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A watch is a timepiece that is made to be worn on a person. It is usually a wristwatch, worn on the wrist with a strap or bracelet. In addition to the time, modern watches often display the day, date, month and year, and electronic watches may have many other functions.

Most inexpensive and medium-priced watches used mainly for timekeeping are electronic watches with quartz movements. Expensive, collectible watches valued more for their workmanship and aesthetic appeal than for simple timekeeping, often have purely mechanical movements and are powered by springs, even though mechanical movements are less accurate than more affordable quartz movements.

Before the inexpensive miniaturization that became possible in the 20th century, most watches were pocket watches, which often had covers and were carried in a pocket and attached to a watch chain or watch fob. Watches evolved in the 1600s from spring powered clocks, which appeared in the 1400s.

Contents

Parts

Movement

Different kinds of movements move the hands differently as shown in this 2 second exposure. The left watch has a mechanical 21,600 bph movement, the right one has a quartz movement.

A movement in watchmaking is the mechanism that measures the passage of time and displays the current time (and possibly other information including date, month and day). Movements may be entirely mechanical, entirely electronic (potentially with no moving parts), or a blend of the two. Most watches intended mainly for timekeeping today have electronic movements, with mechanical hands on the face of the watch indicating the time.

Mechanical movements

Main article Mechanical watch.
A Russian mechanical watch movement.

Compared to electronic movements, mechanical watches are less accurate, often with errors of seconds per day, and they are sensitive to position and temperature. As well, they are costly to produce, they require regular maintenance and adjustment, and they are more prone to failure. Nevertheless, the "old world" craftsmanship of mechanical watches still attracts interest from part of the watch-buying public.

Mechanical movements use an escapement mechanism to control and limit the unwinding of the spring, converting what would otherwise be a simple unwinding into a controlled and periodic energy release. Mechanical movements also use a balance wheel together with the balance spring (also known as a hairspring) to control motion of the gear system of the watch in a manner analogous to the pendulum of a pendulum clock. The tourbillon, an optional part for mechanical movements, is a rotating frame for the escapement, which is used to cancel out or reduce the effects of gravitational bias to the timekeeping. Due to the complexity of designing a tourbillon, they are very expensive, and only found in "prestige" watches.

The pin-lever escapement (also called the Roskopf movement after its inventor, Georges Frederic Roskopf), which is a cheaper version of the fully levered movement, was manufactured in huge quantities by many Swiss manufacturers as well as Timex, until it was replaced by quartz movements.[1][2][3]

Tuning-fork watches use a type of electromechanical movement. Introduced by Bulova in 1960, they use a tuning fork with a precise frequency (most often 360 hertz) to drive a mechanical watch. The task of converting electronically pulsed fork vibration into rotary movement is done via two tiny jeweled fingers, called pawls. Tuning-fork watches were rendered obsolete when electronic quartz watches were developed, because quartz watches were cheaper to produce and even more accurate.

Electronic movements

Electronic movements have few or no moving parts, as they use the piezoelectric effect in a tiny quartz crystal to provide a stable time base for a mostly electronic movement. The crystal forms a quartz oscillator which resonates at a specific and highly stable frequency, and which can be used to accurately pace a timekeeping mechanism. For this reason, electronic watches are often called quartz watches. Most quartz movements are primarily electronic but are geared to drive mechanical hands on the face of the watch in order to provide a traditional analog display of the time, which is still preferred by most consumers.

The first prototypes of electronic quartz watches were made by the CEH research laboratory in Switzerland in 1962. The first quartz watch to enter production was the Seiko 35 SQ Astron, which appeared in 1969. Modern quartz movements are produced in very large quantities, and even the cheapest wristwatches typically have quartz movements. Whereas mechanical movements can typically be off by several seconds a day, an inexpensive quartz movement in a child's wristwatch may still be accurate to within half a second per day—ten times better than a mechanical movement.[4] Some watchmakers combine the quartz and mechanical movements, such as the Seiko Spring Drive, introduced in 2005.

Radio time signal watches are a type of electronic quartz watch which synchronizes (time transfer) its time with an external time source such as in atomic clocks, time signals from GPS navigation satellites, the German DCF77 signal in Europe, WWVB in the US, and others. Movements of this type synchronize not only the time of day but also the date, the leap-year status of the current year, and the current state of daylight saving time (on or off).

Power sources

Traditional mechanical watch movements use a spiral spring called a mainspring as a power source. In manual watches the spring must be rewound by the user periodically by turning the watch crown. Antique pocketwatches were wound by inserting a separate key into a hole in the back of the watch and turning it. Most modern watches are designed to run 40 hours on a winding, so must be wound daily, but some run for several days and a few have 192-hour mainsprings and are wound weekly.

Automatic watch: An eccentric weight, called a rotor, swings with the movement of the wearer's body and winds the spring

A self-winding or automatic mechanism is one that rewinds the mainspring of a mechanical movement by the natural motions of the wearer's body. The first self-winding mechanism, for pocketwatches, was invented in 1770 by Abraham-Louis Perrelet;[5] but the first "self-winding," or "automatic," wristwatch was the invention of a British watch repairer named John Harwood in 1923. This type of watch allows for a constant winding without special action from the wearer: it works by an eccentric weight, called a winding rotor, which rotates with the movement of the wearer's wrist. The back-and-forth motion of the winding rotor couples to a ratchet to automatically wind the mainspring. Self winding watches usually can also be wound manually so they can be kept running when not worn, or if the wearer's wrist motions don't keep the watch wound.

Some electronic watches are also powered by the movement of the wearer of the watch. Kinetic powered quartz watches make use of the motion of the wearer's arm turning a rotating weight, which turns a generator to supply power to charge a rechargeable battery that runs the watch. The concept is similar to that of self-winding spring movements, except that electrical power is generated instead of mechanical spring tension.

Electronic watches require electricity as a power source. Some mechanical movements and hybrid electronic-mechanical movements also require electricity. Usually the electricity is provided by a replaceable battery. The first use of electrical power in watches was as substitute for the mainspring, in order to remove the need for winding. The first electrically-powered watch, the Hamilton Electric 500, was released in 1957 by the Hamilton Watch Company of Lancaster, Pennsylvania.

Watch batteries (strictly speaking cells, a battery is composed of multiple cells) are specially designed for their purpose. They are very small and provide tiny amounts of power continuously for very long periods (several years or more). In most cases, replacing the battery requires a trip to a watch-repair shop or watch dealer; this is especially true for watches that are designed to be water-resistant, as special tools and procedures are required to ensure that the watch remains water-resistant after battery replacement. Silver-oxide and lithium batteries are popular today; mercury batteries, formerly quite common, are no longer used, for environmental reasons. Cheap batteries may be alkaline, of the same size as silver-oxide but providing shorter life. Rechargeable batteries are used in some solar powered watches.

Solar powered watches are powered by light. A photovoltaic cell on the face (dial) of the watch converts light to electricity, which in turn is used to charge a rechargeable battery or capacitor. The movement of the watch draws its power from the rechargeable battery or capacitor. As long as the watch is regularly exposed to fairly strong light (such as sunlight), it never needs battery replacement, and some models need only a few minutes of sunlight to provide weeks of energy (as in the Citizen Eco-Drive).

Some of the early solar watches of the 1970s had innovative and unique designs to accommodate the array of solar cells needed to power them (Synchronar, Nepro, Sicura and some models by Cristalonic, Alba, Seiko and Citizen). As the decades progressed and the efficiency of the solar cells increased while the power requirements of the movement and display decreased, solar watches began to be designed to look like other conventional watches.[6] A rarely used power source is the temperature difference between the wearer's arm and the surrounding environment (as applied in the Citizen Eco-Drive Thermo).

Display

Analogue

An analogue wristwatch with a second hand.

Traditionally, watches have displayed the time in analogue form, with a numbered dial upon which are mounted at least a rotating hour hand and a longer, rotating minute hand. Many watches also incorporate a third hand that shows the current second of the current minute. Watches powered by quartz usually have a second hand that snaps every second to the next marker. Watches powered by a mechanical movement have a "sweep second hand", the name deriving from its uninterrupted smooth (sweeping) movement across the markers, although this is actually a misnomer; the hand merely moves in smaller steps, typically 1/5th of a second, corresponding to the beat (half period) of the balance wheel. In some escapements (for example the duplex escapement), the hand advances every two beats (full period) of the balance wheel, typically 1/2 second in those watches, or even every four beats (two periods, 1 second), in the double duplex escapement. All of the hands are normally mechanical, physically rotating on the dial, although a few watches have been produced with “hands” that are simulated by a liquid-crystal display.

Analog display of the time is nearly universal in watches sold as jewelry or collectibles, and in these watches, the range of different styles of hands, numbers, and other aspects of the analogue dial is very broad. In watches sold for timekeeping, analog display remains very popular, as many people find it easier to read than digital display; but in timekeeping watches the emphasis is on clarity and accurate reading of the time under all conditions (clearly marked digits, easily visible hands, large watch faces, etc.). They are specifically designed for the left wrist with the stem (the knob used for changing the time) on the right side of the watch; this makes it easy to change the time without removing the watch from the hand. This is the case if one is right-handed and the watch is worn on the left wrist (as is traditionally done). If one is left-handed and wears the watch on the right wrist, one has to remove the watch from the wrist to reset the time or to wind the watch.

Analog watches as well as clocks are often marketed showing a display time of approximately 10:09 or 10:10. This creates a visually pleasing smile-like face on upper half of the watch. Digital displays often show a time of 12:38, where the increases in the numbers from left to right culminating in the fully-lit numerical display of the 8 also gives a positive feeling.[7][8]

Digital

Cortébert digital mechanical pocket watch. 1890s
Cortébert digital mechanical wristwatch. 1920s
A digital watch displaying the time (with seconds) and date

A digital display simply shows the time as a number, e.g., 12:08 instead of a short hand pointing towards the number 12 and a long hand 8/60 of the way round the dial.

The first digital mechanical pocket watches appeared in late 19th century. In the 1920s the first digital mechanical wristwatches appeared.

The first digital electronic watch, a Pulsar LED[9] prototype in 1970, was developed jointly by Hamilton Watch Company and Electro-Data. John Bergey, the head of Hamilton's Pulsar division, said that he was inspired to make a digital timepiece by the then-futuristic digital clock that Hamilton themselves made for the 1968 science fiction film 2001: A Space Odyssey. On April 4, 1972, the Pulsar was finally ready, made in 18-carat gold and sold for $2,100. It had a red light-emitting diode (LED) display.

Digital LED watches were very expensive and out of reach to the common consumer until 1975, when Texas Instruments started to mass produce LED watches inside a plastic case. These watches, which first retailed for only $20, reduced to $10 in 1976, saw Pulsar lose $6 million and the Pulsar brand[10] sold to Seiko.

Most watches with LED displays required that the user press a button to see the time displayed for a few seconds, because LEDs used so much power that they could not be kept operating continuously. Usually the LED display color would be red. Watches with LED displays were popular for a few years, but soon the LED displays were superseded by liquid crystal displays (LCDs), which used less battery power and were much more convenient in use, with the display always visible and no need to push a button before seeing the time. The first LCD watch with a six-digit LCD was the 1973 Seiko 06LC, although various forms of early LCD watches with a four-digit display were marketed as early as 1972 including the 1972 Gruen Teletime LCD Watch, and the Cox Electronic Systems Quarza.[11][12]

Timex Datalink USB Dress edition from 2003 with a dot matrix display; the Invasion video game is on the screen.

From the 1980s onward, digital watch technology vastly improved. In 1982 Seiko produced a watch with a small television screen built in, and Casio produced a digital watch with a thermometer as well as another that could translate 1,500 Japanese words into English. In 1985, Casio produced the CFX-400 scientific calculator watch. In 1987 Casio produced a watch that could dial your telephone number and Citizen revealed one that would react to your voice. In 1995 Timex release a watch which allowed the wearer to download and store data from a computer to his wrist. Some watches, such as the Timex Datalink USB, feature dot matrix displays. Since their apex during the late 1980s to mid 1990s high technology fad, digital watches have mostly devolved into a simpler, less expensive basic time piece with little variety between models.

Despite these many advances, almost all watches with digital displays are used as timekeeping watches. Expensive watches for collectors rarely have digital displays since there is little demand for them. Less craftsmanship is required to make a digital watch face and most collectors find that analog dials (especially with complications) vary in quality more than digital dials due to the details and finishing of the parts that make up the dial (thus making the differences between a cheap and expensive watch more evident).


Functions

The Rolex Submariner is an officially certified chronometer

All watches provide the time of day, giving at least the hour and minute, and usually the second. Most also provide the current date, and often the day of the week as well. However, many watches also provide a great deal of information beyond the basics of time and date. Some watches include alarms. Other elaborate and more expensive watches, both pocket and wrist models, also incorporate striking mechanisms or repeater functions, so that the wearer could learn the time by the sound emanating from the watch. This announcement or striking feature is an essential characteristic of true clocks and distinguishes such watches from ordinary timepieces. This feature is available on most digital watches.

A complicated watch has one or more functions beyond the basic function of displaying the time and the date; such a functionality is called a complication. Two popular complications are the chronograph complication, which is the ability of the watch movement to function as a stopwatch, and the moonphase complication, which is a display of the lunar phase. Other more expensive complications include Tourbillion, Perpetual calendar, Minute repeater, and Equation of time. A truly complicated watch has many of these complications at once (see Calibre 89 from Patek Philippe for instance). Among watch enthusiasts, complicated watches are especially collectible. Some watches include a second 12-hour display for UTC (as Pontos Grand Guichet GMT).

The similar-sounding terms chronograph and chronometer are often confused, although they mean altogether different things. A chronograph has a stopwatch complication, as explained above, while a chronometer watch has a high quality mechanical or a thermo-compensated quartz movement that has been tested and certified to operate within a certain standard of accuracy by the COSC (Contrôle Officiel Suisse des Chronomètres). The concepts are different but not mutually exclusive; so a watch can be a chronograph, a chronometer, both, or neither.

Types

Fashion

A sapphire cabochon on the crown of a men's dress watch
A watch with 24-hour mechanism and display; the time shown is 18:07

Wristwatches are often appreciated as jewelry or as collectible works of art rather than just as timepieces. This has created several different markets for wristwatches, ranging from very inexpensive but accurate watches (intended for no other purpose than telling the correct time) to extremely expensive watches that serve mainly as personal adornment or as examples of high achievement in miniaturization and precision mechanical engineering.

Traditionally, men's dress watches appropriate for informal, semi-formal, and formal attire are gold, thin, simple, and plain, but recent conflation of dressiness and high price has led to a belief among some that expensive rugged, complicated, or sports watches are also dressy because of their high cost. Some dress watches have a cabochon on the crown and many women's dress watches have faceted gemstones on the face, bezel, or bracelet. Some are totally made out of facetted sapphire (corundum).

Many fashion and department stores offer a variety of less-expensive, trendy, "costume" watches (usually for women), many of which are similar in quality to basic quartz timepieces but which feature bolder designs. In the 1980s, the Swiss Swatch company hired graphic designers to redesign a new annual collection of non-repairable watches.

Still another market is that of "geek" watches—watches that not only tell the time, but incorporate computers, satellite navigation, complications of various orders, and many other features that may be quite removed from the basic concept of timekeeping. A dual-time watch is designed for travelers, allowing them to see what time it is at home when they are elsewhere.

In a variation of the "geek" watches the time is displayed in a non-standard way: with 24-hour mechanism, the hands turn anticlockwise, the numbers are displayed with LEDs in a binary numbers, etc.

Most companies that produce watches specialize in one or some of these markets. Companies such as Patek Philippe, Blancpain and Jaeger-LeCoultre specialize in simple and complicated mechanical dress watches; companies such as Omega SA,Ball Watch Company,TAG Heuer, Breitling, Panerai and Rolex specialize in rugged, reliable mechanical watches for sport and aviation use. Companies such as Casio, Timex, and Seiko specialize in watches as affordable timepieces or multifunctional computers.

Computerized multi-function watches

Many computerized wristwatches have been developed, but none have had long-term sales success, because they have awkward user interfaces due to the tiny screens and buttons, and a short battery life. As miniaturized electronics became cheaper, watches have been developed containing calculators, tonometers, barometers, altimeters, video games, digital cameras, keydrives, GPS receivers and cellular phones. In the early 1980s Seiko marketed a watch with a television in it. Such watches have also had the reputation as unsightly and thus mainly geek toys. Several companies have however attempted to develop a computer contained in a wristwatch (see also wearable computer).

For space travel

The Omega Speedmaster, selected by U.S. space agencies.

Zero gravity environment and other extreme conditions encountered by astronauts in space requires the use of specially tested watches. On April 12, 1961, Yuri Gagarin wore a Shturmanskie (a transliteration of Штурманские which actually means "navigator's") wristwatch during his historic first flight into space. The Shturmanskie was manufactured at the First Moscow Factory.

Since 1964, the watches of the First Moscow Factory have been marked by the trademark "ПОЛЕТ", transliterated as "POLJOT", which means "flight" in Russian and is a tribute to the many space trips its watches have accomplished. In the late 1970s, Poljot launched a new chrono movement, the 3133. With a 23 jewel movement and manual winding (43 hours), it was a modified Russian version of the Swiss Valjoux 7734 of the early 1970s. Poljot 3133 were taken into space by astronauts from Russia, France, Germany and Ukraine. On the arm of Valeriy Polyakov, a Poljot 3133 chronograph movement-based watch set a space record for the longest space flight in history.[13]

During the 1960s, a large range of watches were tested for durability and precision under extreme temperature changes and vibrations. The Omega Speedmaster Professional was selected by U.S. space agencies. (For a list of NASA-certified watches, see this footnote).[14]

Heuer became the first Swiss watch in space thanks to an Heuer Stopwatch, worn by John Glenn in 1962 when he piloted the Friendship 7 on the first manned U.S. orbital mission.

The Breitling Navitimer Cosmonaute was designed with a 24-hour analog dial to avoid confusion between AM and PM, which are meaningless in space. It was first worn in space by U.S. astronaut Scott Carpenter on May 24, 1962 in the Aurora 7 mercury capsule.[15]

Since 1994 Fortis is the exclusive supplier for manned space missions authorized by the Russian Federal Space Agency.

China National Space Administration (CNSA) astronauts wear the Fiyta[16] spacewatches.

At BaselWorld, 2008, Seiko announced the creation of the first watch ever designed specifically for a space walk, Spring Drive Spacewalk.

For scuba diving

Seiko 7002-7020 Diver's 200 m on a 4-ring NATO style strap.

Watches may be crafted to become water resistant. These watches are sometimes called diving watches when they are suitable for scuba diving or saturation diving. The International Organization for Standardization issued a standard for water resistant watches which also prohibits the term "waterproof" to be used with watches, which many countries have adopted.

Water resistance is achieved by the gaskets which forms a watertight seal, used in conjunction with a sealant applied on the case to help keep water out. The material of the case must also be tested in order to pass as water resistant.[17]

None of the tests defined by ISO 2281 for the Water Resistant mark are suitable to qualify a watch for scuba diving. Such watches are designed for everyday life and must be water resistant during exercises such as swimming. They can be worn in different temperature and pressure conditions but are under no circumstances designed for scuba diving.

The standards for diving watches are regulated by the ISO 6425 international standard. The watches are tested in static or still water under 125% of the rated (water)pressure, thus a watch with a 200 meter rating will be water resistant if it is stationary and under 250 meters of static water. The testing of the water resistance is fundamentally different from non-dive watches, because every watch has to be fully tested. Besides water resistance standards to a minimum of 100 meter depth rating ISO 6425 also provides eight minimum requirements for mechanical diver's watches for scuba diving (quartz and digital watches have slightly differing readability requirements). For diver's watches for mixed-gas saturation diving two additional requirements have to be met.

Watches are classified by their degree of water resistance, which roughly translates to the following (1 meter = 3.281 feet):[18]

Water resistance rating Suitability Remarks
Water Resistant 30 m or 50 m Suitable for washing hands. 50 m suitable for showering and light swimming. not suitable for swimming or diving.
Water Resistant 100 m Suitable for recreational surfing, swimming, snorkeling, sailing and water sports. not suitable for diving.
Water Resistant 200 m Suitable for professional marine activity and serious surface water sports. suitable for diving.
Diver's 100 m Minimum ISO standard (ISO 6425) for scuba diving at depths NOT requiring helium gas. Diver's 100 m and 150 m watches are generally old(er) watches.
Diver's 200 m or 300 m Suitable for scuba diving at depths NOT requiring helium gas. Typical ratings for contemporary diver's watches.
Diver's 300+ m helium safe Suitable for saturation diving (helium enriched environment). Watches designed for helium mixed-gas diving will have additional markings to point this out.

Some watches use bar instead of meters, which may then be multiplied by 10 to be approximately equal to the rating based on meters. Therefore, a 10 bar watch is equivalent to a 100 meter watch. Some watches are rated in atmospheres (atm), which are roughly equivalent to bar.

History

Watches evolved from portable spring driven clocks, which first appeared in the 15th century. Portable timepieces were made possible by the invention of the mainspring. Although some sources erroneously credit Nürnberg clockmaker Peter Henlein (or Henle or Hele) with inventing the mainspring around 1511, many references to 'clocks without weights' and two surviving examples show that spring powered clocks appeared in the 1400s.[19][20][21] Henlein is also often credited with constructing the first pocketwatches, mostly because of a passage by Johann Cochläus in 1511:[21][22]

Peter Hele, still a young man, fashions works which even the most learned mathematicians admire. He shapes many-wheeled clocks out of small bits of iron, which run and chime the hours without weights for forty hours, whether carried at the breast or in a handbag

and because he was popularized in a 19th century novel. However, many German clockmakers were creating miniature timepieces during this period, and there is no evidence Henlein was the first.[21] Also, watches weren't widely worn in pockets until the 1600s.

1500–1600 Clock-watches

The first timepieces to be worn, made in 16th century Europe, were transitional in size between clocks and watches.[23] These 'clock-watches' were fastened to clothing or worn on a chain around the neck. They were heavy drum shaped cylindrical brass boxes several inches in diameter, engraved and ornamented. They had only an hour hand. The face was not covered with glass, but usually had a hinged brass cover, often decoratively pierced with grillwork so the time could be read without opening. The movement was made of iron or steel and held together with tapered pins and wedges, until screws began to be used after 1550. Many of the movements included striking or alarm mechanisms. They usually had to be wound twice a day. The shape later evolved into a rounded form; these were called Nürnberg eggs. Still later in the century there was a trend for unusually shaped watches, and clock-watches shaped like books, animals, fruit, stars, flowers, insects, crosses, and even skulls (Death's head watches) were made.

It should not be thought that the reason for wearing these early clock-watches was to tell the time. The accuracy of their verge and foliot movements was so poor, perhaps several hours per day, that they were practically useless. They were made as jewelry and novelties for the nobility, valued for their fine ornamentation, unusual shape, or intriguing mechanism, and accurate timekeeping was of very minor importance.[24]

1600–1657 Pocketwatches

Styles changed in the 1600s and men began to wear watches in pockets instead of as pendants (the woman's watch remained a pendant into the 20th century).[25] This is said to have occurred in 1675 when Charles II of England introduced waistcoats.[26] To fit in pockets, their shape evolved into the typical pocketwatch shape, rounded and flattened with no sharp edges. Glass was used to cover the face beginning around 1610. Watch fobs began to be used, the name originating from the German word fuppe, a small pocket. The watch was wound and also set by opening the back and fitting a key to a square arbor, and turning it.

The timekeeping mechanism in these early pocketwatches was the same one used in clocks, invented in the 13th century; the verge escapement which drove a foliot, a dumbbell shaped bar with weights on the ends, to oscillate back and forth. However, the mainspring introduced a source of error not present in weight-powered clocks. The force provided by a spring is not constant, but decreases as the spring unwinds. The rate of all timekeeping mechanisms is affected by changes in their drive force, but the primitive verge and foliot mechanism was especially sensitive to these changes, so early watches slowed down during their running period as the mainspring ran down. This problem, called lack of isochronism, plagued mechanical watches throughout their history.

Efforts to improve the accuracy of watches prior to 1657 focused on evening out the steep torque curve of the mainspring.[25] Two devices to do this had appeared in the first clock-watches: the stackfreed and the fusee. The stackfreed, a spring-loaded cam on the mainspring shaft, added a lot of friction and was abandoned after about a century. The fusee was a much more lasting idea. A curving conical pulley with a chain wrapped around it attached to the mainspring barrel, it changed the leverage as the spring unwound, equalizing the drive force. Fusees became standard in all watches, and were used until the early 1800s. The foliot was also gradually replaced with the balance wheel, which had a higher moment of inertia for its size, allowing better timekeeping.

1657–1765 The balance spring

A great leap forward in accuracy occurred in 1657 with the addition of the balance spring to the balance wheel, an invention disputed both at the time and ever since between Robert Hooke and Christiaan Huygens. Prior to this, the only force limiting the back and forth motion of the balance wheel under the force of the escapement was the wheel's inertia. This caused the wheel's period to be very sensitive to the force of the mainspring. The balance spring made the balance wheel a harmonic oscillator, with a natural 'beat' resistant to disturbances. This increased watches' accuracy enormously, from perhaps several hours per day[27] to perhaps 10 minutes per day,[28] resulting in the addition of the minute hand to the face from around 1680 in Britain and 1700 in France. The increased accuracy of the balance wheel focused attention on errors caused by other parts of the movement, igniting a two century wave of watchmaking innovation. The first thing to be improved was the escapement. The verge escapement was replaced in quality watches by the cylinder escapement, invented by Thomas Tompion in 1695 and further developed by George Graham in the 1720s. In Britain a few quality watches went to the duplex escapement, invented by Jean Baptiste Dutertre in 1724. The advantage of these escapements was that they only gave the balance wheel a short push in the middle of its swing, leaving it 'detached' from the escapement to swing back and forth undisturbed during most of its cycle.

During the same period, improvements in manufacturing such as the tooth-cutting machine devised by Robert Hooke allowed some increase in the volume of watch production, although finishing and assembling was still done by hand until well into the 19th century.

1765–1800 Temperature compensation and chronometers

The Enlightenment view of watches as scientific instruments brought rapid advances to their mechanisms. The development during this period of accurate marine chronometers to determine longitude during sea voyages produced many technological advances that were later used in watches. It was found that a major cause of error in balance wheel timepieces was changes in elasticity of the balance spring with temperature changes. This problem was solved by the bimetallic temperature compensated balance wheel invented in 1765 by Pierre Le Roy and improved by Thomas Earnshaw. This type of balance wheel had two semicircular arms made of a bimetallic construction. If the temperature rose, the arms bent inward slightly, causing the balance wheel to rotate faster back and forth, compensating for the slowing due to the weaker balance spring. This system, which could reduce temperature induced error to a few seconds per day, gradually began to be used in watches over the next hundred years.

The going barrel invented in 1760 by Jean-Antoine Lépine provided a more constant drive force over the watch's running period, and its adoption in the 1800s made the fusee obsolete. Complicated pocket chronometers and astronomical watches with many hands and functions were made during this period.

1800–1850 Lever escapement

The lever escapement, invented by Thomas Mudge in 1759 and improved by Josiah Emery in 1785, gradually came into use from about 1800 onwards, chiefly in Britain; it was also adopted by Abraham Louis Breguet, but Swiss watchmakers (who by now were the chief suppliers of watches to most of Europe) mostly adhered to the cylinder until the 1860s. By about 1900, however, the lever was used in almost every watch made. In this escapement the escape wheel pushed on a T shaped 'lever', which was unlocked as the balance wheel swung through its center position and gave the wheel a brief push before releasing it. The advantages of the lever was that it allowed the balance wheel to swing completely free during most of its cycle; due to 'locking' and 'draw' its action was very precise; and it was self-starting, so if the balance wheel was stopped by a jar it would start again. Jewel bearings, introduced in 1702 by Nicolas Fatio de Duillier, also came into use for quality watches during this period.

1850–1900 Mass production

At Vacheron Constantin, Geneva, Georges-Auguste Leschot (1800-1884), pioneered in the field of interchangeability in clockmaking by the invention of various machine tools. 1830 he designed an anchor escapement, which his student, Antoine Léchaud, later mass produced. 1839 he invented a pantograph allowing some degree of standardisation and interchangeability of parts on watches fitted with the same calibre.

Watch manufacturing really changed from assembly in watchmaking shops to mass production with interchangeable parts, as from 1854, pioneered by the Waltham Watch Company, in Waltham, Massachusetts. The railroads' stringent requirements for accurate watches to safely schedule trains drove improvements in accuracy. The engineer Webb C. Ball, established around 1891 the first precision standards and a reliable timepiece inspection system for Railroad chronometers. Temperature compensated balance wheels began to be widely used in watches during this period, and jewel bearings became almost universal. Techniques for adjusting the balance spring for isochronism and positional errors discovered by Abraham Breguet, M. Phillips, and L. Lossier were adopted. The first international watch precision contest took place in 1876, during the International Centennial Exposition in Philadelphia (the winning four top watches, which outclassed all competitors, had been randomly selected out of the mass production line), on display was also the first fully automatic screw making machine. By 1900, with these advances, the accuracy of quality watches, properly adjusted, topped out at a few seconds per day.[29]

From about 1860, key winding was replaced by keyless winding, where the watch was wound by turning the crown. The pin pallet escapement, an inexpensive version of the lever escapement invented in 1876 by Georges Frederic Roskopf was used in cheap mass produced dollar watches, which allowed ordinary workers to own a watch for the first time; other cheap watches used a simplifed version of the duplex escapement, developed by Daniel Buck in the 1870s.

These improvements were mostly originated and applied in the United States, and as a result the American industry ousted that of Switzerland from its long-held position as worldwide leader in the low-to-middle-class market. The Swiss responded, towards the end of the century, by changing their emphasis from economy to quality.

1900–1920 Better materials

During the 20th century, the mechanical design of the watch became standardized, and advances were made in better materials, tighter tolerances, and improved production methods. The bimetallic temperature compensated balance wheel was made obsolete by the discovery of low temperature coefficient alloys invar and elinvar. A balance wheel of invar with a spring of elinvar was almost unaffected by temperature changes, so it replaced the complicated temperature compensated balance. The discovery in 1903 of a process to produce artificial sapphire made jewelling cheap. Bridge construction superseded 3/4 plate construction.

1920–1950 Wristwatches

At the beginning of the century wristwatches were mostly worn by women. In 1904, Brazilian aviator Alberto Santos Dumont asked his friend Louis Cartier to come up with an alternative that would allow him to keep both hands on the controls while timing his performances during flight. Cartier and his master watchmaker, Edmond Jaeger soon came up with the first prototype for a man's wristwatch called the Santos wristwatch. The Santos first went on sale in 1911, the date of Cartier's first production of wristwatches. During the First World War soldiers needed access to their watches while their hands were full. They were given wristwatches, called 'trench watches', which were made with pocketwatch movements, so they were large and bulky and had the crown at the 12 o'clock position like pocketwatches. After the war pocketwatches went out of fashion and by 1930 the ratio of wrist- to pocketwatches was 50 to 1. The first successful self-winding system was invented by John Harwood in 1923.

1950–1969 Electric watches

The first generation electric watches came out during this period. These kept time with a balance wheel powered by a solenoid, or in a few advanced watches that foreshadowed the quartz watch, by a steel tuning fork vibrating at 360 Hz, powered by a solenoid driven by a transistor oscillator circuit. The hands were still moved mechanically by a wheel train. In mechanical watches the self winding mechanism, shockproof balance pivots, and break resistant 'white metal' mainsprings became standard. The jewel craze caused 'jewel inflation' and watches with up to 100 jewels were produced.

1969–present Quartz watches

The introduction of the quartz watch in 1969 was a revolutionary improvement in watch technology.[30] In place of a balance wheel which oscillated at 5 beats per second, it used a quartz crystal resonator which vibrated at 32,768 Hz, driven by a battery powered oscillator circuit. In place of a wheel train to add up the beats into seconds, minutes, and hours, it used digital counters. The higher Q factor of the resonator, along with quartz's low temperature coefficient, resulted in better accuracy than the best mechanical watches, while the elimination of all moving parts made the watch more shock-resistant and eliminated the need for periodic cleaning.

Accuracy increased with the frequency of the crystal used, but so did power consumption. So the first generation watches had low frequencies of a few kilohertz, limiting their accuracy. The power saving use of CMOS logic and LCD displays in the 2nd generation increased battery life and allowed the crystal frequency to be increased to 32,768 Hz resulting in accuracy of 5–10 seconds per month. By the 1980s, quartz watches had taken over most of the watch market from the mechanical watch industry.

See also

References

  1. ^ The original pin-pallet
  2. ^ The Roskopf Watch
  3. ^ Buffat, Eugene, History and Design of the Roskopf Watch
  4. ^ Quartz mechanisms usually have a resonant frequency of 32768 Hz, chosen for ease of use (being 215). Using a simple 15 stage divide-by-two circuit, this is turned into a 1 pulse per second signal responsible for the watch's keeping of time.
  5. ^ "Watchmaking in Europe and China: Watches & Wonders". Richemont. Worldtempus. http://www.worldtempus.com/wt/1/6791/. Retrieved 2007-01-17. 
  6. ^ "History of the Solar Wristwatch". Soluhr.com. http://www.soluhr.com/. Retrieved 2007-01-17. 
  7. ^ The Ten Ten Tenet http://www.snopes.com/business/market/clockhands.asp
  8. ^ "Why Time Stands Still for Watchmakers". New York Times. http://www.nytimes.com/2008/11/28/business/media/28adco.html. Retrieved 2008-11-28. 
  9. ^ Pulsar LED http://www.oldpulsars.com
  10. ^ Pulsar Watches http://www.pulsarwatches.com
  11. ^ Ball, Guy (2003). "Gruen Teletime LCD Watch". LED Watches. http://www.ledwatches.net/photo-pages/gruen-teletime-lcd.htm. Retrieved 2007-01-17. 
  12. ^ "Casio TA-1000 Electronic Clock & Calculator". Magical Gadgets, Sightings & Brags. Pocket Calculator Show. http://pocketcalculatorshow.com/magicalgadget/index3.html#teletime. Retrieved 2007-01-17. 
  13. ^ Russian Space Watches History
  14. ^ FLIGHT-CERTIFIED BY NASA FOR ALL MANNED SPACE MISSIONS: FLIGHT-QUALIFIED BY NASA FOR SPACE MISSIONS:
  15. ^ "Navitimer, the aviator favourite watch". Breitling. http://www.breitling.com/en/models/navitimer/cosmonaute/. Retrieved 2007-01-17. 
  16. ^ "Fiyta.com.cn". Fiyta. http://www.fiyta.com.cn. Retrieved 2007-01-17. 
  17. ^ Europa Star Online article "Watch Industry Questions and Answers: Water-Resistance". Europa Star. VNU eMedia Inc. http://www.europastar.com/europastar/watch_tech/waterresistance.jsp Europa Star Online article. Retrieved 2007-01-17. 
  18. ^ This water resistance classification guide has been developed by the Jewellers and Watchmakers of New Zealand (Inc.) in conjunction with the major watch importers and wholesalers in New Zealand.
  19. ^ Usher, Abbot Payson (1988). A History of Mechanical Inventions. Courier Dover. pp. 305. ISBN 048625593X. http://books.google.com/books?id=xuDDqqa8FlwC&pg=PA305&sig=_SRpwfz0YBAjt2aGxXhmRkZ16GQ. 
  20. ^ White, Lynn Jr. (1966). Medieval Technology and Social Change. New York: Oxford Univ. Press. pp. 126–127. ISBN 0195002660. 
  21. ^ a b c Dohrn-van Rossum, Gerhard (1997). History of the Hour: Clocks and Modern Temporal Orders. Univ. of Chicago Press. pp. 121. ISBN 0-226-15510-2. http://books.google.com/books?id=53K32RiEigMC&pg=PA121&sig=5huN81ukYRbSlxq4MsToTDIXYDY. 
  22. ^ From Cosmographia Pomponii Melae, 1511
  23. ^ Milham, Willis I. (1945). Time and Timekeepers. New York: MacMillan. pp. 133–137. ISBN 0780800087. 
  24. ^ Milham 1945, p.141
  25. ^ a b Perez, Carlos (2001). "Artifacts of the Golden Age, part 1". Carlos's Journal. TimeZone. http://www.timezone.com/library/cjrml/cjrml0006. Retrieved 2007-06-06. 
  26. ^ "Pocketwatch". Encyclopedia of Antiques. Clocks and Watches. Old and Sold. http://www.oldandsold.com/articles02/clocks-p.shtml. 
  27. ^ Milham 1945, p.226
  28. ^ "A Revolution in Timekeeping, part 3". A Walk Through Time. NIST (National Inst. of Standards and Technology). 2002. http://physics.nist.gov/GenInt/Time/revol.html. Retrieved 2007-06-06. 
  29. ^ Milham, 1945, p.475
  30. ^ Perez, Carlos (November 23, 2001). "Prometheus Bound: The final paradigm of horological evolution". Carlos' Journal. TimeZone. http://www.timezone.com/library/cjrml/cjrml0001. Retrieved April 23, 2008. 

External links

lj:iuiu:


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

WATCH (in 0. Eng. woecce, a keeping guard or watching, from wacian, to guard, watch, wacan, to wake), a portable timepiece. This is the most common meaning of the word in its substantival form, and is the subject of the present article. The word, by derivation, means that which keeps watchful or wakeful observation or attention over anything, and hence is used of a person or number of persons whose duty it is to protect anything by vigilance, a guard or sentry; it is thus the term for the body of persons who patrolled the streets, called the hours, and performed the duties of the modern police. The application of the term to a period of time is due to the military division of the night by the Greeks and Romans into "watches" (OvXaxai, vigiliae), marked by the change of sentries; similarly, on shipboard, time is also reckoned by "watches," and the crew is divided into two portions, the starboard and port watches, taking duty alternately.' The transference of the word to that which marks the changing hours is easy.

' In the British navy the twelve hours of the night are divided into three watches of four hours - from eight to twelve the first watch, from twelve to four the middle watch, and from four to eight the morning watch. The twelve hours of the day are divided into four watches, two of four hours - eight to midday, midday to four P.M. - and two of two hours, from four to six and six to eight. These are the "dog watches," and their purpose is to change the turn of the watches every twenty-four hours, so that the men who watch from eight to midnight on one night, shall watch from midnight till 4 AIM. on the next. The "watch bill" is the list of the men appointed to the watch, who are mustered by the officers. Time was originally kept by an hour-glass, every half-hour; the number of the half-hour The invention of portable timepieces dates from the end of the 15th century, and the earliest manufacture of them was in Germany. They were originally small clocks with mainsprings enclosed in boxes; sometimes they were of a globular form and were often called "Nuremberg eggs." Being too large for the pocket they were frequently hung from the girdle. The difficulty with these early watches was the inequality of action of the mainspring. An attempt to remedy this was provided by a contrivance called the stack-freed, which was little more than a sort of rude auxiliary spring. The problem was solved about the years 15251J40 by the invention of the fusee. By this contrivance the mainspring is made to turn a barrel on which is wound a piece of catgut, which in the latter part of the 16th century was replaced by a chain. The other end of the catgut band is wound upon a spiral drum, so contrived that as the spring runs down and becomes weaker the leverage on the axis of the spiral increases, and thus gives a stronger impulse to the works (fig.

In early watches the escapement was the same as in early clocks, namely, a crown wheel and pallets with a balance ending in small weights. Such an escapement was, of course, very imperfect, for since the angular force acting on the balance does not vary with the displacement, the time of oscillation varies with the arc, and this again varies with every variation of the driving force. An immense improvement was therefore effected when the hair-spring was added to the balance, which was replaced by a wheel. This was done about the end of the 17th century. During the 18th century a series of escapements were invented to replace the old crown wheel, ending in the chronometer escapement, and though great improvements in detail have since been made, yet the watch, even as it is to-day, may be called an 18th-century invention.

The watches of the 16th century were usually enclosed in cases ornamented with the beautiful art of that period. Sometimes the case was fashioned like a skull, and the watches were made in the form of octagonal jewels, crosses, purses, little books, dogs, sea-shells, &c., in almost every instance being finely engraved. Queen Elizabeth was very fond of receiving presents, and, as she was also fond of clocks, a number of the gifts presented to her took the form of jewelled watches.

The man to whom watch-making owes perhaps most was Thomas Tompion (1639-1713), who invented the first dead-beat escapement for watches (fig. 2). It consisted of a balance-wheel mounted on an axis of semi-cylindrical form with a notch in it, and a projecting stud. When the teeth of the scape-wheel came against the cylindrical part of the axis they were held from going forward, but when the motion of the axis was reversed, the teeth slipped past the notch and struck the projection, thus giving an impulse. This escapement was afterwards developed by George Graham (1673-1751) into the horizontal cylindrical escapement and into the well-known dead-beat escapement for clocks.

The development of escapements in the 18th century greatly is shown by striking the watch bell, hanging on a beam of the forecastle, or by the mainmast, with the clapper. One stroke is given for each half-hour. Thus 12.30 A.M. is one bell in the middle watch, and 3 A.M. is six bells. The bell was also used to indicate the course of a ship in a fog. A vessel on the starboard tack tolled the bell, a vessel on the port tack beat a drum. The watch guns were fired when setting the watch in the evening and relieving it in the morning. The gun is now only fired at sundown.

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FIG. I.

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improved watches. But a defect still remained, namely, the influence of temperature upon the hair-spring of the balancewheel. Many attempts were made to provide a remedy. John Harrison proposed a curb, so arranged that alterations of temperature caused unequal expansion in two pieces of metal, and thus actuated an arm which moved and mechanically altered the length of the hair-spring, thus compensating the effect of its altered elasticity. But the best solution of the problem was ultimately proposed by Pierre le Roy (1717-1785) and perfected by Thomas Earnshaw (1749-1829). This was to diminish the inertia of the balance-wheel in proportion to the increase of temperature, by means of the unequal expansion of the metals composing the rim.

Invention in watches was greatly stimulated by the need of a good timepiece for finding longitudes at sea, and many successive rewards were offered by the government for watches which would keep accurate time and yet be able to bear the rocking motion of a ship. The difficulty ended by the invention of the chronometer, which was so perfected towards the early part of the 19th century as to have even now undergone but little change of form. In fact the only great triumph of later years has been the invention of watch-making machinery, whereby the price is so lowered that an excellent watch (in a brass case) can now be purchased for about £2 and a really accurate time-keeper for about £18.

A modern watch consists of a case and framework containing the four essential parts of every timepiece, namely, a mainspring and apparatus for winding it up, a train of wheels with hands and a face, an escapement and a balance-wheel and hair-spring. We shall describe these in order.

The Mainspring

As has been said, the mainspring of an oldfashioned watch was provided with a drum and fusee so as to equalize its action on the train. An arrangement was provided to prevent overwinding, consisting of a hook which when the chain was nearly wound up was pushed aside so as to engage a pin, and thus prevent further winding (see fig. I). Another arrangement for watches without a fusee, called a Geneva stop, consists of a wheel with one tooth affixed to the barrel arbour, working into another with only four or five teeth. This allows the barrel arbour only to be turned round four or five times.

The "going-barrel," which is fitted to most modern watches, contains no fusee, but the spring is delicately made to diminish in size from one end to the other, and it is wound up for only a few turns, so that the force derived from it does not vary very substantially. The unevenness of drive is in modern watches sought to be counteracted by the construction of the escapement and balance-wheel.

Watches used formerly to be wound with a separate key. They are now wound by a key permanently fixed to the case. The depression of a small knob gears the winding key with the hands so as to enable them to be set. With this contrivance watches are well protected against the entry of dust and damp.

Watch Escapements

The escapements that have come into practical use are - (I) the old vertical escapement, now disused; (2) the lever, very much the most common in English watches; (3) the horizontal or cylinder, which is equally common in foreign watches, though it was of English invention; (4) the duplex, which used to be more in fashion for first-rate watches than it is now; and (5) the detached or chronometer escapement, so called because it is always used in marine chronometers.

The vertical escapement is simply the original clock escapement adapted to the position of the wheels in a watch and the balance, in the manner exhibited in fig. 3. As it requires considerable thickness in the watch, is inferior in going to all the others and is no cheaper than the level escapement can now be made, it has gone out of use.

The lever escapement, as it is now universally made, was brought into use late in the 18th century by Thomas Mudge. Fig. 4 shows its action. The position of the lever with reference to the pallets is immaterial in principle, and is only a question of convenience in the arrangement; but it is generally such as we have given it. The principle is the same as in the dead-beat clock escapement, with the advantage that there is no friction on the dead faces of the pallets beyond what is necessary for locking. The reason why this friction cannot be avoided with a pendulum is that its arc of vibration is so small that the requisite depth of intersection cannot be got between the two circles described by the end S of the lever and any pin in the pendulum which would work into it; whereas, in a watch, the pin P, which is set in a cylinder on the verge of the balance, does not generally slip out of the nick in the end of the lever until the balance has got 15° past its middle position. The pallets are undercut a little, as it is called, i.e. the dead faces are so sloped as to give a little recoil the wrong way, or slightly to resist the unlocking, because otherwise there would be a risk that a shake of the watch would let a tooth escape while the pin is disengaged from the lever. There is also a further provision added for safety. In the cylinder which carries the impulse pin P there is a notch just in front of P, into which the other pin S on the lever fits as they pass; but when the notch has got past the cylinder it would prevent the lever from returning, because the safety-pin S cannot pass except through the notch, which is only in the position for letting it pass at the same time that the impulse-pin is engaged in the lever. The pallets in a lever escapement (except bad and cheap ones) are always jewelled, and the scape-wheel is of brass. FIG. 4. The staff of the lever also has jewelled pivot holes in expensive watches, and the scape-wheel has in all good ones. The holes for the balance-pivots are now always jewelled. The scape-wheel in this and most of the watch escapements generally beats five times in a second, in large chronometers four times; and the wheel next to the scape-wheel carries the seconds-hand.

Fig. 5 is a plan of the horizontal or cylinder escapement, cutting through the cylinder, which is on the verge of the balance, at the level of the tops of the teeth of the escape-wheel; for the triangular pieces A, B are not flat projections in the same plane as the teeth, but are raised on short stems above the plane of the wheel; and still more of the cylinder than the portion shown at ACD is cut away where the wheel itself has to pass. The author of this escapement was G. Graham, and it resembles his dead escapements in clocks in principle more than the lever escapement does, though much less in appearance, because in this escapement there is the dead friction of the teeth against the cylinder, first on the outside, as here represented, and then on the inside, as shown by the dotted lines, during the whole vibration of the balance, except that portion which belongs to the impulse. The impulse is given by the oblique outside edges Aa, Bb of the teeth against the edges A, D of the cylinder alternately. The portion of the cylinder which is cut away at the point of action is about 30° less than the semicircle. The cylinder itself is made either of steel or ruby, and, from the small quantity of it which is left at the level of the wheel, it is very delicate; and, probably this has been the main reason why, although it is an English invention, it has been most entirely abandoned by the English watchmakers in favour of the lever, which was originally a French invention, though very much improved by Mudge, for before his invention the lever had a rack or portion of a toothed wheel on its end, working into a pinion on the balance verge, and consequently it was affected by the dead friction, and that of this wheel and pinion besides. This used to be called the rack lever, and Mudge's the detached lever; but, the rack lever being now quite obsolete, the word "detached" has become confined to the chronometer, to which it is more appropriate, as will be seen presently. The Swiss watches have almost universally the horizontal escapement. It is found that - for some reason which is apparently unknown, as the rule certainly does not hold in cases seemingly analogous - a steel scape-wheel acts better in this escapement than a brass one, although in some other cases steel upon steel, or even upon a ruby, very soon throws off a film of rust, unless they are kept well oiled, while brass and steel, or stone, will act with scarcely any oil at all, and in some cases with none.

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The duplex escapement (fig. 6) is probably so called because there is a double set of teeth in the scape-wheel - the long ones (like those of the lever escapement in shape) for locking only, and short ones (or rather upright pins on the rim of the wheel) for giving the impulse to the pallet P on the verge of the balance. It is a single-beat escapement; i.e. the balance only receives the impulse one way, or at every alternate beat, as in the chronometer escapement. When the balance is turning in the direction marked by the arrow, and arrives at the position in which the dotted tooth b has its point against the triangular notch V, the tooth end slips into the notch, and, as the verge turns farther round, the tooth goes on with it till at last it escapes when the tooth has got into the position A; and by that time the long tooth or pallet which projects from the verge has moved from p to P, and just come in front of the pin T, which stands on the rim of the scape-wheel, and which now begins to push against P, and so gives the impulse until it also escapes when it has arrived at t; and the wheel is then stopped by the next tooth B having got into the position b, with its point resting against the verge, and there is dead friction between them, and this friction is lessened by the FIG. 3.

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FIG. 6.

distance of the points of the long teeth from the centre of the scapewheel. As the balance turns back, the nick V goes past the end of the tooth and in consequence of its smallness it passes without visibly affecting the motion of the scape-wheel, though of course it does produce a very slight shake in passing. It is evident that, if it did not pass, the tooth could not get into the nick for the next escape. The objection to this escapement is that it requires very great delicacy of adjustment, and the watch also requires to be worn care: fully; for, if by accident the balance is once stopped from swinging back far enough to carry the nick V past the tooth end, it will stop altogether, as it will lose still more of its vibration the next time from receiving no impulse. The performance of this escapement, when well made, and its independence of oil, are nearly equal to those of the detached escapement; but, as lever watches are now made sufficiently good for all but astronomical purposes, for which chronometers are used, and they are cheaper both to make and to mend than duplex ones, the manufacture of duplex watches has almost disappeared.

The chronometer or detached escapement is shown at fig. 7 in the form to which it was brought by Earnshaw, and in which it has remained ever since, with the very slight difference that the pallet P, on which the impulse is given (corresponding exactly to the pallet P in the duplex escapement), is now generally set in a radial direction from the verge, whereas Earnshaw made it sloped backward, or undercut, like the scape-wheel teeth. The early history of escapements on this principle does not seem to be very clear. They appear to have originated in France; but there is no doubt that they were considerably improved by the first Arnold (John), who died in 1799. Earnshaw's watches, however, generally beat his in trials.

In fig. 7 the small tooth or cam V, on the verge of the balance, is just on the point of unlocking the detent DT from the tooth T of the scape-wheel; and the tooth A will immediately begin to give the impulse on the pallet P, which, in good chronometers, is always a jewel set in the cylinder; the tooth V is also a jewel. This part of the action is so evident as to require no further notice. When the balance returns, the tooth V has to get past the end of the detent, without disturbing it; for, as soon as it has been unlocked, it falls against the banking-pin E, and is ready to receive the next tooth B, and must stay there until it is again unlocked. It ends, or rather begins, in a stiffish spring, which is screwed to the block D on the watch frame, so that it moves without FIG. 7. any friction of pivots, like a pendulum. The passing is done by means of another spring VT, called the passing spring, which can be pushed away from the body of the detent towards the left, but cannot be pushed the other way without carrying the detent with it. In the back vibration, therefore, as in the duplex escapement, the balance receives no impulse, and it has to overcome the slight resistance of the passing spring besides; but it has no other friction, and is entirely detached from the scape-wheel the whole time, except when receiving the impulse. That is also the case in the lever escapement; but the impulse in that escapement is given obliquely, and consequently with a good deal of friction; and, besides, the scape-wheel only acts on the balance through the intervention of the lever, which has the friction of its own pivots and of the impulse pin. The locking-pallet T is undercut a little for safety, and is also a jewel in the best chronometers; and the passing spring is usually of gold. In the duplex and detached escapements, the timing of the action of the different parts requires great care, i.e. the adjusting them so that each may be ready to act exactly at the right time; and it is curious that the arrangement which would be geometrically correct, or suitable for a very slow motion of the balance, will not do for the real motion. If the pallet P were really set so as just to point to the tooth A in both escapements at the moment of unlocking (as it has been drawn, because otherwise it would look as if it could not act at all), it would run away some distance before the tooth could catch it, because in the duplex escapement the scape-wheel is then only moving slowly, and in the detached it is not moving at all, and has to start from rest. The pallet P is therefore, in fact, set a little farther back, so that it may arrive at the tooth A just at the time when A is ready for it, without wasting time and force in running after it. The detached escapement has also been made on the duplex plan of having long teeth for the locking and short ones or pins nearer the centre for the impulse; but the advantages do not appear to be worth the additional trouble, and the force required for unlocking is not sensibly diminished by the arrangement, as the spring D must in any case be fairly stiff, to provide against the watch being carried in the position in which the weight of the detent helps to unlock it.

An escapement called the lever chronometer has been several times reinvented, which implies that it has never come into general use. It is a combination of the lever as to the locking and the chronometer as to the impulse. It involves a little drop and therefore waste of force as a tooth of the wheel just escapes at the "passing" beat where no impulse is given. But it should be understood that a single-beat escapement involves no more loss of force and the escape of no more teeth than a double one, except the slight drop in the duplex and this lever chronometer or others on the same principle.

There have been several contrivances for remontoire escapements; but there are defects in all of them; and there is not the same advantage to be obtained by giving the impulse to a watch-balance by means of some other spring instead of the mainspring as there is in turret-clocks, where the force of the train is liable to very much greater variations than in chronometers or small clocks.

The balance-wheel and hair-spring consist of a small wheel, usually of brass, to which is affixed a spiral, or in chronometers a helical, spring. This wheel swings through an angle of from 180° to 270° and its motions are approximately isochronous. The time of the watch can be regulated by an arm to which is attached a pair of pins which embrace the hair-spring at a point near its outer end, and by the movement of which the spring can be lengthened or shortened. The first essential in a balance-wheel is that its centre of gravity should be exactly in the axis, and that the centre of gravity of the hair-spring should also be in the axis of the balance-wheel. True isochronism is disturbed by variations in the driving force of the train or by variations in temperature, and also by variations in barometric pressure. Isochronism is produced in the first place by a proper shape of the spring and its overcoil It is usual to time the watch's going when the mainspring is partly wound up, as well as when it is fully wound up, and then by removing parts of the hair-spring to get such an adjustment that the rate is not influenced by the lesser or greater extent to which the watch has been wound. The variations in length and still more in elasticity caused in a hairspring by changes of temperature were for long not only a trouble to watchmakers but a bar to the progress of the art. A pendulum requires scarcely any compensation except for its own elongation by heat; but a balance requires compensation, not only for its own expansion, which increases its moment of inertia just like the pendulum, but far more on account of the decrease in the strength of the spring under increased heat. E. G. Dent, in a pamphlet on compensation balances, gave the following results of some experiments with a glass balance, which he used for the purpose on account of its less expansibility than a metal one: at 32° F., 3606 vibrations in an hour; at 66°, 3598.5; and at loo°, 3599. If therefore it had been adjusted to go right (or 3600 times in an hour) at 32°. it would have lost 72 and 82 seconds an hour, or more than three minutes a day, for each successive increase of 34°, which is about fifteen times as much as a common wire pendulum would lose under the same increase of heat; and if a metal balance had been used instead of a glass one the difference would have been still greater.

The necessity for this large amount of compensation having arisen from the variation of the elasticity of the spring, the first attempts at correcting it were by acting on the spring itself in the manner of a common regulator. Harrison's compensation consisted of a compound bar of brass and steel soldered together, having one end fixed to the watch-frame and the other carrying two curb pins which embraced the spring. As the brass expands more than the steel, any increase of heat made the bar bend; and so, if it was set the right way, it carried the pins along the spring, so as to shorten it. This contrivance is called a compensation curb; and it has often been reinvented, or applied in a modified form. But there are two objections to it: the motion of the curb pins does not correspond accurately enough to the variations in the force of the spring, and it disturbs the isochronism, which only subsists at certain definite lengths of the spring.

The compensation which was next invented left the spring untouched, and provided for the variations of temperature by the construction of the balance itself. Fig. 8 shows the plan of the ordinary compensation balance. Each portion of the rim of the balance is composed of an t a inner bar of steel with an outer one of brass soldered, or rather melted, upon it, and carrying the weights b, b, which are screwed to it. As the temperature increases, the brass expanding must bend the steel inwards, and so carries the weights farther in, and diminishes the moment of inertia of the balance, the decrease of rate being inversely as the diameter of the balance-wheel. The metals are generally soldered together by pouring melted brass round a solid steel disk, and the whole is afterwards turned and filed away till it leaves only the crossbar in the middle lying flat and the two portions of the rim standing edgeways. The first person to practise this method of uniting them appears to have been either Thomas Earnshaw or Pierre le Roy.

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The adjustment of a balance for compensation can only be done by trial, and requires a good deal of time. It must be done independently of that for time - the former by shifting the weights, because the nearer they are to the crossbar the less distance they will move over as the rim bends with them. The timing is done by screws with heavy heads (t, t, fig. 8), which are just opposite to the ends of the crossbar, and consequently not affected by the bending of the rim; other screws are also provided round the rim for adjusting the moment of inertia and centre of gravity of the balance-wheel. The compensation may be done approximately by FIG. 8.

the known results of previous experience with similar balances; and many watches are sold with compensation balances which have never been tried or adjusted, and sometimes with a mere sham compensation balance, not even cut through.

Secondary Compensation

When chronometers had been brought to great perfection it was perceived that there was a residuary error, which was due to changes of temperature, but which no adjustment of the compensation would correct. The cause of the secondary error is that as the temperature rises the elasticity of the spring decreases, and therefore its accelerating force upon the balancewheel diminishes. Hence the watch tends to go slower.

In order to compensate this the split rim of the balance-wheel is made with the more expansible metal on the outside, and therefore tends to curl inwards with increase of temperature, thus diminishing the moment of inertia of the wheel. Now the rate of error caused by the increase of temperature of the spring varies approximately with the temperature according to a certain law, but the rate of correction due to the diminution of the moment of inertia caused by the change of form of the rim of the wheel does not alter proportionally, but according to a more complex law of its own, varying more rapidly with cold than with heat, so that if the rate of the chronometer is correct, say, at 30° F. and also at 90° F., it will gain at all intermediate temperatures, the spring being thus under-corrected for high temperatures and over-corrected for low. Attempts have been made by alterations of shape of the balance-wheel to harmonize the progress of the error with the progress of the correction, but not with very conspicuous success.

We shall give a short description of the principal classes of inventions for this purpose. The first disclosed was that of J. S. Eiffe (sometimes attributed to Robert Molyneux), which was communicated to the astronomer-royal in 1835. In one of several methods proposed by him a compensation curb was used; and though, for the reasons given before, this will not answer for the primary compensation, it may for the secondary, where the motion required is very much smaller. In another the primary compensation bar, or a screw in it, was made to reach a spring set within it with a small weight attached at some mean temperature, and, as it bent farther in, it carried this secondary compensation weight along with it. The obvious objection to this is that it is discontinuous; but the whole motion is so small, not more than the thickness of a piece of paper, that this and other compensations on the same principle appear to have been on some occasions quite successful.

Another large class of balances, all more or less alike, may be represented by E. J. Dent's, which came next in order of time. He described several forms of his invention; the following description applies to the one he thought the best. In fig. 9 the flat crossbar rr is itself a compensation bar which bends upwards under increased heat; so that, if the weights v, v were merely set upon upright stems rising from the ends of the crossbar, they would approach the axis when that bar bends upwards. But, instead of the stems rising from the crossbar, they rise from the two secondary compensation pieces stu, in the form of staples, which are set on the crossbar; and, as these secondary pieces themselves also bend upwards, they make the weights approach the axis more rapidly FIG. 9. as the heat increases; and by a proper adjustment of the height of the weights on the stems the moment of inertia of the balance can be made to vary in the proper ratio to the variation of the intensity of the spring. The cylindrical spring stands above the crossbar and between the staples.

Fig. Io represents E. T. Loseby's mercurial compensation balance. Besides the weights D, D, set near the end of the primary compensation bars B, B, there are small bent tubes FE, FE with mercury in them, like a thermometer, the bulbs being at F, F. As the heat increases, not only do the primary weights D, D and the bulbs F, F approach the centre of the balance, but some of the mercury is driven along the tube, thus carrying some more of the weight towards the centre, at a ratio increasing more rapidly than the temperature. The tubes are sealed at the thin end, with a little air included. The action is here equally continuous with Dent's, and the adjustments for primary and secondary compensation are apparently more independent of each other; and this modification of Le Roy's use of mercury for compensated balances (which does not appear to have answered) is certainly very elegant and ingenious. Nevertheless an analysis of the Greenwich lists for seven years of Loseby's trials proved that the advantage of this method over the others was more theoretical than practical; Dent's compensation was the most successful of all in three years out of the seven, and Loseby's in only one.

Loseby's method has never been adopted by any other chronometermaker, whereas the principles both of Eiffe's and of Dent's methods have been adopted by several other makers.

A few chronometers have been made with glass balance-springs, which have the advantage of requiring very little primary and no secondary compensation, on account of the very small variation in their elasticity, compared with springs of steel or any other metal.

One of the most important and interesting attempts to correct the temperature errors of a hair-spring by a series of corresponding temperature changes in the moment of inertia of the balance-wheel has been made by means of the use of the nickel-steel compound called invar, which, on account of its very small coefficient of expansion, has been of great use for pendulum rods. In a memoir published in 1904 at Geneva, Dr Charles Guillaume, the inventor of invar, shows that in order to get a true secondary compensation what is wanted is a material having the property of causing the curve of the rim of the wheel to change at an increasing rate as compared with changes in the temperature. This is found in those specimens of invar in which the second coefficient of expansion is negative, i.e. which are less dilatable at higher temperatures than at lower ones. It is satisfactory to add that such balance-wheels have been tried successfully on chronometers, and notably in a deck watch by Paul Ditisheim of Neuchatel, who has made a chronometer with a tourbillon escapement and an invar balance-wheel, which holds the highest record ever obtained by a watch of its class.

It is obvious that in order that a watch may keep good time the centre of gravity of the balance-wheel and hair-spring must be exactly in the axis; for if this were not the case, then the wheel would act partly like a pendulum, so that the time would vary according as the watch was placed in different positions. It is exceedingly difficult to adjust a watch so that these "position errors" are eliminated. Accordingly it has been proposed to neutralize their effect by mounting the balance-wheel and hairspring upon a revolving carriage which shall slowly rotate, so that in succession every possible position of the balance-wheel and spring is assumed, and thus errors are averaged and mutually destroy one another. This is called the tourbillon escapement. There are several forms of it, and watches fitted with it often keep excellent time.

Stop watches or chronographs are of several kinds. In the usual and simplest form there is a centre seconds hand which normally remains at rest, but which, when the winding handle is pressed in, is linked on to the train of the watch and begins to count seconds, usually by fifths. A second pressure arrests its path, enabling the time to be taken since the start. A third pressure almost instantaneously brings the seconds hand back to zero, this result being effected by means of a heart-shaped cam which, when a lever presses on it instantaneously, flies round to zero position. The number of complete revolutions of the seconds hand, i.e. minutes, is recorded on a separate dial.

Calendar work on watches is, of course, fatal to great accuracy of time-keeping, and is very complicated. A watch is made to record days of the week and month, and to take account of leap years usually by the aid of star-wheels with suitable pauls and stops. The type of this mechanism is to be found in the calendar motion of an ordinary grandfather's clock.

Watches have also been made containing small musical boxes and arranged with performing figures on the dials. Repeaters are striking watches which can be made at will to strike the hours and either the quarters or the minutes, by pressing a handle which winds up a striking mechanism. They were much in vogue as a means of discovering the time in the dark before the invention of lucifer matches, when to obtain a light by means of flint and steel was a troublesome affair.

From what has been said it will be seen that for many years the form of escapements and balance-wheels has not greatly altered. The great improvements which modern science has been able to effect in watches are chiefly in the use of new metals and in the employment of machinery, which, though they have altered the form but little, have effected an enormous revolution in the price. The cases of modern watches are made sometimes of steel, artificially blackened, sometimes of compounds of aluminium and copper, known as aluminium gold. Silver is at present being less employed than formerly. The hair-springs are often of palladium in order to render the watch non-magnetizable. An ordinary watch, if the wearer goes near a dynamo, will probably become magnetized and quite useless for time-keeping. One of the simplest cures for this accident is to twirl it rapidly round while retreating from the dynamo and to continue the motion till at a considerable distance. The use of invar has been already noticed.

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It would be impossible to enumerate, still more to describe, the vast number of modern machines that have been invented for making watches. It may be said briefly that every part, including the toothed wheels, is stamped out of metal. The stamped pieces are then finished by cutters and with milling machinery. Each machine as a rule only does one operation, so that a factory will cdntain many hundreds of different sorts of machines. The modern watchmaker therefore is not so much of a craftsman as an engineer. The effect of making all the parts of a watch by machinery is that each is interchangeable, so that one part will fit any watch. It is FIG. IO.

not an easy thing to secure this result, for as the machines are used the cutting edges wear down and require regrinding and resetting. Hence a tool is not allowed to make more than a given quantity of parts without being examined and readjusted, and from time to time the pieces being put out are tested with callipers. The parts thus made are put in groups and sorted into boxes, which are then given over to the watch-adjusters, who put the parts together and make the watch go. The work of adjustment for common watches is a simple matter. But expert adjusters select their pieces, measure them and correct errors with their tools. The finest watches are thus largely machine-made, but hand-finished. The prejudice against machine-made watches has been very strong in England, but is dying out - not, unfortunately, before much of the trade has been lost. A flourishing watch industry exists in Switzerland in the neighbourhood of Neuchatel. A watch in a stamped steel case can now be made for about five shillings. There is no reason why in such a neighbourhood as Birmingham the English watch industry should not revive.

The use of jewelled bearings for watch pivots was introduced by Nicholas Facio about the beginning of the 18th century. Diamonds and sapphires are usually employed and pierced either by diamond drills or by drills covered with diamond dust. Rubies are not a very favourite stone for jewels, but as they and sapphires can now be made artificially for about two shillings a carat the difficulty of obtaining material for watch jewelling has nearly disappeared.

Watches have also been fitted with machinery whereby electric contacts are made by them at intervals, so that if wires are led to and away from them, they can be made to give electric signals and thus mark dots at regular intervals on a moving strip of paper.

As in the case of clocks, the accuracy of going of a watch is estimated by observation of the variations of its mean daily rate. This is officially done at Kew Observatory, near Richmond, and also for admiralty purposes at Greenwich. At Richmond watches are divided into two classes, A and B. For an A certificate the trials last for forty-five days, and include tests in temperatures varying from 40° to 90° F., going in every position with dial vertical, face up and face down. The average daily departure from the mean daily rate, that is the average error due to irregular departures from the average going rate, must not exceed 2 seconds a day except where due to position, when it may amount to 5 seconds. The errors should not increase more than 0.3 seconds a day for each I° F. The trial for the B certificate is somewhat similar but less severe. Chronometers are put through trials lasting 55 days, and their average error from mean rate is expected not to exceed 0.5 seconds per diem. The fees for these tests are various sums from two guineas downwards. In estimating the time-keeping qualities of a watch or clock, the error of rate is of no consequence. It is simply due to the timekeeper going too fast or too slow, and this can easily be corrected. What is wanted for a good watch is that the rate, whatever it is, shall be constant. The daily error is of no account provided it is a uniform daily error and not an irregular one. Hence the object of the trials is to determine not merely the daily rate but the variations of the daily rate, and on the smallness of these the value of the watch as a time-keeper depends. (G.; H. H.C.)


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