Wimbledon Watches a brief history of John Harrison (1693-1776)
John Harrison, a self-educated Yorkshire carpenter, was a crucial part of British Horological History, inventing the maritime chronometer, a device used to determine longitude at sea, a long awaited and needed instrument in the age where sail and discovery were reaching new heights. Until this invention there had been no accurate knowledge of time over a long sea voyage, making navigation almost impossible. It was a remarkable achievement, which has been pivotal in maritime and later areo navigation.
The term chronometer is used more recently to describe wristwatches tested and certified to meet certain precision standards. Timepieces made in Switzerland may only display the word 'chronometer' if certified by the COSC (Official Swiss Chronometer Testing Institute).
The Story of Longitude and John Harrison
A longitude describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. Longitude is given as an angular measurement ranging from 0° at the Prime Meridian to +180° eastward and −180° westward.
The practical methods in the period relied on a comparison of local time with the time at a given place (such as Greenwich or Paris). Many of these methods relied on astronomical observations and were very inaccurate leading to the loss of life from lack of fresh water and provisions or even worse ship wreck. For many intellectuals of the period astronomy was believed to be the only way to calculate longitude.
Harrison instead set out to solve the problem in a direct way: by producing a reliable clock. The difficulty, however, was in producing a clock which could maintain accurate time on a lengthy, rough sea voyage with widely varying conditions of temperature, pressure and humidity.
In 1714, the British government with the responsibility for a worldwide trading empire and supporting naval fleet were determined to find a solution for more accurate navigation of the seas. An award of £20,000 (several million pounds in modern terms) was announced for the person who solved the problem of longitude at sea. John Harrison, a Yorkshire carpenter, and self taught watchmaker submitted a project in 1730, and in 1735 completed a clock based on a pair of counter-oscillating weighted beams connected by springs whose motion was not influenced by gravity or the motion of a ship.
Harrison H1 and H2 Chronometers
His first two sea timepieces H1 and H2 (completed in 1741) used this system, but he realised that they had a fundamental sensitivity to centrifugal force, which meant that they could never be accurate enough at sea. Construction of his third machine, designated H3, in 1759 included novel circular balances and the invention of the bi-metallic strip and caged roller bearings, inventions which are still widely used today. However, H3's circular balances proved too inaccurate and he eventually abandoned the large machines.
Harrison H4 Solves Longitude
Harrison who had dedicated his life to building a longitudinal navigation clock solved the precision problems with his much smaller H4 chronometer design in 1761. H4 looked much like a large five-inch (12 cm) diameter pocket watch. In 1761, Harrison submitted H4 for the £20,000 longitude prize. His design used a fast-beating balance wheel controlled by a temperature-compensated spiral spring. This general layout remained in use until stable electronic oscillators allowed very accurate portable timepieces to be made at affordable cost.
Unfortunately, Nevil Maskelyne had been appointed Astronomer Royal and held a steadfast belief in Astronomy as being the only way to measure longitude.
Maskelyne held a place on the Board of Longitude which had the responsibility of awarding the prize and recognition for solving the problem. He returned a report of the H4 that was negative. Consequently, the H4 failed the needs of the Board despite the fact that it actually succeeded in two previous trials to accurately measure longtitude.
Harrison began working on his H5 while the H4 testing was conducted, After three years he had had enough; Harrison felt "extremely ill used by the gentlemen who I might have expected better treatment from" and decided to enlist the aid of King George III. He obtained an audience with the King, who was extremely annoyed with the Board. King George tested H5 himself at the palace and after ten weeks of daily observations between May and July in 1772, found it to be accurate to within one third of one second per day.
King George then advised Harrison to petition Parliament for the full prize after threatening to appear in person to dress them down. In 1773, when he was 80 years old, Harrison received a monetary award in the amount of £8,750 from Parliament for his achievements, but he never received the official award (which was never awarded to anyone). He was to survive for just three more years.
John Harrisons H1 can be seen at the Royal Observatory in Greenwich London www.nmm.ac.uk/harrison
The John Harrison H5 Chronometer is held in the collection of the Worshipful Company of Watchmakers in London www.clockmakers.org