Ships, clock and stars: The Quest for Longitude March 09 2015

Last year marked the 300th anniversary of the passing of the Longitude Act in 1714, and the National Maritime Museum Greenwich hosted ‘Ships, Clocks & Stars: The Quest for Longitude’, an exhibition telling the extraordinary story of the race to determine longitude at sea.  The race was eventually won by an extraordinary engineer, John Harrison whose maritime timepieces go back on display at the Royal Observatory in Greenwich on 16th March. We love a tale of danger on the high seas and an epic quest by a heroic figure.  For us, the story of John Harrison’s lifelong dedication to accurate maritime timekeeping for measuring longitude is a compelling quest and Harrison is a hero of engineering, navigation and seafaring. 


Exhibition promotion at the National Maritime Museum     The Royal Observatory, Greenwich

For millennia, sailors and navigators used the position of the sun, moon and stars to estimate their position at sea.  Sailors used the magnetic compass from the early 14th century, and estimates of the distances sailed, to help keep their ships on a steady course. However on long journeys when errors occurred or storms and currents threw calculations off, ships could end up hopelessly lost or worse, shipwrecked.  In the 17th and 18th century, sailors needed much more reliable means of navigating in order to travel across oceans, discover new territories and exploit trade routes. Alongside work by explorers and surveyors to produce accurate coastal maps, astronomers were producing navigation tables, measuring the angle of the sun to the horizon at noon local time for various latitudes throughout the year. Armed with navigation tables, navigators could make fairly reliable estimates for latitude (position north to south) but not longitude (position east to west).  For every 15 degrees that a ship travels eastward, the local time moves one hour ahead.  Similarly, travelling westward, the local time moves back one hour for every 15 degrees of longitude travelled.  In order to measure longitude, sailors needed not only accurate navigation tables, but to reliably measure time and be able to compare time at their location to a point of reference. To this end, King Charles II established an observatory at Greenwich in 1675.

“Whereas, in order to the finding out of the longitude of places for perfecting navigation and astronomy, we have resolved to build a small observatory within Our Park at Greenwich.” Charles II

In 1714, the British Government passed the Longitude Act and offered a prize of £20,000 - a sum equivalent to many millions of pounds today - to anyone who could perfect and demonstrate a solution accurate enough over long voyages to be used to locate a ship with the desired precision.  The prize galvanized astronomers, engineers and navigators to work on new solutions, but many people believed that the problem could not be solved.

From 1728 John Harrison, a carpenter from Lincolnshire with little formal education took on the challenge.  Harrison had already established himself as an innovative maker of clocks with a level of timekeeping accuracy that were the best of their day.  Over three decades, Harrison developed a series of revolutionary marine clocks that were spring-driven to counter the motion of a ship.  Harrison’s genius was in inventing devices to regulate his timepieces for changes in temperature and reducing friction.  He submitted two clocks to the Board of Longitude which were tested and rejected.  By 1762, Harrison submitted a hand held chronometer called H4 which was tested and, eventually, in 1773 after much negotiation with the Board and the intervention of King George III, he was awarded the prize at the age of eighty .


 John Harrison and his H4 chronometer

Greenwich was central to the story of the quest for longitude, with the Royal Observatory becoming a testing site for marine timekeepers and the place at which the astronomical observations for comprehensive navigational tables were made.  Harrison's celebrated marine clocks, including H4 – the one that was finally accepted by the Board of Longitude as allowing accurate timekeeping - are preserved at the Royal Observatory Greenwich and go on public display again from 16th March 2015. Go to to find out more.

Three hundred years on from the passing of the Act of Longitude, a new Longitude Prize was launched by the Prime Minister with a prize fund of £10 million to help solve one for the greatest issues of our time.  Following a public vote, the challenge set for the Longitude Prize is to tackle microbial resistance to antibiotics by creating a cost-effective, accurate and easy-to-use test for bacterial infections that will allow health professionals to administer the right antibiotics at the right time. Go to learn about the Longitude Prize.