock could do on land, and 10 times better than required to win the prize.

1875
(How grandfather clocks got their name)

Two brothers named Jenkins owned and managed the George Hotel in Piercebridge, County Durham, England.  The hotel had a floor clock that kept time very well.

One of the two brothers died, and the clock started to lose time.  Repair attempts were made, but they all failed.  When the other brother died at the age of 90, the clock stopped running altogether, and was never repaired (in remembrance of the brothers).

Henry Clay Work, a song writer, was staying at the George Hotel and learned the story of the old floor clock.  He decided to write a song about the clock, entitled; “My Grandfather's Clock”.

1889
Over the next century, refinements led to Siegmund Riefler's nearly pendulum-free clock, which attained an accuracy of a hundredth of a second a day and became the standard in many astronomical observatories.

1898
A true pendulum-free clock was introduced by R.J. Rudd, stimulating more interest and development of this complication.

1921
The demonstration of the W.H. Shortt clock takes place.  The Shortt clock almost immediately replaces Riefler's clock as a supreme timekeeper in many observatories.  This clock contained two pendulums, one a slave and the other a master.  The slave pendulum gave the master pendulum the gentle pushes needed to maintain its motion, and also drove the clock's hands.  This allowed the master pendulum to remain free from mechanical tasks that would, normally, disturb its regularity.  The Shortt clock was the first device accurate enough to detect seasonal variations in the rotation of the Earth.

The Pendulum Clock complication explained:

The pendulum swings within a designated distance.  To keep time accurately, pendulums are usually made to not vary in length, when the temperature changes.  John Harrison invented the grid pendulum, which used the differential expansion of brass and steel to achieve a zero-expansion pendulum.  Modern clocks use a low-expansion alloy such as invar.  Astronomical pendulums were often constructed of fused quartz, which changed length even less, because of temperature variations.

Pendulums are frequently polished and streamlined to reduce the randomizing effects of turbulent air flow on the clock's accuracy.  In the late 19th century and early 20th century, pendulums for clocks in astronomical observatories were often operated in a vacuum to make the pendulum's operation even more accurate.

The escapement (the part that ticks) drives the pendulum, usually from a gear train.  Escapements have a locking state, and a drive state.  In the locking state, nothing moves.  The motion of the pendulum switches the escapement to drive, and the escapement then pushes on the pendulum for a brief part of the pendulum's cycle.

In the late 19th century, electromechanical escapements were developed.  In these, a switch or phototube turned an electromagnet on for a brief section of the pendulum's swing.  These are the most precise escapements known.  They were usually employed with vacuum pendulums, on astronomical clocks.  The pulse of electricity that drove the pendulum would also drive a plunger to move the gear train.

In the 20th century W.H. Shortt invented a twin pendulum clock with an accuracy of one hundredth of a second per day.  In this system the time keeping pendulum does no work and its movement is monitored by electrical devices which drive a slave pendulum which impulses the master pendulum.  This form of clock became a standard for use in observatories.

To convert the motion of the escapement into an accurate analogue representation using 'hands' a gear train divides the motion of the escapement.  Usually, there are at least two gears: an hour gear, and a minute gear.  These two gears are directly connected to the indicators (hands).

It is customary to make smaller gears more precisely, from more expensive materials in order to reduce wear.

Modern gear trains use involute gears, with tooth shapes that are an engineered compromise, between efficiency and wear.  Older clocks use cycloid gears.  The oldest clocks had hand-cut gears, some use gears made from interpenetrating cages of rods known as lantern pinions.

The indicators and clock face show the current time.  Premium pendulum clocks often drive bells, whistles (cuckoo clocks) and dolls in order to help announce the time.

The slowest part of the gear train is attached to an energy storage device.  This is either a spring, or a set of weights that pull on a cogwheel.

* For more information on this subject, please refer to
Wall Clocks and Pendulum Clocks *