Some time ago, the joint model of omega and Swatch was very popular, triggering many people to rush to buy. Although clocks and watches have faded out of the lives of many people, it is enough to look at the time and have a mobile phone, but there are still many people who need clocks.
From watches worn by individuals to quartz watches hanging on the walls of homes, from electronic watches on the big screens in the square to mechanical clocks in towers, clocks and watches come in all shapes.
The birth of modern clocks and watches is highly dependent on the vigorous development of the Industrial Revolution. Even the cheapest and most rudimentary modern clocks and watches, their internal structure is exquisite enough to impress the ancient craftsmen. Before the Industrial Revolution, the development of timekeeping devices went through a long period of time.
In order to figure out the principle of accurate timing of clocks and watches, we may wish to first understand the timing methods of the ancients!
Ancient chronograph devices
The agricultural labor of working at sunrise and resting at sunset allowed the ancients to discover the operation of the sun for a long time. People invented instruments such as gui watches and sundials, which measured the length and angle of the shadow of the pointer to determine the direction of the sun in the sky, so as to know the current time and season. Ancient Eastern and Western civilizations learned to make such timing devices early on.
Sundials of Ancient Egypt Source: Wikipedia
Sundial in the Forbidden City in Beijing Source: Wikipedia
Sundial in Melbourne, Australia Source: Wikipedia
This method of using shadow timing has a large error and cannot work properly on cloudy days. To this end, people have made timekeeping devices such as leaky pots, engravings, and hourglasses with the help of evenly flowing water and sand, and even slow-burning candles can also be used to time.
Leaky pots in the Western Han Dynasty Source: Literature [1] Chinese archaeology
However, the flow of water and sand is not strictly uniform, and the combustion of candles is also easily affected by the flow of combustion and air, which is not a perfect timing device after all. Are there some things in nature that are changing at a uniform rate that are both precise and easy to use? Italian scientist Galileo Galileo gave the answer.
Swinging clock
About 600 years ago, Galileo inadvertently discovered that when the chandeliers in the church swayed with the wind, the time of each swing back and forth was always similar. Realizing that this phenomenon was extraordinary, Galileo then prepared many weights of different weights and ropes of different lengths, combined these objects into various styles of pendulums, and then measured their swing laws separately. Eventually Galileo discovered the isochronic principle of a pendulum: for an arbitrary pendulum, as long as its rope length remains constant, the time of each swing is relatively consistent, regardless of which weight is suspended.
The swing speed of the pendulum is easier to observe and more accurate than the sun rising and falling, water flow, sand and fire candles, etc., it follows the most basic mechanical laws, and the error is relatively small, so it is very suitable for making timing tools.
Schematic diagram of the pendulum clock conceived by Galileo Source: Wikipedia
After Galileo, the Dutch scientist Huygens built the first pendulum clock in 1658 and published the book "The Theory of Pendulum Clocks", which detailed the production method of pendulum clocks. Later, under the improvement of British scientist Hooke, watchmaker William Clement and Joseph Nibb, the pendulum clock production technology became more and more mature, and gradually entered thousands of households, becoming a common timekeeping tool.
A replica of the Huygens pendulum clock Image source: Chicago Museum of Science and Industry/Getty Picture Agency eferrit
Escapement – the heart of the pendulum clock
So, how is the time signal contained inside the pendulum transmitted to the dial pointer? This is thanks to the escapement, known as the "heart" of the clock. Inside the pendulum clock, the pendulum receives power through the escapement and can control the rotation of the dial hands with the help of the escapement, thus fulfilling the function of indicating time.
The traditional anchor escapement is shown in the figure below. Among them, the yellow gear is called the escape wheel, the axle is connected to the spring drive, and the gray anchor structure is called the escapement fork, which is connected to the pendulum of the pendulum clock.
Principles of anchor escapements Source: Wikipedia
Driven by devices such as clockwork, the escape wheel tends to rotate freely, but is limited by the pallet fork. As the pendulum swings back and forth, the pallet fork releases only one tooth at a time, so the escape wheel is forced to rotate little by little, and the angle and time required for each rotation are basically the same. In this way, the time signal of the pendulum is transmitted to the other mechanical structures of the pendulum clock through the escape wheel, and finally the dial hand indicates the time. This braking and release link of the ingresist fork to the pallet wheel is the origin of the names "tackle" and "longitudinal".
At the same time, when the pallet fork controls the rotation of the escape wheel, the teeth of the pallet wheel in turn exert a push on the pallet fork, so that the pendulum has the ability to continuously swing. Well, the escapement is very cleverly designed!
The further evolution of pendulum clocks
Pendulum clocks cannot meet the timing needs of all occasions. For example, the volume of the pendulum clock is very large, which is not conducive to carrying; the swing of the pendulum is easily affected by external vibrations, so it cannot be placed on a carriage or ship; with the development of science and technology, the accuracy of the pendulum clock is gradually inadequate, and it is impossible to meet the higher accuracy requirements.
In response to the miniaturization of pendulum clocks, Huygens further improved the pendulum into a small balance wheel. This device can do isochronous circular motion, so it can be used instead of the role of the pendulum. The balance wheel is mounted with a spiral-shaped fine spring structure called a hairspring and can run more precisely. In this way, bulky pendulum clocks have evolved into small watches, pocket watches, wall clocks, etc.
So, how to improve the accuracy of clocks so that it can accurately measure tenths of a second, a hundredth of a second, or even more than a thousandth of a second?
In 1918, the French physicist Lang Zhiwan found that if the quartz crystal was connected to the alternating current, the quartz crystal would begin to vibrate at a high frequency and steadily, and was not much affected by temperature, humidity and external vibrations. In this way, the possibility of quartz crystals being applied to high-precision clocks was discovered.
In 1928, Warren Maison, a researcher at Bell Telephone Laboratories, invented the quartz clock by replacing the balance-hairspring system in mechanical clocks with quartz crystals. Under the excitation of electric current, quartz crystals can vibrate 10 million times per second. By installing electrical signal amplification, adjustment, and conversion circuits, this high-frequency vibration can be converted into the low-frequency vibration we need, allowing the second hand to move once a second.
Since this high-frequency vibration is a physical property of quartz crystals, high-precision timing can be achieved as long as the purity of the quartz crystal is guaranteed. Since then, due to its reliable quality and low cost advantages, quartz watches have quickly subverted the traditional watch market, and are equal to mechanical watches, which is quite popular with people.
The interior of the quartz watch (left) is simpler than the mechanical watch (right) Source: medium
At present, high-quality quartz watches can achieve an error of plus or minus one hundred thousandth of a second, that is, an error of plus or minus 1 second after 270 years of operation. Even if the quality of the poor quartz watch, its error will be within ten thousandths of a second, can fully meet the needs of our daily life.
However, in some high-tech fields that require very high time accuracy, the accuracy of quartz watches is no longer enough. For example, in the Beidou global positioning system, multiple navigation satellites need to transmit radio wave signals to each other to confirm the location. Since the transmission of radio wave signals has a delay phenomenon, it is necessary to accurately calculate the delay time. It has been calculated that if the error of the clock carried by the navigation satellite is one millionth of a second, then the positioning error of the Beidou navigation is as much as 300 meters. Therefore, quartz watches are not up to the task of navigation.
To this end, scientists have proposed the use of atomic energy level oscillations to make atomic clocks.
Compared with the vibration of quartz crystals, atomic energy level oscillation is a physical phenomenon that is closer to the origin of matter, with unparalleled accuracy. The cesium atomic clock, manufactured in 1999, can already run for 20 million years without a second; and in 2020, scientists designed a high-precision atomic clock with the help of quantum entanglement to achieve an accuracy of 14 billion years without a second.
This thorium atomic clock requires only a tiny imperceptible thorium atom to achieve high-precision timing Source: scitechdaily
There are a large number of cyclical phenomena in nature, from the macroscopic sun and moon operation, single pendulum shaking, to microscopic crystal vibrations, atomic oscillations, the accurate timing ability of clocks and watches is inseparable from these physical movement laws that control everything in the world. Hopefully, in the near future, we can discover some more subtle cycle phenomena and create more wonderful clocks and watches!
Bibliography:
Lü Zhangshen, editor-in-chief. Ancient China in Cultural Relics During the Middle Qin to Five Dynasties Period[M]. Beijing:China Social Sciences Press, 2010.
Guo Zhi, eds. History of clocks and watches[M]. Shenyang:Liaoning Children's Publishing House, 1996.06.
[3] (Soviet Union) И.С. Beliaokov; translated by Liu Yuanheng, Li Baoshan, Luo Yaojie, Qiao Wansheng, etc. Watch mechanism[M]. Beijing:China Finance and Economic Press, 1963.11.
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Audit expert: Luo Huiqian, associate researcher of the Institute of Physics, Chinese Academy of Sciences.
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Editor-in-charge/Heart & Paper