Now we cannot imagine our life without clocks: wristwatches, telephones, wall clocks at home, on buildings; mechanical, electronic. It's hard to imagine what would have happened if they suddenly disappeared?! It seems they have always been and that now they are the most, the most ...
What if we look at history?
The first clocks were created by nature itself: the daily alternation of day and night, the movement of the Sun across the sky, the phases of the Moon. For our distant ancestors, these natural "clocks" were enough for a long time. But everything flows, everything changes.
When the celestial bodies began to gradually lose their dominant role in measuring time, the situation turned in the opposite direction: now watchmakers for many centuries began to try to display their movement across the sky on the dials of complex and not very complex mechanisms. Knowledge of astronomical phenomena, mainly the change of phases of the moon, in ancient times was of great practical importance in agriculture and navigation, as well as for the calendar of religious events, largely oriented to the alternation of lunar months. Don't forget astrology. Probably, thanks to all this, astronomical functions did not disappear from watch dials.
And, perhaps, the inhabitants of Ancient Greece were more technically advanced and somehow looked at this whole world in a different way, trying to study and tame it. This is confirmed by the Antikythera Mechanism.
The Antikythera Mechanism has been dated from 150 to 100 BC. This is an ancient mechanical calculating machine for calculating astronomical positions. The device was discovered in 1902 among the remains of a sunken ancient ship near the island of Antikythera (between Crete and Kitera). It is currently kept in the Greek National Archaeological Museum in Athens, in the form of a large number of fragments of bronze gears, which are supposed to have been located in a wooden case.
The Antikythera mechanism consists of 32 bronze gears and several dials with arrows. Dimensions of the device: height - 33 cm, width - 17 cm, depth - 9 cm. The Antikythera mechanism looks like a clock. The mechanism uses a differential gear, which, as previously thought, was invented no earlier than the 16th century. The complexity of the mechanism is comparable to mechanical clocks of the 18th century. On the outer side of the device there are two discs responsible for the calendar and signs of the Zodiac. Using disks, you can find out the exact date and study the position of the zodiac constellations relative to the Sun, Moon and five planets known in antiquity - Mercury, Venus, Mars, Jupiter and Saturn. The reverse side of the Antikythera mechanism also has two disks that allow you to calculate the lunar phases and predict solar eclipses. The mechanism is able to take into account the ellipticity of the lunar orbit. Studies have proven that the mechanical device found at the bottom of the sea is not just a clock, but a complex calculating machine that can perform addition, subtraction and division operations. At the moment, it is not known whether the Antikythera mechanism was a single product or similar devices were available to many. A similar technology is not found over the next thousand years of the development of civilization.
A similar mechanism is described in the work of Ivan Efremov "Thais of Athens" along with a calendar appointment. Also featured in the short story "The Fix" by Alistair Reynolds.
So the prototype of the future astronomical clock turned out to be not a primitive mechanism.
Nowadays, for an ordinary person, all these subtleties are not needed, but it is interesting to look at the astronomical clock that has come down to us, which has become an architectural and cultural landmark. There are a great many of them on different continents and in different countries, but I will tell you about those that I saw. All of them are in Europe and everyone has probably seen them and can expand their list.
I'll start with the astronomical clock that I saw in the Czech Republic, in Olomouc.
The astronomical clock is located in a niche of the northern wall of the town hall in the form of a lancet arch 14 m high. According to one version, watchmaker Antonin Pohl from Silesia received an order for its manufacture from the Olomouc Council. He made them in 1422 based on his dream. According to the legend, an angel came to the master in a dream and showed a clock in a niche in the wall of the town hall - the future work of Pokhla.
Another version speaks of the creation of the clock in 1474. These disputes have been going on for a long time, because. there is no specific written confirmation of the date of their installation. The first written records - the works of the poet Stefan of Taurin - date back to 1519.
The Olomouc astronomical clock was created in the style of the oldest astronomical clock in Strasbourg (France). A similar clock in the Czech Republic is only in Prague, they have a mechanism that sets in motion a number of figurines.
Even the legend about the fate of their creator is the same. According to her, upon completion of the work, the master was blinded by order of the city council so that he could not do the same in other cities.
The clock has been repeatedly repaired, they have been changed externally, incl. adding new figurines. The oldest watch parts that have survived to this day date back to 1898, when the watch was equipped with a planetary dial. The most valuable is its baroque style, created in 1747 by Jan Christoph Handke.
After the declaration of independence of the Czechoslovak Republic in 1918, the town hall clock was slightly changed. At that time, everything that was connected with the German past was eradicated. Prior to that, most Germans lived in Olomouc, and the clock was considered a German heritage, so all German names were replaced with it, and the figure personifying God was replaced with an allegory of Moravia.
In May 1945, during the liberation of the city from the Nazis, the clock was damaged. The damage mainly affected the facade: the clock mechanism, dials, and figurines generally survived.
After the war, the era of socialism began in the Czech Republic and the new authorities decided that the former imperial style was not relevant and during the restoration it was replaced with the corresponding style of socialist realism. The design was entrusted to Karl Slavinsky, who used the technique of decorating with mosaics.
The entire niche of the lancet arch was covered with mosaics, the upper part of which was decorated with scenes of folk festivals. Below them are located on the sides of 3 arches for moving figures and six dials (two large in the center - one under one) and two on each side of them). In addition to time, on the dials you can determine the sign of the zodiac, phases, moons, consider the location of the planets, day of the week, month. It also contains the dates of religious and proletarian holidays, biographical dates of famous figures of the socialist era. Figurines depicting various professions were made of wood by the wife of Karl Slavinsky Maria. Between the arches for the figurines there is a gilded figurine of a rooster. Previously, this place was a figurine of an angel.
Below, on the sides of large dials, on a mosaic canvas, two figures are depicted - a worker and a scientist (chemist), with a flask in their hand, in which copper sulfate, presumably by color, symbolizes high technology and the people's intelligentsia.
The side and upper part of the niche is decorated with mosaic medallions - allegories on the theme of 12 months, which depict people of the profession that is most suitable for a particular month of the year.
At noon, a small performance begins - to the musical accompaniment, the clock figures begin to move, which always attracts tourists.
Another astronomical clock ("Orloj") is located in Prague.
The history of these watches began in 1410. This beautiful symbol of Prague was created by Jan Schindel, a professor of mathematics and astronomy at the University, and Mikulas, a watchmaker from Kadany. The clock was placed on the south side of the city hall.
A hundred years later, the clock stopped for the first time. They were repaired by another watchmaker - Ganush z Ruzhe. In addition to repairs, Ganush modernized the chiming mechanism. And he improved them so much that the city authorities were afraid that a talented master could make a new watch in another city and ordered to blind him. In retaliation, the watchmaker decided to stop the chimes. The legend of the blinding of the Prague watchmaker was invented by the Czech writer and historian Alois Jirasek. No one knows if this really happened, but most of the inhabitants of Prague believe it.
The Twelve Apostles appeared in 1659. The clock periodically stopped or went wrong, so in 1865 the mechanism was dismantled, and Romuald Bozek made a chronometer, which still controls the clock. This chronometer, which is almost 200 years old, is only half a minute behind in a week. In 1866, the astronomical clock started working again and continued to run until May 5, 1945, when the town hall tower was destroyed by the Germans. The tower and the clock were restored in two years. The figurines of the apostles burned down and in 1948 the wood carver Vojtěch Suchard made copies.
The creators of the clock managed to put into their device a lot of information about celestial mechanics known by that time. On the outer dial, the time of day is marked, on the smaller inner disk, the position of the constellations of the Zodiac. In the center of the dial is the Earth, around which the Sun revolves.
Every hour a skeleton - a symbol of death - begins a procession of figures. With one hand he pulls the bell string, and with the other he raises the hourglass. The strike of the clock is accompanied by the procession of the apostles in small windows at the top of the chimes, which open at the beginning of the procession and close after it ends. The procession ends with a loud cry of a rooster flapping its wings in a niche above the windows. This is followed by the sound of a clock striking every hour of the day. The figures of the apostles and the rooster are complemented by the image of the Turk on the side of the chimes. The Turk shakes his head as a sign of unwillingness to abandon his aggressive policy (a reminder of the Turkish invasion of Central Europe in the 16th-17th centuries). Two figures on the left side of the chimes are allegories of human stinginess and vanity. Every hour everything is repeated from the beginning. Saints that appear in the window:
Left window: Saint Paul with a book; St. Andrew with a cross in the shape of the letter X; Saint Thaddeus with the board with which he was killed; Saint Thomas with a spear; Saint John with a cup; Saint Barnabas with parchment and a stone in his hand (was stoned to death).
Right window: Saint Peter with keys; Saint Matthew with the ax with which he was killed; Saint Philip with a T-shaped cross; Saint Bartholomew with a knife with which he was skinned; Saint Simon with the saw with which he was cut; Saint James with a staff. This peculiar performance has been shown with short breaks for more than 600 years.
Another astronomical clock is located in France in Lyon in the Cathedral of Saint-Jean (St. John the Baptist).
The cathedral took 300 years to build from 1180 to 1480. Since then, its appearance has not changed much. In 1600, King Henry IV, after a divorce from Queen Margot, decided to marry Marie de Medici, their meeting was scheduled in Lyon, midway between Florence and Paris. The bride and groom liked each other and the king ordered them to be married immediately in this very cathedral. It really has nothing to do with the clock.
The astronomical clock located in the cathedral is the oldest in France.
They trace their history back to the 14th century. After being destroyed by the Huguenots, they were restored from 1572 to 1600. They acquired their Baroque appearance in 1655. In the 18th century, a minute dial with an arrow appeared on them. Despite numerous repairs and alterations, the clock contains some iron parts smelted at the end of the 16th century. Show hours, minutes, date, position of the Moon and the Sun relative to the Earth, as well as the rising of the brightest stars over Lyon. The clock also shows religious holidays up to 2019.
The figurines upstairs, angels and saints, play a little pantomime four times a day. At the beginning of the pantomime, a rooster jumps out of the clock and crows three times. Crowing is also not simple, but holy, because it symbolizes the Good News. One of the angels plays the hymn on the bells. Then the Virgin Mary herself appears, and a swallow flies to her, while the archangel Gabriel approaches her through the open door in the clock. God - the cause of all this commotion - sits at the top and releases three blessings. This is where the pantomime ends - until next time. Unfortunately, I myself did not see this "performance", since we were there early in the morning, but I looked at the recording.
In the center of Venice, on Piazza San Marco, there is a clock tower or, as it is also called, the Tower of the Moors, which is one of the most famous monuments of the city.
The tower's astronomical clock is a masterpiece by the mechanics Giampaolo and Giancarlo Ranieri (1499). The clock shows the seasons, hours, lunar phases and the transition of the Sun from one constellation to another. Above the arch is a clock face made of blue enamel and gold. The dial is divided into 24 hours, and the indicators for noon (XII) and midnight (XXIIII; this spelling was adopted) are located on the horizontal axis. In the niche above the clock is a statue of the Virgin. Even higher is the Venetian winged lion. The first time the clock was restored in 1757, the last restoration was carried out in 2006. The clock is equipped with an additional mechanism, which, according to tradition, is launched on Epiphany (the arrival of the Magi): the clock carousel spins, and traditional Christmas figurines and Magi figurines leave.
Particular attention is drawn to the bronze figurines dressed as shepherds at the very top of the clock tower - the Venetian Moors, named so for their brown color. Every hour they strike a huge bell with sticks, but not at the moment when the minute hand passes the number 12. All are much more symbolic. One of the shepherds - the one with the beard - is old, the other is young. The old man symbolizes the past - he strikes the bell five minutes before the next hour. The young man personifies the future and rings at the sixth minute of the new hour.
There are such interesting astronomical clocks. Some of them are more complex, others less, but all of them are a work of art and a triumph of the technical thought of mankind.
Lund Cathedral has long been the main cathedral of Denmark and all of Scandinavia - before the transfer of the city to Sweden, it was built in 1085.
The medieval astronomical clock in Lund Cathedral was installed in 1424. The dial of the clock located on top shows, in addition to the time of day, the time of sunrise and sunset, the location of the Sun, and the phases of the Moon.
The bottom panel of the clock is a calendar. With its help, you can calculate when there will be a passing church holiday and on which weekday a certain date will fall. In the middle of the calendar is Saint Lawrence, the patron saint of the cathedral, surrounded by the symbols of the four evangelists.
Instead of a chime in the clock, you can hear the melody In dulci jubilo of the smallest church organ. At this time, six wooden figures, representing the three wise men and their servants, pass in front of Mary with the baby Jesus. The clock is played twice a day - at 12:00 and 15:00 every day except on Sundays when the earliest game takes place at 13:00 so as not to interrupt the morning mass.
The watch has been restored several times. Their dial changes once every hundred years. It will next need to be replaced in 2123.
The main attraction of Bern (Switzerland) is the medieval clock tower - Zytglogge (translated from German as "time bell").
The tower was built at the beginning of the 13th century. It was part of the city wall and performed a defensive function, serving as the western gate of the city.
The clock device on its eastern side was installed in the first half of the 16th century. The chimes, installed in 1530, are among the oldest clock towers in Switzerland.
Under the clock face, showing the time, there is an astronomical clock, which determines the days of the week, the month, the phase of the moon and the zodiac sign.
The mechanism of Kaspar Brunner's work is connected with a golden hammer, which strikes a small bell every hour, and before the chimes strike, a golden rooster crows, figures of bears (the symbol of the city of Bern) come out of the window on the tower and show their outfits with the symbols of the city.
According to legend, this watch inspired Albert Einstein's theory of relativity, which made a real revolution in science. Living near the Zytglogge and each time watching the movement of buses passing by the tower, he once suggested what would happen if the buses traveled at the speed of light
The Zimmertoren Astronomical Clock on the Zimmer Tower in Lier, Belgium
One of the most interesting sights in the Flemish city of Lier is the 14th-century Zimmertoren, once part of the city wall and converted into an astronomical clock by Louis Zimmer in 1930. This watch has a central dial showing the time and surrounded by 12 small dials showing the signs of the zodiac, lunar and solar calendar, day of the week, month, season, tides and the like.
The statues of the burgomasters and the kings of Belgium ring the bell every hour on the right side of the tower. Inside the tower is a planetarium with 57 astronomical dials powered by a complex system of gears. This clock was shown in 1939 at the World's Fair in New York.
Astronomical clock in Lund
Time is one of the most difficult categories to understand in philosophy and physics. It is most simply defined as a necessary condition for the possibility of any change. People already at the dawn of their history realized the need to somehow determine the course of time. At first, only fairly large intervals were measured: a year, a month, a day. Drop by drop, people noticed the running away of time by sunrises and sunsets, the change of seasons, and their own aging. Gradually, the need to define shorter intervals became apparent. Hours, minutes, seconds appear. With the complication of human activity, the methods of measuring time were also improved. Each interval began to acquire more and more precise meaning. An atomic and ephemeral second, an astronomical hour arose (“How much is this?” You ask. The answer is a little lower). Today, the focus of our attention is the hour, the most commonly used unit of time in everyday life, as well as the clock, without which it is difficult to imagine the modern world.
A bit of history
It is easy to see that time calculation is fundamentally different from the method of calculation accepted today. It is based on the duodecimal system, which was used by the Sumerians in ancient times. The division of the hour into minutes is also rooted in time. It is based on the sexagesimal number system, also invented in the Tigris and Euphrates valley.
The Egyptians were the first to divide the day into 24 hours. The hour then had a different duration depending on the season and whether it belonged to the night or the day. The Egyptians and Babylonians divided the day into two equal parts. Day and night, that is, dark and light time, included 12 hours each. Accordingly, the length of the hour varied in each half, depending on the season.
Similar systems existed in Greece and Rome. In the Middle Ages in Europe, the day was divided according to church services.
The term "hour" was first used by the Greeks. Variable lengths of time spans have persisted throughout the world for quite some time. In our country in the XVI-XVII centuries, the duration of the hour was constant, but the number of hours changed day and night depending on the season. In Russia, they began to measure time similarly to Europe after 1722.
What is the astronomical hour?
The word "hour" is often used to denote periods of time of various lengths, close to 60 minutes. Everyone knows what, for example, a quiet or curfew is. The lengths of time denoted by these and similar concepts can last the usual 60 minutes, a little less or a little more, or designate not an interval, but a specific moment of the day, after which one process should end and a new one should begin.
And an astronomical hour is how many minutes? This concept denotes a standard period of time, a fixed duration. It is the astronomical hour that is equal to 60 minutes or 3600 seconds and is most often referred to simply as "hour". This unit of time is not included in the modern metric SI system (International One of the reasons is that the hour does not belong to the decimal notation familiar today. However, it is actively used all over the world along with the accepted SI units.
How long is the lesson?
Academic and astronomical hour are different concepts. The first term refers to the period of time during which the lesson lasts. Its value is not the same for different age groups. When working with children in kindergartens, educators shorten the duration to 20-30 minutes; in the year before graduation, it sometimes increases to 40 minutes. In schools, lessons last 40-45 minutes, couples at the university - 90 minutes. The reason for these differences is the ability to concentrate. It increases with age. If classes of 45 minutes are introduced in kindergarten, and 90 minutes at school, students will get very tired and are unlikely to remember and learn the material in the required volume.
Measuring minutes
Time in our minds is inextricably linked with the mechanisms by which we notice its running. The clock appeared at the same time when people first felt the need to somehow measure intervals shorter than a day. It is now impossible to know the exact date of their occurrence - it was so long ago. The first copies measured time by noting the movement of the Sun across the sky, and with the help of running water. Also, sand and fire were used as the basis of the clock.
With the improvement of knowledge and the increase in the pace of life, more and more accurate designs were required. Sand, fire and water clocks were refined and complicated, then they were replaced by mechanical time meters.
Gears, spring and pendulum
The oldest mechanical clock was found at the bottom of the sea near the island of Antikythera. They date back to 100 BC. The Antikythera astronomical clock is unique: it has a rather complex design and has no analogues in the culture of the Hellenes. The mechanism, according to several reconstructions undertaken, consisted of 32 gears. The clock showed the change of days, the movement of the Sun and the Moon. The signs of the zodiac were depicted on the dial. It is possible that the design was also capable of simulating the movement of Venus, Mars, Mercury and Jupiter across the sky.
Escapement clocks first appeared in China in 725. A little later, in 1000, a pendulum began to be used in Germany. The first tower clock in Western Europe was built in Westminter in 1288.
Mechanisms that measure time became more and more accurate. Making them required a lot of skill. In the Middle Ages and the Renaissance in Europe, the most amazing astronomical clocks in terms of beauty and subtlety of work were created, which the whole world admires today.
Masterpiece from Lyon
The oldest working astronomical clock in France adorns the cathedral in Saint-Jean (Lyon). They were created in the XIV century, destroyed, then restored from 1572 to 1600, decorated with baroque decor in 1655. Initially, like all watches of this era, they were equipped with only an hour hand. The minute dial was installed only in the 18th century.
In addition to time, by looking at the Lyon astronomical clock, anyone can find out the date, the position in the sky of the two main luminaries, the Moon and the Sun. The mechanism also shows when the brightest stars rise above the city. During the day, the clock strikes four times (at 12, 14, 15, 16 hours). In the upper part of the structure there are pupae that begin to move during the ringing.
Pride of Prague
The astronomical clock eagle, located on the tower of the town hall in Prague, is famous all over the world. Their history can be called dramatic. Created by Orla was more than 600 years ago, in 1402, earned a little later - in 1410. The "fathers" of watches are considered to be astronomer Jan Schindel and craftsman Mikulash from Kadan.
The decoration of the city hall had to be repaired several times. In 1490, Hanush from Ruže made changes to the mechanism and, according to legend, was blinded by order of the Prague authorities so that he could not repeat what he had created again. At the same time, the clock was decorated with allegorical figures and equipped with calendar discs.
New significant design changes occurred in 1865. Then Josef Manes added an eagle with a calendar dial with medallions decorated with symbolic images of the months, signs of the zodiac. The Golden Cockerel, which appears after the movement of the figurines is completed, appeared on the clock in 1882.
Orloi today
The Prague clock impresses not only with its beauty, but also with the virtuosity of the work of the masters who created them. Orloi shows the Old Bohemian, Babylonian, Starry, Italian and, of course, the "present" time. By the clock you can find out the date, the position of the Earth and the signs of the zodiac. They celebrate the rising and setting of the Sun and the Moon. Every hour, the figurines decorating the eagle begin to move, they talk about human vices, remind of the eternal.
Clock of Strasbourg Cathedral
The astronomical clock was finally completed in 1857. Their predecessors were installed in 1354 and 1574. The uniqueness of the clock is in its ability to calculate the dates of the passing church holidays, as well as the mechanism showing its full turn is completed in more than 25 thousand years. The Strasbourg clock shows local and solar time, the orbits of the Earth, the Moon and the planet from Mercury to Saturn.
This is not a complete list of masterpieces that adorn different cities around the world. Even 1 astronomical hour (the one that is equal to 60 minutes) will not contain a description of all the subtleties of the mechanisms and delightful decorations of such creations. However, this is not necessary - it is better to see such masterpieces, embodying a fusion of knowledge, skill, mathematical calculation and creative inspiration with your own eyes.
Obtaining time points solves only the first task of the time service. The next task is to store the exact time in the intervals between its astronomical definitions. This problem is solved with the help of astronomical clocks.
In order to obtain a high accuracy of time reading in the manufacture of astronomical clocks, as far as possible, all sources of error are taken into account and eliminated, and the most favorable conditions are created for their operation.
The most important part of a clock is the pendulum. The springs and wheels serve as a transmission mechanism, the arrows serve as pointers, and the pendulum measures the time. Therefore, in astronomical clocks, they try to create the best possible conditions for its operation: to make the temperature of the room constant, to eliminate shocks, to weaken air resistance, and, finally, to make the mechanical load as small as possible.
To ensure high accuracy, the astronomical clock is placed in a deep basement, protected from shocks. The room is maintained at a constant temperature all year round. To reduce air resistance and eliminate the effect of changes in atmospheric pressure, the pendulum of the clock is placed in a casing in which the air pressure is slightly reduced (Fig. 20).
An astronomical clock with two pendulums (Short's clock) has a very high accuracy, of which one - not free, or "slave" - is associated with transmission and indicating mechanisms, and it is controlled by another - a free pendulum, not connected to any wheels and springs ( Fig. 21).
The free pendulum is placed in a deep basement in a metal case. This case creates a reduced pressure. The connection of a free pendulum with a non-free one is carried out through two small electromagnets, near which it swings. The free pendulum controls the "slave" pendulum, causing it to swing in time with itself.
It is possible to achieve a very small error in the readings of the clock, but it cannot be completely eliminated. However, if the clock is running incorrectly, but it is known in advance that they are in a hurry or behind by a certain number of seconds per day, then it is not difficult to calculate the exact time from such incorrect clocks. To do this, it is enough to know what the course of the clock is, that is, how many seconds per day they are in a hurry or behind. Correction tables are compiled for a given instance of an astronomical clock over the course of months and years. The hands of astronomical clocks almost never show the time accurately, but with the help of correction tables it is quite possible to obtain timestamps with an accuracy of thousandths of a second.
Unfortunately, the clock does not stay constant. When external conditions change - room temperature and air pressure - due to the always existing inaccuracies in the manufacture of parts and the operation of individual parts, the same clock can change its course over time. Change, or variation, of the course of a watch is the main indicator of the quality of its work. The smaller the variation of the clock rate, the better the clock.
Thus, a good astronomical clock may be too hasty and too slow, may run ahead or lag even by tenths of a second a day, and yet they can reliably keep time and give sufficiently accurate readings, if only their behavior is constant, i.e., the diurnal variation is small.
In Short's pendulum astronomical clock, the daily variation of the rate is 0.001-0.003 sec. For a long time, such high accuracy remained unsurpassed. In the fifties of our century, engineer F. M. Fedchenko improved the suspension of the pendulum and improved its thermal compensation. This allowed him to design a watch whose daily rate variation was reduced to 0.0002-0.0003 seconds.
In recent years, the design of astronomical clocks has been taken up not by mechanics, but by electricians and radio engineers. They made watches in which, instead of pendulum oscillations, elastic vibrations of a quartz crystal were used to measure time.
A plate cut appropriately from a quartz crystal has interesting properties. If such a plate, called piezoquartz, is compressed or bent, then electric charges of different signs appear on its opposite surfaces. If an alternating electric current is applied to the opposite surfaces of the piezoelectric plate, then the piezoquartz oscillates. The lower the attenuation of the oscillatory device, the more constant the oscillation frequency. Piezoquartz has exceptionally good properties in this respect, since the damping of its oscillations is very small. This is widely used in radio engineering to maintain a constant frequency of radio transmitters. The same property of piezoquartz - the high constancy of the oscillation frequency - made it possible to build very accurate astronomical quartz clocks.
Quartz clocks (Fig. 22) consist of a radio-technical generator stabilized by piezoelectric quartz, frequency division cascades, a synchronous electric motor and a dial with pointer arrows.
The radio generator generates a high-frequency alternating current, and the piezoquartz maintains a constant frequency of its oscillations with great accuracy. In frequency division stages, the frequency of the alternating current is reduced from several hundred thousand to several hundred oscillations per second. A synchronous electric motor running on low-frequency alternating current rotates pointers, closes relays that give time signals, etc.
The speed of rotation of a synchronous electric motor depends on the frequency of the alternating current that it is powered by. Thus, in a quartz watch, the speed of rotation of the pointer hands is ultimately determined by the oscillation frequency of the piezoquartz. The high constancy of the oscillation frequency of the quartz plate ensures the uniformity of the course and the high accuracy of the indications of the quartz astronomical clock.
Currently, quartz watches of various types and purposes are being manufactured with a daily rate variation not exceeding hundredths and even thousandths of a second.
The first designs of quartz watches were quite bulky. After all, the natural frequency of oscillations of a quartz plate is relatively high, and in order to count seconds and minutes, it is necessary to reduce it using a number of frequency division cascades. Meanwhile, the tube radio devices used for this purpose take up a lot of space. In recent decades, semiconductor radio engineering has developed rapidly, and miniature and microminiature radio equipment has been developed on its basis. This made it possible to build small-sized portable quartz watches for sea and air navigation, as well as for various expeditionary work. These portable quartz chronometers are no larger and heavier than conventional mechanical chronometers.
However, if a mechanical marine chronometer of the second class has a daily rate error of no more than ±0.4 seconds, and of the first class - no more than ±0.2 seconds, then modern quartz portable chronometers have a daily rate instability of ±0.1; ±0.01 and even ±0.001 sec.
For example, the "Chronotom" manufactured in Switzerland has dimensions of 245X137X100 mm, and the instability of its course per day does not exceed ±0.02 seconds. Stationary quartz chronometer "Isotom" has a long-term relative instability of no more than 10 -8, ie, the error in the daily cycle is about ±0.001 sec.
However, quartz watches are not without serious shortcomings, the presence of which is essential for high-precision astronomical measurements. The main disadvantages of quartz astronomical clocks are the dependence of the frequency of quartz oscillations on the ambient temperature and the "aging of quartz", i.e., the change in the frequency of its oscillations over time. The first drawback was overcome by careful temperature control of the part of the clock in which the quartz plate is located. The aging of quartz, which leads to a slow drift of the clock, has not yet been eliminated.
"Molecular clock"
Is it possible to create a device for measuring time intervals that has a higher accuracy than pendulum and quartz astronomical clocks?
In search of suitable methods for this, scientists turned to systems in which molecular vibrations occur. Such a choice, of course, was not accidental, and it was he who predetermined further success. "Molecular clocks" made it possible at first to increase the accuracy of time measurement by thousands, and by borrowing hundreds of thousands of times. However, the path from the molecule to the time indicator turned out to be complex and very difficult.
Why was it not possible to improve the accuracy of pendulum and quartz astronomical clocks? In what way did molecules turn out to be better than pendulums and quartz plates in terms of measuring time? What is the principle of operation and device of the molecular clock?
Recall that any clock consists of a block in which periodic oscillations occur, a counting mechanism for counting their number, and a device in which the energy necessary to maintain them is stored. However, the clock accuracy is mainly depends on the stability of the work of that element which measures time.
To increase the accuracy of pendulum astronomical clocks, their pendulum is made of a special alloy with a minimum coefficient of thermal expansion, placed in a thermostat, suspended in a special way, located in a vessel from which air is pumped out, etc. As is known, all these measures made it possible to reduce stroke variations astronomical pendulum clocks to thousandths of a second per day. However, the gradual wear of moving and rubbing parts, slow and irreversible changes in structural materials, in general - the "aging" of such watches did not allow for further improvement in their accuracy.
In astronomical quartz clocks, time is measured by an oscillator stabilized by quartz, and the accuracy of the readings of these clocks is determined by the constancy of the oscillation frequency of the quartz plate. Over time, irreversible changes occur in the quartz plate and the electrical contacts associated with it. Thus, this master element of a quartz watch "gets old". In this case, the oscillation frequency of the quartz plate changes somewhat. This is the reason for the instability of such clocks and puts a limit to further increase in their accuracy.
Molecular clocks are designed in such a way that their readings are ultimately determined by the frequency of electromagnetic vibrations absorbed and emitted by molecules. Meanwhile, atoms and molecules absorb and emit energy only intermittently, only in certain portions, called energy quanta. These processes are currently presented as follows: when an atom is in a normal (unexcited) state, then its electrons occupy the lower energy levels and, at the same time, are at the closest distance from the nucleus. If atoms absorb energy, such as light, then their electrons jump to new positions and are located somewhat further from their nuclei.
Let us denote the energy of the atom, corresponding to the lowest position of the electron, through Ei, and the energy corresponding to its more distant location from the nucleus, through E 2 . When atoms, radiating electromagnetic oscillations (for example, light), from an excited state with energy E 2 pass into an unexcited state with energy E 1, then the emitted portion of electromagnetic energy is equal to ε = E 2 -E 1 . It is easy to see that the given relation is nothing but one of the expressions of the law of conservation of energy.
Meanwhile, it is known that the energy of a light quantum is proportional to its frequency: ε = hv, where ε is the energy of electromagnetic oscillations, v is their frequency, h = 6.62 * 10 -27 erg * sec is Planck's constant. From these two relations it is not difficult to find the frequency v of the light emitted by the atom. Obviously, v \u003d (E 2 - E 1) / h sec -1
Each atom of a given type (for example, an atom of hydrogen, oxygen, etc.) has its own energy levels. Therefore, each excited atom, during the transition to the lower states, emits electromagnetic oscillations with a well-defined set of frequencies, i.e., it gives a glow characteristic only for it. The situation is exactly the same with molecules, with the only difference that they have a number of additional energy levels associated with the different arrangement of their constituent particles and with their mutual motion,
Thus, atoms and molecules are capable of absorbing and emitting electromagnetic vibrations of only a limited frequency. The stability with which atomic systems do this is extremely high. It is billions of times higher than the stability of any macroscopic devices that perceive or emit certain types of vibrations, for example, strings, tuning forks, microphones, etc. This is explained by the fact that in any macroscopic devices, for example, machines, measuring instruments, etc. ., the forces that ensure their stability are in most cases only tens or hundreds of times greater than the external forces. Therefore, over time and as external conditions change, the properties of such devices change somewhat. This is why musicians have to tune their violins and pianos so often. On the contrary, in microsystems, such as atoms and molecules, there are such strong forces between the particles that make them up that ordinary external influences are much smaller in magnitude. Therefore, ordinary changes in external conditions - temperature, pressure, etc. - do not cause any noticeable changes within these microsystems.
This explains the high accuracy of spectral analysis and many other methods and instruments based on the use of atomic and molecular vibrations. This is what makes it so attractive to use these quantum systems as a master element in astronomical clocks. After all, such microsystems do not change their properties over time, that is, they do not "age".
When engineers started designing molecular clocks, the methods of excitation of atomic and molecular vibrations were already well known. One of them is that high-frequency electromagnetic oscillations are applied to a vessel filled with one or another gas. If the frequency of these oscillations corresponds to the excitation energy of these particles, then resonant absorption of electromagnetic energy occurs. After some time (less than a millionth of a second), the excited particles (atoms and molecules) spontaneously pass from the excited state to the normal state, and at the same time they themselves emit quanta of electromagnetic energy.
It would seem that the next step in designing such a clock should be to count the number of these oscillations, because the number of swings of the pendulum is calculated in the pendulum clock. However, such a direct, "frontal" path turned out to be too difficult. The fact is that the frequency of electromagnetic oscillations emitted by molecules is very high. For example, in the ammonia molecule for one of the main transitions, it is 23,870,129,000 periods per second. The frequency of electromagnetic oscillations emitted by various atoms is of the same order of magnitude or even higher. No mechanical device is suitable for counting the number of such high-frequency vibrations. Moreover, conventional electronic devices also turned out to be unsuitable for this.
A way out of this difficulty was found with the help of an original detour. Ammonia gas was placed in a long metal tube (waveguide). For ease of handling, this tube is coiled. High-frequency electromagnetic oscillations were supplied from the generator to one end of this tube, and a device was installed at its other end to measure their intensity. The generator made it possible, within certain limits, to change the frequency of the electromagnetic oscillations excited by it.
For the transition of ammonia molecules from an unexcited to an excited state, a well-defined energy and, accordingly, a well-defined frequency of electromagnetic oscillations are needed (ε \u003d hv, where ε is the quantum energy, v is the frequency of electromagnetic oscillations, h is Planck's constant). As long as the frequency of the electromagnetic oscillations produced by the generator is greater or less than this resonant frequency, the ammonia molecules do not absorb energy. When these frequencies coincide, a significant number of ammonia molecules absorb electromagnetic energy and pass into an excited state. Of course, in this case (due to the law of conservation of energy) at the end of the waveguide where the measuring device is installed, the intensity of electromagnetic oscillations is less. If you smoothly change the frequency of the generator and record the readings of the measuring device, then at the resonant frequency, a dip in the intensity of electromagnetic oscillations is detected.
The next step in designing a molecular clock is precisely to exploit this effect. For this, a special device was assembled (Fig. 23). In it, a high-frequency generator equipped with a power supply generates high-frequency electromagnetic oscillations. To increase the constancy of the frequency of these oscillations, the generator is stabilized with. using a piezoelectric crystal. In existing devices of this type, the oscillation frequency of the high-frequency generator is chosen to be several hundred thousand periods per second in accordance with the natural oscillation frequency of the quartz plates used in them.
Rice. 23. Scheme of "molecular clock"
Since this frequency is too high to directly control any mechanical device, it is reduced to several hundred oscillations per second with the help of a frequency division unit and only after that it is fed to signal relays and a synchronous electric motor that rotates pointer arrows located on the watch face. Thus, this part of the molecular clock repeats the scheme of the quartz clocks described earlier.
In order to excite the ammonia molecules, part of the electromagnetic oscillations generated by the high frequency generator is applied to an alternating current frequency multiplier (see Fig. 23). The frequency multiplication factor in it is chosen so as to bring it to the resonant one. From the output of the frequency multiplier, electromagnetic oscillations enter the waveguide with ammonia gas. The device at the output of the waveguide - the discriminator - notes the intensity of the electromagnetic oscillations that have passed through the waveguide and acts on the high-frequency generator, changing the frequency of the oscillations excited by it. The discriminator is designed so that when oscillations with a frequency below the resonant frequency arrive at the input of the waveguide, it adjusts the generator, increasing the frequency of its oscillations. If, however, oscillations with a frequency higher than the resonant frequency arrive at the input of the waveguide, then it reduces the frequency of the generator. In this case, the tuning to resonance is the more accurate, the steeper the absorption curve goes. Thus, it is desirable that the dip in the intensity of electromagnetic oscillations, due to the resonant absorption of their energy by molecules, be as narrow and deep as possible.
All these interconnected devices - generator, multiplier, ammonia gas waveguide and discriminator - constitute a feedback circuit in which ammonia molecules are excited by the generator and at the same time control it, causing it to generate oscillations of the desired frequency. Thus, the molecular clock ultimately uses ammonia molecules as the frequency and time standard. In the first molecular ammonia clock, developed according to this principle by G. Lyons in 1953, the rate instability was about 10 -7, i.e., the frequency change did not exceed ten millionths. Subsequently, the instability was reduced to 10 -8 , which corresponds to an error in measuring time intervals by 1 sec for several years.
In general, this is, of course, excellent accuracy. However, it turned out that in the constructed device the electromagnetic energy absorption curve turned out to be far from being as sharp as expected, but rather "smeared". Accordingly, the accuracy of the entire device turned out to be significantly lower than expected. Careful studies of these molecular clocks carried out in subsequent years made it possible to find out that their readings depend to some extent on the design of the waveguide, as well as on the temperature and pressure of the gas contained in it. It was found that these effects are the sources of instability of such clocks and limit their accuracy.
In the future, these defects in the molecular clock have not been completely eliminated. However, it was possible to come up with other, more advanced types of quantum time meters.
Atomic cesium clock
Further improvement in frequency and time standards has been achieved on the basis of a clear understanding of the reasons for the shortcomings of ammonia molecular clocks. Recall that the main disadvantages of ammonia molecular clocks are some "smearing" of the resonant absorption curve and the dependence of the renderings of these clocks on the temperature and pressure of the gas in the waveguide.
What are the reasons for these defects? Can they be eliminated? It turned out that the spreading of the resonance occurs as a result of the thermal motion of gas particles filling the waveguide. After all, some of the gas particles move towards the electromagnetic wave and therefore for them the oscillation frequency is somewhat higher than that given by the generator. Other gas particles, on the contrary, move from the incoming electromagnetic wave, as if running away from it; for them, the frequency of electromagnetic oscillations is somewhat lower than the nominal one. Only for a relatively small number of motionless gas particles, the frequency of electromagnetic oscillations perceived by them is equal to the nominal one, i.e. given by the generator.
The described phenomenon is the well-known longitudinal Doppler effect. It is he who leads to the fact that the resonance curve is flattened and smeared and the dependence of the current strength at the output of the waveguide on the velocity of gas particles is found, i.e. on the gas temperature.
A group of scientists from the American Bureau of Standards managed to cope with these difficulties. However, what they did was, in general, a new and much more accurate standard of frequency and time, although some already known things were used.
This device no longer uses molecules, but atoms. These atoms do not just fill the vessel, but move in a beam. And so that the direction of their movement is perpendicular to the direction of propagation of the electromagnetic wave. It is easy to understand that in this case there is no longitudinal Doppler effect. The device uses cesium atoms, the excitation of which occurs at a frequency of electromagnetic oscillations equal to 9,192,631,831 periods per second.
The corresponding device is mounted in a tube, at one end of which there is an electric furnace 1, which heats the metal cesium up to evaporation, and at the other end there is a detector 6, which counts the number of cesium atoms that have reached it (Fig. 24). Between them are: the first magnet 2, the waveguide 3, which supplies high-frequency electromagnetic oscillations, the collimator 4, and the second magnet 5. fields created by permanent magnets, and a high-frequency electromagnetic field supplied by a waveguide from the generator to the tube so that the direction of wave propagation is perpendicular to the direction of particle flight.
Such a device makes it possible to solve the first part of the problem: to excite atoms, that is, to transfer them from one state to another, and at the same time to avoid the longitudinal Doppler effect. If researchers had limited themselves to this improvement only, then the accuracy of the device would have increased, but not by much. Indeed, in a beam of atoms emitted from an incandescent source, there are always unexcited and excited atoms. Thus, when the atoms that have flown out of the source fly through the electromagnetic field and are excited, then a certain number of excited atoms are added to the already existing excited atoms. Therefore, the change in the number of excited atoms turns out to be relatively not very large and, consequently, the effect of the action of electromagnetic waves on the particle beam turns out to be not very sharp. It is clear that if at first there were no excited atoms at all, and then they appeared, then the overall effect would be much more contrasting.
So, an additional task arises: in the section from the source to the electromagnetic field, skip the atoms that are in the normal state and remove the excited ones. Nothing new had to be invented to solve it, since back in the forties of our century, Rabbi, and then Ramsey, developed the appropriate methods for spectroscopic studies. These methods are based on the fact that all atoms and molecules have certain electrical and magnetic properties, and these properties are different for excited and unexcited particles. Therefore, in electric and magnetic fields, excited and unexcited atoms and molecules deviate differently.
In the described atomic cesium clock, on the path of the particle beam between the source and the high-frequency electromagnetic field, permanent magnet 2 (see Fig. 24) was installed so that the unexcited particles were focused on the collimator slit, and the excited ones were removed from the beam. The second magnet 5, standing between the high-frequency electromagnetic field and the detector, on the contrary, was installed in such a way that unexcited particles were removed from the beam, and only excited ones were focused on the detector. Such a double separation leads to the fact that only those particles reach the detector, which were unexcited before entering the electromagnetic field, and then in this field passed into an excited state. In this case, the dependence of the detector readings on the frequency of electromagnetic oscillations turns out to be very sharp and, accordingly, the resonance curve of the absorption of electromagnetic energy turns out to be very narrow and steep.
As a result of the measures described, the driving unit of the atomic cesium clock turned out to be able to respond even to a very small detuning of the high-frequency generator, and thus a very high stabilization accuracy was achieved.
The rest of the device, in general, repeats the principle diagram of a molecular clock: a high-frequency generator controls an electric clock and simultaneously excites particles through frequency multiplication circuits. A discriminator connected to a cesium tube and a high-frequency generator reacts to the operation of the tube and adjusts the generator so that the frequency of oscillations produced by it coincides with the frequency at which the particles are excited.
All this device as a whole is called the atomic cesium clock.
In the first models of cesium clocks (for example, the cesium clock of the National Physical Laboratory of England), the instability was only 1 -9 . In devices of this type, developed and built in recent years, the instability has been reduced to 10 -12 -10 -13 .
It has already been said before that even the best mechanical astronomical clocks, due to the wear of their parts, change their course somewhat over time. Even quartz astronomical clocks are not without this drawback, since due to the aging of quartz, there is a slow drift of their readings. No frequency drift was found in cesium atomic clocks.
When comparing different instances of these clocks, the frequency of their oscillations was observed to coincide within ± 3 * 10 -12, which corresponds to an error of only 1 second in 10,000 years.
However, this device is not without drawbacks: distortions of the shape of the electromagnetic field and the relative short duration of its impact on beam atoms limit further increase in the accuracy of measuring time intervals using such systems.
Astronomical clock with a quantum generator
Another step towards increasing the accuracy of measuring time intervals was made using molecular generators- appliances that use radiation of electromagnetic waves by molecules.
This discovery was unexpected and natural. Unexpected - because it seemed that the possibilities of the old methods were exhausted, while there were no others. Natural - because a number of well-known effects already constituted almost all parts of the new method and it only remained to properly combine these parts. However, a new combination of known things is the essence of many discoveries. It always takes a lot of courage to think in order to come up with it. Quite often, after this is done, everything seems very simple.
Devices in which radiation from molecules is used to obtain a frequency standard are called masers; this word is formed from the initial letters of the expression: microwave amplification by stimulated emission of radiation, i.e. amplification of centimeter-range radio waves using induced radiation. Currently, devices of this type are most often called quantum amplifiers or quantum generators.
What prepared the discovery of the quantum generator? What is its principle of operation and device?
Researchers knew that when excited molecules, such as ammonia, go to lower energy levels and emit electromagnetic radiation, the natural width of these emission lines is extremely small, at least many times smaller than the absorption linewidth used in molecular clocks. Meanwhile, when comparing the frequency of two oscillations, the sharpness of the resonance curve depends on the width of the spectral lines, and the achievable stabilization accuracy depends on the sharpness of the resonance curve.
It is clear that researchers were extremely interested in the possibility of achieving a higher accuracy in measuring time intervals using not only absorption, but also the emission of electromagnetic waves by molecules. It would seem that everything is already there for this. Indeed, in the waveguide of a molecular clock, excited ammonia molecules spontaneously emit light, i.e., they pass to lower energy levels and at the same time emit electromagnetic radiation with a frequency of 23,870,129,000 periods per second. The width of this spectral emission line is indeed very small. In addition, since the molecular clock waveguide is filled with electromagnetic oscillations supplied from the generator, and the frequency of these oscillations is equal to the frequency of energy quanta emitted by ammonia molecules, then in the waveguide induced radiation of excited ammonia molecules, the probability of which is much greater than spontaneous. Thus, this process increases the total number of radiation events.
Nevertheless, for the observation and use of molecular radiation, a system such as a molecular clock waveguide turned out to be completely unsuitable. Indeed, in such a waveguide there are much more unexcited ammonia particles than excited ones, and even taking into account induced radiation, the acts of absorption of electromagnetic energy occur much more often than the acts of emission. In addition, it is not clear how to isolate the energy quanta emitted by molecules in such a waveguide when the same volume is filled with electromagnetic radiation from the generator, and this radiation has the same frequency and much greater intensity.
Isn't it true that all processes turn out to be so mixed up that at first glance it seems impossible to single out the right one from them? However, it is not. After all, it is known that excited molecules differ in their electrical and magnetic properties from unexcited ones, and this makes it possible to separate them.
In 1954-1955. this problem was brilliantly solved by N. G. Basov and A. M. Prokhorov in the USSR and by Gordon, Zeiger, and Towns in the USA*. These authors took advantage of the fact that the electrical state of excited and unexcited ammonia molecules is somewhat different and, flying through an inhomogeneous electric field, they deviate differently.
* (J. Singer, Mathers, IL, M., 1961; Basov N. G., Letokhov V. S. Optical frequency standards, UFN, vol. 96, no. 4, 1968.)
Recall that between two electrically charged parallel plates, for example, the plates of a capacitor, a uniform electric field is created; between a charged plate and a point or two charged points - inhomogeneous. If electric fields are depicted using lines of force, then uniform fields are represented by lines of the same density, and inhomogeneous fields by lines of unequal density, for example, less at the plane and more at the point where the lines converge. Methods for obtaining inhomogeneous electric fields of one form or another have long been known.
A molecular generator is a combination of a source of molecules, an electrical separator, and a resonator assembled in a tube from which air is pumped out. For deep cooling, this tube is placed in liquid nitrogen. This achieves high stability of the entire device. The source of particles in the molecular generator is a bottle with a narrow opening filled with ammonia gas. Through this hole, a narrow beam of particles enters the tube at a certain speed (Fig. 25a).
The beam always contains unexcited and excited ammonia molecules. However, there are usually many more unexcited than excited. In the tube, in the path of these particles, there is a capacitor charged with electricity, consisting of four rods, the so-called quadrupole capacitor. In it, the electric field is non-uniform, and has such a shape (Fig. 25, b) that, passing through it, unexcited ammonia molecules scatter to the sides, and excited ones deviate towards the axis of the tube and are thus focused. Therefore, particles are separated in such a condenser and only excited ammonia molecules reach the other end of the tube.
At this other end of the tube there is a vessel of a certain size and shape - the so-called resonator. Once in it, the excited ammonia molecules after a short period of time spontaneously pass from the excited state to the unexcited state and at the same time emit electromagnetic waves of a certain frequency. About this process they say that the molecules are highlighted. Thus, it is possible not only to obtain molecular radiation, but also to isolate it.
Let us consider the further development of these ideas. Electromagnetic radiation of resonant frequency, interacting with unexcited molecules, transfers them to an excited state. The same radiation, interacting with excited molecules, transfers them to an unexcited state, thus stimulating their radiation. Depending on which molecules are more, unexcited or excited, the process of absorption or induced emission of electromagnetic energy prevails.
By creating in a certain volume, for example, a resonator, a significant predominance of excited ammonia molecules and applying electromagnetic oscillations of the resonant frequency to it, it is possible to amplify the microwave frequency. It is clear that this amplification occurs due to the continuous pumping of excited ammonia molecules into the resonator.
The role of the resonator is not limited to the fact that it is a vessel in which the emission of excited molecules occurs. Since electromagnetic radiation of the resonant frequency stimulates the radiation of excited molecules, the greater the density of this radiation, the more actively this process of induced radiation proceeds.
By choosing the dimensions of the resonator in accordance with the wavelength of these electromagnetic oscillations, it is thus possible to create conditions for the occurrence of standing waves in it (similar to the choice of the dimensions of organ pipes for the occurrence of standing waves of the corresponding elastic sound vibrations in them). Having made the walls of the resonator from the appropriate material, it is possible to ensure that they reflect electromagnetic oscillations with the least losses. Both of these measures make it possible to create a high density of electromagnetic energy in the resonator and thus increase the efficiency of the entire device as a whole.
Ceteris paribus, the gain in this device is the greater, the higher the flux density of excited molecules. It is remarkable that at some sufficiently high flux density of excited molecules and suitable parameters of the resonator, the radiation intensity of the molecules becomes large enough to cover various energy losses, and the amplifier turns into a molecular generator of microwave oscillations - the so-called quantum generator. In this case, it is no longer necessary to supply high-frequency electromagnetic energy to the resonator. The process of stimulated emission of some excited particles is supported by the emission of others. Moreover, under suitable conditions, the process of generating electromagnetic energy does not stop even if some of it is diverted to the side.
Quantum oscillator with very high stability Gives high-frequency electromagnetic oscillations of a strictly defined frequency and can be used to measure time intervals. It does not need to run continuously. It is enough Periodically at certain intervals to compare the frequency of the electric generator of the astronomical clock with this molecular frequency standard and, if necessary, introduce a correction.
An astronomical clock corrected by a molecular ammonia generator was built in the late fifties. Their short-term instability did not exceed 10 -12 for 1 minute, and the long-term instability was about 10 -10, which corresponds to distortions in the reading of time intervals of only 1 sec in several hundred years.
Further improvement in frequency and time standards was achieved on the basis of the same ideas and the use of some other particles as a working medium, such as thallium and hydrogen. In this case, the quantum generator operating on a beam of hydrogen atoms, developed and built in the early sixties by Goldenberg, Klepner and Ramsay, turned out to be especially promising. This generator also consists of a particle source, a separator and a resonator mounted in a tube (Fig. 26) immersed in an appropriate coolant. The source emits a beam of hydrogen atoms. In this beam there are unexcited and excited hydrogen atoms, and there are much more unexcited than excited ones.
Since excited hydrogen atoms differ from unexcited ones in their magnetic state (magnetic moment), their separation is no longer an electric, but a magnetic field created by a pair of magnets. The resonator of the hydrogen generator also has significant features. It is made in the form of a flask made of fused quartz, the inner walls of which are coated with paraffin. Due to multiple (about 10,000) elastic reflections of hydrogen atoms from the paraffin layer, the length of flight of particles and, accordingly, their residence time in the resonator, in comparison with the molecular generator, increases thousands of times. In this way, it is possible to obtain very narrow spectral emission lines of hydrogen atoms and, in comparison with a molecular generator, reduce the instability of the entire device by a factor of thousands.
Modern designs of astronomical clocks with a hydrogen quantum generator have surpassed the cesium atomic beam standard in their performance. No systematic drift was found. Their short-term instability is only 6 * 10 -14 per minute, and long-term - 2 * 10 -14 per day, which is ten times less than that of the cesium standard. The reproducibility of clock readings with a hydrogen quantum generator is ±5*10 -13 , while the reproducibility of the cesium standard is ±3*10 -12 . Consequently, the hydrogen generator is about ten times better in this indicator as well. Thus, with the help of a hydrogen astronomical clock, it is possible to provide an accuracy of time measurement of the order of 1 sec for an interval of about a hundred thousand years.
Meanwhile, a number of studies in recent years have shown that this high accuracy of measuring time intervals, achieved on the basis of atomic beam generators, is not yet the limit and can be improved.
Transmission of the exact time
The task of the time service is not limited to obtaining and storing the exact time. An equally important part of it is such an organization of the transfer of exact time, in which this accuracy would not be lost.
In the old days, the transmission of time signals was carried out using mechanical, sound or light devices. In St. Petersburg, a cannon fired at exactly noon; one could also check one's watch against the tower clock of the Institute of Metrology, now named after D. I. Mendeleev. In seaports, a falling ball was used as a time signal. From the ships in the port, one could see how exactly at noon the ball broke off from the top of a special mast and fell to its foot.
For the normal course of modern intensive life, a very important task is to provide accurate time for railways, post offices, telegraphs and large cities. It does not require such high accuracy as in astronomical and geographical work, but it is necessary that, with an accuracy of up to a minute, in all parts of the city, in all parts of our vast country, all clocks show the time in the same way. This task is usually solved with the help of an electric clock.
In the watch industry of railways and communications institutions, in the watch industry of a modern city, electric clocks play an important role. Their device is very simple, and yet, with an accuracy of one minute, they show the same time in all points of the city.
Electric clocks are primary and secondary. Primary electric clocks have a pendulum, wheels, escapement and are real time meters. Secondary electric clocks are only pointers: there is no clockwork in them, but there is only a relatively simple device that moves the hands once a minute (Fig. 27). With each opening of the current, the electromagnet releases the anchor and the "dog" attached to the anchor, resting against the ratchet wheel, turns it by one tooth. Electric current signals are supplied to the secondary clock either from the central installation or from the primary electric clock. In recent years, talking clocks have appeared, designed on the principle of sound films, which not only show, but also tell the time.
For transmission exact time now serve mainly electrical signals sent by telephone, telegraph and radio. Over the past decades, the technique of their transmission has been improved, and the accuracy has increased accordingly. In 1904, Bigourdant transmitted rhythmic time signals from the Paris Observatory, which were received by the Montsouris Observatory with an accuracy of 0.02-0.03 sec. In 1905, the Washington Naval Observatory began regular transmission of time signals, from 1908 they began to transmit rhythmic time signals from the Eiffel Tower, and from 1912 from the Greenwich Observatory.
Currently, the transmission of accurate time signals is carried out in many countries. In the USSR, such transmissions are conducted by the State Astronomical Institute named after V.I. P.K. Sternberg, as well as a number of other organizations. At the same time, a number of different programs are used to transmit readings of mean solar time by radio. For example, the broadcast time signal program is transmitted at the end of every hour and consists of six short pulses. The beginning of the last of them corresponds to the time of this or that hour and 00 min 00 sec. In maritime and air navigation, a program of five series of 60 pulses and three series of six short signals, separated by longer signals, is used. In addition, there are a number of special time signal programs. Information about various special time signal programs is published in special publications.
The error in the transmission of time signals for broadcast programs is about ±0.01 - 0.001 sec, and for some special ones ±10 -4 and even ±10 -5 sec. Thus, methods and devices have now been developed that make it possible to receive, store and transmit time with a very high degree of accuracy.
Recently, significant new ideas have been implemented in the field of storing and transmitting accurate time. Suppose that it is necessary that at a number of points in any territory the accuracy of the readings of the clocks standing there be no worse than ± 30 seconds, provided that all these clocks work continuously throughout the year. Such requirements apply, for example, to city and railway clocks. The requirements are not very strict, however, in order to fulfill them using autonomous watches, it is necessary that the daily rate of each instance of the watch be better than ± 0.1 seconds, and this requires precision quartz chronometers.
Meanwhile, if this problem is solved using common time system, consisting of primary clocks and a large number of secondary clocks associated with them, then only primary clocks should have high accuracy. Therefore, even with an increased cost for the primary clock and a correspondingly low cost for the secondary clock, good accuracy can be achieved throughout the system at a relatively low total cost.
Of course, in this case, you need to make sure that the secondary clock itself does not introduce errors. The previously described secondary clock with a ratchet wheel and a pawl, in which the hand moves once a minute on a signal, sometimes malfunctions. Moreover, over time, the error of their testimony accumulates. In modern secondary clocks, various kinds of verification and correction of readings are used. Even greater accuracy is provided by the secondary clock, which uses alternating current of industrial frequency (50 Hz), the frequency of which is strictly stabilized. The main part of this watch is a synchronous electric motor driven by alternating current. Thus, in this clock, the alternating current itself is a continuous time signal with a repetition period of 0.02 seconds.
Currently, the World-wide Synchronization of Atomic Clocks (WOSAC; the name is composed of the first letters of the words: World-wide Synchronization of Atomic Clocks) has been created. The main primary clock of this system is located in Rome, New York, USA, and consists of three atomic cesium clocks, the readings of which are averaged. Thus, the accuracy of the time reading is equal to (1-3)*10 -11 . These primary clocks are connected to a worldwide network of secondary clocks.
The test showed that when transmitting accurate time signals via WHOAC from the state of New York (USA) to Oahu (Hawaii), i.e. approximately 30,000 km, time indications were coordinated with an accuracy of 3 microseconds.
The high accuracy of storage and transmission of time stamps, achieved today, makes it possible to solve complex and new problems of deep space navigation, as well as, although old, but still important and interesting questions about the movement of the earth's crust.
Where are the continents going?
Now we can return to the problem of the motion of continents, described in the previous chapter. This is all the more interesting because in the half century that has passed since the appearance of Wegener's works to our time, scientific disputes around these ideas have not yet subsided. For example, W. Munk and G. Macdonald wrote in 1960: "Some of Wegener's data are undeniable, but most of his arguments are entirely based on arbitrary assumptions." And further: "Great shifts of the continents took place before the invention of the telegraph, medium shifts - before the invention of radio, and after that practically no shifts were observed."
These caustic remarks are not without foundation, at least in their first part. Indeed, the longitudinal measurements that Wegeper and his collaborators once made during their expeditions to Greenland (in one of which Wegener tragically died) were performed with an accuracy insufficient for a rigorous solution of the problem. This was also noted by his contemporaries.
One of the most convinced supporters of the theory of the movement of continents in its modern version is P. N. Kropotkin. In 1962, he wrote: "Paleomagnetic and geological data indicate that during the Mesozoic and Cenozoic, the leitmotif of the movement of the earth's crust was the fragmentation of two ancient continents - Laurasia and Gondwana and the spread of their parts towards the Pacific Ocean and towards the Tethys geosynclinal belt." Recall that Laurasia covered North America, Greenland, Europe and the entire northern half of Asia, Gondwana - the southern continents and India. The Tethys Ocean stretched from the Mediterranean through the Alps, the Caucasus and the Himalayas to Indonesia.
The same author further wrote: “The unity of Gondwana has now been traced from the Precambrian to the middle of the Cretaceous, and its fragmentation now looks like a long process that began in the Paleozoic and reached a particularly large scale from the middle of the Cretaceous. Eighty million years have passed since that time. Consequently, the distance between Africa and South America increased at a rate of 6 cm per year. The same rate is obtained from paleomagnetic data for the movement of Hindustan from the southern hemisphere to the northern." Having reconstructed the location of the continents in the past using paleomagnetic data, P. N. Kropotkin came to the conclusion that “at that time the continents were really knocked together into such a block that resembled the outlines of the Wegener primary continental platform.”
So, the sum of the data obtained by different methods shows that the current location of the continents and their outlines were formed in the distant past as a result of a series of faults and a significant movement of continental blocks.
The question of the current movement of the continents is decided on the basis of the results of longitudinal studies carried out with sufficient accuracy. What in this case means sufficient accuracy can be seen from the fact that, for example, at the latitude of Washington, a change in longitude of one ten-thousandth of a second corresponds to a shift of 0.3 cm. Since the estimated speed of movement is about 1 m per year, and modern time services already If it is possible to determine time points, store and transmit exact time with an accuracy of thousandths and ten thousandths of a second, then to obtain convincing results, it is enough to carry out the corresponding measurements at intervals of several years or several tens of years.
For this purpose, in 1926, a network of 32 observation points was created and astronomical longitudinal studies were carried out. In 1933, repeated astronomical longitudinal studies were carried out, and 71 observatories were already involved in the work. These measurements, carried out at a good modern level, although over a not very long time interval (7 years), showed, in particular, that America is not moving away from Europe by 1 m per year, as Wegener thought, but is approaching it at approximately the speed 60 cm per year.
Thus, with the help of very accurate longitudinal measurements, the presence of the modern movement of large continental blocks was confirmed. Moreover, it was possible to find out that separate parts of these continental blocks have a slightly different movement.
town hall towerPrague chimes show three hour measurements(Central European, Old Bohemian and sidereal time), as well as indicate the zodiacal location of the Sun and Moon. Chimes include astronomical(upper) and calendar(lower) dials. Every hour, from 8 a.m. to 8 p.m., Orloi puts on a small performance in a medieval spirit (see video at the end of the article), and on holidays (in the evening) they put on a light show here. At this time, in front of the attraction is especially crowded. A comfortable place to watch the clock is a few terraced cafes opposite (convenient, but expensive: the cost of a glass of beer is from 150 kroons).
The astronomical (upper) dial is an astrolabe with a clockwork. It was created by Jan Schindel (professor of mathematics and astronomy, rector of Charles University), and made in 1410 watchmaker Mikulas from Kadani. In 1490, the master Ganush (real name - Jan from Rouge) added a calendar (lower) dial and decorated the facade with Gothic sculptures. Moving figures of the apostles appeared in the 17th century.
A special caretaker was responsible for maintaining the Old Town Clock in working order. There were long periods when a knowledgeable specialist could not be found for this position, and then the astronomical clock was left unattended or stopped for an indefinite time. As a rule, the difficulties in repair were associated with a misunderstanding of the design, because there was no written description or operating instructions. For example, during the years 1791-1866. only the clockwork worked, and the astrolabe remained broken.
On May 8, 1945, the Prague Astronomical Clock (Orloj), along with the entire Old Town Hall, burned down from an incendiary shell. The restoration took three years. Now they are 3/4 of old, original parts. The mechanism of the Old Town Clock also remained the same (with the exception of minor improvements). Serious changes were made only in decoration and decor.
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According to medieval thinking, any building is susceptible to the unfavorable influence of supernatural forces, so the astronomical clock in Prague has a lot of security decorative elements. On the conical roof are two mythical basilisks(they have a bird's beak, a crown, two wings and a snake body). The basilisk is a dangerous creature, people, animals and plants can be petrified from its gaze.
The next "guard" of the Old Town Clock - rooster, an ancient symbol of courage and vigilance; he meets the new day and the sun. In legends and fairy tales, at his first singing, spirits and devils run away. The presence of a rooster can be found on almost all medieval large-scale buildings. It is always installed at the top.
Under the rooster is angel- the best possible protection. It is believed that this is the very first sculpture on the Prague Astronomical Clock. To the left and right of the angel are windows from which 12 apostles appear. The Czechs also call them "doctors", since not all of them were the very first 12 apostles of Christ. Faith teachers participate in a theatrical performance, which you can read about here.
The astronomical (upper) dial is clockwork and astrolabe simultaneously (to be more precise: the dial is a derivative of the planispherical astrolabe common at that time, which is set in motion by the clock mechanism). The dial depicts the region of the Sun's movement - it is based on the projection of the sky from the North Pole to the plane of the equator. There are no minute hands.
From the outside, the dial is girded with Arabic numerals, which are made in the Schwabacher font popular in the 15th century and show Old Bohemian time. Next you can see the Roman numerals - they show Central European Time. The arrow for Arabic and Roman numbers is a pointer with a golden hand. Before the advent of the era of technological progress and the beginning of globalization, Prague lived according to Old Bohemian local time. The countdown of the day began at sunset, which means it varied throughout the year. A shot from a cannon announced the approach of noon to the inhabitants of the capital.
Figures for Central European Time have appeared recently. It turns out that the beginning of the Old Czech day is the onset of darkness in modern time. Since it gets dark earlier or later during the year, the circle with the old Czech time moves forward or backward relative to the main part of the dial.
The next element of the Prague Astronomical Clock is again Arabic numerals, although this time there are only 12 of them. They are on a blue background at the top of the dial and indicate daylight hours of a sidereal day. In the sector with the numbers "1" and "12" there are inscriptions in Latin ORTUS (sunrise) and OCCASUS (sunset), and on a dark orange background - AURORA (dawn) and CREPUSCULUM (twilight). The pointer for sidereal days is an arrow with a small asterisk. The night time of a sidereal day is indicated by a dark blue circle in the lower half of the dial.
In the center of the dial is the planet Earth (blue circle), around which the Zodiac ring, showing which constellation the Sun is in. The outer circle of the Zodiac ring is divided into 72 cells, which serve to separate months into days. One cell represents 5 days. The pointer for the Zodiac ring is an arrow with the Sun. There is also an arrow with the Moon, showing its phases depending on the position of the Sun: at night it glows with reflected light, and on a new moon it shows the entire bright half.
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Decor and exterior finish of the Astronomical Dial
Around the dial you can see a circular gallery of sculptures of various animals (some are fictitious). Each has its own meaning, in addition, many of them continue the defensive line of the basilisk-rooster-angel-12 apostles):
- a lion rests on top of the circular gallery. In the kingdom of animals, mythology and symbolism, he always has the meaning of a king and protector. The lion commands respect and is a symbol of valor in an equal and fair fight;
- next to the lion is a dog. She was the first domesticated animal and symbolizes loyalty and vigilance. In the legends, the dog guards treasures. On knightly tombstones, the dog at the feet symbolizes natural death;
- an amazing figure with a snake body and a sharp cone-shaped cap. This is a Phrygian cap - a symbol of the freedom of ancient Rome. By handing it over to a slave, the master granted him freedom. Perhaps the builders conceived it as a symbol of purification and perfection, the transformation of a crawling unclean snake (a symbol of low, sinful and diabolical creatures) into a person;
- the guard line is continued by the cat. She also sometimes guards treasures, but is not so reliable. The cat is a companion of magicians and sorcerers, as well as a symbol of independence, cheap and false affection, malice;
- mascarons scare away and drive away dangerous external elements. Such an element, when it flies by and sees that it is already occupied here, is looking for another place. No less fantastic companions of mascarons are gargoyle sculptural gutters that protect the masonry from moisture;
- the sleeping bat is a symbol of the transformed devil who drinks blood and can turn into other animals;
- the toad is a Christian symbol of sin and heretics. They supposedly dwell in mud (in lies) and croak their untruth;
- the hedgehog is a nocturnal animal, considered the protector of domestic happiness, but greed, aggressiveness and anger prevail in the character;
- the shapeless face in the east and the goblin in the west emphasize the expressiveness of the warning against the dark forces. Goblin - a symbol of natural, forest and underworld forces;
- below, under the astrolabe, is the devil himself (animal face, alert ears, bulging eyes).
Statues on the sides of the Astronomical dial
- Miser- a miserly man shakes a bag of money (there is a version that there used to be a Jewish moneylender in his place, but his appearance was changed, trying to be politically correct).
- Mage- with the help of a mirror looks beyond the boundaries of the world of sensations. This is considered a noble spiritual pursuit, as opposed to the Miser who is busy accumulating possessions. Some believe that the statue symbolizes Vanity, looking at his face in the mirror.
- Skeleton- a warning that everything around is perishable. Its bell and hourglass emphasize Memento mori.
- Turk- the meaning is not clear. Perhaps a symbol of sin and pleasure. Or perhaps a reminder of the long-term Turkish threat to the entire Austrian Empire.
The lower dial of the Orloi is a calendar. Its original version has not been preserved, and today tourists watch the dial, which was designed by the poet and Prague archivist Karel Jaromir Erben in the middle of the 19th century based on a 1659 copy. The artwork was done by Josef Manes. Understanding the historical value of the project, he agreed to a very modest fee, and also ignored the superstition that a person who made significant changes to Orloi would not live a long life. In 1866, Manes completed the painting. The next few years of his life, the artist experienced physical pain, depression and mental suffering. In 1871 he died.
The calendar dial of the Prague Astronomical Clock includes internal gold-plated disc with constellations and external copper disk with cells for each day of the year. In order to protect the masterpiece-dial of Manes from the destructive effects of the weather, it was transferred to the Capital Gallery of Prague, and a copy was ordered for Orloy. Ironically, the author of the copy (E. K. Lischka) achieved more payment than Josef Manes received for the original.
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Internal gold-plated disc
The disc depicts the coat of arms of Prague, the signs of the zodiac and a calendar cycle of frescoes on the theme of Czech rural life in the Middle Ages. The frescoes symbolizing the 12 months depict:
- in January, the celebration of the birth of a child, as the onset of the new year;
- in February, the peasant warms his feet by the fire, and the wife brings firewood;
- in March the peasant plows;
- in April - ties up trees;
- in May, a guy decorates a hat, and a girl picks flowers;
- in June they mow the grass;
- wheat is harvested in July;
- in August, grain is threshed;
- in September, the time of sowing winter crops;
- grapes are harvested in October;
- in November, trees are cut down and firewood is harvested;
- in December a piglet is slaughtered.
External copper disk
The disk is divided into 365 cells, in which is recorded tsisioyan - a poetic syllabic calendar, where the days of the holidays of the most important saints are mentioned. The first syllable of the saint's name is written on the corresponding day of the calendar. Non-holiday days are filled with any syllables (not related to saints) so that the verses make some sense.
Qisioyan on an external copper disk Decor and exterior finish of the Manes Calendar Dial
The surroundings of the calendar are made on the themes of plant motifs and symbols of life. The dial is surrounded by a vine on all sides. Wine was considered a divine drink that frees from earthly worries, brings joy, youth and eternal life.
To the right of the dial are a monkey and a phoenix bird. The fire bird was revered by all civilizations as a symbol of eternity, the cycle of renewal and resurrection. In the stone branches, she seems to be talking with a monkey, which in Antiquity was a pet, dexterous and intelligent, but in the Middle Ages it became a symbol of sinfulness, greed and the embodiment of the devil.
