supported by springs

1) Military: spring-actuated

2) Railway term: spring borne

3) Automobile industry: cushioned, mounted elastically, spring-mounted, sprung, supported by springs

4) Mining: spring-loaded

5) Astronautics: shock-mounted, spring loaded

6) Makarov: elastically mounted

SUBJECT AREA: Horology, Ports and shipping

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John Harrison was the son of a carpenter and was brought up to that trade. He was largely self-taught and learned mechanics from a copy of Nicholas Saunderson's lectures that had been lent to him. With the assistance of his younger brother, James, he built a series of unconventional clocks, mainly of wood. He was always concerned to reduce friction, without using oil, and this influenced the design of his "grasshopper" escapement. He also invented the "gridiron" compensation pendulum, which depended on the differential expansion of brass and steel. The excellent performance of his regulator clocks, which incorporated these devices, convinced him that they could also be used in a sea dock to compete for the longitude prize. In 1714 the Government had offered a prize of £20,000 for a method of determining longitude at sea to within half a degree after a voyage to the West Indies. In theory the longitude could be found by carrying an accurate timepiece that would indicate the time at a known longitude, but the requirements of the Act were very exacting. The timepiece would have to have a cumulative error of no more than two minutes after a voyage lasting six weeks.

In 1730 Harrison went to London with his proposal for a sea clock, supported by examples of his grasshopper escapement and his gridiron pendulum. His proposal received sufficient encouragement and financial support, from George Graham and others, to enable him to return to Barrow and construct his first sea clock, which he completed five years later. This was a large and complicated machine that was made out of brass but retained the wooden wheelwork and the grasshopper escapement of the regulator clocks. The two balances were interlinked to counteract the rolling of the vessel and were controlled by helical springs operating in tension. It was the first timepiece with a balance to have temperature compensation. The effect of temperature change on the timekeeping of a balance is more pronounced than it is for a pendulum, as two effects are involved: the change in the size of the balance; and the change in the elasticity of the balance spring. Harrison compensated for both effects by using a gridiron arrangement to alter the tension in the springs. This timekeeper performed creditably when it was tested on a voyage to Lisbon, and the Board of Longitude agreed to finance improved models. Harrison's second timekeeper dispensed with the use of wood and had the added refinement of a remontoire, but even before it was tested he had embarked on a third machine. The balance of this machine was controlled by a spiral spring whose effective length was altered by a bimetallic strip to compensate for changes in temperature. In 1753 Harrison commissioned a London watchmaker, John Jefferys, to make a watch for his own personal use, with a similar form of temperature compensation and a modified verge escapement that was intended to compensate for the lack of isochronism of the balance spring. The time-keeping of this watch was surprisingly good and Harrison proceeded to build a larger and more sophisticated version, with a remontoire. This timekeeper was completed in 1759 and its performance was so remarkable that Harrison decided to enter it for the longitude prize in place of his third machine. It was tested on two voyages to the West Indies and on both occasions it met the requirements of the Act, but the Board of Longitude withheld half the prize money until they had proof that the timekeeper could be duplicated. Copies were made by Harrison and by Larcum Kendall, but the Board still continued to prevaricate and Harrison received the full amount of the prize in 1773 only after George III had intervened on his behalf.

Although Harrison had shown that it was possible to construct a timepiece of sufficient accuracy to determine longitude at sea, his solution was too complex and costly to be produced in quantity. It had, for example, taken Larcum Kendall two years to produce his copy of Harrison's fourth timekeeper, but Harrison had overcome the psychological barrier and opened the door for others to produce chronometers in quantity at an affordable price. This was achieved before the end of the century by Arnold and Earnshaw, but they used an entirely different design that owed more to Le Roy than it did to Harrison and which only retained Harrison's maintaining power.

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See also: Burgi, Jost; Huygens, Christiaan

SUBJECT AREA: Automotive engineering, Land transport

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He spent his childhood at The Hall in Bradfordon-Avon. He was educated at Marlborough College, and in 1937 was apprenticed to the Sentinel Steam Wagon Company of Shrewsbury. About that same time he went to King's College, Cambridge, where he took the Mechanical Sciences Tripos. It was then wartime, and he did research on aero-engines at the Bristol Aeroplane Company, where he became Personal Assistant to Sir Roy Fedden. He left Bristol's in 1945 to join his family firm, Spencer \& Moulton, of which he eventually became Technical Director and built up the Research Department. In 1948 he invented his first suspension unit, the "Flexitor", in which an inner shaft and an outer shell were separated by an annular rubber body which was bonded to both.

In 1848 his great-grandfather had founded the family firm in an old woollen mill, to manufacture vulcanized rubber products under Charles Goodyear's patent. The firm remained a family business with Spencer's, consultants in railway engineering, until 1956 when it was sold to the Avon Rubber Company. He then formed Moulton Developments to continue his work on vehicle suspensions in the stables attached to The Hall. Sponsored by the British Motor Corporation (BMC) and the Dunlop Rubber Company, he invented a rubber cone spring in 1951 which was later used in the BMC Mini (see Issigonis, Sir Alexander Arnold Constantine): by 1994 over 4 million Minis had been fitted with these springs, made by Dunlop. In 1954 he patented the Hydrolastic suspension system, in which all four wheels were independently sprung with combined rubber springs and damper assembly, the weight being supported by fluid under pressure, and the wheels on each side being interconnected, front to rear. In 1962 he formed Moulton Bicycles Ltd, having designed an improved bicycle system for adult use. The conventional bicycle frame was replaced by a flat-sided oval steel tube F-frame on a novel rubber front and rear suspension, with the wheel size reduced to 41 cm (16 in.) with high-pressure tyres. Raleigh Industries Ltd having refused his offer to produce the Moulton Bicycle under licence, he set up his own factory on his estate, producing 25,000 bicycles between 1963 and 1966. In 1967 he sold out to Raleigh and set up as Bicycle Consultants Ltd while continuing the suspension development of Moulton Developments Ltd. In the 1970s the combined firms employed some forty staff, nearly 50 per cent of whom were graduates.

He won the Queen's Award for Industry in 1967 for technical innovation in Hydrolastic car suspension and the Moulton Bicycle. Since that time he has continued his innovative work on suspensions and the bicycle. In 1983 he introduced the AM bicycle series of very sophisticated space-frame design with suspension and 43 cm (17 in.) wheels; this machine holds the world speed record fully formed at 82 km/h (51 mph). The current Rover 100 and MGF use his Hydragas interconnected suspension. By 1994 over 7 million cars had been fitted with Moulton suspensions. He has won many design awards and prizes, and has been awarded three honorary doctorates of engineering. He is active in engineering and design education.

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