reading+accuracy

prae-sĕco, cŭi, ctum, or cātum, 1, v. a., to cut off before or in front, to cut off or out (not in Cic.).

Lit.:

pars cultello praesecatur,

Varr. R. R. 3, 16, 34:

brassica ut praesica, quod ex ejus scapo minutatim praesecatur,

id. L. L. 5, § 104 Müll.:

partem,

Ov. R. Am. 112:

projecturas tignorum,

Vitr. 4, 2:

lineam,

Plin. 32, 2, 5, § 13:

praesecta vitis,

id. 17, 15, 25, § 115:

praesecata gula,

App. M. 1, p. 108, 15.—

Trop.: praesectum decies non castigavit ad unguem, has not corrected by the pared nail, i. e. to perfect accuracy, Hor. A. P. 294 Bentl. and Haupt (but the better reading is perfectum).

SUBJECT AREA: Horology

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Burgi entered the service of Duke William IV of Hesse in 1579 as Court Clockmaker, although he also assisted William with his astronomical observations. In 1584 he invented the cross-beat escapement which increased the accuracy of spring-driven clocks by two orders of magnitude. During the last years of the century he also worked on the development of geometrical and astronomical instruments for the Royal Observatory at Kassel.

On the death of Duke Wilhelm in 1603, and with news of his skills having reached the Holy Roman Emperor Rudolph II, in 1604 he went to Prague to become Imperial Watchmaker and to assist in the creation of a centre of scientific activity, subsequently becoming Assistant to the German astronomer, Johannes Kepler. No doubt this association led to an interest in mathematics and he made significant contributions to the concept of decimal fractions and the use of exponential notation, i.e. the use of a raised number to indicate powers of another number. It is likely that he was developing the idea of logarithms at the same time (or possibly even before) Napier, for in 1620 he made his greatest contribution to mathematics, science and, eventually, engineering, namely the publication of tables of anti-logarithms.

At Prague he continued the series of accurate clocks and instruments for astronomical measurements that he had begun to produce at Kassel. At that period clocks were very poor timekeepers since the controller, the foliot or balance, had no natural period of oscillation and was consequently dependent on the driving force. Although the force of the driving weight was constant, irregularities occurred during the transmission of the power through the train as a result of the poor shape and quality of the gearing. Burgi attempted to overcome this directly by superb craftsmanship and indirectly by using a remontoire. This device was wound at regular intervals by the main driving force and fed the power directly to the escape wheel, which impulsed the foliot. He also introduced the crossbeat escapement (a variation on the verge), which consisted of two coupled foliots that swung in opposition to each other. According to contemporary evidence his clocks produced a remarkable improvement in timekeeping, being accurate to within a minute a day. This improvement was probably a result of the use of a remontoire and the high quality of the workmanship rather than a result of the cross-beat escapement, which did not have a natural period of oscillation.

Burgi or Prague clocks, as they were known, were produced by very few other makers and were supplanted shortly afterwards by the intro-duction of the pendulum clock. Burgi also produced superb clockwork-driven celestial globes.

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See also: Briggs, Henry

KF / DV

SUBJECT AREA: Civil engineering, Mechanical, pneumatic and hydraulic engineering, Railways and locomotives

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The son of a lawyer, he entered an academy in Cape Cod and, at the age of 19, the English Academy at Andover, Massachusetts, for five terms. He was then in the employ of Samuel L. Fenton of Charlestown, Massachusetts. He served a three-year apprenticeship, then went to the Windsor White River Division of the Vermont Central Railroad. He was Resident Engineer of the Cheshire Railroad at Walpote, New Hampshire, from 1847 to 1849, and then worked in independent practice as a civil engineer and surveyor until his death. He was involved with nearly all the railroads running out of Boston, especially the Boston \& Maine. In April 1863 he was appointed Chief Engineer of the Hoosac Tunnel, which was already being built. He introduced new engineering methods, relocated the line of the tunnel and achieved great accuracy in the meeting of the borings. He was largely responsible for the development in the USA of the advanced system of tunnelling with machinery and explosives, and pioneered the use of compressed air in the USA. In 1869 he was Chief Engineer of the Burlington \& Missouri River Railroad in Nebraska, laying down some 240 miles (386 km) of track in four years. During this period he became interested in the building of a Congregational College at Crete, Nebraska, for which he gave the land and which was named after him. In 1873 he returned to Charlestown and was again appointed Chief Engineer of the Hoosac Tunnel. At the final opening of the tunnel on 9 February 1875 he drove the first engine through. He remained in charge of construction for a further two years.

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SUBJECT AREA: Horology

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Louis Essen joined the National Physical Laboratory (NPL) at Teddington in 1927 after graduating from London University. He spent his whole working life at the NPL and retired in 1972; his research there was recognized by the award of a DSc in 1948. At NPL he joined a team working on the development of frequency standards using quartz crystals and he designed a very successful quartz oscillator, which became known as the "Essen ring". He was also involved with radio frequency oscillators. His expertise in these fields was to play a crucial role in the development of the caesium clock. The idea of an atomic clock had been proposed by I.I.Rabbi in 1945, and an instrument was constructed shortly afterwards at the National Bureau of Standards in the USA. However, this device never realized the full potential of the concept, and after seeing it on a visit to the USA Essen was convinced that a more successful instrument could be built at Teddington. Assisted by J.V.L.Parry, he commenced work in the spring of 1953 and by June 1955 the clock was working reliably, with an accuracy that was equivalent to one second in three hundred years. This was significantly more accurate than the astronomical observations that were used at that time to determine the second: in 1967 the second was redefined in terms of the value for the frequency of vibration of caesium atoms that had been obtained with this clock.

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See also: Marrison, Warren Alvin

SUBJECT AREA: Horology

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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.

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See also: Barlow, Edward; Guillaume, Charles-Edouard

SUBJECT AREA: Textiles

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Heathcote was the son of a small farmer who became blind, obliging the family to move to Long Whatton, near Loughborough, c.1790. He was apprenticed to W.Shepherd, a hosiery-machine maker, and became a frame-smith in the hosiery industry. He moved to Nottingham where he entered the employment of an excellent machine maker named Elliott. He later joined William Caldwell of Hathern, whose daughter he had married. The lace-making apparatus they patented jointly in 1804 had already been anticipated, so Heathcote turned to the problem of making pillow lace, a cottage industry in which women made lace by arranging pins stuck in a pillow in the correct pattern and winding around them thread contained on thin bobbins. He began by analysing the complicated hand-woven lace into simple warp and weft threads and found he could dispense with half the bobbins. The first machine he developed and patented, in 1808, made narrow lace an inch or so wide, but the following year he made much broader lace on an improved version. In his second patent, in 1809, he could make a type of net curtain, Brussels lace, without patterns. His machine made bobbin-net by the use of thin brass discs, between which the thread was wound. As they passed through the warp threads, which were arranged vertically, the warp threads were moved to each side in turn, so as to twist the bobbin threads round the warp threads. The bobbins were in two rows to save space, and jogged on carriages in grooves along a bar running the length of the machine. As the strength of this fabric depended upon bringing the bobbin threads diagonally across, in addition to the forward movement, the machine had to provide for a sideways movement of each bobbin every time the lengthwise course was completed. A high standard of accuracy in manufacture was essential for success. Called the "Old Loughborough", it was acknowledged to be the most complicated machine so far produced. In partnership with a man named Charles Lacy, who supplied the necessary capital, a factory was established at Loughborough that proved highly successful; however, their fifty-five frames were destroyed by Luddites in 1816. Heathcote was awarded damages of £10,000 by the county of Nottingham on the condition it was spent locally, but to avoid further interference he decided to transfer not only his machines but his entire workforce elsewhere and refused the money. In a disused woollen factory at Tiverton in Devonshire, powered by the waters of the river Exe, he built 300 frames of greater width and speed. By continually making inventions and improvements until he retired in 1843, his business flourished and he amassed a large fortune. He patented one machine for silk cocoon-reeling and another for plaiting or braiding. In 1825 he brought out two patents for the mechanical ornamentation or figuring of lace. He acquired a sound knowledge of French prior to opening a steam-powered lace factory in France. The factory proved to be a successful venture that lasted many years. In 1832 he patented a monstrous steam plough that is reputed to have cost him over £12,000 and was claimed to be the best in its day. One of its stated aims was "improved methods of draining land", which he hoped would develop agriculture in Ireland. A cable was used to haul the implement across the land. From 1832 to 1859, Heathcote represented Tiverton in Parliament and, among other benefactions, he built a school for his adopted town.

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SUBJECT AREA: Electronics and information technology, Horology

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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.

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SUBJECT AREA: Textiles

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The family firm of Paget's of Loughborough was of long standing in hosiery manufacture. They were well aware of the importance of modernizing their factory with the latest improvements in machinery, as well as developing their own inventions. They discovered Marc Brunel's circular knitting machine c.1844 and constructed many on that principle, with modifications that performed very well. Arthur Paget took out three patents. The first, was in 1857, was for making the machine self-acting so that it could be driven by power. In his patent of 1859 he introduced modifications on the earlier patent, and his third patent, in 1860, described further alterations. These machines produced excellent work with speed and accuracy.

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SUBJECT AREA: Mechanical, pneumatic and hydraulic engineering

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Educated at Queens College, Belfast, Perry became Physics Master at Clifton College in 1870 until 1874. This was followed by a brief period of study under Sir William Thomson in Glasgow. He was then appointed Professor of Engineering at the Imperial College of Japan in Tokyo, where he formed a remarkable research partnership with W.E. Ayrton. On his return to England he became Professor of Engineering and Mathematics at City and Guilds College, Finsbury. Perry was the co-inventor with Ayrton of many electrical measuring instruments between 1880 and 1890, including an energy meter incorporating pendulum clocks and the first practicable portable ammeter and voltmeter, the latter being extensively used until superseded by instruments of greater accuracy. An optical indicator for high-speed steam engines was among Perry's many patents. Having made a notable contribution to education, particularly in the teaching of mathematics, he turned his attention in the latter period of his life to the improvement of the gyrostatic compass.

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SUBJECT AREA: Steam and internal combustion engines

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Porter graduated from Hamilton College, New York, in 1845, read law in his father's office, and in the autumn of 1847 was admitted to the Bar. He practised for six or seven years in Rochester, New York, and then in New York City. He was drawn into engineering when aged about 30, first through a client who claimed to have invented a revolutionary type of engine and offered Porter the rights to it as payment of a debt. Having lent more money, Porter saw neither the man nor the engine again. Porter followed this with a similar experience over a patent for a stone dressing machine, except this time the machine was built. It proved to be a failure, but Porter set about redesigning it and found that it was vastly improved when it ran faster. His improved machine went into production. It was while trying to get the steam engine that drove the stone dressing machine to run more smoothly that he made a discovery that formed the basis for his subsequent work.

Porter took the ordinary Watt centrifugal governor and increased the speed by a factor of about ten; although he had to reduce the size of the weights, he gained a motion that was powerful. To make the device sufficiently responsive at the right speed, he balanced the centrifugal forces by a counterweight. This prevented the weights flying outwards until the optimum speed was reached, so that the steam valves remained fully open until that point and then the weights reacted more quickly to variations in speed. He took out a patent in 1858, and its importance was quickly recognized. At first he manufactured and sold the governors himself in a specially equipped factory, because this was the only way he felt he could get sufficient accuracy to ensure a perfect action. For marine use, the counterweight was replaced by a spring.

Higher speed had brought the advantage of smoother running and so he thought that the same principles could be applied to the steam engine itself, but it was to take extensive design modifications over several years before his vision was realized. In the winter of 1860–1, J.F. Allen met Porter and sketched out his idea of a new type of steam inlet valve. Porter saw the potential of this for his high-speed engine and Allen took out patents for it in 1862. The valves were driven by a new valve gear designed by Pius Fink. Porter decided to display his engine at the International Exhibition in London in 1862, but it had to be assembled on site because the parts were finished in America only just in time to be shipped to meet the deadline. Running at 150 rpm, the engine caused a sensation, but as it was non-condensing there were few orders. Porter added condensing apparatus and, after the failure of Ormerod Grierson \& Co., entered into an agreement with Joseph Whitworth to build the engines. Four were exhibited at the 1867 Paris Exposition Universelle, but Whitworth and Porter fell out and in 1868 Porter returned to America.

Porter established another factory to build his engine in America, but he ran into all sorts of difficulties, both mechanical and financial. Some engines were built, and serious production was started c. 1874, but again there were further problems and Porter had to leave his firm. High-speed engines based on his designs continued to be made until after 1907 by the Southwark Foundry and Machine Company, Philadelphia, so Porter's ideas were proved viable and led to many other high-speed designs.

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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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Shortt entered the Engineering Department of the London and South Western Railway as an engineering cadet in 1902, remaining with the company and its successors until he retired in 1946. He became interested in precision horology in 1908, when he designed an instrument for recording the speed of trains; this led to a long and fruitful collaboration with Frank HopeJones, the proprietor of the Synchronome Company. This association culminated in the installation of a free-pendulum clock, with an accuracy of the order of one second per year, at Edinburgh Observatory in 1921. The clock's performance was far better than that of existing clocks, such as the Riefler, and a slightly modified version was produced commercially by the Synchronome Company. These clocks provided the time standard at Greenwich and many other observatories and scientific institutions across the world until they were supplanted by the quartz clock.

The period of a pendulum is constant if it swings freely with a constant amplitude in a vacuum. However, this ideal state cannot be achieved in a clock because the pendulum must be impulsed to maintain its amplitude and the swings have to be counted to indicate time. The free-pendulum clock is an attempt to approach this ideal as closely as possible. In 1898 R.J. Rudd used a slave clock, synchronized with a free pendulum, to time the impulses delivered to the free pendulum. This clock was not successful, but it provided the inspiration for Shortt's clock, which operates on the same principle. The Shortt clock used a standard Synchronome electric clock as the slave, and its pendulum was kept in step with the free pendulum by means of the "hit and miss" synchronizer that Shortt had patented in 1921. This allowed the pendulum to swing freely (in a vacuum), apart from the fraction of a second in which it received an impulse each half-minute.

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See also: Marrison, Warren Alvin

SUBJECT AREA: Weapons and armour

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The youngest of nine children, Shrapnel was commissioned into the Royal Artillery in July 1779. His early military service was in Newfoundland and it was on his return to England in 1784 that he began to interest himself in artillery ammunition. His particular concern was to develop a round that would be more effective against infantry than the existing solid cannon-ball and canister round. The result was a hollow, spherical shell filled with lead musket balls and fitted with a bursting charge and fuse. His development of the shell was interrupted by active service in the Low Countries in 1793–4, during which he was wounded, and duty in the West Indies. Nevertheless, in 1803 the British Army adopted his shell, which during the next twelve years played a significant part on the battlefield.

In 1804 Shrapnel was appointed Assistant Inspector of Artillery and made further contributions to the science of gunnery, drawing up a series of range tables to improve accuracy of fire, inventing the brass tangent slide for better sighting of guns, and improving the production of howitzers and mortars by way of the invention of parabolic chambers. His services were recognized in 1814 by a Treasury grant of £1,200 per annum for life. He was promoted Major-General in 1819 and appointed a Colonel-Commandant of the Royal Artillery in 1827, and in the 1830s there was talk of him being made a baronet, but nothing came of it. Shrapnel remains a current military term, although modern bursting shells rely on the fragmentation of the casing of the projectile for their effect rather than his original concept of having shot inside them.

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