Britten's Watch and Clock Maker's Handbook

SUBJECT AREA: Mechanical, pneumatic and hydraulic engineering

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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.

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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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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