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The H4 (also known as "H-4") today become one of the most famous watches in the watchmaking industry. John Harrison was an English clockmaker born in 1683, who designed and built the world's first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances.
History
Back in Harrison's day the problem of determining longitude was one of the great unsolved scientific puzzles. Determining latitude was relatively easy, but longitude defied calculation. Not knowing their accurate position caused many ships to be wrecked with great loss of life.
In 1714 the British Parliament passed the "Longitude Act" which set up the Longitude Board to award a hefty prize to the first person to solve the problem. This prize was eventually won by John Harrison in 1773 for the H4, the first genuine shipboard chronometer (although due to political wrangling Harrison had by then progressed to the H5).
Evolution
The H4 took Harrison a massive 13 years to construct-but this was only the end of a lifetime's work. His genius was clear from the very beginning. Unfortunately many astronomers such as Nevil Maskelyne were convinced that a mechanical solution would not work and that only astronomy could solve the longitude problem. The fact that Harrison was from a working class family and had little formal education probably didn't help his prospects.
To be fair to Maskelyne et al,Fashion boots, the clocks and watches before Harrison were simply incapable of maintaining anywhere near accurate time at sea.
H1
Solving the longitude problem through horology meant designing a timepiece that could work accurately at sea. When you consider the rolling waves, changes in temperature and generally adverse conditions the dificulty of this task becomes apparent.
The H1 (Harrison Number One) was itself a great achievement. It was a smaller version of one of Harrison's wooden clocks and used counterbalanced springs to ovecome the problem of rolling at sea.
The H1 was completed in 1735 and proved successful at sea. However the Board of Longitude demanded a full a transatlantic voyage. They gave Harrison a grant of 500 pounds with which he began work on the H2.
H2
The H2 was completed in 1741, however Britain was then at war with Spain and a sea voyage would have risked the new technology falling into enemy hands. In addition Harrison was unhappy with some aspects of the design. He received another grant of 500 pounds to continue his work.
H3
The H3 was completed in 1759 however it failed to reach the levels of accuracy demanded by the Board. Despite this it must be one of the most successful "failures" ever! The H3 incorporated both an advanced anti-friction bearing and a bimetallic strip to compensate for temperature variations,uggs outlet, two brilliant innovations. However Harrison felt that he had one as far as was possible with his basic design.
H4
The H1 to H3 had all been portable clocks. The H4 was completely different-a pocket watch, albeit it one rather too large for the average pocket (about five inches in diameter and weighing several pounds).
The H4 was completed in 1761 and sent on a transatlantic trial in the care of Harrison's son William. The H4 left Britain on 18 November 1761 and arrived in Jamaica on 19 January 1762. During the entire voyage it lost just 5.1 seconds. Despite this the Board of Longitude refused to award Harrison the prize and demanded a second trial.
The second trial was accompanied by Nevil Maskelyne himself. The H4 exceeded the level of accuracy demanded by the Board - but they still refused to pay the full reward. Instead they added all sorts of extra conditions such as Harrison surrendering all the H series timepieces, detailing their design and making additional copies of the H4.
Harrison reluctantly complied with these conditions, yet the Board still tried to avoid paying him the full reward.
H5
In 1772, an approach was made to King George III, via a letter to his private astronomer at Richmond, Dr Stephen Demainbray. Harrison's son William was summoned for an interview with the King himself, at which the King is said to have remarked: "By God, Harrison, I will see you righted!".
H5 (the latest version of the H4) was put on trial by the King himself in 1772, and performed superbly. The Board of Longitude,gucci handbags, however, refused to recognise the results of this trial, so John and William petitioned Parliament. They were finally awarded. Perhaps more importantly, John Harrison was finally recognized as having solved the longitude problem.

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