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1 Breguet, Abraham-Louis
SUBJECT AREA: Horology[br]baptized 10 January 1747 Neuchâtel, Switzerlandd. 17 September 1823 Paris, France[br]Swiss clock-and watchmaker who made many important contributions to horology.[br]When Breguet was 11 years old his father died and his mother married a Swiss watchmaker who had Paris connections. His stepfather introduced him to horology and this led to an apprenticeship in Paris, during which he also attended evening classes in mathematics at the Collège Mazarin. In 1775 he married and set up a workshop in Paris, initially in collaboration with Xavier Gide. There he established a reputation among the aristocracy for elegant and innovative timepieces which included a perpétuelle, or self-winding watch, which he developed from the ideas of Perrelet. He also enjoyed the patronage of Marie Antoinette and Louis XVI. During the French Revolution his life was in danger and in 1793 he fled to Neuchâtel. The two years he spent there comprised what was intellectually one of his most productive periods and provided many of the ideas that he was able to exploit after he had returned to Paris in 1795. By the time of his death he had become the most prestigious watchmaker in Europe: he supplied timepieces to Napoleon and, after the fall of the Empire, to Louis XVIII, as well as to most of the crowned heads of Europe.Breguet divided his contributions to horology into three categories: improvements in appearance and functionality; improvements in durability; and improvements in timekeeping. His pendule sympathique was in the first category and consisted of a clock which during the night set a watch to time, regulated it and wound it. His parachute, a spring-loaded bearing, made a significant contribution to the durability of a watch by preventing damage to its movement if it was dropped. Among the many improvements that Breguet made to timekeeping, two important ones were the introduction of the overcoil balance spring and the tourbillon. By bending the outside end of the balance spring over the top of the coils Breguet was able to make the oscillations of the balance isochronous, thus achieving for the flat spring what Arnold had already accomplished for the cylindrical balance spring. The timekeeping of a balance is also dependent on its position, and the tourbillon was an attempt to average-out positional errors by placing the balance wheel and the escapement in a cage that rotated once every minute. This principle was revived in a simplified form in the karussel at the end of the nineteenth century.[br]Principal Honours and DistinctionsHorloger de la marine 1815. Chevalier de la Légion d'honneur 1815.BibliographyBreguet gathered information for a treatise on horology that was never published but which was later plagiarized by Louis Moinet in his Traité d'horlogerie, 1848.Further ReadingG.Daniels, 1974, The An of Breguet, London (an account of his life with a good technical assessment of his work).DV -
2 Breguet, Louis
SUBJECT AREA: Aerospace[br]b. 2 January 1880 Paris, Franced. 4 May 1955 Paris, France[br]French aviation pioneer who built a helicopter in 1907 and designed many successful aircraft.[br]The Breguet family had been manufacturing fine clocks since before the French Revolution, but Louis Breguet and his brother Jacques used their mechanical skills to produce a helicopter, or "gyroplane" as they named it. It was a complex machine with four biplane rotors (i.e. thirty-two lifting surfaces). Louis Breguet had carried out many tests to determine the most suitable rotor design. The Breguet brothers were assisted by Professor Charles Richet and the Breguet-Richet No. 1 was tested in September 1907 when it succeeded in lifting itself, and its pilot, to a height of 1.5 metres. Unfortunately, the gyroplane was rather unstable and four helpers had to steady it; consequently, the flight did not qualify as a "free" flight. This was achieved two months later, also in France, by Paul Cornu who made a 20-second free flight.Louis Breguet turned his attention to aeroplane design and produced a tractor biplane when most other biplanes followed the Wright brothers' layout with a forward elevator and pusher propeller. The Breguet I made quite an impression at the 1909 Reims meeting, but the Breguet IV created a world record the following year by carrying six people. During the First World War the Breguet Type 14 bomber was widely used by French and American squadrons. Between the First and Second World Wars a wide variety of designs were produced, including flying boats and another helicopter, the Breguet- Dorand Gyroplane which flew for over one hour in 1936. The Breguet company survived World War II and in the late 1940s developed a successful four-engined airliner/transport, the Deux-Ponts, which had a bulbous double-deck fuselage.Breguet was an innovative designer, although his designs were functional rather than elegant. He was an early advocate of metal construction and developed an oleo- (oil-spring) undercarriage leg.[br]Bibliography1925, Le Vol à voile dynamique des oiseaux. Analyse des effets des pulsations du vent sur la résultante aérodynamique moyenne d'un planeur, Paris.Further ReadingP.Faure, 1938, Louis Breguet, Paris (biography).C.H.Gibbs-Smith, 1965, The Invention of the Aeroplane 1799–1909, London (provides a careful analysis of Breguet's early aircraft).JDS -
3 Hetzel, Max
[br]b. 5 March 1921 Basle, Switzerland[br]Swiss electrical engineer who invented the tuning-fork watch.[br]Hetzel trained as an electrical engineer at the Federal Polytechnic in Zurich and worked for several years in the field of telecommunications before joining the Bulova Watch Company in 1950. At that time several companies were developing watches with electromagnetically maintained balances, but they represented very little advance on the mechanical watch and the mechanical switching mechanism was unreliable. In 1952 Hetzel started work on a much more radical design which was influenced by a transistorized tuning-fork oscillator that he had developed when he was working on telecommunications. Tuning forks, whose vibrations were maintained electromagnetically, had been used by scientists during the nineteenth century to measure small intervals of time, but Niaudet- Breguet appears to have been the first to use a tuning fork to control a clock. In 1866 he described a mechanically operated tuning-fork clock manufactured by the firm of Breguet, but it was not successful, possibly because the fork did not compensate for changes in temperature. The tuning fork only became a precision instrument during the 1920s, when elinvar forks were maintained in vibration by thermionic valve circuits. Their primary purpose was to act as frequency standards, but they might have been developed into precision clocks had not the quartz clock made its appearance very shortly afterwards. Hetzel's design was effectively a miniaturized version of these precision devices, with a transistor replacing the thermionic valve. The fork vibrated at a frequency of 360 cycles per second, and the hands were driven mechanically from the end of one of the tines. A prototype was working by 1954, and the watch went into production in 1960. It was sold under the tradename Accutron, with a guaranteed accuracy of one minute per month: this was a considerable improvement on the performance of the mechanical watch. However, the events of the 1920s were to repeat themselves, and by the end of the decade the Accutron was eclipsed by the introduction of quartz-crystal watches.[br]Principal Honours and DistinctionsNeuchâtel Observatory Centenary Prize 1958. Swiss Society for Chronometry Gold Medal 1988.Bibliography"The history of the “Accutron” tuning fork watch", 1969, Swiss Watch \& Jewellery Journal 94:413–5.Further ReadingR.Good, 1960, "The Accutron", Horological Journal 103:346–53 (for a detailed technical description).J.D.Weaver, 1982, Electrical \& Electronic Clocks \& Watches, London (provides a technical description of the tuning-fork watch in its historical context).DV -
4 Dassault (Bloch), Marcel
SUBJECT AREA: Aerospace[br]b. 22 January 1892 Paris, Franced. 18 April 1986 Paris, France[br]French aircraft designer and manufacturer, best known for his jet fighters the Mystère and Mirage.[br]During the First World War, Marcel Bloch (he later changed his name to Dassault) worked on French military aircraft and developed a very successful propeller. With his associate, Henri Potez, he set up a company to produce their Eclair wooden propeller in a furniture workshop in Paris. In 1917 they produced a two-seater aircraft which was ordered but then cancelled when the war ended. Potez continued to built aircraft under his own name, but Bloch turned to property speculation, at which he was very successful. In 1930 Bloch returned to the aviation business with an unsuccessful bomber followed by several moderately effective airliners, including the Bloch 220 of 1935, which was similar to the DC-3. He was involved in the design of a four-engined airliner, the SNCASE Languedoc, which flew in September 1939. During the Second World War, Bloch and his brothers became important figures in the French Resistance Movement. Marcel Bloch was eventually captured but survived; however, one of his brothers was executed, and after the war Bloch changed his name to Dassault, which had been his brother's code name in the Resistance. During the 1950s, Avions Marcel Dassault rapidly grew to become Europe's foremost producer of jet fighters. The Ouragon was followed by the Mystère, Etendard and then the outstanding Mirage series. The basic delta-winged Mirage III, with a speed of Mach 2, was soon serving in twenty countries around the world. From this evolved a variable geometry version, a vertical-take-off aircraft, an enlarged light bomber capable of carrying a nuclear bomb, and a swept-wing version for the 1970s. Dassault also produced a successful series of jet airliners starting with the Fan Jet Falcon of 1963. When the Dassault and Breguet companies merged in 1971, Marcel Dassault was still a force to be reckoned with.[br]Principal Honours and DistinctionsGuggenheim Medal. Deputy, Assemblée nationale 1951–5 and 1958–86.Bibliography1971, Le Talisman, Paris: Editions J'ai lu (autobiography).Further Reading1976, "The Mirage Maker", Sunday Times Magazine (1 June).Jane's All the World's Aircraft, London: Jane's (details of Bloch and Dassault aircraft can be found in various years' editions).JDSBiographical history of technology > Dassault (Bloch), Marcel
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5 Brunel, Isambard Kingdom
SUBJECT AREA: Civil engineering, Land transport, Mechanical, pneumatic and hydraulic engineering, Ports and shipping, Public utilities, Railways and locomotives[br]b. 9 April 1806 Portsea, Hampshire, Englandd. 15 September 1859 18 Duke Street, St James's, London, England[br]English civil and mechanical engineer.[br]The son of Marc Isambard Brunel and Sophia Kingdom, he was educated at a private boarding-school in Hove. At the age of 14 he went to the College of Caen and then to the Lycée Henri-Quatre in Paris, after which he was apprenticed to Louis Breguet. In 1822 he returned from France and started working in his father's office, while spending much of his time at the works of Maudslay, Sons \& Field.From 1825 to 1828 he worked under his father on the construction of the latter's Thames Tunnel, occupying the position of Engineer-in-Charge, exhibiting great courage and presence of mind in the emergencies which occurred not infrequently. These culminated in January 1828 in the flooding of the tunnel and work was suspended for seven years. For the next five years the young engineer made abortive attempts to find a suitable outlet for his talents, but to little avail. Eventually, in 1831, his design for a suspension bridge over the River Avon at Clifton Gorge was accepted and he was appointed Engineer. (The bridge was eventually finished five years after Brunel's death, as a memorial to him, the delay being due to inadequate financing.) He next planned and supervised improvements to the Bristol docks. In March 1833 he was appointed Engineer of the Bristol Railway, later called the Great Western Railway. He immediately started to survey the route between London and Bristol that was completed by late August that year. On 5 July 1836 he married Mary Horsley and settled into 18 Duke Street, Westminster, London, where he also had his office. Work on the Bristol Railway started in 1836. The foundation stone of the Clifton Suspension Bridge was laid the same year. Whereas George Stephenson had based his standard railway gauge as 4 ft 8½ in (1.44 m), that or a similar gauge being usual for colliery wagonways in the Newcastle area, Brunel adopted the broader gauge of 7 ft (2.13 m). The first stretch of the line, from Paddington to Maidenhead, was opened to traffic on 4 June 1838, and the whole line from London to Bristol was opened in June 1841. The continuation of the line through to Exeter was completed and opened on 1 May 1844. The normal time for the 194-mile (312 km) run from Paddington to Exeter was 5 hours, at an average speed of 38.8 mph (62.4 km/h) including stops. The Great Western line included the Box Tunnel, the longest tunnel to that date at nearly two miles (3.2 km).Brunel was the engineer of most of the railways in the West Country, in South Wales and much of Southern Ireland. As railway networks developed, the frequent break of gauge became more of a problem and on 9 July 1845 a Royal Commission was appointed to look into it. In spite of comparative tests, run between Paddington-Didcot and Darlington-York, which showed in favour of Brunel's arrangement, the enquiry ruled in favour of the narrow gauge, 274 miles (441 km) of the former having been built against 1,901 miles (3,059 km) of the latter to that date. The Gauge Act of 1846 forbade the building of any further railways in Britain to any gauge other than 4 ft 8 1/2 in (1.44 m).The existence of long and severe gradients on the South Devon Railway led to Brunel's adoption of the atmospheric railway developed by Samuel Clegg and later by the Samuda brothers. In this a pipe of 9 in. (23 cm) or more in diameter was laid between the rails, along the top of which ran a continuous hinged flap of leather backed with iron. At intervals of about 3 miles (4.8 km) were pumping stations to exhaust the pipe. Much trouble was experienced with the flap valve and its lubrication—freezing of the leather in winter, the lubricant being sucked into the pipe or eaten by rats at other times—and the experiment was abandoned at considerable cost.Brunel is to be remembered for his two great West Country tubular bridges, the Chepstow and the Tamar Bridge at Saltash, with the latter opened in May 1859, having two main spans of 465 ft (142 m) and a central pier extending 80 ft (24 m) below high water mark and allowing 100 ft (30 m) of headroom above the same. His timber viaducts throughout Devon and Cornwall became a feature of the landscape. The line was extended ultimately to Penzance.As early as 1835 Brunel had the idea of extending the line westwards across the Atlantic from Bristol to New York by means of a steamship. In 1836 building commenced and the hull left Bristol in July 1837 for fitting out at Wapping. On 31 March 1838 the ship left again for Bristol but the boiler lagging caught fire and Brunel was injured in the subsequent confusion. On 8 April the ship set sail for New York (under steam), its rival, the 703-ton Sirius, having left four days earlier. The 1,340-ton Great Western arrived only a few hours after the Sirius. The hull was of wood, and was copper-sheathed. In 1838 Brunel planned a larger ship, some 3,000 tons, the Great Britain, which was to have an iron hull.The Great Britain was screwdriven and was launched on 19 July 1843,289 ft (88 m) long by 51 ft (15.5 m) at its widest. The ship's first voyage, from Liverpool to New York, began on 26 August 1845. In 1846 it ran aground in Dundrum Bay, County Down, and was later sold for use on the Australian run, on which it sailed no fewer than thirty-two times in twenty-three years, also serving as a troop-ship in the Crimean War. During this war, Brunel designed a 1,000-bed hospital which was shipped out to Renkioi ready for assembly and complete with shower-baths and vapour-baths with printed instructions on how to use them, beds and bedding and water closets with a supply of toilet paper! Brunel's last, largest and most extravagantly conceived ship was the Great Leviathan, eventually named The Great Eastern, which had a double-skinned iron hull, together with both paddles and screw propeller. Brunel designed the ship to carry sufficient coal for the round trip to Australia without refuelling, thus saving the need for and the cost of bunkering, as there were then few bunkering ports throughout the world. The ship's construction was started by John Scott Russell in his yard at Millwall on the Thames, but the building was completed by Brunel due to Russell's bankruptcy in 1856. The hull of the huge vessel was laid down so as to be launched sideways into the river and then to be floated on the tide. Brunel's plan for hydraulic launching gear had been turned down by the directors on the grounds of cost, an economy that proved false in the event. The sideways launch with over 4,000 tons of hydraulic power together with steam winches and floating tugs on the river took over two months, from 3 November 1857 until 13 January 1858. The ship was 680 ft (207 m) long, 83 ft (25 m) beam and 58 ft (18 m) deep; the screw was 24 ft (7.3 m) in diameter and paddles 60 ft (18.3 m) in diameter. Its displacement was 32,000 tons (32,500 tonnes).The strain of overwork and the huge responsibilities that lay on Brunel began to tell. He was diagnosed as suffering from Bright's disease, or nephritis, and spent the winter travelling in the Mediterranean and Egypt, returning to England in May 1859. On 5 September he suffered a stroke which left him partially paralysed, and he died ten days later at his Duke Street home.[br]Further ReadingL.T.C.Rolt, 1957, Isambard Kingdom Brunel, London: Longmans Green. J.Dugan, 1953, The Great Iron Ship, Hamish Hamilton.IMcNBiographical history of technology > Brunel, Isambard Kingdom
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6 Graham, George
SUBJECT AREA: Horology[br]b. c.1674 Cumberland, Englandd. 16 November 1751 London, England[br]English watch-and clockmaker who invented the cylinder escapement for watches, the first successful dead-beat escapement for clocks and the mercury compensation pendulum.[br]Graham's father died soon after his birth, so he was raised by his brother. In 1688 he was apprenticed to the London clockmaker Henry Aske, and in 1695 he gained his freedom. He was employed as a journeyman by Tompion in 1696 and later married his niece. In 1711 he formed a partnership with Tompion and effectively ran the business in Tompion's declining years; he took over the business after Tompion died in 1713. In addition to his horological interests he also made scientific instruments, specializing in those for astronomical use. As a person, he was well respected and appears to have lived up to the epithet "Honest George Graham". He befriended John Harrison when he first went to London and lent him money to further his researches at a time when they might have conflicted with his own interests.The two common forms of escapement in use in Graham's time, the anchor escapement for clocks and the verge escapement for watches, shared the same weakness: they interfered severely with the free oscillation of the pendulum and the balance, and thus adversely affected the timekeeping. Tompion's two frictional rest escapements, the dead-beat for clocks and the horizontal for watches, had provided a partial solution by eliminating recoil (the momentary reversal of the motion of the timepiece), but they had not been successful in practice. Around 1720 Graham produced his own much improved version of the dead-beat escapement which became a standard feature of regulator clocks, at least in Britain, until its supremacy was challenged at the end of the nineteenth century by the superior accuracy of the Riefler clock. Another feature of the regulator clock owed to Graham was the mercury compensation pendulum, which he invented in 1722 and published four years later. The bob of this pendulum contained mercury, the surface of which rose or fell with changes in temperature, compensating for the concomitant variation in the length of the pendulum rod. Graham devised his mercury pendulum after he had failed to achieve compensation by means of the difference in expansion between various metals. He then turned his attention to improving Tompion's horizontal escapement, and by 1725 the cylinder escapement existed in what was virtually its final form. From the following year he fitted this escapement to all his watches, and it was also used extensively by London makers for their precision watches. It proved to be somewhat lacking in durability, but this problem was overcome later in the century by using a ruby cylinder, notably by Abraham Louis Breguet. It was revived, in a cheaper form, by the Swiss and the French in the nineteenth century and was produced in vast quantities.[br]Principal Honours and DistinctionsFRS 1720. Master of the Clockmakers' Company 1722.BibliographyGraham contributed many papers to the Philosophical Transactions of the Royal Society, in particular "A contrivance to avoid the irregularities in a clock's motion occasion'd by the action of heat and cold upon the rod of the pendulum" (1726) 34:40–4.Further ReadingBritten's Watch \& Clock Maker's Handbook Dictionary and Guide, 1978, rev. Richard Good, 16th edn, London, pp. 81, 84, 232 (for a technical description of the dead-beat and cylinder escapements and the mercury compensation pendulum).A.J.Turner, 1972, "The introduction of the dead-beat escapement: a new document", Antiquarian Horology 8:71.E.A.Battison, 1972, biography, Biographical Dictionary of Science, ed. C.C.Gillespie, Vol. V, New York, 490–2 (contains a résumé of Graham's non-horological activities).DV -
7 Harwood, John
SUBJECT AREA: Horology[br]b. 1893 Bolton, Englandd. 9 August 1964[br]English watchmaker, inventor and producer of the first commercial self-winding wrist watch.[br]John Harwood served an apprenticeship as a watch repairer in Bolton, and after service in the First World War he obtained a post with a firm of jewellers in Douglas, Isle of Man. He became interested in the self-winding wrist watch, not because of the convenience of not having to wind it, but because of its potential to keep the mainspring fully wound and to exclude dust and moisture from the watch movement. His experience at the bench had taught him that these were the most common factors to affect adversely the reliability of watches. Completely unaware of previous work in this area, in 1922 he started experimenting and two years later he had produced a serviceable model for which he was granted a patent in 1924. The watch operated on the pedometer principle, the mainspring being wound by a pivoted weight that oscillated in the watch case as a result of the motion of the arm. The hands of his watch were set by rotating the bezel surrounding the dial, dispensing with the usual winding/hand-setting stem which allowed dust and moisture to enter the watch case. He took the watch to Switzerland, but he was unable to persuade the watchmaking firms to produce it until he had secured independent finance to cover the cost of tooling. The Harwood Self-Winding Watch Company Ltd was set up in 1928 to market the watches, but although several thousand were produced the company became a victim of the slump and closed down in 1932. The first practical self-winding watch also operated on the pedometer principle and is attributed to Abraham-Louis Perrellet (1770). The method was refined by Breguet in France and by Recordon, who patented the device in England, but it proved troublesome and went out of fashion. There was a brief revival of interest in self-winding watches towards the end of the nineteenth century, but they never achieved great popularity until after the Second World War, when they used either self-winding mechanisms similar to that devised by Harwood or weights which rotated in the case.[br]Principal Honours and DistinctionsBritish Horological Institute Gold Medal 1957.Bibliography1 September 1924, Swiss patent no. 106,582.Further ReadingA.Chapuis and E.Jaquet, 1956, The History of the Self-Winding Watch, London (provides general information)."How the automatic wrist watch was invented", 1957, Horological Journal 99:612–61 (for specific information).DV -
8 Jablochkoff, Paul
[br]b. 14 September 1847 Serdobsk, Russiad. April 1894 St Petersburg, Russia[br]Russian military engineer and inventor of an electric "candle", the invention of which gave an immense impetus to electric lighting in the 1870s.[br]Jablochkoff studied at the Military Engineering College in St Petersburg. Having a scientific bent, he was sent to the Military Galvano Technical School. At the end of his military service in 1871 he was appointed Director General of the Moscow-Kursk telegraph lines for the Midi Railway Company. At this time he began to develop an interest in electric lighting, and in 1875 he left the Imperial Telegraph Service to devote his time exclusively to scientific pursuits. He found employment at the workshop of M Bréguet in Paris, where Gramme dynamos and Serrin arc lamps were being constructed. After some experimentation he found a means of producing a carbon arc that regulated itself without any mechanism. This lamp, the Jablochkoff candle, with two carbon rods placed parallel to each other and so close that an arc formed at the ends, could continue to burn until the rods were consumed. Plaster of Paris was used to separate the two electrodes and crumbled away as the carbon burned, thus exposing fresh carbon. These lamps were used in May 1878 in Paris to illuminate the avenue de l'Opéra, and later in Rome and London, and in essence were the first practical electric street lighting. Since there was no regulating mechanism, several candles could be placed in a single circuit. Despite inherent defects, such as the inability to restart the lamps after they were extinguished by wind or interruption of supply, they remained in use for some purposes for several years on account of their simplicity and cheapness. In 1877 Jablochkoff obtained the earliest patent to employ transformers to distribute current in an alternating-current circuit.[br]Bibliography11 September 1876, British patent no. 3,552 (Jablochkoff's candle).22 May 1877, British patent no. 1,996 (transformer or induction coil distribution).Further ReadingW.J.King, 1962, The Development of Electrical Technology in the 19th Century, Washington, DC: Smithsonian Institution, Paper 30, pp. 393–407 (a detailed account). W.E.Langdon, 1877, "On a new form of electric light", Journal of the Society ofTelegraph Engineers 6:303–19 (an early report on Jablochkoffs system).Engineering (1878) 26:125–7.GW -
9 Phillips, Edouard
SUBJECT AREA: Mechanical, pneumatic and hydraulic engineering[br]b. 21 May 1821 Paris, Franced. 14 December 1889 Pouligny-Saint-Martin, France[br]French engineer and mathematician who achieved isochronous oscillations of a balance by deriving the correct shape for the balance spring.[br]Phillips was educated in Paris, at the Ecole Polytechnic and the Ecole des Mines. In 1849 he was awarded a doctorate in mathematical sciences by the University of Paris. He had a varied career in industry, academic and government institutions, rising to be Inspector- General of Mines in 1882.It was well known that the balance of a watch or chronometer fitted with a simple spiral or helical spring was not isochronous, i.e. the period of the oscillation was not entirely independent of the amplitude. Watch-and chronometer-makers, notably Breguet and Arnold, had devised empirical solutions to the problem by altering the curvature of the end of the balance spring. In 1858 Phillips was encouraged to tackle the problem mathematically, and two years later he published a complete solution for the helical balance spring and a partial solution for the more complex spiral spring. Eleven years later he was able to achieve a complete solution for the spiral spring by altering the curvature of both ends of the spring. Phillips published a series of typical curves that the watch-or chronometer-maker could use to shape the ends of the balance spring.[br]Principal Honours and DistinctionsAcadémie des Sciences 1868. Chairman, Jury on Mechanics, Universal Exhibition 1889.Bibliography1861, "Mémoire sur l'application de la Théorie du Spiral Réglant", Annales des Mines 20:1–107.1878, Comptes Rendus 86:26–31.An English translation (by J.D.Weaver) of both the above papers was published by the Antiquarian Horological Society in 1978 (Monograph No. 15).Further ReadingJ.D.Weaver, 1989, "Edouard Phillips: a centenary appreciation", Horological Journal 132: 205–6 (a good short account).F.J.Britten, 1978, Britten's Watch and Clock Maker's Handbook, 16th edn, rev. R Good (a description of the practical applications of the balance spring).DV
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