clockmaker

амер.; разг.

SUBJECT AREA: Chemical technology, Domestic appliances and interiors, Public utilities

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Son of a clockmaker, he studied physics and chemistry under H.-D. de Saussure (1740– 99). In 1775 he moved to Paris, where he taught chemistry and presented a paper on electrical phenomena to the Académie Royale des Sciences. He assisted the Montgolfier brothers in their Paris balloon ascents.

From 1780 Argand spent some time in Montpellier, where he conceived the idea of the lamp that was to make him famous. It was an oil lamp with gravity oil feed, in which the flame was enlarged by burning it in a current of air induced by two concentric iron tubes. It produced ten times the illumination of the simple oil lamp. From the autumn of 1783 to summer 1785, Argand travelled to London and Birmingham to promote the manufacture and sale of his lamp. Upon his return to Paris, he found that his design had been plagiarized; with others, Argand sought to establish his priority, and Paul Abeille published a tract, Déscouverte des lampes à courant d'air et à cylindre (1785). As a result, the Académie granted Argand a licence to manufacture the lamp. However, during the Revolution, Argand's factories were destroyed and his licence annulled. He withdrew to Versoix, near Geneva. In 1793, the English persuaded him to take refuge in England and tried, apparently without success, to obtain recompense for his losses.

Argand is also remembered for his work on distillation and on the water distributor or hydraulic ram, which was conceived with Joseph Montgolfier in 1797 and recognized by the grant of a patent in the same year.

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SUBJECT AREA: Horology, Telecommunications

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Alexander Bain was born into a crofting family in a remote part of Scotland. He was apprenticed to a watchmaker in Wick and during that time he was strongly influenced by a lecture on "Heat, sound and electricity" that he heard in nearby Thurso. This lecture induced him to take up a position in Clerkenwell in London, working as a journeyman clockmaker, where he was able to further his knowledge of electricity by attending lectures at the Adelaide Gallery and the Polytechnic Institution. His thoughts naturally turned to the application of electricity to clockmaking, and despite a bitter dispute with Charles Wheatstone over priority he was granted the first British patent for an electric clock. This patent, taken out on 11 January 1841, described a mechanism for an electric clock, in which an oscillating component of the clock operated a mechanical switch that initiated an electromagnetic pulse to maintain the regular, periodic motion. This principle was used in his master clock, produced in 1845. On 12 December of the same year, he patented a means of using electricity to control the operation of steam railway engines via a steam-valve. His earliest patent was particularly far-sighted and anticipated most of the developments in electrical horology that occurred during the nineteenth century. He proposed the use of electricity not only to drive clocks but also to distribute time over a distance by correcting the hands of mechanical clocks, synchronizing pendulums and using slave dials (here he was anticipated by Steinheil). However, he was less successful in putting these ideas into practice, and his electric clocks proved to be unreliable. Early electric clocks had two weaknesses: the battery; and the switching mechanism that fed the current to the electromagnets. Bain's earth battery, patented in 1843, overcame the first defect by providing a reasonably constant current to drive his clocks, but unlike Hipp he failed to produce a reliable switch.

The application of Bain's numerous patents for electric telegraphy was more successful, and he derived most of his income from these. They included a patent of 12 December 1843 for a form of fax machine, a chemical telegraph that could be used for the transmission of text and of images (facsimile). At the receiver, signals were passed through a moving band of paper impregnated with a solution of ammonium nitrate and potassium ferrocyanide. For text, Morse code signals were used, and because the system could respond to signals faster than those generated by hand, perforated paper tape was used to transmit the messages; in a trial between Paris and Lille, 282 words were transmitted in less than one minute. In 1865 the Abbé Caselli, a French engineer, introduced a commercial fax service between Paris and Lyons, based on Bain's device. Bain also used the idea of perforated tape to operate musical wind instruments automatically. Bain squandered a great deal of money on litigation, initially with Wheatstone and then with Morse in the USA. Although his inventions were acknowledged, Bain appears to have received no honours, but when towards the end of his life he fell upon hard times, influential persons in 1873 secured for him a Civil List Pension of £80 per annum and the Royal Society gave him £150.

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See also: Bakewell, Frederick C.

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SUBJECT AREA: Agricultural and food technology

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He was the fifth child of Charles and Ann Stalcrop Evans, and by the age of 15 he had four sisters and seven brothers. Nothing is known of his schooling, but at the age of 17 he was apprenticed to a Newport wheelwright and wagon-maker. At 19 he was enrolled in a Delaware Militia Company in the Revolutionary War but did not see active service. About this time he invented a machine for bending and cutting off the wires in textile carding combs. In July 1782, with his younger brother, Joseph, he moved to Tuckahoe on the eastern shore of the Delaware River, where he had the basic idea of the automatic flour mill. In July 1782, with his elder brothers John and Theophilus, he bought part of his father's Newport farm, on Red Clay Creek, and planned to build a mill there. In 1793 he married Sarah Tomlinson, daughter of a Delaware farmer, and joined his brothers at Red Clay Creek. He worked there for some seven years on his automatic mill, from about 1783 to 1790.

His system for the automatic flour mill consisted of bucket elevators to raise the grain, a horizontal screw conveyor, other conveying devices and a "hopper boy" to cool and dry the meal before gathering it into a hopper feeding the bolting cylinder. Together these components formed the automatic process, from incoming wheat to outgoing flour packed in barrels. At that time the idea of such automation had not been applied to any manufacturing process in America. The mill opened, on a non-automatic cycle, in 1785. In January 1786 Evans applied to the Delaware legislature for a twenty-five-year patent, which was granted on 30 January 1787 although there was much opposition from the Quaker millers of Wilmington and elsewhere. He also applied for patents in Pennsylvania, Maryland and New Hampshire. In May 1789 he went to see the mill of the four Ellicot brothers, near Baltimore, where he was impressed by the design of a horizontal screw conveyor by Jonathan Ellicot and exchanged the rights to his own elevator for those of this machine. After six years' work on his automatic mill, it was completed in 1790. In the autumn of that year a miller in Brandywine ordered a set of Evans's machinery, which set the trend toward its general adoption. A model of it was shown in the Market Street shop window of Robert Leslie, a watch-and clockmaker in Philadelphia, who also took it to England but was unsuccessful in selling the idea there.

In 1790 the Federal Plant Laws were passed; Evans's patent was the third to come within the new legislation. A detailed description with a plate was published in a Philadelphia newspaper in January 1791, the first of a proposed series, but the paper closed and the series came to nothing. His brother Joseph went on a series of sales trips, with the result that some machinery of Evans's design was adopted. By 1792 over one hundred mills had been equipped with Evans's machinery, the millers paying a royalty of $40 for each pair of millstones in use. The series of articles that had been cut short formed the basis of Evans's The Young Millwright and Miller's Guide, published first in 1795 after Evans had moved to Philadelphia to set up a store selling milling supplies; it was 440 pages long and ran to fifteen editions between 1795 and 1860.

Evans was fairly successful as a merchant. He patented a method of making millstones as well as a means of packing flour in barrels, the latter having a disc pressed down by a toggle-joint arrangement. In 1801 he started to build a steam carriage. He rejected the idea of a steam wheel and of a low-pressure or atmospheric engine. By 1803 his first engine was running at his store, driving a screw-mill working on plaster of Paris for making millstones. The engine had a 6 in. (15 cm) diameter cylinder with a stroke of 18 in. (45 cm) and also drove twelve saws mounted in a frame and cutting marble slabs at a rate of 100 ft (30 m) in twelve hours. He was granted a patent in the spring of 1804. He became involved in a number of lawsuits following the extension of his patent, particularly as he increased the licence fee, sometimes as much as sixfold. The case of Evans v. Samuel Robinson, which Evans won, became famous and was one of these. Patent Right Oppression Exposed, or Knavery Detected, a 200-page book with poems and prose included, was published soon after this case and was probably written by Oliver Evans. The steam engine patent was also extended for a further seven years, but in this case the licence fee was to remain at a fixed level. Evans anticipated Edison in his proposal for an "Experimental Company" or "Mechanical Bureau" with a capital of thirty shares of $100 each. It came to nothing, however, as there were no takers. His first wife, Sarah, died in 1816 and he remarried, to Hetty Ward, the daughter of a New York innkeeper. He was buried in the Bowery, on Lower Manhattan; the church was sold in 1854 and again in 1890, and when no relative claimed his body he was reburied in an unmarked grave in Trinity Cemetery, 57th Street, Broadway.

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SUBJECT AREA: Medical technology

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The younger son of a landed Midlands family, Floyer embarked on medical studies at Oxford at the age of 15 and graduated in 1674. He returned to Lichfield where he resided and practised, as well as being acquainted with the family of Samuel Johnson, for the remainder of a long life. Described by a later biographer as "fantastic, whimsical, pretentious, research-minded and nebulous", he none the less, as his various medical writings testify, became a pioneer in several fields of medical endeavour. It seems likely that he was well aware of the teachings of Sanctorius in relation to measurement in medicine and he probably had a copy of Sanctorius's weighing-machine made and put to use in Lichfield.

He also embarked on extensive studies relating to pulse, respiration rate, temperature, barometric readings and even latitude. Initially he used the minute hand of a pendulum clock or a navigational minute glass. He then commissioned from Samuel Watson, a London watch-and clockmaker, a physicians' pulse watch incorporating a second-hand and a stop mechanism. In 1707 and 1710 he published a massive work, dedicated to Queen Anne, that emphasized the value of the accurate measurement of pulse rates in health and disease.

His other interests included studies of blood pressure, asthma, and the medical value of cold bathing. It is of interest that it was at his suggestion that the young Samuel Johnson was taken to London to receive the Royal Touch, from Queen Anne, for scrofula.

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SUBJECT AREA: Textiles

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The claims of Highs to have invented both the spinning jenny and the waterframe have been dismissed by most historians. Thomas Highs was a reedmaker of Leigh, Lancashire. In about 1763 he had as a neighbour John Kay, the clockmaker from Warrington, whom he employed to help him construct his machines. During this period they were engaged in making a spinning jenny, but after several months of toil, in a fit of despondency, they threw the machine through the attic window. Highs persevered, however, and made a jenny that could spin six threads. The comparatively sophisticated arrangements for drawing and twisting at the same time, as depicted by Guest (1823), suggest that this machine came after the one invented by James Hargreaves. Guest claims that Highs made this machine between 1764 and 1766 and in the following two years constructed another, in which the spindles were placed in a circle. In 1771 Highs moved to Manchester, where he constructed a double jenny that was displayed at the Manchester Exchange, and received a subscription of £200 from the cotton manufacturers. However, all this occurred after Hargreaves had constructed his jenny. In the trial of Arkwright's patent during 1781, Highs gave evidence. He was recalled from Ireland, where he had been superintending the building of cotton-spinning machinery for Baron Hamilton's newly erected mill at Balbriggan, north of Dublin. Then in 1785, during the next trial of Arkwright's patent, Highs claimed that in 1767 he had made rollers for drawing out the cotton before spinning. This would have been for a different type of spinning machine, similar to the one later constructed by Arkwright. Highs was helped by John Kay and it was these rollers that Kay subsequently built for Arkwright. If the drawing shown by Guest is correct, then Highs was working on the wrong principles because his rollers were spaced too far apart and were not held together by weights, with the result that the twist would have passed into the drafting zone, producing uneven drawing.

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SUBJECT AREA: Metallurgy

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Of Dutch descent, Hunstman was apprenticed to a clockmaker at Epworth, Lincolnshire. In 1725 he set up in Doncaster as a maker of clocks, locks and roasting jacks. He made improvements in his tools but found himself hampered by the poor quality of the steel available, then made by the cementation process, which yielded a steel with a non-uniform carbon content. Around 1740, Huntsman moved to Handsworth, now part of Sheffield, and began experimenting by heating varying compositions of fuel and flux with crude steel in a crucible, to obtain a steel of uniform composition. During the years 1745 to 1750 he attained his object, but not without many unsuccessful "heats", as excavations of the site of his works now reveal. Although his steel was far better than that previously available, however, the conservative cutlers of Sheffield rejected it, claiming it was too hard to work; therefore Huntsman exported his product to France, where the cutlers promptly worked it into high-quality knives and razors that were exported to England. The Sheffield cutlers' attempts to prevent Huntsman from exporting his steel proved unsuccessful. Huntsman did not patent his process, preferring to retain his advantage by shrouding his work in secrecy, carrying out his melting at night to escape observation, but a rival cutler, Samuel Walker, gained admittance to Huntsman's works disguised as a tramp seeking food. As a result, Walker was able to make crucible steel at a handsome profit. Huntsman fought back and earned success through the sheer quality of his steel, and had to move to.a larger site at Attercliffe in 1770. Crucible steelmaking remained important through the nineteenth century although, as it was a small-scale process, its application was restricted to engineers' cutting tools and the cutting edges of certain tools.

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SUBJECT AREA: Textiles

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William Kelly, a Larnack clockmaker, was Manager of David Dale's New Lanark cotton-spinning mills. He was writing to Boulton \& Watt in 1796 about the different ways in which he heated the mills and the New Institution. He must also have been responsible for supervising the millwrights' and mechanics' shops where much of the spinning machinery for the mills was constructed. At one time there were eighty-seven men employed in these shops alone. He devised a better method of connecting the water wheel to the line shafting which he reckoned would save a quarter of the water power required. Kelly may have been the first to apply power to the mule, for in 1790 he drove the spinning sequence from the line shafting, which operated the gear mechanism to turn the rollers and spindles as well as draw out the carriage. The winding on of the newly spun yarn still had to be done by hand. Then in 1792 he applied for a patent for a self-acting mule in which all the operations would be carried out by power. However, winding the yarn on in a conical form was a problem; he tried various ways of doing this, but abandoned his attempts because the mechanism was cumbersome and brought no economic advantage as only a comparatively small number of spindles could be operated. Even so, his semi-automatic mule became quite popular and was exported to America in 1803. Kelly was replaced as Manager at New Lanark by Robert Owen in 1800.

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SUBJECT AREA: Horology

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Le Roy was born into a distinguished horological family: his father, Julien, was Clockmaker to the King. Pierre became Master in 1737 and continued to work with his father, taking over the business when his father died in 1759. However, he seems to have left the commercial side of the business to others so that he could concentrate on developing the marine chronometer. Unlike John Harrison, he believed that the solution lay in detaching the escapement from the balance, and in 1748 he submitted a proposal for the first detached escapement to the Académie des Sciences in Paris. He also differed from Harrison in his method of temperature compensation, which acted directly on the balance by altering its radius of gyration. This was achieved either by mounting thermometers on the balance or by using bimetallic strips which effectively reduced the diameter of the balance as the temperature rose (with refinements, this later became the standard method of temperature compensation in watches and chronometers). Le Roy had already discovered that for every spiral balance spring there was a particular length at which it would be isochronous, and this method of temperature compensation did not destroy that isochronism by altering the length, as other methods did. These innovations were incorporated in a chronometer with an improved detached escapement which he presented to Louis XV in 1766 and described in a memoir to the Académie des Sciences. This instrument contained the three essential elements of all subsequent chronometers: an isochronous balance spring, a detached escapement and a balance with temperature compensation. Its performance was similar to that of Harrison's fourth timepiece, and Le Roy was awarded prizes by the Académie des Sciences for the chronometer and for his memoir. However, his work was never fully appreciated in France, where he was over-shadowed by his rival Ferdinand Berthoud. When Berthoud was awarded the coveted title of Horloger de la Marine, Le Roy became disillusioned and shortly afterwards gave up chronometry and retired to the country.

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SUBJECT AREA: Horology, Mining and extraction technology

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By about 1843, Leschot, who was renowned for designing machines to produce parts of clocks on an industrialized scale, had gathered that the fine, deep lines he found on an Egyptian red porphyry plate must have been cut by diamonds. He thus resurrected a technology that had been largely forgotten over the centuries, when in 1862 his son, who was engaged in constructing a railway line in Italy, was confronted with the problems of tunnelling through hard rock. In Paris he developed a drilling machine consisting of a casing that rotated in a similar way to the American rope drilling method. The crown of the machine was mounted with eight black diamonds, and inside the casing a stream of water circulated continuously to flush out the mud.

He took out his first patent in France in 1862, and followed it with further ones in many European countries and in America. He continued to concentrate on his watchmaker's profession and left the rights to his patents to his son. It was Leschot's ingenious idea of utilizing diamonds for drilling hard rock that was later applied in different mining processes. It influenced a series of further developments in many countries, including those of Alfred Brandt and Major Beaumont in England. In particular, the fact that the hollow casing produced a complete core was of importance for the increasing amount of petroleum prospecting in Pennsylvania after Edwin Laurentine Drake's find of 1859, where M.C.Bullock sunk the first deep well (200 m) in the world by diamond drilling in 1870. The efforts of Per Anton Crælius in Sweden made diamond drilling a success worldwide.

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SUBJECT AREA: Paper and printing

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Mergenthaler came from a family of teachers, but following a mechanical bent he was apprenticed to a clockmaker. Having served his time, Mergenthaler emigrated to the USA in 1872 to avoid military service. He immediately secured work in Washington, DC, in the scientific instrument shop of August Hahl, the son of his former master. He steadily acquired a reputation for skill and ingenuity, and in 1876, when Hahl transferred his business to Baltimore, Mergenthaler went too. Soon after, they were commissioned to remedy the defects in a model of a writing machine devised by James O.Clephane of Washington. It produced print by typewriting, which was then multiplied by lithography. Mergenthaler soon corrected the defects and Clephane ordered a full-size version. This was completed in 1877 but did not work satisfactorily. Nevertheless, Mergenthaler was moved to engage in the long battle to mechanize the typesetting stage of the printing process. Clephane suggested substituting stereotyping for lithography in his device, but in spite of their keen efforts Mergenthaler and Hahl were again unsuccessful and they abandoned the project. In spare moments Mergenthaler continued his search for a typesetting machine. Late in 1883 it occurred to him to stamp matrices into type bars and to cast type metal into them in the same machine. From this idea, the Linotype machine developed and was completed by July 1884. It worked well and a patent was granted on 26 August that year, and Clephane and his associates set up the National Typographic Company of West Virginia to manufacture it. The New York Tribune ordered twelve Linotypes, and on 3 July 1886 the first of these set part of that day's issue. During the previous year the company had passed into the hands of a group of newspaper owners; increasing differences with the Board led to Mergenthaler's resignation in 1888, but he nevertheless continued to improve the machine, patenting over fifty modifications. The Linotype, together with the Monotype of Tolbert Lanston, rapidly supplanted earlier typesetting methods, and by the 1920s it reigned supreme, the former being used more for newspapers, the latter for book work.

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SUBJECT AREA: Horology

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Thomas Mudge was the son of a clergyman and schoolmaster who, recognizing his son's mechanical aptitude, apprenticed him to the eminent London clock-and watchmaker George Graham. Mudge became free of the Clockmakers' Company in 1738 and set up on his own account after Graham's death in 1751. Around 1755 he formed a partnership with William Dutton, another apprentice of Graham. The firm produced conventional clocks and watches of excellent quality, but Mudge had also established a reputation for making highly innovative individual pieces. The most significant of these was the watch with a detached-lever escapement that he completed in 1770, although the idea had occurred to him as early as 1754. This watch was purchased by George III for Queen Charlotte and is still in the Royal Collection. Shortly afterwards Mudge moved to Plymouth, to devote his time to the perfection of the marine chronometer, leaving the London business in the hands of Dutton. The chronometers he produced were comparable in performance to those of John Harrison, but like them they were too complicated and expensive to be produced in quantity.

Mudge's patron, Count Bruhl, recognized the potential of the detached-lever escapement, but Mudge was too involved with his marine chronometers to make a watch for him. He did, however, provide Bruhl with a large-scale model of his escapement, from which the Swiss expatriate Josiah Emery was able to make a watch in 1782. Over the next decade Emery made a limited number of similar watches for wealthy clients, and it was the performance of these watches that demonstrated the worth of the escapement. The detached-lever escapement took some time to be adopted universally, but this was facilitated in the nineteenth century by the development of a cheaper form, the pin lever.

By the end of the century the detached-lever escapement was used in one form or another in practically all mechanical watches and portable clocks. If a watch is to be a good timekeeper the balance must be free to swing with as little interference as possible from the escapement. In this respect the cylinder escapement is an improvement on the verge, although it still exerts a frictional force on the balance. The lever escapement is a further improvement because it detaches itself from the balance after delivering the impulse which keeps it oscillating.

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SUBJECT AREA: Horology

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Riefler's father was a scientific-instrument maker and clockmaker who in 1841 had founded the firm of Clemens Riefler to make mathematical instruments. After graduating in engineering from the University of Munich Sigmund worked as a surveyor, but when his father died in 1876 he and his brothers ran the family firm. Sigmund was responsible for technical development and in this capacity he designed a new system of drawing-instruments which established the reputation of the firm. He also worked to improve the performance of the precision clock, and in 1889 he was granted a patent for a new form of escapement. This escapement succeeded in reducing the interference of the clock mechanism with the free swinging of the pendulum by impulsing the pendulum through its suspension strip. It proved to be the greatest advance in precision timekeeping since the introduction of the dead-beat escapement about two hundred years earlier. When the firm of Clemens Riefler began to produce clocks with this escapement in 1890, they replaced clocks with Graham's dead-beat escapement as the standard regulator for use in observatories and other applications where the highest precision was required. In 1901 a movement was fitted with electrical rewind and was encapsulated in an airtight case, at low pressure, so that the timekeeping was not affected by changes in barometric pressure. This became the standard practice for precision clocks. Although the accuracy of the Riefler clock was later surpassed by the Shortt free-pendulum clock and the quartz clock, it remained in production until 1965, by which time over six hundred instruments had been made.

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See also: Marrison, Warren Alvin

SUBJECT AREA: Horology

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Little is known about Tompion's early life except that he was born into a family of blacksmiths. When he was admitted into the Clockmakers' Company in 1671 he was described as a "Great Clockmaker", which meant a maker of turret clocks, and as these clocks were made of wrought iron they would have required blacksmithing skills. Despite this background, he also rapidly established his reputation as a watchmaker. In 1674 he moved to premises in Water Lane at the sign of "The Dial and Three Crowns", where his business prospered and he remained for the rest of his life. Assisted by journeymen and up to eleven apprentices at any one time, the output from his workshop was prodigious, amounting to over 5,000 watches and 600 clocks. In his lifetime he was famous for his watches, as these figures suggest, but although they are of high quality they do not differ markedly from those produced by other London watchmakers of that period. He is now known more for the limited number of elaborate clocks that he produced, such as the equation clock and the spring-driven clock of a year's duration, which he made for William III. Around 1711 he took into partnership his nephew by marriage, George Graham, who carried on the business after his death.

Although Tompion does not seem to have been particularly innovative, he lived at a time when great advances were being made in horology, which his consummate skill as a craftsman enabled him to exploit. In this he was greatly assisted by his association with Robert Hooke, for whom Tompion constructed a watch with a balance spring in 1675; at that time Hooke was trying to establish his priority over Huygens for this invention. Although this particular watch was not successful, it made Tompion aware of the potential of the balance spring and he became the first person in England to apply Huygens's spiral spring to the balance of a watch. Although Thuret had constructed such a watch somewhat earlier in France, the superior quality of Tompion's wheel work, assisted by Hooke's wheel-cutting engine, enabled him to dominate the market. The anchor escapement (which reduced the amplitude of the pendulum's swing) was first applied to clocks around this time and produced further improvements in accuracy which Tompion and other makers were able to utilize. However, the anchor escapement, like the verge escapement, produced recoil (the clock was momentarily driven in reverse). Tompion was involved in attempts to overcome this defect with the introduction of the dead-beat escapement for clocks and the horizontal escapement for watches. Neither was successful, but they were both perfected later by George Graham.

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SUBJECT AREA: Electricity, Land transport, Railways and locomotives

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Volk was the son of a German immigrant clockmaker and continued the business with his mother after his father died in 1869, although when he married in 1879 his profession was described as "electrician". He installed Brighton's first telephone the same year and in 1880 he installed electric lighting in his own house, using a Siemens Brothers dynamo (see Siemens, Dr Ernst Werner von) driven by a Crossley gas engine. This was probably one of the first half-dozen such installations in Britain. Magnus Volk \& Co. became noted electrical manufacturers and contractors, and, inter alia, installed electric light in Brighton Pavilion in place of gas.

By 1883 Volk had moved house. He had kept the dynamo and gas engine used to light his previous house, and he also had available an electric motor from a cancelled order. After approaching the town clerk of Brighton, he was given permission for a limited period to build and operate a 2 ft (61 cm) gauge electric railway along the foreshore. Using the electrical equipment he already had, Volk built the line, a quarter of a mile (400 m) long, in eight weeks. The car was built by a local coachbuilder, with the motor under the seat; electric current at 50 volts was drawn from one running rail and returned through the other.

The railway was opened on 4 August 1883. It operated regularly for several months and then, permission to run it having been renewed, it was rebuilt for the 1884 season to 2 ft 9 in. (84 cm) gauge, with improved equipment. Despite storm damage from time to time, Volk's Electric Railway, extended in length, has become an enduring feature of Brighton's sea front. In 1887 Volk made an electric dogcart, and an electric van which he built for the Sultan of Turkey was probably the first motor vehicle built in Britain for export. In 1896 he opened the Brighton \& Rottingdean Seashore Electric Tramroad, with very wide-gauge track laid between the high-and low-tide lines, and a long-legged, multi-wheel car to run upon it, through the water if necessary. This lasted only until 1901, however. Volk subsequently became an early enthusiast for aircraft.

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SUBJECT AREA: Horology

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Most clepsydra clocks, such as that of al-Jarazi, measured time continuously by the constant flow of a liquid and most mechanical clocks measure time discontinuously by means of an escapement. The clepsydra clock devised by Zhang Sixun in 976 and completed in 979 was unusual as it incorporated an escapement. It consisted of a large wheel with buckets around its periphery. A constant stream of water was directed into one of the buckets until it reached a predetermined weight, this released the wheel, allowing it to rotate to a new position where the process was repeated (this mechanism may have been introduced by the Chinese astronomer and mathematician Zhang Heng in the second century). The water was later replaced by mercury to prevent freezing in winter. With suitable gearing the movement of the wheel was used to drive a celestial globe, a carousel for written time announcements and jacks for audible time signals. This clock has not survived and is known only from the work Hsin I Hsiang Fa Yao (New Armillary Sphere and Celestial Globe System Essentials), which was printed in 1172 and is ascribed to Su Song. This work also describes two similar but later astronomical clock towers with water-wheel escape-ments. Several models of the water-wheel escapement have been constructed from the description in this work.

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