| Chronicle of Timekeeping
From the Beginnings to the 15th Century
The earliest time-keeping instruments, sundials, water clocks, or candle clocks, gave not more than a rough approximation of the passage of time. The first weight-driven clocks with a gearwork that came up in the 13th and 14th century did, initially, not perform much better. An hour hand was all that was needed, a minute indication would have been an unjustified luxury considering that these clocks had daily rates of an hour or more. In this era, time was publicly distributed by worldly and clerical authorities: The first clocks were found in church towers, monasteries, or city halls. We know from such early clocks in Italy , e.g., in Orvieto (1307), Ragusa (1322), Milan (1336), or Padua (1344). The oldest preserved clock tower is found in the Cathedral of Salisbury (UK), it dates from 1386. In the 14th and 15th century, the "individual" or "private" time was a privilege that only few people could enjoy; clocks were only found in the households of the nobility and a few wealthy citizens. The Portable Clock (16th century)
The use of a spring instead of a weight in a time-keeping device was a major revolution. It is not exactly known when and where this invention was made; we know that the mainspring in a barrel with a chain and fusee (initially, gut and fusee ) was established by 1430. In the first half of the 16th century, the box-like table clocks developed into the next generation: a clock that could be worn by an individual, usually on a chain around the neck. (We may call them "watches" from now on.) A beautiful example of such an early watch from 1530, made in southern Germany , is found at the Smithsonian Institution in Washington .
Job Description: Clockmaker
It is not quite clear when the first clockmaker or watchmaker actually called himself a clockmaker. It may be assumed that the early clockmakers were plate-smiths who then specialized in this new field and started to train apprentrices in the art and craft of clockmaking .
The foundation of the Watchmaker's Guild in Geneva in 1601 is a well-known date - Breguet made a special watch in 2001 to commemorate this event. The first professional organization of clock- and watchmakers, however, was founded in Paris on July 1, 1544. In Germany , the first guild was founded in Nuremberg in 1565. |
These early 16th century watches often had striking mechanisms, sometimes even an alarm.
In the late 16th century, watches already had what we call "complications" today: calendar displays and astronomical indications were found. Precision, however, still left much to be desired. The Early Pocket Watch (17th century) In the 17th century, watches lost their box-like appearance; cases became slimmer and rounded; the typical pocket watch design developed. The master watchmakers started to sign their watches, and the art of enamel painting on the case was at its peak. The technical development of pocket watches, however, didn't show much progress for more than half of the 17th century. Since 1630/1640, the gut cord was replaced by a chain resulting in the classic chain-and- fusee design that we find deep into the 19th century, but that was all until about 1675. Then, the next real revolution began; it is linked to the name of a Dutch physicist and astronomer who had made his first great horological invention in the 1650s: Christian Huygens (1629-1695). Huygens had discovered the laws of the pendulum independently from Galilei ; he had realized that these principles could be applied to time-keeping, and he had the first pendulum clock built after his plans by Salomon Coster in 1657.
Nearly two decades later, Huygens invented the balance-spring for watches. Today, Huygens is generally acknowledged as the inventor; then, he had to defend himself against Robert Hooke in London and the Abbé Jean de Hautefeuille in Paris who also claimed this invention as theirs. Admittedly, Hooke and de Hautefeuille had used springs, but they did hardly improve the watches' precision as they were straight or S-shaped springs and did not spiral around the balance-staff. Much work still had to be done (and was done by later generations of watchmakers), but with this new horological technology, it made sense, for the first time, to add a minute hand to a watch. There had been watches with hour- and minute-hands before, but, considering the precision of these watches, the latter were more a decoration than a useful instrument.
Important Improvements of the Pocket Watch (18th century)
The 18th century began with an invention that we often do not even think about today because we take it for granted :
In 1704, the Swiss Nicolas Fatio de Duillier and the Frenchmen Pierre and Jean Debaufre , all three living in London then, developed a technique that allowed to drill holes into small jewels, mostly rubies, so that these could be used as bearings. This method remained a specialty of English watchmakers for nearly all of the 18th century; Breguet was the first watchmaker outside
England who used "jewels" (as we call them today) in his watches. As rubies were (and are) precious stones, this was a costly luxury in a watch. This changed only in the early 20th century; in 1902, Verneuil made the first artificial rubies that have, since then, become the only rubies used in watches. Not an invention, but an interesting footnote: In 1715, the term " calibre " was first used in connection with horology by Sully to describe the size and design of various parts of the movement. Most noticeable, however, were the numerous new escapements that were invented in the 18th century :
Graham's cylinder escapement, introduced around 1720/1725 and used by Graham in all his watches since 1727, drastically improved the precision of watches in comparison to the verge escapement that had been used since ~ 1500.
Numerous other escapements, partly still in use today, were also developed in the 18th century:
Duplex Escapement
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Around 1730, Baptiste Dutertre constructed the duplex escapement which was improved to be really usable by Pierre Le Roy around 1759.
Fig. from Pellaton , J.C. (1928) |
Jean Antoine Lépine (according to other sources, Jean André Lepaute ) invented the virgule escapement around 1750. "Virgule" is the French word for "comma" which is appropriate when you look at the moving part of the balance-staff; in German, this escapement is therefore called " Kommahemmung ." Functionally, it is a combination of cylinder and duplex escapement.
Fig. from Pellaton , J.C. (1928) |
Virgule Escapement
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1757 was the year when an invention was made that we still find, though modified, in practically all mechanical pocket and wristwatches today: Thomas Mudge invented the lever escapement. Due to the lever's characteristic form, it is known as "anchor escapement" in French ( échappement à ancre ) and German ( Ankerhemmung ). I have seen "anchor escapement" in English texts, but this is more the exception than the rule.
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Swiss lever escapements around 1850 (left) and 1950 (right)
Pictures from Pellaton , J. (1950) |
Although the function of a lever escapement is easily understood, its construction requires a lot of mathematics, and its making is precision work:
English Lever Escapement
Note the pointed teeth (cf. text below)
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The Swiss lever escapement shown here (for good reason: It's the type that you find in today's watches) is actually a later development that is based on Georges Auguste Leschot's invention of the "draw" in 1825. The initial version is known as "English lever escapement," and there were numerous variants like the " Glashütter Ankerhemmung " ( Glashütte lever escapement) invented by Grossmann in 1866 and used by Adolf Lange (yes, you know the name from "A. Lange & Söhne "), Cole's elastic lever escapement (around 1830), and the lever escapements by Mairet , Robin, or Girard- Perregaud .
There are two basic differences between English and Swiss lever escapements:
· In the English lever escapement, the full impulse is taken by the pallet-stones, and the teeth of the escape-wheel are pointed (cf. figure above). In the Swiss lever escapement, the impulse is taken by both the pallet-stones and the teeth; the teeth are made " à talon" to form an impulse face.
· In the Swiss lever escapement, the axes of the balance-staff, the lever, and the escape wheel lie on a straight line (" ligne droite "). In the English lever escapement, the line between the pallet-staff and the escape-wheel and the line between the pallet-staff and the balance-staff are perpendicular to each other (" ancre de côté " or " ligne rectangulaire ").
As the new escapements allowed for a precision of ± 1 minute per day, other sources of irregularity in a watch's daily rate became apparent (and really annoying) only now: irregularities due to temperature changes. Numerous watchmakers tried numerous constructions to compensate for these temperature errors in the spiral (where its effect is greatest); soon, however, efforts concentrated on temperature compensation in the balance.
The "Longitude Problem" and the Marine Chronometer
An important step in improving the precision of timekeeping that was made in the late 18th century was triggered by political and economical needs. The great sea-faring nations of these times, i.e., France, Spain, the Netherlands, but, above all, the island Great Britain, were all searching for an answer to the "longitude problem" - how can the crew of a ship on sea determine the longitude of its position?
Before the times of wireless communication and global positioning satellites, this was accomplished by measuring the position of the sun to exactly determine 12:00 noon (which also allowed to measure the latitude) and by simultaneously reading the local time of the port of departure (or a fixed point, e.g., Greenwich ) on a separate clock. The difference in time could easily be converted to a difference in longitude as one hour in time equals 15 degrees of longitude. The clock that was used to keep the "reference time" of the home port had to be extremely precise as, e.g., a difference of one second means an error in determining the ship's position of more than 460 metres at the equator!
In 1714, the British Parliament had issued the "Longitude Act" which promised the then enormous sum of 20,000 pound sterling to anyone who invented a device that didn't deviate by more than half a degree of longitude after a six-week-journey on the seas.
John Harrison solved this problem; the story behind his invention and his long struggle for recognition (and the money that had been promised) as well as descriptions of his chronometers are found in Dava Sobel's "Longitude."
Harrison 's chronometers, however, as well as later constructions by the Frenchmen Le Roy and Berthoud, were, for various reasons, not suitable for "serial" production.
The English watchmaker John Arnold (1736-1799) has to be given credit for creating the extraordinarily precise watch that the world was waiting for, at least the sea-faring world - the true "marine chronometer" was born.
Arnold 's two major inventions were the helical balance spring (patented in December 1775) and a chronometer escapement (patented in May 1782) that was later modified by Earnshaw . Arnold 's watches were affordable and could be made in the necessary numbers to become really universal instruments. |
As a result of these inventions, a good quality English watch from the mid-18th century had a daily rate of about one minute. Since 1750, a seconds hand was seen increasingly often; contrary to earlier watches where it had also been found occasionally, it made sense now that a new level of accuracy had been reached. A well cared-for late 18th century watch is, even today, a perfectly usable timepiece. Nevertheless, the pocket watch had not yet reached the peak of its development - this was still to come in the 19th century.
Abraham-Louis Breguet
The history of horology in the 18th century would not be complete without the probably greatest genius of watchmaking that ever lived, Abraham Louis Breguet .
Among his numerous inventions, the best-known are the Breguet spiral, found until today in every quality watch and wristwatch, and the " tourbillon ," the "whirlwind" - an ingenious device that Breguet invented to compensate for gravity influences on the balance spring in pocket watches.
Among his other inventions were a new striking mechanism for repeaters, a new escapement, the so-called " échappement naturel ," similar to the chronometer escapement (1789), in 1790, the "parachute" shock protection system, the cylinder escapement with a ruby cylinder, and improvements of Perrelet's automatic winding mechanism, implemented in his around forty " Perpétuelles ."
Furthermore, Breguet made what we consider today as the first "Grande Complication" in the history of horology, the watch known as "the Marie-Antoinette." This watch was commissioned by the French queen's guard Monsieur de la Croizette with the explicit order that it should contain all known complications and the greatest possible number of parts made of gold. There were no restrictions as to the time for making the watch or the price. This watch was only finished in 1827 which means that neither the unfortunate queen (Marie-Antoinette was guillotined in 1793) nor the master watchmaker himself ( Breguet died in 1823) ever saw the completed watch. The "Marie-Antoinette" was a self-winding watch with a perpetual calendar, equation of time indication and a minute repeater. It has disappeared since 1983 when it was stolen from the Jerusalem Institute of Islamic Art.
Breguet was not only a gifted watchmaker, but also a clever businessman. He invented a payment scheme for a special series of watches which are known as the " montres à souscription ". These watches had a symmetrically built Lépine caliber, a ruby cylinder escapement, a temperature-compensated balance and the above mentioned shock protection for the balance-staff. They had only one hand, but reading the time is no problem thanks to the finely detailed dial. These "subscription watches" were made in small series of twelve to twenty at a time; customers had to make a down-payment when ordering a watch which allowed Breguet to finance production of the whole series. About 1500 of these " Souscriptions " were made; today, they are the least expensive Breguet watches due to this relatively large number - if you are lucky, you may find one for less than twenty thousand dollars ...
It should be noted that even such a " montre à souscription " was not a watch for John Doe: They cost between 550 and 900 Francs - this was an average working man's annual income. |
Another invention of the late 18th century that was, however, more for comfort than for precision, must not be forgotten: Automatic winding. Abraham Louis Perrelet is unanimously acknowledged as the inventor of automatic winding, he made his first "perpetual watches" around 1760 or 1770. It is said that Breguet and the English watchmaker Recordon were among his first customers. Breguet made his first " perpétuelle " around 1780; he had improved Perrelet's mechanism by an excentric arrangement of the oscillating weight. At about the same time, Recordon sold his first self-winding watches in London . Honi soit qui mal y pense ...
Where Legends Begin
In the 19th century, many of the famous names and great brands appeared for the first time.
Let us look at the foundation data of some companies; you will recognize many of these names:
When |
Who |
Where |
Today |
1833 |
LeCoultre & Cie . |
Le Sentier |
Jaeger- LeCoultre |
1839 |
Patek & Czapek |
Geneva |
Patek Philippe |
1846 |
Ulysse Nardin |
Le Locle |
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1856 |
Eterna |
Grenchen |
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1858 |
Minerva |
Villeret |
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1860 |
Chopard |
Geneva |
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1864 |
Heuer |
Biel |
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1865 |
Georges Favre-Jacot |
Le Locle |
Zenith |
1868 |
IWC |
Schaffhausen |
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1875 |
Audemars Piguet |
Le Brassus |
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1884 |
Breitling |
La Chaux-de-Fonds |
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1887 |
Eberhard & Cie . |
La Chaux-de-Fonds |
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Obviously, watches had become generally usable instruments, and there was an increasing demand. Switzerland had silently become the leader, a position that had formerly been held by France and England ; the "Swiss Watch" was on its way to become a legend and a guarantee for quality that few products or product categories have achieved since then. The social and political conditions that had made it possible that a small and sparsely populated country became the world leader in precision watchmaking are fascinating, but they are beyond the scope of this "Brief History." What had happened to watch precision? The cylinder escapement was generally used since about 1820. Around 1860, the days of the verge escapement were counted - cylinder and lever escapements had taken over. Crown winding, probably invented by Louis Audemars in Le Brassus around 1837 and made popular by Adrien Philippe (author of "Les montres sans clef," i.e., "Watches without key," in 1863) was used increasingly often since about 1860-1870. Complicated watches with perpetual calendars, moon phase indications, and chronographs were the pride of all major manufacturers (although the movements were often made by some anonymous genius in an obscure village in the Vallée de Joux ). Parallel to this development of more and more complicated watches, we find the beginning of industrial-style watchmaking , introduced in the USA by Terry around 1840. Standardization of parts helped a great deal in achieving better precision. The watches that were sent to competitions, however, were still carefully assembled by hand and meticulously regulated by specialists, the " régleurs ." Competition in Precision
In the 19th century, observatories started to issue certificates to companies for extremely precise watches, initially marine chronometers where precision is not a luxury but a requirement. An "Observatory Prize" from Kew in England or Neuchâtel in Switzerland made an excellent argument in advertising, and soon, no major company could afford to stay away from the annual contests. (Until today, the world record holder in precision prizes is Zenith with 1565 first prizes.) Other companies specialized in particular types of watches; the records of the OAN, the Observatoire Astronomique de Neuchâtel , from 1860 to 1975 show that, e.g., Ulysse Nardin was without serious competition in marine chronometers. Furthermore, the world came closer together thanks to developments like the railway or the steamship. "International" or "World Expositions" were held since the late 19th century, and watchmakers were keen on obtaining medals - these, too, made excellent advertising material.
Medals awarded to Zenith at the Paris Fair 1900 on Zenith watches
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Another category of precision watches came into being in the late 19th century: the "Railroad Watch." A major railroad accident in Kipton near Cleveland , Ohio , on April 19, 1891 that cost eleven lives happened because of a watch that was several minutes off the correct time. As a result, a commission with members from all major railroad companies in the US was founded that defined the "General Railroad Timepiece Standards;" they were adopted in 1893. Besides US watch companies, some European watch manufacturers (e.g., Zenith) also made "railroad watches." In Europe , they were popular in the southern and eastern countries. Germany , in spite of all the strict Prussian imperial regulations, never knew "railroad watches."
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Zenith Railroad Watch made for the Bulgarian State Railroad in 1896 |
New Materials
The 20th century began with a major breakthrough: The Frenchman Charles Edouard Guillaume invented a material called "Invar," a nickel-steel alloy. (Guillaume was awarded the Nobel Prize for Physics in 1920.) Invar (derived from "invariable" due to its particular characteristics) was the ideal material for balances as its coefficient of expansion is 15 times lower than that of steel. Until today, watch companies are trying to improve the balance's and the spiral's temperature stability. " Glucydur " is another extremely stable material, it is a copper- glucinum alloy. Furthermore, companies developed special compensation mechanisms that are more complex than the simple screws on the balance ring, e.g., Patek Philippe's " Gyromax " balance with eight weights - adjusting this balance is definitely not a job for a week-end hobby horologist! A New Challenge
Around the turn of the century, the good old pocket watch got competition: People actually started to wear timepieces on their wrist! Watchmakers were horrified: The strain of the continuous movement, the dirt, the humidity, the shocks - who would, in his right mind, ever subject something as delicate as a watch to these influences? Today, we know the answer: After one generation, about thirty years, practically everybody! The new challenge led to new solutions, and within this one generation, everything that you could ever wish for in a watch had been achieved - in a wristwatch! Automatic winding, absolutely waterproof cases, new shock-protection mechanisms, it was all there. Initially, wristwatches were simply pocket watches with lugs, often with ladies' size movements (9'''). (The tradition of putting a pocket watch movement into a wristwatch case still continues with IWC's oversized " Portugieser " models.) Gradually, however, watchmakers faced the challenge of making small and precise movements. While an oscillating frequency of 18,000 a/h had been sufficient for pocket watches for virtually hundreds of years, fast-beat movements were developed for wristwatches to allow for higher precision. Today, the standard is 21,600 or 28,800 a/h; Zenith's "El Primero " with its 36,000 a/h is still unique and marks the peak of this development. The Quartz Revolution
While electrically driven clocks had been used in observatories since the 1930s, and experiments had been made with electrically driven wristwatches, it was the quartz technology that came up in the late 1960s and early 1970s that marked the beginning of a new era. Now, it was possible to achieve daily rates of one second or less in a wristwatch with a rather cheap technology that could be produced in enormous numbers. A split-seconds chronograph, an alarm, a perpetual calendar, complications that had been the pride of watchmakers for centuries, now only required some additional instructions in the chip that controlled the watch. The social impact of this new technology on the Swiss watch industry was enormous. Suddenly, "watchmakers" became superfluous - all that was required was an occasional change of the battery, and if the movement had a serious flaw, it was replaced by another one (if you didn't prefer to simply throw away the watch and get a new one).
The wristwatch, formerly a prestigious gift and an item that you cared for, became an article that was about as exciting as a pocket comb. If it didn't work any more, you threw it away. In Switzerland , dozens of companies, among them some old and traditional names, went out of business - what business could you do with a product that nobody wanted any more? Others adopted to the demands of the market and changed their production accordingly - if people want quartz watches, give them quartz watches. While I am writing this, I have an Eterna catalog from the early 1980s before me - really sad to look at. There is still the logo with the five balls symbolizing the ball-bearing that was found in the first " Eternamatic ," but all watches in this catalog are quartz-driven. The Renaissance of the Mechanical Wristwatch
In the early to mid-eighties, something strange happened: People re-discovered the mechanical watch. Over a period of just two or three years, beginning around 1983, there was a new demand for mechanical movements, automatic or hand-wound. The industry reacted quickly: This second generation of mechanical wristwatches whose development we have followed for the last twenty years has led to developments that nobody had expected. Complications that had formerly only been found in pocket watches were built into wristwatches now. In the 180 years between 1801 and 1980, about 650 pocket watches with a tourbillon had been made world-wide. Now, when the mechanical wristwatch came back, it came back with a vengeance: In 1986, Audemars Piguet presented to an astonished world the first automatic tourbillon in a wristwatch (cal. 2870). Since then, we have seen wristwatches that nobody would have dreamt of in the 1960s: IWC's "Grande Complication" and " Destriero Scafusiae ," Blancpain's "1735," or Patek Philippe's "Sky Moon Tourbillon " to name just a few of the ultimate masterpieces from recent years. Precision has greatly improved; you may expect a daily rate of less than ten seconds from a low-end automatic wristwatch. There is, however, a steady increase in the number of movements tested by the COSC (cf. insert). It seems that people are ready to accept these small deviations; the pleasure of wearing a mechanical wristwatch more than compensates for the small trouble of setting it back a minute once in two weeks.
The Chronometer Certificate
Watches may be called chronometers if they have passed a special test performed by the COSC ( Contrôle Officiel Suisse des Chronomètres , i.e., Official Swiss Chronometer Control).
Currently, the COSC has three offices: Biel (since 1877), Geneva (1886) and Le Locle (1901). Two other bureaus were active in Le Sentier (1942-1978) and Solothurn (1951-1976).
Each movement is tested individually and receives a "Bulletin de Marche " (Watch Rate Certificate) if it passes the test:
Watch Rate Certificate
for a "Wristwatch Type I"
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These watches usually have an inscription like "Chronometer," "Certified Chronometer" or similar on the dial.
The tests are defined for various types of watches. "Type I" (as shown above) is the usual men's chronometer with a caliber diameter of more than 20 millimeters. Each of these movements is tested for 15 days in five different positions and at three different temperatures.
Watch Rate Certificate - Results
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Several values are calculated from the individual tests; the minimal requirements for a "chronometer" are defined in the ISO-norm 3159-1976. It defines that, e.g., a movement with a diameter of more than 20 millimeters may show a maximum deviation of five seconds per day, a deviation of ± 0.6 seconds per day per degree centigrade and numerous other values.
A different type of certificate is made out for, e.g., marine chronometers. Here, you find " Epreuves pour instruments horaires utilisés dans une seule position," i.e., "Tests for a time-keeping device used in only one position." There is no need to test a marine chronometer, e.g., with the crown up as its gimbal -mount makes sure that it is always in an horizontal position:
Watch Rate Certificate for a Zenith 5011 K Marine Chronometer
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It should be noted that the COSC tests movements, not watches ! The certificate is valid for a movement at the time when it is tested; nobody knows what happens later at the factory when it is set into the case, packed, shipped, shown to customers in the watchmaker's shop or, last not least, worn on your wrist ...
The above example nicely illustrates this problem: This Zenith 5011 K marine chronometer has a COSC certificate with the additional stamp "Especially good results" which is awarded when a watch performs exceptionally well. According to the certificate, it has a mean daily rate of + 1.5 seconds. When I bought it, 13 years after the certificate was issued, it had a daily rate of + 12 seconds! This is nothing to get excited about - it is normal.
When you buy a new COSC certified chronometer from an authorized dealer, it should perform as indicated. When you buy it second-hand, years later, it may show substantial deviations from the former test results. Have the watch regulated and/or cleaned by a good watchmaker, and it should perform fine - at least, for the next three to five years when it will need another cleaning/adjustment. |
The 21st Century ...
I don't have a crystal ball on my desk that shows me the wristwatches that we will be wearing in the 2030s - or, who knows, perhaps the pocket watch will be back by then?
We can, however, look at developments in recent years and try to make an educated guess about the future course of these developments. What we have seen is a concentration of watch companies in large holdings, and this is probably a development that can't be turned back. A similar development can be seen in the automobile industry. There are analysts that predict that there will be no more than six companies left world-wide by 2020. Just remember that "Volkswagen," literally translated the "People's Car," is the owner of Bugatti , Lamborghini, and Rolls-Royce, and you will not be astonished to see Swatch and Breguet under one roof. This is not bad for the customer: The development of a new movement is a multi-million dollar affair, and if we want to have innovations in watches, we need companies that have the financial background for such developments.
We have recently seen an example from the Swatch group: The co-axial escapement that you find in the latest Omega models was a risk - would the customer accept something else than the trusted and proven Swiss lever escapement? The customer did, and this hopefully sets a sign for the whole industry that taking a risk can pay off nicely. There are rumours that the next three to five years will bring other new escapements from other companies - not bad for a technology that was said to be dead thirty years ago. Developments like Ludwig Oechslin's "Freak" from Ulysse Nardin show that the mechanical wristwatch still has an enormous potential for innovations - let us wait and see! There will probably be even more "manufactories" in future if the Swatch group is really going to be more restrictive about selling movements to other companies. This will put these in a position where the in-house development of movements becomes a question of survival - for the customer, this would mean that there are more movements to choose from. The mechanical wristwatch's future may not only be considered established - it will probably be more exciting than ever before. Just remember when you look at a wristwatch "Grande Complication" that without the work of men like Huygens, Mudge , Guillaume, and all the others, we wouldn't have these masterpieces today. Understanding horology means understanding its history; remember: La montre n'est pas l'oeuvre d'un seul homme , mais celle de plusieurs générations .
The watch is not the work of a single man, but of several generations.
F. Jung
References:
· Pellaton , J.C.: Cours d'Échappements . Écoles Suisses d'Horlogerie , Cours d'Horlogerie IIème partie . Technicum du Locle , Le Locle 1928
· Pellaton , J.: Centenaire de la Fabrication de l'Assortiment à Ancre au Locle 1850-1950. Fabriques d'Assortiments Réunies , Le Locle 1950
· Jung, F.: Début de l'industrie horlogère au Locle . Fabriques d'Assortiments Réunies , Le Locle 1951
· Jaquet , E. and Chapuis , A.: Technique and History of the Swiss Watch. 2nd ed., The Hamlyn Publishing Group Ltd., London /New York/Sydney/Toronto 1970
· Meis , R.: Taschenuhren - Von der Halsuhr zum Tourbillon . 5th ed., Verlag Georg D.W. Callwey GmbH & Co., München 1994
· Nardin , R.: Les Chronomètres de Marine Ulysse Nardin . Institut l'Homme et le Temps, La Chaux-de-Fonds 1994
· Chapiro , A.: Taschenuhren aus vier Jahrhunderten . Die Geschichte der französischen Taschenuhr . Verlag Georg D.W. Callwey GmbH & Co., München 1995
· Sobel , D.: Longitude - The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time. Walker Publishing Company, 1995
· Stolberg , L.: Lexikon der Taschenuhr . 4th ed., Carinthia-Verlag , Klagenfurt 1995
· v. Osterhausen , F.: Taschenuhren . Von der Balkenwaag des Mittelalters zur Integralunruh der Gegenwart . Wilhelm Heyne Verlag , München 1997
· Berner , G.-A.: Dictionnaire Professionnel Illustré de l'Horlogerie . Edition 1988, Réimpression 1998, Société du Journal La Suisse Horlogère S.A., Bienne 1998
· Shugart C., Engle T., Gilbert R.E.: Complete Price Guide to Watches No. 18. Cooksey Shugart Publications, Cleveland 1998
· Britten , F.J.: The Watch and Clock Makers' Handbook, Dictionary and Guide. 11th ed ., first published 1915. Reprint, Antique Collectors' Club, Woodbridge 2000
· Errico , C., Suessmeier , L., Siegenthaler , J. (eds.): Star Caliber 2000. Patek Philippe, Genève and Editions Scriptar SA, Lausanne 2000
· v. Osterhausen , F.: Taschenuhren . Weltbild Verlag GmbH, Augsburg 2000
· Gazeley , W.J.: Clock and Watch Escapements. Robert Hale Limited, London 2001
· Chronos Special " Audemars Piguet ." Ebner Verlag GmbH & Co. KG, Ulm 2002 |
