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A longcase clock, also tall-case clock, grandfather clock or floor clock, is a freestanding, weight-driven, pendulum clock with the pendulum held inside the tower, or waist of the case. Clocks of this style are commonly around 1.8-2.4m (6-8 feet) tall. The case often features elaborately carved ornamentation on the hood, or bonnet, which surrounds and frames the dial, or clock face. The English clockmaker William Clement is credited with the development of this form in 1670. Most longcase clocks are striking clocks, which means they sound the time on each hour or fraction of an hour.

 

The terms "grandfather", "grandmother", and "granddaughter" have been applied to longcase clocks. Although there is no specifically defined difference among these terms, the general perception seems to be that a clock smaller than 1.5m (5 feet) is a granddaughter; over 1.5m (5 feet) is a grandmother; and over 1.8m (6 feet) is a grandfather.

 

The advent of the longcase clock is due to the invention of the anchor escapement mechanism around 1670. Prior to that, pendulum clock movements used an older verge escapement mechanism, which required very wide pendulum swings of about 100°. Long pendulums with such wide swings could not be fitted within a case, so most clocks had short pendulums. The anchor mechanism reduced the pendulum's swing to around 4° to 6°, allowing clockmakers to use longer pendulums, which had slower "beats". These needed less power to keep going, caused less friction and wear in the movement, and were more accurate. Most longcase clocks use a "seconds" pendulum, meaning that each swing takes one second. These are about a metre (39 inches) long (to the centre of the bob). This requirement for height, along with the need for a long drop space for the weights which power the clock, gave rise to the design of the long narrow case.

 

Traditionally, such clocks were made with two types of movement: eight-day movements and 30-hour movements. A clock with an eight-day movement required winding only once a week, while the generally lower-priced 30-hour clock had to be wound every day. Eight-day clocks are often driven by two weights - one driving the pendulum and the other the striking mechanism, which usually consisted of a bell or chimes. Such movements usually have two keyholes on either side of the dial to wind each one (as can be seen in the Thomas Ross clock illustrated to the right). By contrast, 30-hour clocks often had a single weight to drive both the pendulum and the chimes. Some 30-hour clocks were made with false keyholes, for customers who wished that guests to their home would think that the household was able to afford the more expensive eight-day clock. All modern chiming grandfather clocks have 8-day movements. Most grandfather clocks are cable-driven, meaning that the weights are suspended by cables that wrap around a pulley mounted to the top of each weight. Such clocks are wound by inserting a special crank (called a "key") into holes in the clock's face and turning it. Others, however, are chain-driven, meaning that the weights are suspended by chains that wrap around gears in the clock's mechanism, with the other end of the chain hanging down next to the weight. To wind a chain-driven grandfather clock, simply pull on the other end of each chain until the weights come up to just under the clock's face.

 

In the early 20th century, quarter-hour chime sequences were added to grandfather clocks. At the top of each hour, the full chime sequence sounds, immediately followed by the hour strike. At 15 minutes after each hour, 1/4 of the chime sequence plays, at the bottom of each hour, half of the chime sequence plays, and at 15 minutes before each hour, 3/4 of the chime sequence plays. Almost all modern mechanical grandfather clocks have at least Westminster Quarters, and many also offer the option of Whittington chimes or St. Michael's chimes, selectable by a switch mounted on the right side of the dial, which also allows one to silence the chimes if desired. As a result of adding chime sequences, all modern mechanical grandfather clocks have three weights instead of just two. The left weight provides power for the hour strike, the middle weight provides power for the clock's pendulum and general timekeeping functions, while the right weight provides power for the quarter-hour chime sequences.

 

The origin of the term "grandfather clock"
 
Most of a longcase clock's height is used to hold the long pendulum and weights.During the 19th century, two brothers named Jenkins worked as managers at the George Hotel in Piercebridge, County Durham, England. One of the brothers died and, according to the story told to Henry Clay Work in 1875, the clock (made by James Thompson) began to lose time. Repair attempts were made, but 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.

Work decided to write a song about the story of this clock, which he called My Grandfather's Clock. The song became popular, and it is from this song that the current usage derives.