Pendulum clock

From its invention in 1656 by Christiaan Huygens, inspired by Galileo Galilei, until the 1930s, the pendulum clock was the world's most precise timekeeper, accounting for its widespread use.

[1][2] Throughout the 18th and 19th centuries, pendulum clocks in homes, factories, offices, and railroad stations served as primary time standards for scheduling daily life, work shifts, and public transportation.

The pendulum clock was invented on 25 December 1656 by Dutch scientist and inventor Christiaan Huygens, and patented the following year.

By 1659 pendulum clocks were being manufactured in France by clockmaker Nicolaus Hanet, and in England by Ahasuerus Fromanteel.

The increased accuracy resulting from these developments caused the minute hand, previously rare, to be added to clock faces beginning around 1690.

During the Industrial Revolution, the faster pace of life and scheduling of shifts and public transportation like trains depended on the more accurate timekeeping made possible by the pendulum.

Wooden rods were often used in quality clocks because wood had a lower coefficient of thermal expansion than metal.

The rod is usually suspended from the clock frame with a short straight spring of metal ribbon (d); this avoids instabilities that were introduced by a conventional pivot.

In the most accurate regulator clocks the pendulum is suspended by metal knife edges resting on flat agate (a hard mineral that will retain a highly polished surface).

Small swing angles tend toward isochronous behavior due to the mathematical fact that the approximation

Many older quality clocks used wooden pendulum rods to reduce this error, as wood expands less than metal.

Beginning around 1900, some of the highest precision scientific clocks had pendulums made of ultra-low-expansion materials such as the nickel steel alloy Invar or fused silica, which required very little compensation for the effects of temperature.

Traditionally the pendulum bob is made with a narrow streamlined lens shape to reduce air drag, which is where most of the driving power goes in a quality clock.

In the late 19th century and early 20th century, pendulums for precision regulator clocks in astronomical observatories were often operated in a chamber that had been pumped to a low pressure to reduce drag and make the pendulum's operation even more accurate by avoiding changes in atmospheric pressure.

Fine adjustment of the rate of the clock could be made by slight changes to the internal pressure in the sealed housing.

This problem can easily cause the clock to stop working, and is one of the most common reasons for service calls.

varies with latitude and elevation on Earth, the highest precision pendulum clocks must be readjusted to keep time after a move.

Thus precision regulator clocks used for celestial navigation in the early 20th century had to be recalibrated when moved to a different latitude.

Torsion pendulums are also used in "perpetual" clocks which do not need winding, as their mainspring is kept wound by changes in atmospheric temperature and pressure with a bellows arrangement.

The escapement is a mechanical linkage that converts the force from the clock's wheel train into impulses that keep the pendulum swinging back and forth.

During most of the pendulum's swing the wheel is prevented from turning because a tooth is resting against one of the pallets; this is called the "locked" state.

These releases allow the clock's wheel train to advance a fixed amount with each swing, moving the hands forward at a constant rate, controlled by the pendulum.

The remontoire, a small spring mechanism rewound at intervals which serves to isolate the escapement from the varying force of the wheel train, was used in a few precision clocks.

In tower clocks the wheel train must turn the large hands on the clock face on the outside of the building, and the weight of these hands, varying with snow and ice buildup, put a varying load on the wheel train.

By the end of the 19th century specialized escapements were used in the most accurate clocks, called astronomical regulators, which were employed in naval observatories and for scientific research.

Pendulum clocks are usually designed to be set by opening the glass face cover and manually pushing the minute hand around the dial to the correct time.

Pendulum clocks are long lived and don't require a lot of maintenance, which is one reason for their popularity.

Specific low viscosity lubricants have been developed for clocks, one of the most widely used being a polyalcanoate[clarification needed] synthetic oil.

Pendulum clocks were more than simply utilitarian timekeepers; due to their high cost they were status symbols that expressed the wealth and culture of their owners.

Experts can often pinpoint when an antique clock was made within a few decades by subtle differences in their cases and faces.