page_title: John Harrison
section_title: The first three marine timekeepers
hierarchical_section_title: John Harrison / The first three marine timekeepers
caption_attribution_description: Deutsch: Royal Observatory, Greenwich English: Harrison's third timekeeper H3: This timekeeper took 19 years to build. In 1759 it was not quite accurate enough to win the 20,000 pound prize.
context_page_description: John Harrison was a self-educated English carpenter and clockmaker who invented the marine chronometer, a long-sought-after device for solving the problem of calculating longitude while at sea.
  Harrison's solution revolutionized navigation and greatly increased the safety of long-distance sea travel. The problem he solved was considered so important following the Scilly naval disaster of 1707 that the British Parliament offered financial rewards of up to £20,000 under the 1714 Longitude Act.
  In 1730, Harrison presented his first design, and worked over many years on improved designs, making several advances in time-keeping technology, finally turning to what were called sea watches. Harrison gained support from the Longitude Board in building and testing his designs. Toward the end of his life, he received recognition and a reward from Parliament. Harrison came 39th in the BBC's 2002 public poll of the 100 Greatest Britons.
context_section_description: In the 1720s, the English clockmaker Henry Sully invented a marine clock that was designed to determine longitude: this was in the form of a clock with a large balance wheel that was vertically mounted on friction rollers and impulsed by a frictional rest Debaufre type escapement. Very unconventionally, the balance oscillations were controlled by a weight at the end of a pivoted horizontal lever attached to the balance by a cord. This solution avoided temperature error due to thermal expansion, a problem which affects steel balance springs. Sully's clock only kept accurate time in calm weather, because the balance oscillations were affected by the pitching and rolling of the ship. However his clocks were amongst the first serious attempts to find longitude in this way. Harrison's machines, though much larger, are of similar layout: H3 has a vertically mounted balance wheel and is linked to another wheel of the same size, an arrangement that eliminates problems arising from the ship's motion.
  In 1716, Sully presented his first Montre de la Mer to the French Académie des Sciences and in 1726 he published Une Horloge inventée et executée par M. Sulli.
  
  In 1730, Harrison designed a marine clock to compete for the Longitude prize and travelled to London, seeking financial assistance. He presented his ideas to Edmond Halley, the Astronomer Royal, who in turn referred him to George Graham, the country's foremost clockmaker. Graham must have been impressed by Harrison's ideas, for he loaned him money to build a model of his "Sea clock". As the clock was an attempt to make a seagoing version of his wooden pendulum clocks, which performed exceptionally well, he used wooden wheels, roller pinions and a version of the 'grasshopper' escapement. Instead of a pendulum, he used two dumbbell balances, linked together.
  It took Harrison five years to build his first sea clock (or H1). He demonstrated it to members of the Royal Society who spoke on his behalf to the Board of Longitude.  The clock was the first proposal that the Board considered to be worthy of a sea trial.  In 1736, Harrison sailed to Lisbon on HMS Centurion under the command of Captain George Proctor and returned on HMS Orford after Proctor died at Lisbon on 4 October 1736.  The clock lost time on the outward voyage.  However, it performed well on the return trip: both the captain and the sailing master of the Orford praised the design. The master noted that his own calculations had placed the ship sixty miles east of its true landfall which had been correctly predicted by Harrison using H1.
  This was not the transatlantic voyage demanded by the Board of Longitude, but the Board was impressed enough to grant Harrison £500 for further development. Harrison had moved to London by 1737 and went on to develop H2,
  a more compact and rugged version. In 1741, after three years of building and two of on-land testing, H2 was ready, but by then Britain was at war with Spain in the War of Austrian Succession and the mechanism was deemed too important to risk falling into Spanish hands. In any event, Harrison suddenly abandoned all work on this second machine when he discovered a serious design flaw in the concept of the bar balances. He had not recognized that the period of oscillation of the bar balances could be affected by the yawing action of the ship (when the ship turned such as 'coming about' while tacking). It was this that led him to adopt circular balances in the Third Sea Clock (H3).
  The Board granted him another £500, and while waiting for the war to end, he proceeded to work on H3.
  Harrison spent seventeen years working on this third 'sea clock', but despite every effort it did not perform exactly as he would have wished. The problem was that, because Harrison did not fully understand the physics behind the springs used to control the balance wheels, the timing of the wheels was not isochronous, a characteristic that affected its accuracy. The engineering world was not to fully understand the properties of springs for such applications for another two centuries. Despite t
caption: Harrison's third sea clock (H3)
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